Two-dimensional iterative APP channel estimation and decoding for OFDM systems

We present a channel estimation method for coherent detection of multicarrier signals which is based on the a posteriori probability calculation algorithm (APP estimator). A two-dimensional channel estimation is performed by applying a concatenation of two one-dimensional APP estimators. The combination with an outer soft in/soft out channel decoder allows one to further improve the bit error rate by means of iterative estimation and decoding. The robustness of the new channel estimator permits one to reduce the number of pilot symbols which are required as phase references for coherent detection. It is readily applicable to current multicarrier systems (e.g. DVB-T) without changing the transmission format. A combination with an inner convolutional code is suggested to further improve the performance.