Noise in communication systems
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Introduction
Noise is always present in all systems and any receiver must in one way or another contend with noise. Noise is a limiting factor in communication systems that involve unwanted signals interfering with a wanted signal. The unwanted signals originate from different sources mainly from two categories that is, naturally occurring, and manmade interference. The naturally occurring noise comes from atmospheric disturbance or from extraterrestrial noise. Manmade interference noise originates from other communication systems and harmonics. This research paper discusses noise in communication systems, different types of noise, as well as how different frequencies and filters eliminate the noise.
Noise in communication system
In communication systems, noise is an unwanted disturbance that interferes with a useful signal and hence obscures the content of the information. In an electrical system, noise is any unwanted energy form that usually interferes with correct reception and produces unwanted signal(Mayor, 1992). Noise is therefore random and undesirable energy in a communication system.Noise in communication systems can be classified into external and internal noises. a. External noises
These include noise in the communication system that originates externally. External noise can be either atmospheric, extraterrestrial or manmade noises. i. Atmospheric noise- Also known as static noise, atmospheric noise comes from electrical disturbances in the atmosphere like lighting discharged from thunderstorms. These electrical disturbances are random and so spread across a broad frequency spectrum for communication. The disturbances consists of radio signals gets to the earth with the same frequency with a desired radio signal. This noise has a field strength that varies inversely with the frequency. A large atmospheric noise is generated in broadcast while little noise in UHF and VHF bands. ii. Extraterrestrial noise- This noise can be either solar or cosmic. Solar noise comes from the sun that steadily produces radiation in form of electrical energy over a broad range of frequency spectrum. Cosmic noise comes from distant stars and suns that radiate noise just like the sun. This type of noise is thermal. iii. Manmade noise- This is electrical noise that comes from electrical motors, fluorescent light, high voltage lines leakage, automobiles, aircraft ignition, and other electrical noise produced by heavy electrical machines. Manmade electrical noises come from arc discharge when these machines are operated. Manmade noise is more frequent in industrial areas and has a frequency range of between 1MHz and 600MHz(Mayor, 1992). b. Internal noises
Internal noise in communication is generated within the communication system or within the receiver and include; i. Shot noise- This includes the noise that is produced by random electron fluctuations from cathodes in vacuum tubes. Random electron movement at the PN junction also produces it. External voltages produce current flow but discontinuities in the electric device might cause some random movement of electrons. The fluctuating random movement of electrons createsamounts of charge that create a current with a series of current pulses. Shot noise has a uniform spectral density similar to thermal noise. ii. Thermal noise (Johnson noise)- This noise is produced is generated by all kind of resistances. Energy conductors usually have a high number of electrons that vibrate randomly at temperatures above zero degrees K. As the random motion increases, so does the temperature that produces thermal noise. The randomly moving electrons also produce a current giving rise to the thermal noise. iii. Transit time noise- This is the noise that occurs in transistors. Transit time is the time duration that a current carrier takes from power input to the output. Current carrier devices are small but still cover distances from the input to the output. At a high frequency, the signal produced during transit time produces transit noise. iv. Miscellaneous internal noise- This occurs in transistors that operate at low audio frequencies. The emitter and collector internal resistances produce transistor thermal noise. Partition noise occurs when a current divides several current paths(Mayor, 1992).
Reducing noise in communication
Noise in communication systems is mostly unwanted and several techniques are used to reduce communication system noise. They include: a. Filters- filters like notch, low-pass and band-rejection filters can be used to eliminate particular noise frequencies. Filters remove portions of signals above the required cut off frequencies. b. Faraday cage- This works by protecting or keeping away unwanted electromagnetic pulse from the atmosphere. It has a conductive layer that reflects incoming energy fields and reduces overall noise in a communication system circuit. c. Different frequencies- Frequencies determine the length of a radio wave or signal. Different frequencies can be used to reduce communication noise by altering the wavelengths and signals (Ott, 1988).
Conclusion
In conclusion, noise in communication arises in different forms depending on the source of the noise. All these types of noise degrade the efficiency of communication systems and deteriorates the received signal quality during an audio transmission. In digital communication, noise leads to degradation of the throughput as it will require retransmission of datapackets. Noise will also require extra coding of the process so as to recover accurate data. External noise can only be reduced by changing location of the entire system or that of the receiver. Internal noise originates from within and can be evaluated mathematically and reduced by a proper design. Different filters and frequencies can eliminate communication noise(Ott, 1988).

References
Mayor, J. (1992).The Radio Amateur’s Digital Communications Handbook. Blue Ridge
Summit, Pa.: TAB Books.
Ott, H. (1988). Noise reduction techniques in electronic systems.2nd Ed. John Wiley & Sons,
Inc. Canada.