Question

The power amplifiers or the power combiners, when operated at or near saturation for maximum power efficiency, are nonlinear. The nonlinearities cause signal spreading in the frequency domain and generate intermodulation (IM) frequencies. The given phenomenon is associated with: 
1. OFDMA
2. FDMA
3. TDMA
4. CDMA

Answer 1

Correct Answer - Option 2 : FDMA

Concept:

Nonlinear effects in FDMA

There are some nonlinear effects while using the FDMA technique.

1. In the FDMA system, many channels share the same antenna at the base station. The power amplifiers or the power combiners, when operated at or near saturation for maximum power efficiency are nonlinear.
2. Nonlinearities cause signal spreading in the frequency domain and generate intermodulation frequencies.
3. IM is undesired RF radiation that can interfere with other channels in FDMA systems,
4. Spreading of the spectrum results in adjacent channel interference.
5. Intermodulation is the generation of undesirable harmonics. Harmonics generated outside the mobile radio band cause interference to adjacent services, while those present inside the band cause interference to other users in the wireless system.
6. To minimize the effects of intermodulation distortion, stringent RF filters are required to reject intermodulation distortion.

 

A number of channels in FDMA are:

\(N=\frac{B_t - B_{guard}}{B_c}\)

B_t: Total spectrum allocation

B_guard: Guard band

B_c: Channel bandwidth

Conclusion: Option 2 is correct.