Reduced-state variant of optimum MAP equaliser

Although the reduced-state technique has been widely used in Viterbi equali sers, its application to maximum a posteriori probability (MAP) equalisers is not satisfactory because it cannot operate due to the backward recursion of the conventional MAP algorithm. A new kind of MAP algorithm is proposed in which the forward and backward recursions are exactly symmetric. The re duced-state technique can thus be applied to both forward and backward recu rsions and a gain in performance is achieved over that of conventional redu ced-state MAP equalisers at the cost of double the computational overhead.