Interference rejection and equalization in band-limited channels

In addition to thermal noise and intersymbol interference (IsI), a transmitted wideband signal of a wireless communication system may suffer from interference caused by other cochannel narrowband users or other radio frequency interference (RFI). Although spread spectrum (SS) signals is inherently resistant to interference the system performance would be greatly enhanced if we can eliminate most of the interference before despreading or demodulation takes place. This paper provides a workable solution for direct sequence systems when the channel can be modeled as an FIR filter and the narrowband interference (NBI) is either multiple CW tones, or an AR process driven by a white Gaussian sequence. Unlike earlier solutions, the proposed NBI rejection scheme is based on a cost function evaluated at the output of the PN despreader. It is simpler to implement and is capable of removing ISI. When the delay spread of the multi-path channel is comparable to a bit time our proposal renders better BER performance.