Filtered spreading sequences for interference avoidance

Due to the scarcity of available spectrum, it may be convenient to overlay a DS-spread spectrum system on a band already sparsely occupied by narrowband users. The processing gain of the spread system serves to reduce the cross-interference between the spread and narrowband systems. However, much further isolation can be gained by passing the spreading sequence through a short FIR filter at the transmitter, before spreading. The authors investigate the benefit of doing this, and give numerical results for a specific system.<
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