Optimal training and pilot pattern design for OFDM systems in Rayleigh fading

This paper deals with two major considerations for pilot symbol assisted orthogonal frequency division multiplexing (PSA-OFDM) systems when operated over Rayleigh fading channels. One of them is to decide how many pilot symbols should be used and the other is where to place these pilot symbols, i.e. pilot pattern. Incorporating linear interpolation and choosing appropriate system parameters, we first derive analytically the bit-error-rate (BER) for frequency-selective fading, time-selective fading and correlated fading, respectively. Based on the theoretical BER, the optimal training can be determined numerically for a specific fading environment. Furthermore, we propose a new and simple pilot pattern for PSA-OFDM system and its performance is analyzed in terms of the BER. The proposed scheme clusters two neighboring pilots together so as to increase the channel estimate accuracy by averaging over the two pilot symbols. Analytical and simulation results show that this clustered pilot pattern gives better performance in terms of BER than the existing equi-spaced pilot pattern when the channel SNR is moderate, without sacrificing the bandwidth efficiency.