Working conditions for an influencing factor on the performance of adaptive OFDM system under a varying channel

A main issue in wireless communications is to improve the transmission quality of service (QoS), which may be represented by the bit error rate (BER). In [H. Che, et al., 2002] we studied the combining effect of channel situation and OFDM modulation on BER performance and defined a factor P_FR based on both OFDM parameter and channel parameter that influences BER performance. But this parameter doesn´t influence BER in all the situations. In this paper we find out by simulation results that the factor PFR is effective on BER within a certain range of signal to noise ratio (SNR). And our simulation results indicate that this SNR range is different for different Rician K factor and for different modulation levels. This paper demonstrates that for each modulation level there is a relationship between the effective SNR range and Rician K factor and gives out the formula to describe the relationship. The result is quite useful to build up an optimum criteria for adaptive OFDM systems.