1. Frequency Division Multiple Access (FDMA) :
FDMA is a type of channelization protocol. In this bandwidth is divided into various frequency bands. Each station is allocated with band to send data and that band is reserved for particular station for all the time which is as follows :
The frequency bands of different stations are separated by small band of unused frequency and that unused frequency bands are called as guard bands that prevents the interference of stations. It is like access method in data link layer in which data link layer at each station tells its physical layer to make a band pass signal from the data passed to it. The signal is created in the allocated band and there is no physical multiplexer at the physical layer.
2. Time Division Multiple Access (TDMA) :
TDMA is the channelization protocol in which bandwidth of channel is divided into various stations on the time basis. There is a time slot given to each station, the station can transmit data during that time slot only which is as follows :
Each station must aware of its beginning of time slot and the location of the time slot. TDMA requires synchronization between different stations. It is type of access method in the data link layer. At each station data link layer tells the station to use the allocated time slot.
3. Code Division Multiple Access (CDMA) :
In CDMA, all the stations can transmit data simultaneously. It allows each station to transmit data over the entire frequency all the time. Multiple simultaneous transmissions are separated by unique code sequence. Each user is assigned with a unique code sequence.
In the above figure, there are 4 stations marked as 1, 2, 3 and 4. Data assigned with respective stations as d1, d2, d3 and d4 and the code assigned with respective stations as c1, c2, c3 and c4.
Difference between FDMA, CDMA and TDMA :
|FDMA stands for Frequency Division Multiple Access.||TDMA stands for Time Division Multiple Access.||CDMA stands for Code Division Multiple Access.|
|In this, sharing of bandwidth among different stations takes place.||In this, only the sharing of time of satellite transponder takes place.||In this, there is sharing of both i.e. bandwidth and time among different stations takes place.|
|There is no need of any codeword.||There is no need of any codeword.||Codeword is necessary.|
|In this, there is only need of guard bands between the adjacent channels are necessary.||In this, guard time of the adjacent slots are necessary.||In this, both guard bands and guard time are necessary.|
|Synchronization is not required.||Synchronization is required.||Synchronization is not required.|
|The rate of data is low.||The rate of data is medium.||The rate of data is high.|
|Mode of data transfer is continuous signal.||Mode of data transfer is signal in burts.||Mode of data transfer is digital signal.|
|It is little flexible.||It is moderate flexible.||It is highly flexible.|
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