Pilot symbol initiated sub-optimal sequence estimation algorithm for QAM signals

A sub-optimal decision directed decoding algorithm based on the expectation-maximisation algorithm is proposed. The algorithm performs iterative sequence estimation assuming quadrature amplitude modulation signals in a frequency non-selective fading channel. The iteration begins using periodically inserted pilot symbols, and it was observed that the algorithm converges mostly within two iterations. The bit error rate performances of the proposed algorithm are evaluated using computer simulation. The results show that the proposed algorithm performs better than conventional schemes.