IV. SIMULATION RESULTS
In this paper, a downlink cognitive-CDMA system with N =64 spectrum bins is considered. Unless otherwise specified, a multipath channel model of six paths is used.
To perform zero-padding DFT in the receiver, a ZP of length 1/4 is added in the transmitter as guard interval, and more zeros are added to the received signal. The padding length depends on the FDO factor M.
System performances in terms of bit error rate (BER) with and without FDO are compared to per-user MMSE (PU-MMSE) detection methods. More simulation parameters can be found in the table 1.
TABLE 1. Simulation parameters for different multiuser cognitive-CDMA receivers.