A novel coherent demodulation for M-QAM OFDM signal operating in the burst mode

This paper proposes a novel coherent demodulation method for orthogonal frequency division multiplexing (OFDM) systems with multi-level quadrature amplitude modulation (M-QAM) that are operating in a burst mode such as wireless LAN communications systems. The salient feature of the proposed method is that two training symbols placing at the start of every burst frame are used both for the synchronization of received burst signal and the estimation of channel frequency response under frequency selective fading environments. Furthermore, this paper proposes a simple phase tracking method for compensating the phase rotation of signal constellation points due to the residual frequency offset as the result of frequency offset estimation method of using two training symbols. The coherent demodulator including the phase tracking method proposed in this paper offers excellent C/N performance even under severe frequency selective fading environments without any assistance of the pilot tones which is usually employed in the conventional coherent demodulation for the M-QAM OFDM signal.