Chapter 5
Hybrid Multi-user Detection for SDMA-OFDM Systems
5.1 Introduction1
In the previous chapter, the MMSE MUD was investigated in the context of various CM-assisted SDMA-OFDM systems. Furthermore, the WHT-based frequency-domain spreading technique was incorporated into the CM-assisted MMSE-SDMA-OFDM system to attain performance enhancements. However, the SDMA system’s performance is somewhat limited owing to the employment of the low-complexity MMSE MUD, which is devised based on the suboptimal linear MMSE algorithm. On the other hand, the high-complexity optimum Maximum Likelihood (ML) MUD is capable of achieving the best performance owing to the invocation of an exhaustive search. However, the computational complexity of the ML MUD typically increases exponentially with the number of simultaneous users supported by the SDMA-OFDM system, which may render its implementation prohibitive. In the literature, a range of suboptimal nonlinear MUDs have been proposed, such as for example the MUDs based on Successive Interference Cancellation (SIC) [3, 193, 197, 439–441] or Parallel Interference Cancellation (PIC) [3, 439, 441, 442] techniques. Instead of detecting and demodulating the users’ signals in a sequential manner, as the MMSE MUD does, the PIC and SIC MUDs invoke an iterative processing technique that combines detection and demodulation. More specifically, the output signal generated during the previous detection iteration is demodulated and fed back to the input of the ...
