Parity Assisted Decision Making for QAM Modulation

A simple technique which involves the transmission of a quadrature amplitude modulation (QAM) symbol and two parity bits in separate channels to improve the performance of communication systems is devised. When a symbol is received, a decision is made not solely by its Euclidean distances to the constellation points. Rather, the two parity bits are used to assist in making the decision. Unlike standard error correcting codes (ECC), the proposed method operates on the received symbols at the detector level and before the ECC. The parity bits and the information symbols can be sent in different channels (frequency division) or at different times on the same channel (time division). The available energy for transmission can be distributed unevenly among the information bits and the parity bits to improve the performance. Simulation results show large gains in required signal to noise ratios over uncoded system to achieve the same performance. The scheme is simple and is well suited for systems with low computational power.