Analysis on tradeoff between frequency diversity and inter-code interference considering fading correlation in forward link for VSF-OFCDM wireless access

This paper investigates the frequency diversity and inter-code interference tradeoff relationship in variable spreading factor-orthogonal frequency and code division multiplexing (VSF-OFCDM) wireless access in a frequency-selective (multipath) fading channel. In the paper, we establish the tradeoff relationship based on a numerical analysis considering that different subcarriers experience a correlated flat fading channel depending on the spreading factor and delay spread for coherent maximum ratio combining (MRC) and minimum mean squared error combining (MMSEC). We derive the instantaneous output signal-to-interference plus noise power ratio (SINR) and compute the average bit error rate (BER) by using the approach for M-array data modulation such as M-QAM as well as QPSK modulation. We compute the average BER for QPSK and 16QAM numerically and verify the analytical results by computer simulation. Using the average BER, we then numerically investigate the diversity-interference tradeoff relationship for both combiners with respect to different radio parameters such as the spreading factor, channel load, modulation scheme, and different channel conditions such as the delay spread.