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An improved channel quality estimation technique for OFDM system

Adaptive transmission to the channel conditions has been shown to considerably improve the BER performance as well as transmission throughput. Application of the adaptive transmission technique to the OFDM system has been considered in many areas in order to utilize the advantage of the adaptive schemes. However, accurate estimation of channel conditions, especially signal to interference ratio (SIR) must be advanced for efficient adaptive schemes. In this paper, we propose a channel quality estimation technique for adaptive OFDM systems which suffer from interference due to channel estimation error and thermal noise. The proposed scheme estimates the variance of thermal noise by using the null space of the channel gain matrix in an OFDM symbol first, then evaluates the total interference power from the estimated thermal noise variance. Simulation results show that the proposed estimation algorithm produces more than an order of better estimates than the conventional algorithm even with fewer of pilots.