Turbo APPA carrier phase recovery and signal detection for OFDM systems

Abstract

This paper examined the problem of carrier phase recovery in turbo-coded OFDM systems. Then introduced a novel a priori probability aided (APPA) OFDM joint carrier phase recovery and signal detection algorithms to eliminate disadvantage impact brought by phase offset. The algorithms utilized the soft value of the extrinsic information generated by iterative maximum a posteriori (MAP) turbo decoders operating iteratively. The iteration structure provided robust carrier phase estimation along with reliable signal decoding with a wide range of phase errors at such low signal-to-noise ratio (SNR) conditions that turbo coded systems operate on. In order to take full advantage of iterative soft information output by turbo decoders, we improved turbo decoding iterative structure and applied the above iterative structure into APPA carrier estimator for turbo-coded OFDM systems. We simulated the algorithm in turbo-coded QPSK OFDM systems over the classic COST207 HT channel conditions. Simulation results show that the performance of this technique is very close to the ideal synchronized system. The tracking region is from -45 to 45 degrees and the overall BER decreases greatly at the 2 iteration numbers under certain phase offset. Moreover this structure is straightforward to other application such as other constellation, channel estimation and so on. Keywords-OFDM systems; a priori probability aided (APPA); iterative decoding; carrier phase recovery; iterative maximum a posteriori (MAP)I.