Frequency-division multiple access (FDMA) :
Frequency-division multiple access is one among the only multiple access methods. During this method, the channel bandwidth is subdivided into a variety of sub-channels. This multiple access method used for voice and data transmission. During this method the general channel bandwidth is being shared by multiple users, therefore the variety of users can transmit their information simultaneously. The adjacent frequency bands within the FDMA spectrum are likely to interfere with one another. Therefore, it’s necessary to incorporate the guard bands between the adjacent frequency bands. No code words and synchronization are required. Power efficiency reduced using FDMA, it’s an old and proven system and used for analog signals.
Advantages of FDMA :
- Use of efficient numerical codes increases the capacity.
- It reduces the worth.
- Lowers the inter symbol interference (Equalization isn’t required).
- An FDMA system is often easily implemented, system are often configured so, the improvements in terms of speech encoder and bit rate reduction could even be easily incorporated.
- Simple to implement, from a hardware standpoint.
- Fairly efficient with a little base population and when traffic is constant.
- FDMA includes its applicability to both analog and digital transmission systems, the actual fact that no special coding is required, the allocation of capacity is simple, no network synchronization or timing is required, which the baseband signal are often recovered using simple and cheap receiver equipment.
- Reducing the knowledge bit rate and using efficient digital codes can obtain capacity increases.
- As FDMA systems use low bit rates (large symbol time) compared to average delay spread, they reduce the worth, and there is low Inter Symbol Interference (ISI).
- There is hardly any equalization required.
- Technological advances required for implementation are simple. A system is often configured so as that improvement in terms of speech coder bit-rate reduction could be readily incorporated.
Disadvantages of FDMA :
- Due to the simultaneous transmission of a large number of frequencies, there is a possibility of inter modulation distortion at the transponder.
- It is suitable only for analog signals.
- Storage, enhancement of signals is not possible.
- The large bandwidth requirement for transponders.
- Guard bands may waste capacity.
- It requires RF(Radio Frequency) filters to meet stringent adjacent channel rejection specifications. This may increase the cost of the system.
- Network planning is cumbersome and time-critical.
- There is not much flexibility so, need to slowly change already assigned traffic patterns.
- The carrying capacity of traffic is relatively low.
- In a general system, because the channels are assigned for a single user, idle channels add to the spectrum.
- Frequency planning is time-consuming.
- Required multi-channel receivers that are expensive.
- The highest bit rate per channel is fixed and small.
- Hardware involves narrowband filters, which cannot be realized in VLSI.