MOBILE COMPUTING ASSIGNMENT
NAME: SOPHIA EHINOMEN ATIVIE
MATRIC NO: 2010/1336
DEPT: INFORMATION TECHNOLOGY

1. CDMA (CODE DIVISION MULTIPLE ACCESS).
CDMA (Code-Division Multiple Access) is a channel access method used by various radio communication technologies. It is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes, which enhances privacy and makes cloning difficult.

The original CDMA standard, also known as CDMA One and still common in cellular telephones in the U.S offers a transmission speed of only up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and Wideband CDMA deliver data many times faster.

Characteristics of CDMA:

1. Spread spectrum techniques use a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. These systems were designed using spread spectrum because of its security and resistance to jamming. 2. CDMA can effectively reject narrow band interference. Since narrow band interference affects only a small portion of the spread spectrum signal, it can easily be removed through notch filtering without much loss of information. 3. CDMA devices use a rake receiver, which exploits multipath delay components to improve the performance of the system. 4. In a CDMA system, the same frequency can be used in every cell, because channelization is done using the pseudo-random codes. 5. Reusing the same frequency in every cell eliminates the need for frequency planning in a CDMA system; 6. CDMA systems use the soft hand off, which is undetectable and provides a more reliable and higher quality signal.

General Specification of CDMA 1. Rx: 869-894MHz Tx: 824-849MHz
2. 20 Channels spaced 1250kHz apart (798 users/channel)
3. QPSK/(Offset) OQPSK modulation scheme
4. 1.2288Mbps bit rate
5. IS-95 standard
6. Operates at both 800 and 1900 MHz frequency bands

Advantages of CDMA techniques:
1. Efficient practical utilization of fixed frequency spectrum.
2. Flexible allocation of resources.
3. Many users of CDMA use the same frequency, TDD or FDD may be used
4. Multipath fading may be substantially reduced because of large signal bandwidth
5. No absolute limit on the number of users, Easy addition of more users.
6. Impossible for hackers to decipher the code sent
7. Better signal quality
8. No sense of handoff when changing cells
9. The CDMA channel is nominally 1.23 MHz wide.
10. CDMA networks use a scheme called soft handoff, which minimizes signal breakup as a handset passes from one cell to another.
11. CDMA is compatible with other cellular technologies; this allows for nationwide roaming.
12. The combination of digital and spread-spectrum modes supports several times as many signals per unit bandwidth as analog modes.

Disadvantages to using CDMA:

1. As the number of users increases, the overall quality of service decreases 2. Self-jamming 3. Near- Far- problem arises

2. GENREAL PACKET RADIO SERVICE.
General Packet Radio System is also known as GPRS is a third-generation step toward internet access. GPRS is also known as GSM-IP that is a Global-System Mobile Communications Internet Protocol as it keeps the users of this system online, allows to make voice calls, and access internet on-the-go. Even Time-Division Multiple Access (TDMA) users benefit from this system as it provides packet radio access.
GPRS also permits the network operators to execute an Internet Protocol (IP) based core architecture for integrated voice and data applications that will continue to be used and expanded for 3G services.
GPRS supersedes the wired connections, as this system has simplified access to the packet data networks like the internet. The packet radio principle is employed by GPRS to transport user data packets in a structure way between GSM mobile stations and external packet data networks. These packets can be directly routed to the packet switched networks from the GPRS mobile stations.

KEY FEATURES
Following three key features describe wireless packet data:

1. The always online feature - Removes the dial-up process, making applications only one click away.

2. An upgrade to existing systems - Operators do not have to replace their equipment; rather, GPRS is added on top of the existing infrastructure.

3. An integral part of future 3G systems - GPRS is the packet data core network for 3G systems EDGE and WCDMA.

GOALS OF GPRS
GPRS is the first step toward an end-to-end wireless infrastructure and has the following goals: 1. Open architecture 2. Consistent IP service 3. Same infrastructure for different air interfaces 4. Integrated telephony and Internet infrastructure 5. Leverage industry investment in IP 6. Service innovation independent of infrastructure 7. Benefits of GPRS 8. Higher Data Rate

ADVANTAGES OF GPRS 1. Higher Data Rate
GPRS benefits the users in many ways, one of which is higher data rates in turn of shorter access times. In the typical GSM mobile, setup alone is a lengthy process and equally, rates for data permission are restrained to 9.6 kbit/s. The session establishment time offered while GPRS is in practice is lower than one second and ISDN-line data rates are up to many 10 kbit/s.

2. Easy Billing
GPRS packet transmission offers a more user-friendly billing than that offered by circuit switched services. In circuit switched services, billing is based on the duration of the connection. This is unsuitable for applications with bursty traffic. The user must pay for the entire airtime, even for idle periods when no packets are sent (e.g., when the user reads a Web page).

DISADVANTAGES OF GPRS