Low-complexity iterative equalisation and decoding for wireless optical communications
A low-complexity scheme of iterative equalisation and decoding by combining a recursive systematic convolutional code and a pulse-position modulation is proposed here. A graph-based equalisation for intersymbol interference (ISI) known at both transmitter and receiver is considered. By representing the memory channel with ISI as the factor graph and applying sum–product (SP) algorithm to this graph, a posteriori probability (APP) of the desired symbol necessary to implement iterative equalisation and decoding is derived. A partial response precoding is used to reduce the span of ISI from a possible infinite number of two baud periods. This precoding scheme makes the factor graph of memory channel cycle-free, and SP algorithm for combating ISI converges to an optimum detection. Numerical results show that the proposed low-complexity strategy has almost the same performance as the optimum turbo equalisation.
