Modeling of Digital Communication Systems Using SIMULINK

Chapter 12Adaptive Equalization in Digital Communications

12.1 Adaptive Equalization

This chapter presents Simulink models that incorporate adaptive equalization. Specific topics include the following:

• Linear least mean square (LMS) equalizers with BPSK in dispersive multipath channels and AWGN including
  • Sample based
  • Frame based
  • Simulink library model
• Linear LMS equalizer with QPSK in a channel with Intersymbol Interference (ISI)
• Decision feedback equalizers (DFEs) with BPSK in a dispersive multipath channel and AWGN
• Recursive least squares (RLS) equalizers with BPSK in a dispersive multipath channel, AWGN, and Rayleigh fading

12.2 BER Performance of BPSK in Dispersive Multipath Channel Using an LMS Linear Equalizer

Equalization algorithms are used for mitigating ISI and/or multipath introduced by the channel. The channel is modeled as a discrete-time channel filter with delay values corresponding to the symbol interval T and channel coefficients that represent the channel distortion. The channel model seen in Figure 12.1 includes AWGN. In the figure, the data signal symbols from the BPSK modulator are identified by the sequence {s_k} and are corrupted by the channel coefficients {a_m}. The received signal {r_k} is then expressed in terms of the channel coefficients as

where {} represents zero mean AWGN with variance and L is the number of tap coefficients in the channel. ...