The impact of delay spread on multilevel FM systems in a Rayleigh fading, CCI and AWGN environment

An experimental study of the impact of delay spread on the performance of 4 PAM-FM mobile systems in a Rayleigh fading, cochannel interference (CCI) and additive white Gaussian noise (AWGN) environment is presented. The increase of the modulation index can improve the BER if the reflected signal power is 10 dB less than the direct signal in the two-ray fading model. A strategy which reduces the impact of delay spread even in the worst case situation is proposed. By increasing the roll-off factor of the lowpass filters and by lowering the modulation index, for a BER of 0.01, the delay spread immunity is increased 300% without the need for adaptive equalization. In the delay spread environment, CCI is not significant if it is less than -20 dB. AWGN interference is noticeable only when it is higher than -13 dB.<
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