(Prepared from website Radio-Electronics.com with thanks http://www.radio-electronics.com/)

3G LTE Tutorial - 3GPP Long Term Evolution
- developed by 3GPP, LTE, Long Term Evolution is the successor to 3G UMTS and HSPA providing much higher data download speeds and setting the foundations for 4G LTE Advanced..

LTE, Long Term Evolution, the successor to UMTS and HSPA is now being deployed and is the way forwards for high speed cellular services.
In its first forms it is a 3G or as some would call it a 3.99G technology, but with further additions the technology can be migrated to a full 4G standard and here it is known as LTE Advanced.
There has been a rapid increase in the use of data carried by cellular services, and this increase will only become larger in what has been termed the "data explosion". To cater for this and the increased demands for increased data transmission speeds and lower latency, further development of cellular technology have been required.
The UMTS cellular technology upgrade has been dubbed LTE - Long Term Evolution. The idea is that 3G LTE will enable much higher speeds to be achieved along with much lower packet latency (a growing requirement for many services these days), and that 3GPP LTE will enable cellular communications services to move forward to meet the needs for cellular technology to 2017 and well beyond.
Many operators have not yet upgraded their basic 3G networks, and 3GPP LTE is seen as the next logical step for many operators, who will leapfrog straight from basic 3G straight to LTE as this will avoid providing several stages of upgrade. The use of LTE will also provide the data capabilities that will be required for many years and until the full launch of the full 4G standards known as LTE Advanced.

3G LTE evolution
Although there are major step changes between LTE and its 3G predecessors, it is nevertheless looked upon as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different form of radio interface, using OFDMA / SC-FDMA instead of CDMA, there are many similarities with the earlier forms of 3G architecture and there is scope for much re-use.
In determining what is LTE and how does it differ from other cellular systems, a quick look at the specifications for the system can provide many answers. LTE can be seen for provide a further evolution of functionality, increased speeds and general improved performance.

| WCDMA
(UMTS) | HSPA
HSDPA / HSUPA | HSPA+ | LTE | Max downlink speed bps | 384 k | 14 M | 28 M | 100M | Max uplink speed bps | 128 k | 5.7 M | 11 M | 50 M | Latency round trip time approx | 150 ms | 100 ms | 50ms (max) | ~10 ms | 3GPP releases | Rel 99/4 | Rel 5 / 6 | Rel 7 | Rel 8 | Approx years of initial roll out | 2003 / 4 | 2005 / 6 HSDPA
2007 / 8 HSUPA | 2008 / 9 | 2009 / 10 | Access methodology | CDMA | CDMA | CDMA | OFDMA / SC-FDMA | | | | | |

In addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. Originally there was also no basic provision for voice, although Voice over LTE, VoLTE was added was chosen by GSMA as the standard for this. In the interim, techniques including circuit switched fallback, CSFB are expected to be used

What is LTE? - specification overview
It is worth summarizing the key parameters of the 3G LTE specification. In view of the fact that there are a number of differences between the operation of the uplink and downlink, these naturally differ in the performance they can offer.

WHAT IS LTE? - BASIC SPECIFICATIONS | PARAMETER | DETAILS | | | | Peak downlink speed
64QAM
(Mbps) | 100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO) | | | | Peak uplink speeds
(Mbps) | 50 (QPSK), 57 (16QAM), 86 (64QAM) | | | | Data type | All packet switched data (voice and data). No circuit switched. | | | | Channel bandwidths
(MHz) | 1.4, 3, 5, 10, 15, 20 | | | | Duplex schemes | FDD and TDD | | | | Mobility | 0 - 15 km/h (optimised),
15 - 120 km/h (high performance) | | | | Latency | Idle to active less than 100ms
Small packets ~10 ms | | | | Spectral efficiency | Downlink: 3 - 4 times Rel 6 HSDPA
Uplink: 2 -3 x Rel 6 HSUPA | | | | Access schemes | OFDMA (Downlink)
SC-FDMA (Uplink) | | | | Modulation types supported | QPSK, 16QAM, 64QAM (Uplink and downlink) | | | |

These highlight specifications give an overall view of the performance that LTE will offer. It meets the requirements of industry for high data download speeds as well as reduced latency - a factor important for many applications from VoIP to gaming and interactive use of data. It also provides significant improvements in the use of the available spectrum.

What are the main LTE technologies?
LTE has introduced a number of new technologies when compared to the previous cellular systems. They enable LTE to be able to operate more efficiently with respect to the use of spectrum, and also to provide the much higher data rates that are being required. * OFDM (Orthogonal Frequency Division Multiplex): OFDM technology has been incorporated into LTE because it enables high data bandwidths to be transmitted efficiently while still providing a high degree of resilience to reflections and interference. The access schemes differ between the uplink and downlink: OFDMA (Orthogonal Frequency Division Multiple Access is used in the downlink; while SC-FDMA(Single Carrier - Frequency Division Multiple Access) is used in the uplink. SC-FDMA is used in view of the fact that its peak to average power ratio is small and the more constant power enables high RF power amplifier efficiency in the mobile handsets - an important factor for battery power equipment. Read more about LTE OFDM / OFDMA / SCFMDA * MIMO (Multiple Input Multiple Output): One of the main problems that previous telecommunications systems has encountered is that of multiple signals arising from the many reflections that are encountered. By using MIMO, these additional signal paths can be used to advantage and are able to be used to increase the throughput.

When using MIMO, it is necessary to use multiple antennas to enable the different paths to be distinguished. Accordingly schemes using 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used. While it is relatively easy to add further antennas to a base station, the same is not true of mobile handsets, where the dimensions of the user equipment limit the number of antennas which should be place at least a half wavelength apart. Read more about LTE MIMO * SAE (System Architecture Evolution): With the very high data rate and low latency requirements for 3G LTE, it is necessary to evolve the system architecture to enable the improved performance to be achieved. One change is that a number of the functions previously handled by the core network have been transferred out to the periphery. Essentially this provides a much "flatter" form of network architecture. In this way latency times can be reduced and data can be routed more directly to its destination.Read more about LTE SAE
A fuller description of what LTE is and the how the associated technologies work is all addressed in much greater detail in the following pages of this tutorial.
By Ian Poole

LTE OFDM, OFDMA and SC-FDMA
- overview, information, tutorial about the basics of LTE OFDM, OFDMA and SC-FDMA including cyclic prefix, CP.

One of the key elements of LTE is the use of OFDM (Orthogonal Frequency Division Multiplex) as the signal bearer and the associated access schemes, OFDMA (Orthogonal Frequency Division Multiplex) and SC-FDMA (Single Frequency Division Multiple Access).
OFDM is used in a number of other of systems from WLAN, WiMAX to broadcast technologies including DVB and DAB. OFDM has many advantages including its robustness to multipath fading and interference. In addition to this, even though, it may appear to be a particularly complicated form of modulation, it lends itself to digital signal processing techniques.
In view of its advantages, the use of ODFM and the associated access technologies, OFDMA and SC-FDMA are natural choices for the new LTE cellular standard.

OFDM basics
The use of OFDM is a natural choice for LTE. While the basic concepts of OFDM are used, it has naturally been tailored to meet the exact requirements for LTE. However its use of multiple carrier each carrying a low data rate remains the same.

Note on OFDM:
Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..
Click on the link for an OFDM tutorial

The actual implementation of the technology will be different between the downlink (i.e. from base station to mobile) and the uplink (i.e. mobile to the base station) as a result of the different requirements between the two directions and the equipment at either end. However OFDM was chosen as the signal bearer format because it is very resilient to interference. Also in recent years a considerable level of experience has been gained in its use from the various forms of broadcasting that use it along with Wi-Fi and WiMAX. OFDM is also a modulation format that is very suitable for carrying high data rates - one of the key requirements for LTE.
In addition to this, OFDM can be used in both FDD and TDD formats. This becomes an additional advantage.

LTE channel bandwidths and characteristics
One of the key parameters associated with the use of OFDM within LTE is the choice of bandwidth. The available bandwidth influences a variety of decisions including the number of carriers that can be accommodated in the OFDM signal and in turn this influences elements including the symbol length and so forth.
LTE defines a number of channel bandwidths. Obviously the greater the bandwidth, the greater the channel capacity.
The channel bandwidths that have been chosen for LTE are: 1. 1.4 MHz 2. 3 MHz 3. 5 MHz 4. 10 MHz 5. 15 MHz 6. 20 MHz
In addition to this the subcarriers are spaced 15 kHz apart from each other. To maintain orthogonality, this gives a symbol rate of 1 / 15 kHz = of 66.7 µs.
Each subcarrier is able to carry data at a maximum rate of 15 ksps (kilosymbols per second). This gives a 20 MHz bandwidth system a raw symbol rate of 18 Msps. In turn this is able to provide a raw data rate of 108 Mbps as each symbol using 64QAM is able to represent six bits.
It may appear that these rates do not align with the headline figures given in the LTE specifications. The reason for this is that actual peak data rates are derived by first subtracting the coding and control overheads. Then there are gains arising from elements such as the spatial multiplexing, etc.

LTE OFDM cyclic prefix, CP
One of the primary reasons for using OFDM as a modulation format within LTE (and many other wireless systems for that matter) is its resilience to multipath delays and spread. However it is still necessary to implement methods of adding resilience to the system. This helps overcome the inter-symbol interference (ISI) that results from this.
In areas where inter-symbol interference is expected, it can be avoided by inserting a guard period into the timing at the beginning of each data symbol. It is then possible to copy a section from the end of the symbol to the beginning. This is known as the cyclic prefix, CP. The receiver can then sample the waveform at the optimum time and avoid any inter-symbol interference caused by reflections that are delayed by times up to the length of the cyclic prefix, CP.
The length of the cyclic prefix, CP is important. If it is not long enough then it will not counteract the multipath reflection delay spread. If it is too long, then it will reduce the data throughput capacity. For LTE, the standard length of the cyclic prefix has been chosen to be 4.69 µs. This enables the system to accommodate path variations of up to 1.4 km. With the symbol length in LTE set to 66.7 µs.
The symbol length is defined by the fact that for OFDM systems the symbol length is equal to the reciprocal of the carrier spacing so that orthogonality is achieved. With a carrier spacing of 15 kHz, this gives the symbol length of 66.7 µs.

LTE OFDMA in the downlink
The OFDM signal used in LTE comprises a maximum of 2048 different sub-carriers having a spacing of 15 kHz. Although it is mandatory for the mobiles to have capability to be able to receive all 2048 sub-carriers, not all need to be transmitted by the base station which only needs to be able to support the transmission of 72 sub-carriers. In this way all mobiles will be able to talk to any base station.
Within the OFDM signal it is possible to choose between three types of modulation: 1. QPSK (= 4QAM) 2 bits per symbol 2. 16QAM 4 bits per symbol 3. 64QAM 6 bits per symbol
The exact format is chosen depending upon the prevailing conditions. The lower forms of modulation, (QPSK) do not require such a large signal to noise ratio but are not able to send the data as fast. Only when there is a sufficient signal to noise ratio can the higher order modulation format be used.

Downlink carriers and resource blocks
In the downlink, the subcarriers are split into resource blocks. This enables the system to be able to compartmentalise the data across standard numbers of subcarriers.
Resource blocks comprise 12 subcarriers, regardless of the overall LTE signal bandwidth. They also cover one slot in the time frame. This means that different LTE signal bandwidths will have different numbers of resource blocks.

Channel bandwidth
(MHz) | 1.4 | 3 | 5 | 10 | 15 | 20 | Number of resource blocks | 6 | 15 | 25 | 50 | 75 | 100 |

LTE SC-FDMA in the uplink
For the LTE uplink, a different concept is used for the access technique. Although still using a form of OFDMA technology, the implementation is called Single Carrier Frequency Division Multiple Access (SC-FDMA).
One of the key parameters that affects all mobiles is that of battery life. Even though battery performance is improving all the time, it is still necessary to ensure that the mobiles use as little battery power as possible. With the RF power amplifier that transmits the radio frequency signal via the antenna to the base station being the highest power item within the mobile, it is necessary that it operates in as efficient mode as possible. This can be significantly affected by the form of radio frequency modulation and signal format. Signals that have a high peak to average ratio and require linear amplification do not lend themselves to the use of efficient RF power amplifiers. As a result it is necessary to employ a mode of transmission that has as near a constant power level when operating. Unfortunately OFDM has a high peak to average ratio. While this is not a problem for the base station where power is not a particular problem, it is unacceptable for the mobile. As a result, LTE uses a modulation scheme known as SC-FDMA - Single Carrier Frequency Division Multiplex which is a hybrid format. This combines the low peak to average ratio offered by single-carrier systems with the multipath interference resilience and flexible subcarrier frequency allocation that OFDM provides.
By Ian Poole

LTE MIMO: Multiple Input Multiple Output Tutorial
- MIMO is used within LTE to provide better signal performance and / or higher data rates by the use of the radio path reflections that exist.
MIMO, Multiple Input Multiple Output is another of the LTE major technology innovations used to improve the performance of the system. This technology provides LTE with the ability to further improve its data throughput and spectral efficiency above that obtained by the use of OFDM.
Although MIMO adds complexity to the system in terms of processing and the number of antennas required, it enables far high data rates to be achieved along with much improved spectral efficiency. As a result, MIMO has been included as an integral part of LTE.

LTE MIMO basics
The basic concept of MIMO utilises the multipath signal propagation that is present in all terrestrial communications. Rather than providing interference, these paths can be used to advantage.

Note on MIMO:
Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.
Click on the link for a MIMO tutorial

MIMO is being used increasingly in many high data rate technologies including Wi-Fi and other wireless and cellular technologies to provide improved levels of efficiency. Essentially MIMO employs multiple antennas on the receiver and transmitter to utilise the multi-path effects that always exist to transmit additional data, rather than causing interference.
The schemes employed in LTE again vary slightly between the uplink and downlink. The reason for this is to keep the terminal cost low as there are far more terminals than base stations and as a result terminal works cost price is far more sensitive.
For the downlink, a configuration of two transmit antennas at the base station and two receive antennas on the mobile terminal is used as baseline, although configurations with four antennas are also being considered.
For the uplink from the mobile terminal to the base station, a scheme called MU-MIMO (Multi-User MIMO) is to be employed. Using this, even though the base station requires multiple antennas, the mobiles only have one transmit antenna and this considerably reduces the cost of the mobile. In operation, multiple mobile terminals may transmit simultaneously on the same channel or channels, but they do not cause interference to each other because mutually orthogonal pilot patterns are used. This techniques is also referred to as spatial domain multiple access (SDMA).

LTE FDD, TDD, TD-LTE Duplex Schemes
- information, overview, or tutorial about the LTE TDD and LTE FDD duplex schemes used with LTE and including TD-LTE.
LTE has been defined to accommodate both paired spectrum for Frequency Division Duplex, FDD and unpaired spectrum for Time Division Duplex, TDD operation. It is anticipated that both LTE TDD and LTE FDD will be widely deployed as each form of the LTE standard has its own advantages and disadvantages and decisions can be made about which format to adopt dependent upon the particular application.
LTE FDD using the paired spectrum is anticipated to form the migration path for the current 3G services being used around the globe, most of which use FDD paired spectrum. However there has been an additional emphasis on including TDD LTE using unpaired spectrum. TDD LTE which is also known as TD-LTE is seen as providing the evolution or upgrade path for TD-SCDMA.
In view of the increased level of importance being placed upon LTE TDD or TD-LTE, it is planned that user equipments will be designed to accommodate both FDD and TDD modes. With TDD having an increased level of importance placed upon it, it means that TDD operations will be able to benefit from the economies of scale that were previously only open to FDD operations.

Duplex schemes
It is essential that any cellular communications system must be able to transmit in both directions simultaneously. This enables conversations to be made, with either end being able to talk and listen as required. Additionally when exchanging data it is necessary to be able to undertake virtually simultaneous or completely simultaneous communications in both directions.
It is necessary to be able to specify the different direction of transmission so that it is possible to easily identify in which direction the transmission is being made. There are a variety of differences between the two links ranging from the amount of data carried to the transmission format, and the channels implemented. The two links are defined: * Uplink: the transmission from the UE or user equipment to the eNodeB or base station. * Downlink the transmission from the eNodeB or base station to the UE or user equipment.

Uplink and downlink transmission directions
In order to be able to be able to transmit in both directions, a user equipment or base station must have a duplex scheme. There are two forms of duplex that are commonly used, namely FDD, frequency division duplex and TDD time division duplex..

Note on TDD and FDD duplex schemes:
In order for radio communications systems to be able to communicate in both directions it is necessary to have what is termed a duplex scheme. A duplex scheme provides a way of organizing the transmitter and receiver so that they can transmit and receive. There are several methods that can be adopted. For applications including wireless and cellular telecommunications, where it is required that the transmitter and receiver are able to operate simultaneously, two schemes are in use. One known as FDD or frequency division duplex uses two channels, one for transmit and the other for receiver. Another scheme known as TDD, time division duplex uses one frequency, but allocates different time slots for transmission and reception.
Click on the link for more information on TDD FDD duplex schemes

Both FDD and TDD have their own advantages and disadvantages. Accordingly they may be used for different applications, or where the bias of the communications is different.

Advantages / disadvantages of LTE TDD and LTE FDD for cellular communications
There are a number of the advantages and disadvantages of TDD and FDD that are of particular interest to mobile or cellular telecommunications operators. These are naturally reflected into LTE. PARAMETER | LTE-TDD | LTE-FDD | Paired spectrum | Does not require paired spectrum as both transmit and receive occur on the same channel | Requires paired spectrum with sufficient frequency separation to allow simultaneous transmission and reception | Hardware cost | Lower cost as no diplexer is needed to isolate the transmitter and receiver. As cost of the UEs is of major importance because of the vast numbers that are produced, this is a key aspect. | Diplexer is needed and cost is higher. | Channel reciprocity | Channel propagation is the same in both directions which enables transmit and receive to use on set of parameters | Channel characteristics different in both directions as a result of the use of different frequencies | UL / DL asymmetry | It is possible to dynamically change the UL and DL capacity ratio to match demand | UL / DL capacity determined by frequency allocation set out by the regulatory authorities. It is therefore not possible to make dynamic changes to match capacity. Regulatory changes would normally be required and capacity is normally allocated so that it is the same in either direction. | Guard period / guard band | Guard period required to ensure uplink and downlink transmissions do not clash. Large guard period will limit capacity. Larger guard period normally required if distances are increased to accommodate larger propagation times. | Guard band required to provide sufficient isolation between uplink and downlink. Large guard band does not impact capacity. | Discontinuous transmission | Discontinuous transmission is required to allow both uplink and downlink transmissions. This can degrade the performance of the RF power amplifier in the transmitter. | Continuous transmission is required. | Cross slot interference | Base stations need to be synchronised with respect to the uplink and downlink transmission times. If neighbouring base stations use different uplink and downlink assignments and share the same channel, then interference may occur between cells. | Not applicable |

LTE TDD / TD-LTE and TD-SCDMA
Apart from the technical reasons and advantages for using LTE TDD / TD-LTE, there are market drivers as well. With TD-SCDMA now well established in China, there needs to be a 3.9G and later a 4G successor to the technology. With unpaired spectrum allocated for TD-SCDMA as well as UMTS TDD, it is natural to see many operators wanting an upgrade path for their technologies to benefit from the vastly increased speeds and improved facilities of LTE. Accordingly there is a considerable interest in the development of LTE TDD, which is also known in China as TD-LTE.
With the considerable interest from the supporters of TD-SCDMA, a number of features to make the mode of operation of TD-LTE more of an upgrade path for TD-SCDMA have been incorporated. One example of this is the subframe structure that has been adopted within LTE TDD / TD-LTE.
While both LTE TDD (TD-LTE) and LTE FDD will be widely used, it is anticipated that LTE FDD will be the more widespread, although LTE TDD has a number of significant advantages, especially in terms of higher spectrum efficiency that can be used by many operators. It is also anticipated that phones will be able to operate using either the LTE FDD or LTE-TDD (TD-LTE) modes. In this way the LTE UEs or user equipments will be dual standard phones, and able to operate in countries regardless of the flavour of LTE that is used - the main problem will then be the frequency bands that the phone can cover.

LTE Frame and Subframe Structure
- information, overview, or tutorial about the LTE frame and subframe structure including LTE Type 1 and LTE Type 2 frames.
In order that the 3G LTE system can maintain synchronisation and the system is able to manage the different types of information that need to be carried between the base-station or eNodeB and the User Equipment, UE, 3G LTE system has a defined LTE frame and subframe structure for the E-UTRA or Evolved UMTS Terrestrial Radio Access, i.e. the air interface for 3G LTE.
The frame structures for LTE differ between the Time Division Duplex, TDD and the Frequency Division Duplex, FDD modes as there are different requirements on segregating the transmitted data.
There are two types of LTE frame structure: 1. Type 1: used for the LTE FDD mode systems.

2. Type 2: used for the LTE TDD systems.

Type 1 LTE Frame Structure
The basic type 1 LTE frame has an overall length of 10 ms. This is then divided into a total of 20 individual slots. LTE Subframes then consist of two slots - in other words there are ten LTE subframes within a frame.

Type 1 LTE Frame Structure

Type 2 LTE Frame Structure
The frame structure for the type 2 frames used on LTE TDD is somewhat different. The 10 ms frame comprises two half frames, each 5 ms long. The LTE half-frames are further split into five subframes, each 1ms long.

Type 2 LTE Frame Structure
(shown for 5ms switch point periodicity).
The subframes may be divided into standard subframes of special subframes. The special subframes consist of three fields; * DwPTS - Downlink Pilot Time Slot * GP - Guard Period * UpPTS - Uplink Pilot Time Stot.
These three fields are also used within TD-SCDMA and they have been carried over into LTE TDD (TD-LTE) and thereby help the upgrade path. The fields are individually configurable in terms of length, although the total length of all three together must be 1ms.

LTE TDD / TD-LTE subframe allocations
One of the advantages of using LTE TDD is that it is possible to dynamically change the up and downlink balance and characteristics to meet the load conditions. In order that this can be achieved in an ordered fashion, a number of standard configurations have been set within the LTE standards.
A total of seven up / downlink configurations have been set, and these use either 5 ms or 10 ms switch periodicities. In the case of the 5ms switch point periodicity, a special subframe exists in both half frames. In the case of the 10 ms periodicity, the special subframe exists in the first half frame only. It can be seen from the table below that the subframes 0 and 5 as well as DwPTS are always reserved for the downlink. It can also be seen that UpPTS and the subframe immediately following the special subframe are always reserved for the uplink transmission. UPLINK-DOWNLINK CONFIGURATION | DOWNLINK TO UPLINK SWITCH PERIODICITY | SUBFRAME NUMBER | | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | 5 ms | D | S | U | U | U | D | S | U | U | U | 1 | 5 ms | D | S | U | U | D | D | S | U | U | D | 2 | 5 ms | D | S | U | D | D | D | S | U | D | D | 3 | 10 ms | D | S | U | U | U | D | D | D | D | D | 4 | 10 ms | D | S | U | U | D | D | D | D | D | D | 5 | 10 ms | D | S | U | D | D | D | D | D | D | D | 6 | 5 ms | D | S | U | U | U | D | S | U | U | D |
Where:
D is a subframe for downlink transmission S is a "special" subframe used for a guard time U is a subframe for uplink transmission
Uplink / Downlink subframe configurations for LTE TDD (TD-LTE)

LTE Physical, Logical and Transport Channels
- overview, information, tutorial about the physical, logical, control and transport channels used within 3GPP, 3G LTE and the LTE channel mapping.
In order that data can be transported across the LTE radio interface, various "channels" are used. These are used to segregate the different types of data and allow them to be transported across the radio access network in an orderly fashion.
Effectively the different channels provide interfaces to the higher layers within the LTE protocol structure and enable an orderly and defined segregation of the data.

3G LTE channel types
There are three categories into which the various data channels may be grouped. * Physical channels: These are transmission channels that carry user data and control messages. * Transport channels: The physical layer transport channels offer information transfer to Medium Access Control (MAC) and higher layers. * Logical channels: Provide services for the Medium Access Control (MAC) layer within the LTE protocol structure.

3G LTE physical channels
The LTE physical channels vary between the uplink and the downlink as each has different requirements and operates in a different manner. * Downlink: * Physical Broadcast Channel (PBCH): This physical channel carries system information for UEs requiring to access the network. It only carries what is termed Master Information Block, MIB, messages. The modulation scheme is always QPSK and the information bits are coded and rate matched - the bits are then scrambled using a scrambling sequence specific to the cell to prevent confusion with data from other cells.

The MIB message on the PBCH is mapped onto the central 72 subcarriers or six central resource blocks regardless of the overall system bandwidth. A PBCH message is repeated every 40 ms, i.e. one TTI of PBCH includes four radio frames.

The PBCH transmissions has 14 information bits, 10 spare bits, and 16 CRC bits. * Physical Control Format Indicator Channel (PCFICH) : As the name implies the PCFICH informs the UE about the format of the signal being received. It indicates the number of OFDM symbols used for the PDCCHs, whether 1, 2, or 3. The information within the PCFICH is essential because the UE does not have prior information about the size of the control region.

A PCFICH is transmitted on the first symbol of every sub-frame and carries a Control Format Indicator, CFI, field. The CFI contains a 32 bit code word that represents 1, 2, or 3. CFI 4 is reserved for possible future use.

The PCFICH uses 32,2 block coding which results in a 1/16 coding rate, and it always uses QPSK modulation to ensure robust reception. * Physical Downlink Control Channel (PDCCH) : The main purpose of this physical channel is to carry mainly scheduling information of different types: * Downlink resource scheduling * Uplink power control instructions * Uplink resource grant * Indication for paging or system information
The PDCCH contains a message known as the Downlink Control Information, DCI which carries the control information for a particular UE or group of UEs. The DCI format has several different types which are defined with different sizes. The different format types include: Type 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A, and 4. * Physical Hybrid ARQ Indicator Channel (PHICH) : As the name implies, this channel is used to report the Hybrid ARQ status. It carries the HARQ ACK/NACK signal indicating whether a transport block has been correctly received. The HARQ indicator is 1 bit long - "0" indicates ACK, and "1" indicates NACK.

The PHICH is transmitted within the control region of the subframe and is typically only transmitted within the first symbol. If the radio link is poor, then the PHICH is extended to a number symbols for robustness. * Uplink: * Physical Uplink Control Channel (PUCCH) : The Physical Uplink Control Channel, PUCCH provides the various control signalling requirements. There are a number of different PUCCH formats defined to enable the channel to carry the required information in the most efficient format for the particular scenario encountered. It includes the ability to carry SRs, Scheduling Requests.

The basic formats are summarised below: PUCCH FORMAT | UPLINK CONTROL INFORMATION | MODULATION SCHEME | BITS PER SUB-FRAME | NOTES | Format 1 | SR | N/A | N/A | | Format 1a | 1 bit HARQ ACK/NACK with or without SR | BPSK | 1 | | Format 1b | 2 bit HARQ ACK/NACK with or without SR | QPSK | 2 | | Format 2 | CQI/PMI or RI | QPSK | 20 | | Format 2a | CQI/PMI or RI and 1 bit HARQ ACK/NACK | QPSK + BPSK | 21 | | Format 2b | CQI/PMI or RI and 2 bit HARQ ACK/NACK | QPSK + BPSK | 22 | | Format 3 | | | | Provides support for carrier aggregation. | * Physical Uplink Shared Channel (PUSCH) : This physical channel found on the LTE uplink is the Uplink counterpart of PDSCH * Physical Random Access Channel (PRACH) : This uplink physical channel is used for random access functions. This is the only non-synchronised transmission that the UE can make within LTE. The downlink and uplink propagation delays are unknown when PRACH is used and therefore it cannot be synchronised.

The PRACH instance is made up from two sequences: a cyclic prefix and a guard period. The preamble sequence may be repeated to enable the eNodeB to decode the preamble when link conditions are poor.

LTE transport channels
The LTE transport channels vary between the uplink and the downlink as each has different requirements and operates in a different manner. Physical layer transport channels offer information transfer to medium access control (MAC) and higher layers. * Downlink: * Broadcast Channel (BCH) : The LTE transport channel maps to Broadcast Control Channel (BCCH) * Downlink Shared Channel (DL-SCH) : This transport channel is the main channel for downlink data transfer. It is used by many logical channels. * Paging Channel (PCH) : To convey the PCCH * Multicast Channel (MCH) : This transport channel is used to transmit MCCH information to set up multicast transmissions.

* Uplink: * Uplink Shared Channel (UL-SCH) : This transport channel is the main channel for uplink data transfer. It is used by many logical channels. * Random Access Channel (RACH) : This is used for random access requirements.

LTE logical channels
The logical channels cover the data carried over the radio interface. The Service Access Point, SAP between MAC sublayer and the RLC sublayer provides the logical channel. * Control channels: these LTE control channels carry the control plane information: * Broadcast Control Channel (BCCH) : This control channel provides system information to all mobile terminals connected to the eNodeB. * Paging Control Channel (PCCH) : This control channel is used for paging information when searching a unit on a network. * Common Control Channel (CCCH) : This channel is used for random access information, e.g. for actions including setting up a connection. * Multicast Control Channel (MCCH) : This control channel is used for Information needed for multicast reception. * Dedicated Control Channel (DCCH) : This control channel is used for carrying user-specific control information, e.g. for controlling actions including power control, handover, etc..

* Traffic channels:These LTE traffic channels carry the user-plane data: * Dedicated Traffic Channel (DTCH) : This traffic channel is used for the transmission of user data. * Multicast Traffic Channel (MTCH) : This channel is used for the transmission of multicast data.
It will be seen that many of the LTE channels bear similarities to those sued in previous generations of mobile telecommunications.

LTE Frequency Bands & Spectrum Allocations
- a summary and tables of the LTE frequency band spectrum allocations for 3G & 4G LTE - TDD and FDD.
There is a growing number of LTE frequency bands that are being designated as possibilities for use with LTE. Many of the LTE frequency bands are already in use for other cellular systems, whereas other LTE bands are new and being introduced as other users are re-allocated spectrum elsewhere.

FDD and TDD LTE frequency bands
FDD spectrum requires pair bands, one of the uplink and one for the downlink, and TDD requires a single band as uplink and downlink are on the same frequency but time separated. As a result, there are different LTE band allocations for TDD and FDD. In some cases these bands may overlap, and it is therefore feasible, although unlikely that both TDD and FDD transmissions could be present on a particular LTE frequency band.
The greater likelihood is that a single UE or mobile will need to detect whether a TDD or FDD transmission should be made on a given band. UEs that roam may encounter both types on the same band. They will therefore need to detect what type of transmission is being made on that particular LTE band in its current location.
The different LTE frequency allocations or LTE frequency bands are allocated numbers. Currently the LTE bands between 1 & 22 are for paired spectrum, i.e. FDD, and LTE bands between 33 & 41 are for unpaired spectrum, i.e. TDD.

LTE frequency band definitions

FDD LTE frequency band allocations
There is a large number of allocations or radio spectrum that has been reserved for FDD, frequency division duplex, LTE use.
The FDDLTE frequency bands are paired to allow simultaneous transmission on two frequencies. The bands also have a sufficient separation to enable the transmitted signals not to unduly impair the receiver performance. If the signals are too close then the receiver may be "blocked" and the sensitivity impaired. The separation must be sufficient to enable the roll-off of the antenna filtering to give sufficient attenuation of the transmitted signal within the receive band.

LTE BAND
NUMBER | UPLINK
(MHZ) | DOWNLINK
(MHZ) | WIDTH OF BAND (MHZ) | DUPLEX SPACING (MHZ) | BAND GAP (MHZ) | 1 | 1920 - 1980 | 2110 - 2170 | 60 | 190 | 130 | 2 | 1850 - 1910 | 1930 - 1990 | 60 | 80 | 20 | 3 | 1710 - 1785 | 1805 -1880 | 75 | 95 | 20 | 4 | 1710 - 1755 | 2110 - 2155 | 45 | 400 | 355 | 5 | 824 - 849 | 869 - 894 | 25 | 45 | 20 | 6 | 830 - 840 | 875 - 885 | 10 | 35 | 25 | 7 | 2500 - 2570 | 2620 - 2690 | 70 | 120 | 50 | 8 | 880 - 915 | 925 - 960 | 35 | 45 | 10 | 9 | 1749.9 - 1784.9 | 1844.9 - 1879.9 | 35 | 95 | 60 | 10 | 1710 - 1770 | 2110 - 2170 | 60 | 400 | 340 | 11 | 1427.9 - 1452.9 | 1475.9 - 1500.9 | 20 | 48 | 28 | 12 | 698 - 716 | 728 - 746 | 18 | 30 | 12 | 13 | 777 - 787 | 746 - 756 | 10 | -31 | 41 | 14 | 788 - 798 | 758 - 768 | 10 | -30 | 40 | 15 | 1900 - 1920 | 2600 - 2620 | 20 | 700 | 680 | 16 | 2010 - 2025 | 2585 - 2600 | 15 | 575 | 560 | 17 | 704 - 716 | 734 - 746 | 12 | 30 | 18 | 18 | 815 - 830 | 860 - 875 | 15 | 45 | 30 | 19 | 830 - 845 | 875 - 890 | 15 | 45 | 30 | 20 | 832 - 862 | 791 - 821 | 30 | -41 | 71 | 21 | 1447.9 - 1462.9 | 1495.5 - 1510.9 | 15 | 48 | 33 | 22 | 3410 - 3500 | 3510 - 3600 | 90 | 100 | 10 | 23 | 2000 - 2020 | 2180 - 2200 | 20 | 180 | 160 | 24 | 1625.5 - 1660.5 | 1525 - 1559 | 34 | -101.5 | 135.5 | 25 | 1850 - 1915 | 1930 - 1995 | 65 | 80 | 15 |

TDD LTE frequency band allocations
With the interest in TDD LTE, there are several unpaired frequency allocations that are being prepared for LTR TDD use. The TDD LTE allocations are unpaired because the uplink and downlink share the same frequency, being time multiplexed.

LTE BAND
NUMBER | ALLOCATION (MHZ) | WIDTH OF BAND (MHZ) | 33 | 1900 - 1920 | 20 | 34 | 2010 - 2025 | 15 | 35 | 1850 - 1910 | 60 | 36 | 1930 - 1990 | 60 | 37 | 1910 - 1930 | 20 | 38 | 2570 - 2620 | 50 | 39 | 1880 - 1920 | 40 | 40 | 2300 - 2400 | 100 | 41 | 2496 - 2690 | 194 | 42 | 3400 - 3600 | 200 | 43 | 3600 - 3800 | 200 |
There are regular additions to the LTE frequency bands / LTE spectrum allocations as a result of negotiations at the ITU regulatory meetings. These LTE allocations are resulting in part from the digital dividend, and also from the pressure caused by the ever growing need for mobile communications. Many of the new LTE spectrum allocations are relatively small, often 10 - 20MHz in bandwidth, and this is a cause for concern. With LTE-Advanced needing bandwidths of 100 MHz, channel aggregation over a wide set of frequencies many be needed, and this has been recognised as a significant technological problem. . . . . . . . .
Additional information on LTE frequency bands.
LTE UE Category and Class Definitions
- LTE utilises UE or User Equipment categories or classes to define the performance specifications an enable base stations to be able to communicate effectively with them knowing their performance levels.
In the same way that a variety of other systems adopted different categories for the handsets or user equipments, so too there are 3G LTE UE categories. These LTE categories define the standards to which a particular handset, dongle or other equipment will operate.

LTE UE category rationale
The LTE UE categories or UE classes are needed to ensure that the base station, or eNodeB, eNB can communicate correctly with the user equipment. By relaying the LTE UE category information to the base station, it is able to determine the performance of the UE and communicate with it accordingly.
As the LTE category defines the overall performance and the capabilities of the UE, it is possible for the eNB to communicate using capabilities that it knows the UE possesses. Accordingly the eNB will not communicate beyond the performance of the UE.

LTE UE category definitions there are five different LTE UE categories that are defined. As can be seen in the table below, the different LTE UE categories have a wide range in the supported parameters and performance. LTE category 1, for example does not support MIMO, but LTE UE category five supports 4x4 MIMO.
It is also worth noting that UE class 1 does not offer the performance offered by that of the highest performance HSPA category. Additionally all LTE UE categories are capable of receiving transmissions from up to four antenna ports.
A summary of the different LTE UE category parameters provided by the 3GPP Rel 8 standard is given in the tables below.

CATEGORY | 1 | 2 | 3 | 4 | 5 | Downlink | 10 | 50 | 100 | 150 | 300 | Uplink | 5 | 25 | 50 | 50 | 75 |
LTE UE category data rates

CATEGORY | 1 | 2 | 3 | 4 | 5 | Downlink | QPSK, 16QAM, 64QAM | Uplink | QPSK, 16QAM | QPSK,
16QAM,
64QAM |
LTE UE category modulation formats supported

CATEGORY | 1 | 2 | 3 | 4 | 5 | 2 Rx diversity | Assumed in performance requirements across all LTE UE categories | 2 x 2 MIMO | Not supported | Mandatory | 4 x 4 MIMO | Not supported | Mandatory |
LTE UE category MIMO antenna configurations
Note: Bandwidth for all categories is 20 MHz.

LTE UE category summary
In the same way that category information is used for virtually all cellular systems from GPRS onwards, so the LTE UE category information is of great importance. While users may not be particularly aware of the category of their UE, it will match the performance an allow the eNB to communicate effectively with all the UEs that are connected to it.

LTE SAE System Architecture Evolution
- information, overview, or tutorial about the basics of the 3G LTE SAE, system architecture evolution and the LTE Network
Along with 3G LTE - Long Term Evolution that applies more to the radio access technology of the cellular telecommunications system, there is also an evolution of the core network. Known as SAE - System Architecture Evolution. This new architecture has been developed to provide a considerably higher level of performance that is in line with the requirements of LTE.
As a result it is anticipated that operators will commence introducing hardware conforming to the new System Architecture Evolution standards so that the anticipated data levels can be handled when 3G LTE is introduced.
The new SAE, System Architecture Evolution has also been developed so that it is fully compatible with LTE Advanced, the new 4G technology. Therefore when LTE Advanced is introduced, the network will be able to handle the further data increases with little change.

Reason for SAE System Architecture Evolution
The SAE System Architecture Evolution offers many advantages over previous topologies and systems used for cellular core networks. As a result it is anticipated that it will be wide adopted by the cellular operators.
SAE System Architecture Evolution will offer a number of key advantages: 1. Improved data capacity: With 3G LTE offering data download rates of 100 Mbps, and the focus of the system being on mobile broadband, it will be necessary for the network to be able to handle much greater levels of data. To achieve this it is necessary to adopt a system architecture that lends itself to much grater levels of data transfer. 2. All IP architecture: When 3G was first developed, voice was still carried as circuit switched data. Since then there has been a relentless move to IP data. Accordingly the new SAE, System Architecture Evolution schemes have adopted an all IP network configuration. 3. Reduced latency: With increased levels of interaction being required and much faster responses, the new SAE concepts have been evolved to ensure that the levels of latency have been reduced to around 10 ms. This will ensure that applications using 3G LTE will be sufficiently responsive. 4. Reduced OPEX and CAPEX: A key element for any operator is to reduce costs. It is therefore essential that any new design reduces both the capital expenditure (CAPEX)and the operational expenditure (OPEX). The new flat architecture used for SAE System Architecture Evolution means that only two node types are used. In addition to this a high level of automatic configuration is introduced and this reduces the set-up and commissioning time.

SAE System Architecture Evolution basics
The new SAE network is based upon the GSM / WCDMA core networks to enable simplified operations and easy deployment. Despite this, the SAE network brings in some major changes, and allows far more efficient and effect transfer of data.
There are several common principles used in the development of the LTE SAE network: * a common gateway node and anchor point for all technologies. * an optimised architecture for the user plane with only two node types. * an all IP based system with IP based protocols used on all interfaces. * a split in the control / user plane between the MME, mobility management entity and the gateway. * a radio access network / core network functional split similar to that used on WCDMA / HSPA. * integration of non-3GPP access technologies (e.g. cdma2000, WiMAX, etc) using client as well as network based mobile-IP.
The main element of the LTE SAE network is what is termed the Evolved Packet Core or EPC. This connects to the eNodeBs as shown in the diagram below.

LTE SAE Evolved Packet Core
As seen within the diagram, the LTE SAE Evolved Packet Core, EPC consists of four main elements as listed below: * Mobility Management Entity, MME: The MME is the main control node for the LTE SAE access network, handling a number of features: * Idle mode UE tracking * Bearer activation / de-activation * Choice of SGW for a UE * Intra-LTE handover involving core network node location * Interacting with HSS to authenticate user on attachment and implements roaming restrictions * It acts as a termination for the Non-Access Stratum (NAS) * Provides temporary identities for UEs * The SAE MME acts the termination point for ciphering protection for NAS signaling. As part of this it also handles the security key management. Accordingly the MME is the point at which lawful interception of signalling may be made. * Paging procedure * The S3 interface terminates in the MME thereby providing the control plane function for mobility between LTE and 2G/3G access networks. * The SAE MME also terminates the S6a interface for the home HSS for roaming UEs.
It can therefore be seen that the SAE MME provides a considerable level of overall control functionality. * Serving Gateway, SGW: The Serving Gateway, SGW, is a data plane element within the LTE SAE. Its main purpose is to manage the user plane mobility and it also acts as the main border between the Radio Access Network, RAN and the core network. The SGW also maintains the data paths between the eNodeBs and the PDN Gateways. In this way the SGW forms a interface for the data packet network at the E-UTRAN.

Also when UEs move across areas served by different eNodeBs, the SGW serves as a mobility anchor ensuring that the data path is maintained. * PDN Gateway, PGW: The LTE SAE PDN gateway provides connectivity for the UE to external packet data networks, fulfilling the function of entry and exit point for UE data. The UE may have connectivity with more than one PGW for accessing multiple PDNs. * Policy and Charging Rules Function, PCRF: This is the generic name for the entity within the LTE SAE EPC which detects the service flow, enforces charging policy. For applications that require dynamic policy or charging control, a network element entitled the Applications Function, AF is used.

LTE SAE PCRF Interfaces

LTE SAE Distributed intelligence
In order that requirements for increased data capacity and reduced latency can be met, along with the move to an all-IP network, it is necessary to adopt a new approach to the network structure.
For 3G UMTS / WCDMA the UTRAN (UMTS Terrestrial Radio Access Network, comprising the Node B's or basestations and Radio Network Controllers) employed low levels of autonomy. The Node Bs were connected in a star formation to the Radio Network Controllers (RNCs) which carried out the majority of the management of the radio resource. In turn the RNCs connected to the core network and connect in turn to the Core Network.
To provide the required functionality within LTE SAE, the basic system architecture sees the removal of a layer of management. The RNC is removed and the radio resource management is devolved to the base-stations. The new style base-stations are called eNodeBs or eNBs.
The eNBs are connected directly to the core network gateway via a newly defined "S1 interface". In addition to this the new eNBs also connect to adjacent eNBs in a mesh via an "X2 interface". This provides a much greater level of direct interconnectivity. It also enables many calls to be routed very directly as a large number of calls and connections are to other mobiles in the same or adjacent cells. The new structure allows many calls to be routed far more directly and with only minimum interaction with the core network.
In addition to the new Layer 1 and Layer 2 functionality, eNBs handle several other functions. This includes the radio resource control including admission control, load balancing and radio mobility control including handover decisions for the mobile or user equipment (UE).
The additional levels of flexibility and functionality given to the new eNBs mean that they are more complex than the UMTS and previous generations of base-station. However the new 3G LTE SAE network structure enables far higher levels of performance. In addition to this their flexibility enables them to be updated to handle new upgrades to the system including the transition from 3G LTE to 4G LTE Advanced.
The new System Architecture Evolution, SAE for LTE provides a new approach for the core network, enabling far higher levels of data to be transported to enable it to support the much higher data rates that will be possible with LTE. In addition to this, other features that enable the CAPEX and OPEX to be reduced when compared to existing systems, thereby enabling higher levels of efficiency to be achieved.

LTE SON Self Organizing Networks
- LTE, Long Term Evolution and the requirements for LTE SON, Self Organising Networks
With LTE requiring smaller cell sizes to enable the much greater levels of data traffic to be handled, there networks have become considerably more complicated and trying to plan and manage the network centrally is not as viable. Coupled with the need to reduce costs by reducing manual input, there has been a growing impetus to implement self organising networks.
Accordingly LTE can be seen as one of the major drivers behind the self-organising network, SON philosophy.
Accordingly 3GPP developed many of the requirements for LTE SON to sit alongside the basic functionality of LTE. As a result the standards for LTE SON are embedded within the 3GPP standards.

LTE SON development
The term SON came into frequent use after the term was adopted by the Next Generation Mobile Networks, NGMN alliance. The idea came about as result of the need within LTE to be able to deploy many more cells. Femtocells and other microcells are an integral part of the LTE deployment strategy. With revenue per bit falling, costs for deployment must be kept to a minimum as well as ensuring the network is operating to its greatest efficiency.
3GPP, the Third Generation Partnership Programme has created the standards for SON and as they are generally first to be deployed with LTE, they are often referred to as LTE SON.
While 3GPP has generated the standards, they have been based upon long term objectives for a 'SON-enabled broadband mobile network' set out by the NGMN.
NGMN has defined the necessary use cases, measurements, procedures and open interfaces to ensure that multivendor offerings are available. 3GPP has incorporated these aspirations into useable standards.

Major elements of LTE SON
Although LTE SON self-optimising networks is one of the major drivers for the generic SON technology, the basic requirements remain the same whatever the technology to which it will be applied.
The main elements of SON include:
Self configuration: The aim for the self configuration aspects of LTE SON is to enable new base stations to become essentially "Plug and Play" items. They should need as little manSON Self Configuration major features
There are a number of major elements that are included within the self-configuration of the new base station. These include aspects such as the following: * Automatic configuration of initial radio transmission parameters : The automatic configuration of the radio transmission parameters within the SON Self configuration is of great importance. While some information will be available centrally, other information is best gathered by the base station or eNB itself. With a base station in place it is normally found that the planned data is not quite as expected and some adjustments need to be made to provide the optimum performance and this procedure can be very time consuming.

A technique called Dynamic Radio Configuration, DRC is used which allows the base station to become adaptive to the current radio network topology. The DRC configures a variety of items including the cell ID, initial power and antenna tilt settings, etc..

The various settings required can be determined by the base station, eNB when it is in its installation process. These will ensure that real measured parameters are used rather than estimated ones from any planning tools. * Automatic neighbour relation, ANR, management: One of the major labour intensive activities for mobile network operators is the updates for neighbour cell relationships to facilitate easy handovers. It is necessary to have the correct neighbour relationships in place otherwise this will result in dropped calls as a result of handovers failing to complete correctly.

The manual update of neighbour relationships become even more complicated as the network needs to decide if it can handover to a neighbour cell with a similar radio access technology, or whether it has to change, e.g. from LTE to HSPA, etc.. The UE is provided with a neighbour list by the base station or Node B, and this provides the frequencies the UE should monitor for handover.

The elements of Self Organising Networks, SON that provide this element of SON self-configuration includes the automatic neighbour cell configuration and this can be largely automated. Network performance will also benefit from the optimised and up to date lists as correct neighbour lists will increase the number of successful handovers, and also reduce the network load from additional set-ups required for poor handovers.

An additional advantage is that with LTE possessing a very flat structure to improve latency, etc, the operator would need to manually configure huge amounts of neighbour data within the LTE eNBs. In this way SON self-configuration of the neighbour relationships can significantly reduce OPEX and improve performance and efficiency while providing a better service for the users, thereby having a positive impact on churn. * Automatic connectivity management: The auto-connectivity system provides the ability for the new base station, eNB to automatically connect to its domain management system. There are several stages involved in the set-up of the connectivity: * Basic connectivity set-up: The base station, eNB requires an initial IP configuration to enable backhaul connectivity to be established. This initial IP configuration may be replaced later with a more permanent, post set-up IP configuration. * Initial secure connection set-up: The security of the backhaul connection is based upon the use of keys. Once the keys have been set up and verified, the secure communications is possible. Only when secure communication is available can data be transferred. * Site identification: This is required to define which configuration data is to be used. This is needed because most sites require some pre-configuration data to be used. * Download of final configuration and transport parameters: This stage must be completed before the next stage in the connectivity management can take place. * Secure connection set-up: At this stage the temporary secure connection is taken down and a new connection with full security is established. This may use either TLS or IPsec.
The SON auto-connectivity management / SON self-configuration requires functionality to reside both at the base station, eNB and also within the core network as well. * Self-test: A self-test is normally performed as part of the SON self-configuration to ensure the correct operation of the equipment prior to final active service. * Automatic inventory: This activity includes aspects such as identifying what hardware boards are fitted, software level, antennas, etc. In this way the base station is able to identify its capabilities. As most of the base stations will have various options that could be fitted dependent upon the capabilities required, it is necessary for the SON self-configuration software to perform an inventory check before proceeding further.

SON self-configuration deployment
The adoption of SON self-configuration involves the whole network. Capability must be introduced into many areas of the network to provide for the self-configuration to be undertaken. While many of the facilities can be self-configured, so pre-planning is normally required to enable the system to start operation.
However in many instances new cells can be added with the minimum of input from the operator. Femtocells are a prime example of this, they are deployed on an ad-hoc bases. They need to undertake all the stages of self-configuration that are outlined here. * ual intervention in the configuration process as possible. Not only will they be able to organise the RF aspects, but also configure the backhaul as well. * Self optimisation: Once the system has been set up, LTE SON capabilities will enable the base station to optimise the operational characteristics to best meet the needs of the overall network. * Self-healing: Another major feature of LTE SON is to enable the network to self-heal. It will do this by changing the characteristics of the network to mask the problem until it is fixed. For example, the boundaries of adjacent cells can be increased by changing antenna directions and increasing power levels, etc..
Typically an LTE SON system is a software package with relevant options that is incorporated into an operator's network.

Note on SON, Self Organizing Networks:
SON mainly came out of the requirements of LTE and the more complicated networks that will arise. However the concepts behind SON can be applied at any network enabling its efficiency to be increased while keeping costs low. Accordingly, it is being used increasingly to reduce operational and capital expenditure by adding software to the network to enable it to organise and run itself.
Click on the link for further information about Self Organising Networks, SON

LTE SON and 3GPP standards
LTE Son has been standardised in the various 3GPP standards. It was first incorporated into 3GPP release 8, and further functionality has been progressively added in the further releases of the standards.
One of the major aims of the 3GPP standardization is the support of SON features is to ensure that multi-vendor network environments operate correctly with LTE SON. As a result, 3GPP has defined a set of LTE SON use cases and the associated SON functions.
As the functionality of LTE advances, the LTE SON standardisation effectively track the LTE network evolution stages. In this way SON will be applicable to the LTE networks.
Voice over LTE - VoLTE
- operation of Voice over LTE VoLTE system for providing a unified format of voice traffic on LTE, and other systems including CSFB, and SV-LTE.
The Voice over LTE, VoLTE scheme was devised as a result of operators seeking a standardised system for transferring voice traffic over LTE. Originally LTE was seen as a completely IP cellular system just for carrying data, and operators would be able to carry voice either by reverting to 2G / 3G systems or by using VoIP.
Operators, however saw the fact that a voice format was not defined as a major omission for the system. It was seen that the lack of standardisation may provide problems with scenarios including roaming. In addition to this, SMS is a key requirement. It is not often realised, that SMS is used to set-up many mobile broadband connections, and a lack of SMS is seen as a show-stopper by many.
As mobile operators receive over 80% of their revenues from voice and SMS traffic, it is necessary to have a viable and standardized scheme to provide these services and protect this revenue.

Options for Voice over LTE
When looking at the options for ways of carrying voice over LTE, a number of possible solutions were investigated. A number of alliances were set up to promote different ways of providing the service. A number of systems were prosed as outlined below: * CSFB, Circuit Switched Fall Back: The circuit switched fallback, CSFB option for providing voice over LTE has been standardised under 3GPP specification 23.272. Essentially LTE CSFB uses a variety of processes and network elements to enable the circuit to fall back to the 2G or 3G connection (GSM, UMTS, CDMA2000 1x) before a circuit switched call is initiated.

The specification also allows for SMS to be carried as this is essential for very many set-up procedures for cellular telecommunications. To achieve this the handset uses an interface known as SGs which allows messages to be sent over an LTE channel.

In addition to this CSFB requires modification to elements within the network, in particular the MSCs as well as support, obviously on new devices. MSC modifications are also required for the SMS over SGs facilities. For CSFB, this is required from the initial launch of CSFB in view of the criticality of SMS for many procedures. * SV-LTE - simultaneous voice LTE: SV-LTE allows to run packet switched LTE services simultaneously with a circuit switched voice service. SV-LTE facility provides the facilities of CSFB at the same time as running a packet switched data service. This is an option that many operators will opt for. However it has the disadvantage that it requires two radios to run at the same time within the handset. This has a serious impact on battery life. * VoLGA, Voice over LTE via GAN: The VoLGA standard was based on the existing 3GPP Generic Access Network (GAN) standard, and the aim was to enable LTE users to receive a consistent set of voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks.

For mobile operators, the aim of VoLGA was to provide a low-cost and low-risk approach for bringing their primary revenue generating services (voice and SMS) onto the new LTE network deployments. * One Voice / later called Voice over LTE, VoLTE: The Voice over LTE, VoLTE schem for providing voice over an LTE system utilises IMS enabling it to become part of a rich media solution.

Issues for Voice services over LTE
Unlike previous cellular telecommunications standards including GSM, LTE does not have dedicated channels for circuit switched telephony. Instead LTE is an all-IP system providing an end-to-end IP connection from the mobile equipment to the core network and out again.
In order to provide some form of voice connection over a standard LTE bearer, some form of Voice over IP, VoIP must be used.
The aim for any voice service is to utilise the low latency and QoS features available within LTE to ensure that any voice service offers an improvement over the standards available on the 2G and 3G networks.
However to achieve a full VoIP offering on LTE poses some significant problems which will take time to resolve. With the first deployments having taken place in 2010, it is necessary that a solution for voice is available within a short timescale.

Voice over LTE, VoLTE basics
The One Voice profile for Voice over LTE was developed by a collaboration between over forty operators including: AT&T, Verizon Wireless, Nokia and Alcatel-Lucent.
At the 2010 GSMA Mobile World Congress, GSMA announced that they were supporting the One Voice solution to provide Voice over LTE.
VoLTE, Voice over LTE is an IMS-based specification. Adopting this approach, it enables the system to be integrated with the suite of applications that will become available on LTE.

Note on IMS:
The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem, IMS is an architectural framework for delivering Internet Protocol, IP multimedia services. It enables a variety of services to be run seemlessly rather than having several disparate applications operating concurrently.
Click for a IMS tutorial

To provide the VoLTE service, three interfaces are being defined: * User Network interface, UNI: This interface is located between the user's equipment and the operators network. * Roaming Network Network Interface, R-NNI: The R-NNI is an interface located between the Home and Visited Network. This is used for a user that is not attached to their Home network, i.e. roaming. * Interconnect Network Network Interface, I-NNI: The I-NNI is the interface located between the networks of the two parties making a call.
Work on the definition of VoLTE, Voice over LTE is ongoing. It will include a variety of elements including some of the following: * It will be necessary to ensure the continuity of Voice calls when a user moves from an LTE coverage area to another where a fallback to another technology is required. This form of handover will be achieved using Single Radio Voice Call Continuity, or SR-VCC). * It will be important to provide the optimal routing of bearers for voice calls when customers are roaming. * Another area of importance will be to establish commercial frameworks for roaming and interconnect for services implemented using VoLTE definitions. This will enable roaming agreements to be set up. * Provision of capabilities associated with the model of roaming hubbing. * For any services, including LTE, it is necessary to undertake a thorough security and fraud threat audit to prevent hacking and un-authorised entry into any area within the network..
In many ways the implementation of VoLTE at a high level is straightforward. The handset or phone needs to have software loaded to provide the VoLTE functionality. This can be in the form of an App.
The network then requires to be IMS compatible.
While this may appear straightforward, there are many issues for this to be made operational, especially via the vagaries of the radio access network where time delays and propagation anomalies add considerably to the complexity.

LTE Security
- overview, about the basics of LTE security including the techniques used for LTE authentication, ciphering, encryption, and identity protection.
LTE security is an issue that is of paramount importance. It is necessary to ensure that LTE security measures provide the level of security required without impacting the user as this could drive users away.
Nevertheless with the level of sophistication of security attacks growing, it is necessary to ensure that LTE security allows users to operate freely and without fear of attack from hackers. Additionally the network must also be organised in such a way that it is secure against a variety of attacks.

LTE security basics
When developing the LTE security elements there were several main requirements that were borne in mind: * LTE security had to provide at least the same level of security that was provided by 3G services. * The LTE security measures should not affect user convenience. * The LTE security measures taken should provide defence from attacks from the Internet. * The security functions provided by LTE should not affect the transition from existing 3G services to LTE. * The USIM currently used for 3G services should still be used.
To ensure these requirements for LTE security are met, it has been necessary to add further measures into all areas of the system from the UE through to the core network.
The main changes that have been required to implement the required level of LTE security are summarised below: * A new hierarchical key system has been introduced in which keys can be changed for different purposes. * The LTE security functions for the Non-Access Stratum, NAS, and Access Stratum, AS have been separated. The NAS functions are those functions for which the processing is accomplished between the core network and the mobile terminal or UE. The AS functions encompass the communications between the network edge, i.e. the Evolved Node B, eNB and the UE. * The concept of forward security has been introduced for LTE security. * LTE security functions have been introduced between the existing 3G network and the LTE network.

LTE USIM
One of the key elements within the security of GSM, UMTS and now LTE was the concept of the subscriber identity module, SIM. This card carried the identity of the subscriber in an encrypted fashion and this could allow the subscriber to keep their identity while transferring or upgrading phones.
With the transition form 2G - GSM to 3G - UMTS, the idea of the SIM was upgraded and a USIM - UMTS Subscriber Identity Module, was used. This gave more functionality, had a larger memory, etc.
For LTE, only the USIM may be used - the older SIM cards are not compatible and may not be used.

4G LTE Advanced Tutorial
- overview, information, tutorial about the basics of LTE Advanced, the 4G technology being called IMT Advanced being developed under 3GPP.
With the standards definitions now available for LTE, the Long Term Evolution of the 3G services, eyes are now turning towards the next development, that of the truly 4G technology named IMT Advanced. The new technology being developed under the auspices of 3GPP to meet these requirements is often termed LTE Advanced.
In order that the cellular telecommunications technology is able to keep pace with technologies that may compete, it is necessary to ensure that new cellular technologies are being formulated and developed. This is the reasoning behind starting the development of the new LTE Advanced systems, proving the technology and developing the LTE Advanced standards.
In order that the correct solution is adopted for the 4G system, the ITU-R (International Telecommunications Union - Radiocommunications sector) has started its evaluation process to develop the recommendations for the terrestrial components of the IMT Advanced radio interface. One of the main competitors for this is the LTE Advanced solution.
One of the key milestones is October 2010 when the ITU-R decides the framework and key characteristics for the IMT Advanced standard. Before this, the ITU-R will undertake the evaluation of the various proposed radio interface technologies of which LTE Advanced is a major contender.

Key milestones for ITU-R IMT Advanced evaluation
The ITU-R has set a number of milestones to ensure that the evaluation of IMT Advanced technologies occurs in a timely fashion. A summary of the main milestones is given below and this defines many of the overall timescales for the development of IMT Advanced and in this case LTE Advanced as one of the main technologies to be evaluated.

MILESTONE | DATE | Issue invitation to propose Radio Interface Technologies. | March 2008 | ITU date for cut-off for submission of proposed Radio Interface Technologies. | October 2009 | Cutoff date for evaluation report to ITU. | June 2010 | Decision on framework of key characteristics of IMT Advanced Radio Interface Technologies. | October 2010 | Completion of development of radio interface specification recommendations. | February 2011 |

LTE Advanced development history
With 3G technology established, it was obvious that the rate of development of cellular technology should not slow. As a result initial ideas for the development of a new 4G system started to be investigated. In one early investigation which took place on 25 December 2006 with information released to the press on 9 February 2007, NTT DoCoMo detailed information about trials in which they were able to send data at speeds up to approximately 5 Gbit/s in the downlink within a 100MHz bandwidth to a mobile station moving at 10km/h. The scheme used several technologies to achieve this including variable spreading factor spread orthogonal frequency division multiplex, MIMO, multiple input multiple output, and maximum likelihood detection. Details of these new 4G trials were passed to 3GPP for their consideration
In 2008 3GPP held two workshops on IMT Advanced, where the "Requirements for Further Advancements for E-UTRA" were gathered. The resulting Technical Report 36.913 was then published in June 2008 and submitted to the ITU-R defining the LTE-Advanced system as their proposal for IMT-Advanced.
The development of LTE Advanced / IMT Advanced can be seen to follow and evolution from the 3G services that were developed using UMTS / W-CDMA technology.

| WCDMA
(UMTS) | HSPA
HSDPA / HSUPA | HSPA+ | LTE | LTE ADVANCED
(IMT ADVANCED) | Max downlink speed bps | 384 k | 14 M | 28 M | 100M | 1G | Max uplink speed bps | 128 k | 5.7 M | 11 M | 50 M | 500 M | Latency round trip time approx | 150 ms | 100 ms | 50ms (max) | ~10 ms | less than 5 ms | 3GPP releases | Rel 99/4 | Rel 5 / 6 | Rel 7 | Rel 8 | Rel 10 | Approx years of initial roll out | 2003 / 4 | 2005 / 6 HSDPA
2007 / 8 HSUPA | 2008 / 9 | 2009 / 10 | | Access methodology | CDMA | CDMA | CDMA | OFDMA / SC-FDMA | OFDMA / SC-FDMA |
LTE Advanced is not the only candidate technology. WiMAX is also there, offering very high data rates and high levels of mobility. However it now seems less likely that WiMAX will be adopted as the 4G technology, with LTE Advanced appearing to be better positioned.

LTE Advanced key features
With work starting on LTE Advanced, a number of key requirements and key features are coming to light. Although not fixed yet in the specifications, there are many high level aims for the new LTE Advanced specification. These will need to be verified and much work remains to be undertaken in the specifications before these are all fixed. Currently some of the main headline aims for LTE Advanced can be seen below: 1. Peak data rates: downlink - 1 Gbps; uplink - 500 Mbps. 2. Spectrum efficiency: 3 times greater than LTE. 3. Peak spectrum efficiency: downlink - 30 bps/Hz; uplink - 15 bps/Hz. 4. Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used. 5. Latency: from Idle to Connected in less than 50 ms and then shorter than 5 ms one way for individual packet transmission. 6. Cell edge user throughput to be twice that of LTE. 7. Average user throughput to be 3 times that of LTE. 8. Mobility: Same as that in LTE 9. Compatibility: LTE Advanced shall be capable of interworking with LTE and 3GPP legacy systems.
These are many of the development aims for LTE Advanced. Their actual figures and the actual implementation of them will need to be worked out during the specification stage of the system.

LTE Advanced technologies
There are a number of key technologies that will enable LTE Advanced to achieve the high data throughput rates that are required. MIMO and OFDM are two of the base technologies that will be enablers. Along with these there are a number of other techniques and technologies that will be employed.
OFDM forms the basis of the radio bearer. Along with it there is OFDMA (Orthogonal Frequency Division Multiple Access) along with SC-FDMA (Single Channel Orthogonal Frequency Division Multiple Access). These will be used in a hybrid format. However the basis for all of these access schemes is OFDM.

Note on OFDM:
Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..
Click on the link for an OFDM tutorial

One of the other key enablers for LTE Advanced that is common to LTE is MIMO. This scheme is also used by many other technologies including WiMAX and Wi-Fi - 802.11n. MIMO - Multiple Input Multiple Output enables the data rates achieved to be increased beyond what the basic radio bearer would normally allow.

Note on MIMO:
Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.
Click on the link for a MIMO tutorial

For LTE Advanced, the use of MIMO is likely to involve further and more advanced techniques with additional antennas in the matrix to enable additional paths to be sued, although as the number of antennas increases, the overhead increases and the return per additional path is less.
In additional to the numbers of antennas increasing, it is likely that techniques such as beamforming may be used to enable the antenna coverage to be focused where it is needed.
With data rates rising well above what was previously available, it will be necessary to ensure that the core network is updated to meet the increasing requirements. It is therefore necessary to further improve the system architecture.
These and other technologies will be used with LTE Advanced to provide the very high data rates that are being sought along with the other performance characteristics that are needed. . . . . . . . . . .

LTE CA: Carrier Aggregation Tutorial
- 4G LTE Advanced CA, carrier aggregation or channel aggregation enables multiple LTE carriers to be used together to provide the high data rates required for 4G LTE Advanced.
LTE Advanced offers considerably higher data rates than even the initial releases of LTE. While the spectrum usage efficiency has been improved, this alone cannot provide the required data rates that are being headlined for 4G LTE Advanced.
To achieve these very high data rates it is necessary to increase the transmission bandwidths over those that can be supported by a single carrier or channel. The method being proposed is termed carrier aggregation, CA, or sometimes channel aggregation. Using LTE Advanced carrier aggregation, it is possible to utilise more than one carrier and in this way increase the overall transmission bandwidth.
These channels or carriers may be in contiguous elements of the spectrum, or they may be in different bands.
Spectrum availability is a key issue for 4G LTE. In many areas only small bands are available, often as small as 10 MHz. As a result carrier aggregation over more than one band is contained within the specification, although it does present some technical challenges.
Carrier aggregation is supported by both formats of LTE, namely the FDD and TDD variants. This ensures that both FDD LTE and TDD LTE are able to meet the high data throughput requirements placed upon them.

LTE carrier aggregation basics
The target figures for data throughput in the downlink is 1 Gbps for 4G LTE Advanced. Even with the improvements in spectral efficiency it is not possible to provide the required headline data throughput rates within the maximum 20 MHz channel. The only way to achieve the higher data rates is to increase the overall bandwidth used. IMT Advanced sets the upper limit at 100 MHz, but with an expectation of 40 MHz being used for minimum performance. For the future it is possible the top limit of 100 MHz could be extended.
It is well understood that spectrum is a valuable commodity, and it takes time to re-assign it from one use to another in view - the cost of forcing users to move is huge as new equipment needs to be bought. Accordingly as sections of the spectrum fall out of use, they can be re-assigned. This leads to significant levels of fragmentation.
To an LTE terminal, each component carrier appears as an LTE carrier, while an LTE-Advanced terminal can exploit the total aggregated bandwidth.

RF aspects of carrier aggregation
There are a number of ways in which LTE carriers can be aggregated:

Types of LTE carrier aggregation * Intra-band: This form of carrier aggregation uses a single band. There are two main formats for this type of carrier aggregation: * Contiguous: The Intra-band contiguous carrier aggregation is the easiest form of LTE carrier aggregation to implement. Here the carriers are adjacent to each other.

Contiguous aggregation of two uplink component carriers

The aggregated channel can be considered by the terminal as a single enlarged channel from the RF viewpoint. In this instance, only one transceiver is required within the terminal or UE, whereas more are required where the channels are not adjacent. However as the RF bandwidth increases it is necessary to ensure that the UE in particular is able to operate over such a wide bandwidth without a reduction in performance. Although the performance requirements are the same for the base station, the space, power consumption, and cost requirements are considerably less stringent, allowing greater flexibility in the design. Additionally for the base station, multi-carrier operation, even if non-aggregated, is already a requirement in many instances, requiring little or no change to the RF elements of the design. Software upgrades would naturally be required to cater for the additional capability. * Non-contiguous: Non-contiguous intra-band carrier aggregation is somewhat more complicated than the instance where adjacent carriers are used. No longer can the multi-carrier signal be treated as a single signal and therefore two transceivers are required. This adds significant complexity, particularly to the UE where space, power and cost are prime considerations. * Inter-band non-contiguous: This form of carrier aggregation uses different bands. It will be of particular use because of the fragmentation of bands - some of which are only 10 MHz wide. For the UE it requires the use of multiple transceivers within the single item, with the usual impact on cost, performance and power. In addition to this there are also additional complexities resulting from the requirements to reduce intermodulation and cross modulation from the two transceivers
The current standards allow for up to five 20 MHz carriers to be aggregated, although in practice two or three is likely to be the practical limit. These aggregated carriers can be transmitted in parallel to or from the same terminal, thereby enabling a much higher throughput to be obtained.

Carrier aggregation bandwidths
When aggregating carriers for an LTE signal, there are several definitions required for the bandwidth of the combined channels. As there as several bandwidths that need to be described, it is necessary to define them to reduce confusion.

LTE Carrier Aggregation Bandwidth Definitions for Intra-Band Case

LTE carrier aggregation bandwidth classes
There is a total of six different carrier aggregation, CA bandwidth classes which are being defined.

CARRIER AGGREGATION
BANDWIDTH CLASS | AGGREGATED TRANSMISSION
BW CONFIGURATION | NUMBER OF COMPONENT CARRIERS | A | ≤100 | 1 | B | ≤100 | 2 | C | 100 - 200 | 2 |
NB: classes D, E, & F are in the study phase.

LTE aggregated carriers
When carriers are aggregated, each carrier is referred to as a component carrier. There are two categories: * Primary component carrier: This is the main carrier in any group. There will be a primary downlink carrier and an associated uplink primary component carrier. * Secondary component carrier: There may be one or more secondary component carriers.
There is no definition of which carrier should be used as a primary component carrier - different terminals may use different carriers. The configuration of the primary component carrier is terminal specific and will be determined according to the loading on the various carriers as well as other relevant parameters.
In addition to this the association between the downlink primary carrier and the corresponding uplink primary component carrier is cell specific. Again there are no definitions of how this must be organised. The information is signalled to the terminal of user equipment as part of the overall signalling between the terminal and the base station.

Carrier aggregation cross carrier scheduling
When LTE carrier aggregation is used, it is necessary to be able to schedule the data across the carriers and to inform the terminal of the DCI rates for the different component carriers. This information may be implicit, or it may be explicit dependent upon whether cross carrier scheduling is used.
Enabling of the cross carrier scheduling is achieved individually via the RRC signalling on a per component carrier basis or a per terminal basis.
When no cross carrier scheduling is arranged, the downlink scheduling assignments achieved on a per carrier basis, i.e. they are valid for the component carrier on which they were transmitted.
For the uplink, an association is created between one downlink component carrier and an uplink component carrier. In this way when uplink grants are sent the terminal or UE will know to which uplink component carrier they apply.
Where cross carrier scheduling is active, the PDSCH on the downlink or the PUSCH on the uplink is transmitted on an associate component carrier other than the PDCCH, the carrier indicator in the PDCCH provides the information about the component carrier used for the PDSCH or PUSCH.
It is necessary to be able to indicate to which component carrier in any aggregation scheme a grant relates. To facilitate this, component carriers are numbered. The primary component carrier is numbered zero, for all instances, and the different secondary component carriers are assigned a unique number through the UE specific RRC signalling. This means that even if the terminal or user equipment and the base station, eNodeB may have different understandings of the component carrier numbering during reconfiguration, transmissions on the primary component carrier can be scheduled.

4G LTE CoMP, Coordinated Multipoint Tutorial
- 4G LTE Advanced CoMP, coordinated multipoint is used to send and receive data to and from a UE from several points to ensure the optimum performance is achieved even at cell edges.
LTE CoMP or Coordinated Multipoint is a facility that is being developed for LTE Advanced - many of the facilities are still under development and may change as the standards define the different elements of CoMP more specifically.
LTE Coordinated Multipoint is essentially a range of different techniques that enable the dynamic coordination of transmission and reception over a variety of different base stations. The aim is to improve overall quality for the user as well as improving the utilisation of the network.
Essentially, LTE Advanced CoMP turns the inter-cell interference, ICI, into useful signal, especially at the cell borders where performance may be degraded.
Over the years the importance of inter-cell interference, ICI has been recognised, and various techniques used from the days of GSM to mitigate its effects. Here interference averaging techniques such as frequency hopping were utilised. However as technology has advanced, much tighter and more effective methods of combating and utilising the interference have gained support.

LTE CoMP and 3GPP
The concepts for Coordinated Multipoint, CoMP, have been the focus of many studies by 3GPP for LTE-Advanced as well as the IEEE for their WiMAX, 802.16 standards. For 3GPP there are studies that have focussed on the techniques involved, but no conclusion has been reached regarding the full implementation of the scheme. However basic concepts have been established and these are described below.
CoMP has not been included in Rel.10 of the 3GPP standards, but as work is on-going, CoMP is likely to reach a greater level of consensus. When this occurs it will be included in future releases of the standards.
Despite the fact that Rel.10 does not provide any specific support for CoMP, some schemes can be implemented in LTE Rel.10 networks in a proprietary manner. This may enable a simpler upgrade when standardisation is finally agreed.

LTE CoMP - the advantages
Although LTE Advanced CoMP, Coordinated Multipoint is a complex set of techniques, it brings many advantages to the user as well as the network operator. * Makes better utilisation of network: By providing connections to several base stations at once, using CoMP, data can be passed through least loaded base stations for better resource utilisation. * Provides enhanced reception performance: Using several cell sites for each connection means that overall reception will be improved and the number of dropped calls should be reduced. * Multiple site reception increases received power: The joint reception from multiple base stations or sites using LTE Coordinated Multipoint techniques enables the overall received power at the handset to be increased. * Interference reduction: By using specialised combining techniques it is possible to utilise the interference constructively rather than destructively, thereby reducing interference levels.

What is LTE CoMP? - the basics
Coordinated multipoint transmission and reception actually refers to a wide range of techniques that enable dynamic coordination or transmission and reception with multiple geographically separated eNBs. Its aim is to enhance the overall system performance, utilise the resources more effectively and improve the end user service quality.
One of the key parameters for LTE as a whole, and in particular 4G LTE Advanced is the high data rates that are achievable. These data rates are relatively easy to maintain close to the base station, but as distances increase they become more difficult to maintain.
Obviously the cell edges are the most challenging. Not only is the signal lower in strength because of the distance from the base station (eNB), but also interference levels from neighbouring eNBs are likely to be higher as the UE will be closer to them.
4G LTE CoMP, Coordinated Multipoint requires close coordination between a number of geographically separated eNBs. They dynamically coordinate to provide joint scheduling and transmissions as well as proving joint processing of the received signals. In this way a UE at the edge of a cell is able to be served by two or more eNBs to improve signals reception / transmission and increase throughput particularly under cell edge conditions.

Concept of LTE Advanced CoMP - Coordinated Multipoint
In essence, 4G LTE CoMP, Coordinated Multipoint falls into two major categories: * Joint processing: Joint processing occurs where there is coordination between multiple entities - base stations - that are simultaneously transmitting or receiving to or from UEs. * Coordinated scheduling or beamforming: This often referred to as CS/CB (coordinated scheduling / coordinated beamforming) is a form of coordination where a UE is transmitting with a single transmission or reception point - base station. However the communication is made with an exchange of control among several coordinated entities.
To achieve either of these modes, highly detailed feedback is required on the channel properties in a fast manner so that the changes can be made. The other requirement is for very close coordination between the eNBs to facilitate the combination of data or fast switching of the cells.
The techniques used for coordinated multipoint, CoMP are very different for the uplink and downlink. This results from the fact that the eNBs are in a network, connected to other eNBs, whereas the handsets or UEs are individual elements.

Downlink LTE CoMP
The downlink LTE CoMP requires dynamic coordination amongst several geographically separated eNBs transmitting to the UE. The two formats of coordinated multipoint can be divided for the downlink: * Joint processing schemes for transmitting in the downlink : Using this element of LTE CoMP, data is transmitted to the UE simultaneously from a number of different eNBs. The aim is to improve the received signal quality and strength. It may also have the aim of actively cancelling interference from transmissions that are intended for other UEs.

This form of coordinated multipoint places a high demand onto the backhaul network because the data to be transmitted to the UE needs to be sent to each eNB that will be transmitting it to the UE. This may easily double or triple the amount of data in the network dependent upon how many eNBs will be sending the data. In addition to this, joint processing data needs to be sent between all eNBs involved in the CoMP area. * Coordinated scheduling and or beamforming: Using this concept, data to a single UE is transmitted from one eNB. The scheduling decisions as well as any beams are coordinated to control the interference that may be generated.

The advantage of this approach is that the requirements for coordination across the backhaul network are considerably reduced for two reasons: * UE data does not need to be transmitted from multiple eNBs, and therefore only needs to be directed to one eNB. * Only scheduling decisions and details of beams needs to be coordinated between multiple eNBs.

Uplink LTE CoMP * Joint reception and processing: The basic concept behind this format is to utilise antennas at different sites. By coordinating between the different eNBs it is possible to form a virtual antenna array. The signals received by the eNBs are then combined and processed to produce the final output signal. This technique allows for signals that are very low in strength, or masked by interference in some areas to be receiving with few errors.

The main disadvantage with this technique is that large amounts of data need to be transferred between the eNBs for it to operate. * Coordinated scheduling: This scheme operates by coordinating the scheduling decisions amongst the ENBs to minimise interference.

As in the case of the downlink, this format provides a much reduced load in the backhaul network because only the scheduling data needs to be transferred between the different eNBs that are coordinating with each other.

Overall requirements for LTE CoMP
One of the key requirements for LTE is that it should be able to provide a very low level of latency. The additional processing required for multiple site reception and transmission could add significantly to any delays. This could result from the need for the additional processing as well as the communication between the different sites.
To overcome this, it is anticipated that the different sites may be connected together in a form of centralised RAN, or C-RAN.

4G LTE Advanced Relay
- 4G LTE Advanced relay technology, how LTE relaying works and details about relay nodes, RNs.
Relaying is one of the features being proposed for the 4G LTE Advanced system. The aim of LTE relaying is to enhance both coverage and capacity.
The idea of relays is not new, but LTE relays and LTE relaying is being considered to ensure that the optimum performance is achieved to enable the expectations of the users to be met while still keeping OPEX within the budgeted bounds.

Need for LTE relay technology
One of the main drivers for the use of LTE is the high data rates that can be achieved. However all technologies suffer from reduced data rates at the cell edge where signal levels are lower and interference levels are typically higher.
The use of technologies such as MIMO, OFDM and advanced error correction techniques improve throughput under many conditions, but do not fully mitigate the problems experienced at the cell edge.
As cell edge performance is becoming more critical, with some of the technologies being pushed towards their limits, it is necessary to look at solutions that will enhance performance at the cell edge for a comparatively low cost. One solution that is being investigated and proposed is that of the use of LTE relays.

LTE relay basics
LTE relaying is different to the use of a repeater which re-broadcasts the signal. A relay will actually receive, demodulates and decodes the data, apply any error correction, etc to it and then re-transmitting a new signal. In this way, the signal quality is enhanced with an LTE relay, rather than suffering degradation from a reduced signal to noise ratio when using a repeater.
For an LTE relay, the UEs communicate with the relay node, which in turn communicates with a donor eNB.
Relay nodes can optionally support higher layer functionality, for example decode user data from the donor eNB and re-encode the data before transmission to the UE.
The LTE relay is a fixed relay - infrastructure without a wired backhaul connection, that relays messages between the base station (BS) and mobile stations (MSs) through multihop communication.
There are a number of scenarios where LTE relay will be advantageous. * Increase network density: LTE relay nodes can be deployed very easily in situations where the aim is to increase network capacity by increasing the number of eNBs to ensure good signal levels are received by all users. LTE relays are easy to install as they require no separate backhaul and they are small enabling them to be installed in many convenient areas, e.g. on street lamps, on walls, etc.

LTE relay used to increase network density

* Network coverage extension : LTE relays can be used as a convenient method of filling small holes in coverage. With no need to install a complete base station, the relay can be quickly installed so that it fills in the coverage blackspot.

LTE relay coverage extension - filling in coverage hole

Additionally LTE relay nodes may be sued to increase the coverage outside main area. With suitable high gain antennas and also if antenna for the link to the donor eNB is placed in a suitable location it will be able to maintain good communications and provide the required coverage extension.

LTE relay coverage extension - extending coverage

It can be noted that relay nodes may be cascaded to provide considerable extensions of the coverage. * Rapid network roll-out: Without the need to install backhaul, or possibly install large masts, LTE relays can provide a very easy method of extending coverage during the early roll-out of a network. More traditional eNBs may be installed later as the traffic volumes increase.

LTE relay to provide fast rollout & deployment

LTE relaying full & half duplex
LTE relay nodes can operate in one of two scenarios: * Half-Duplex: A half-duplex system provides communication in both directions, but not simultaneously - the transmissions must be time multiplexed. For LTE relay, this requires careful scheduling. It requires that the RN coordinates its resource allocation with the UEs in the uplink and the assigned donor eNB in the downlink. This can be achieved using static pre-assigned solutions, or more dynamic ones requiring more intelligence and communication for greater flexibility and optimisation. * Full Duplex: For full duplex, the systems are able to transmit and receive at the same time. For LTE relay nodes this is often on the same frequency. The relay nodes will receive the signal, process it and then transmit it on the same frequency with a small delay, although this will be small when compared to the frame duration. To achieve full duplex, there must be good isolation between the transmit and receive antennas.
When considering full or half duplex systems for LTE relay nodes, there is a trade-off between performance and the relay node cost. The receiver performance is critical, and also the antenna isolation must be reasonably high to allow the simultaneous transmission and reception when only one channel is used.

LTE relay types
There is a number of different types of LTE relay node that can be used. However before defining the relay node types, it is necessary to look at the different modes of operation.
One important feature or characteristic of an LTE relay node is the carrier frequency it operates on. There are two methods of operation: * Inband: An LTE relay node is said to be "Inband" if the link between the base station and the relay node are on the same carrier frequency as the link between the LTE relay node and the user equipment, UE, i.e. the BS-RN link and the BS-UE link are on the same carrier frequency. * Outband: For Outband LTE relay nodes, RNs, the BS-RN link operates of a different carrier frequency to that of the RN-UE link.
For the LTE relay nodes themselves there are two basic types that are being proposed, although there are subdivisions within these basic types: * Type 1 LTE relay nodes: These LTE relays control their cells with their own identity including the transmission of their own synchronisation channels and reference symbols. Type 1 relays appear as if they are a Release 8 eNB to Release 8 UEs. This ensures backwards compatibility. The basic Type 1 LTE relay provides half duplex with Inband transmissions.

There are two further sub-types within this category: * Type 1.a: These LTE relay nodes are outband RNs which have the same properties as the basic Type 1 relay nodes, but they can transmit and receive at the same time, i.e. full duplex. * Type 1.b: This form of LTE relay node is an inband form. They have a sufficient isolation between the antennas used for the BS-RN and the RN-UE links. This isolation can be achieved by antenna spacing and directivity as well as specialised digital signal processing techniques, although there are cost impacts of doing this. The performance of these RNs is anticipated to be similar to that of femtocells. * Type 2 LTE relay nodes: These LTE relaying nodes do not have their own cell identity and look just like the main cell. Any UE in range is not able to distinguish a relay from the main eNB within the cell. Control information can be transmitted from the eNB and user data from the LTE relay.

LTE RELAY CLASS | CELL ID | DUPLEX FORMAT | Type 1 | Yes | Inband half duplex | Type 1.a | Yes | Outband full duplex | Type 1.b | Yes | Inband full duplex | Type 2 | No | Inband full duplex |
Summary of Relay Classifications & Features in 3GPP Rel.10
There is still much work to be undertaken on LTE relaying. The exact manner of LTE relays is to be included in Release 10 of the 3GPP standards and specifications.

4G LTE Device to Device, D2D- 4G LTE Advanced device to device, D2D communications for high data rate local communications and machine to machine, M2M links.
One of the schemes that is being researched and considered for 4G LTE Advanced is the concept of Device to Device communications.
4G LTE device to device, D2D would enable the direct link of a device, user equipment UE, etc to another device using the cellular spectrum. This could allow large volumes of media or other data to be transferred from one device to another over short distances and using a direct connection.. This form of device to device transfer would enable the data to be transferred without the need to run it via the cellular network itself, thereby avoiding problems with overloading the network.

LTE device to device concept
There are a number of benefits that arise from developing the LTE device to device standards. It could bring benefits to users and operators alike.
The provision of high data rate local services is likely to emerge as the use of rich multimedia services becomes more commonplace as the use of mobile computers such as tablets, netbooks, and latest generation smartphones increases.
The LTE platform would have the advantage over others such as Wi-Fi and Bluetooth that operate device to device protocols is that they use licence exempt spectrum, and the performance is likely to be poor, especially where large numbers of users are present.
The possibility with LTE device to device communications is that using the LTE spectrum a controlled interference environment could be used. This would provide a much more effective environment for the high data rate communications which could include downloads of video, music, etc.
Another possibility is that the licence free spectrum could be used alongside the licensed spectrum, one being used as the other becomes exhausted.

LTE device to device, D2D concept
There are several advantages to using LTE device to device communications * The network can advertise the presence of the LTE device to device connection possibility. * Devices do not need to scan for available WLANs - this reduces power consumption. * The LTE network can distribute the security keys in a safe fashion.
LTE Advanced Heterogeneous Networks, HetNet
- LTE heterogeneous network, HetNet technology, how LTE HetNets work and details about their operation and deployment..
LTE heterogeneous networks, HetNet are fast becoming a reality.
Within LTE and LTE Advanced, operators see the need to very significantly increase the data capacity of all areas of the network while also reducing the costs as cost per bit rates are falling.
Whilst LTE HetNet technology is starting to be defined, many operators are seeking to utilise the concepts to ensure that the delivery of service to the users meets expectations under the very varying conditions and scenarios that users are placing on the networks.

LTE heterogeneous network basics
To achieve this LTE and LTE Advanced operators need to adopt a variety of approaches to meet the needs of a host of scenarios that will occur within the network.
Different types of user will need use the network in different places and for different applications. Coupled to this operators introducing LTE and LTE Advanced networks will have many legacy systems available. In any LTE heterogeneous network it will be necessary to accommodate other radio access technologies including HSPA, UMTS and even EDGE and GPRS. In addition to this other technologies including Wi-Fi also need to be accommodated.
These solutions for LTE heterogeneous networks need to incorporate not only the radio access network solutions, but also the core network as well. In this way a truly heterogeneous network can become functional.
To ensure the best use is made of the available capabilities, all the various elements need to be operated in a manner that is truly seamless to the user. The user should be given the best experience using the best available technology at any given time. The performance and hence the user experience should also be very much the same whatever the location and whatever the application.

Note on Heterogeneous Networks, HetNet:
The concept of the Heterogeneous Network or HetNet has arisen out of the need for cellular telecommunications operators to be able to operate networks consisting of a variety of radio access technologies, formats of cells and many other aspects, and combining them to operate in a seamless fashion.
Click on the link for further information about Heterogeneous Networks, HetNet

LTE HetNet features
There are a number of features for LTE that can be incorporated into an LTE heterogeneous network above and beyond some of what may be termed the basic wireless heterogeneous network techniques..Although they could conceivably be used with other forms of wireless heterogeneous network, they are currently found in LTE. * Carrier aggregation: With spectrum allocated for 4G networks, operators often find they have a variety of small bands that they have to piece together to provide the required overall bandwidth needed for 4G LTE. Making these bands work seamlessly is a key element of the LTE heterogeneous network operation. * Coordinated multipoint: In order to provide the proper coverage at the cell edges, signal from two or more base stations may be needed. Again, providing the same level of service regardless of network technology and areas within the cell can prove to be challenging. Adopting a heterogeneous network approach can assist in providing he same service quality regardless of the position within the cell, and the possibly differing cell and backhaul technologies used for the different base stations.

Heterogeneous networks are now an established concept within LTE networks. The requirement to provide a better level of coverage and performance in a greater variety of situations means that a greater variety of techniques is required. Making all the different technologies from radio access networks to base station technologies and backhaul paths all come together needs careful planning. Early cellular systems had a far more standard approach, where base stations were characterised by the mast and antennas. Now a much greater variety of approaches is needed.