8.3.6 Advantages And Disadvantages Of FDMA

FDMA is the earliest and conceptually simplest deterministic multiple-access technique and has a number of advantages that reflect its enduring use.

Simplicity: Each user is assigned a distinct frequency band, and transmission may proceed continuously without time-slot coordination.
No tight time synchronization: Unlike TDMA, users do not require a common frame clock or burst alignment. Carrier stability is required, but global timing synchronization is not.
Continuous transmission: Because users transmit continuously rather than in bursts, peak-to-average power ratios are generally lower than in burst-mode systems.
Mature technology base: FDMA has been widely implemented in broadcasting, fixed wireless, satellite links, and early cellular systems. Design methods, filtering techniques, and frequency planning procedures are well established.
Isolation between users: Under linear operating conditions, interference between users is minimized by spectral separation.
Compatibility with analog and digital signals: FDMA can accommodate either analog or digital signals without modification to the access principle.

Despite those advantages, FDMA has a number of limitations:

Guard-band overhead: Unused spectral intervals reduce overall bandwidth efficiency.
Sensitivity to nonlinearity: Multiple simultaneous carriers produce intermodulation distortion in nonlinear amplifiers, requiring output backoff and reducing power efficiency.
Power balancing requirements: Unequal carrier powers can lead to desensitization and capture effects, degrading weaker channels.
Limited flexibility: Reallocating bandwidth or adding users may require frequency re-planning and retuning.
Scaling limitations: Total throughput does not increase linearly with the number of carriers due to composite power and distortion constraints.
Inefficient for bursty traffic: Continuous frequency allocation may waste capacity when user activity is intermittent.

These limitations motivated the development of more spectrally efficient and dynamically adaptable techniques, including orthogonal multicarrier systems.