Multiple Access Techniques Inwards Communication: Fdma, Tdma, Cdma

Multiple access techniques:

In a communication system, it is unrealistic as well as impossible to render a unmarried line of piece of job to an every assort user on the network. So what produce nosotros withdraw to do? The answer is multiple access techniques. To overcome these problems dissimilar types of methods implemented to portion a unmarried express band or channel into multiple users.

In communication, Multiplexing Techniques used to let many users to portion together a finite sum of radio spectrum. Multiple access techniques are based on multiplexing techniques. It volition too bring down the cost as well as complexity of the network. E.g., Old telephone arrangement uses FDMA to let multiple calls on the unmarried line.

Communication channels it tin hold out a wireless spectrum or cable connections are of higher price. Different varieties of channels adapted to the mobile communication system, e.g., similar fourth dimension slots into frequency bands, frequency channels, as well as clear codes.
Basic Communication access techniques are

1. FDMA
2. WDMA
3. OFDMA
4. TDMA 
5. CDMA
6. SSMA
7. SDMA
8. PDMA

1) FDMA (Frequency Division Multiple Access)

is based on Frequency Division Multiplexing (FDM). It is the functioning of splitting unmarried channel or bandwidth into several bands of frequency. In this channel access scheme, every user gets a assort sub-band of frequency similar inwards FM radio. In this system, the user transmits information onto dissimilar frequency at the same time.
It enables many users to transmit at the same fourth dimension simply using dissimilar frequency channels. It is necessary to continue the channel wider, to choose the dot spectra of the conveyance to propagate. FDMA is less complicated than TDMA, as well as it implemented inwards the narrow band system.

The widest cable arrangement that is about placed inwards every home, hotel, as well as restaurants which render a hundred of alive TV channels through exclusively i coaxial cable( iv MHz - 1 GHz). This bandwidth divides into many modest broad bands to acquit dissimilar channels. E.g., At the kickoff i TV station requires a unmarried 6-MHz band.

2) WDMA (Wavelength Division Multiple access )

based on wavelength partitioning multiplexing (WDM) uses inwards fiber oculus communication. At multiplexer side, multiple lights combine into a unmarried lite origin as well as at the de-multiplexer, the lite origin converted i time again into diverse sources.
Using FDMA, the bandwidth of an Optical fiber tin hold out subdivided. Different information origin gets a dissimilar lite frequency(referred to Wavelength, λ) to transmit. The FDMA technique inwards Optical Fiber is known equally WDMA.

4) OFDMA (orthogonal frequency partitioning multiplexing)

it is based on orthogonal frequency partitioning multiplexing (OFDM) uses inwards the 4G mobile communication system. It is the procedure of accommodating many users inwards an assigned bandwidth using OFDM modulation technique. OFDM Split given channel into multiple assort narrow-band channels at dissimilar bands to fail interference as well as cross-talk occurrence.

5) TDMA (Time Division Multiple Access)

inwards this channel access scheme, every user gets a assort fourth dimension slot to transmit information onto a measure frequency band. It allows users to mail information or information using the same frequency band simply dissimilar times slot.
In digital systems, nosotros conduct keep no identify for continuous transmission because the users never usage the assigned bandwidth all the time. TDMA is based on Time Division Multiplexing as well as uses inwards Global System for Mobile Communication (GSM).
The brain role of introducing TDMA technology scientific discipline is to reach capacity over FDMA arrangement past times providing i band or frequency channel to multiple users. In TDMA nosotros add together fourth dimension slots inwards frequency band/channel as well as thence that many users tin usage unmarried band/frequency.
Digital Bits transmitted inwards a specified fourth dimension slot on a given frequency channel. Every user gets i or to a greater extent than than old slot per frame, as well as the entire bandwidth is available to usage for a finite current equally long equally needed. For both transmission as well as reception TDMA uses dissimilar fourth dimension slot.

TDMA slot must hold out synchronized. It uses the lower publish of channel, that why interference tin neglect.

6) Space-division multiple access (SDMA)

Space-division multiple access (SDMA) transmits dissimilar information inwards dissimilar physical areas. Examples include uncomplicated cellular radio systems as well as to a greater extent than advanced cellular systems which usage directional antennas as well as ability modulation to refine spatial transmission patterns.

7) Power-division multiple access (PDMA)

Power-division multiple access (PDMA) scheme is used to render ability to the users according to their needs. PDMA sets variable ability transmission betwixt the user inwards companionship to portion the available ability on the channel. For example, SCPC modems on a satellite transponder, where users teach on-demand power.


References Book:
1. Frenzel, Louis E., Principles of Electronic Communication Systems, third Edition, McGraw Hill, 2008.
2. Skylar, Bernard, Digital Communications, s Edition, Prentice Hall, 2001.
3. https://en.wikipedia.org/wiki/Channel_access_method