Analysis and optimization of pilot-symbol-assisted M-QAM for OFDM systems

Orthogonal frequency division multiplexing (OFDM) is very attractive for next generation high-speed wireless communication because of its various advantages in lessening the severe effects of frequency-selective fading. When using pilot symbol assisted (PSA) M-ary quadrature amplitude modulation (M-QAM) in OFDM systems, if the power of pilot is too low, the channel parameters cannot be accurately estimated, whereas, high pilot power will lead to less power left for data symbols under the condition that the total transmitted power is constrained to be a constant. In this paper, we present how pilot power affects the demodulation performance in Rayleigh fading propagation environments. Consequently, the pilot-to-data power ratio (PDR) is optimized analytically, and degradation of system performance due to inaccurate channel estimation is also evaluated. The theoretical and simulation results show that the optimum PDR is affected by the signal-to-noise ratio (SNR), Doppler frequency and interpolation size etc. When the optimum PDR is adopted for an OFDM system, the total transmission power will be minimal for certain bit error rate (BER) target. Copyright (c) 2005 John Wiley & Sons, Ltd.