M-algorithm combined equalization and decoding for mobile/personal communications

Third-generation tetherless mobile/personal communication system development is faced with the conflicting requirements of providing both highest protection against noise/interference and keeping the transmission delay as low as possible. A novel algorithm for combined equalization and decoding of interleaved coded modulation is presented. The new M-CED algorithm is an extension of the "conventional" CED in two ways: (i) per-survivor processing is used in the equalizer section in order to reduce the decoding latency, and (ii) M>1 equalizer states per code state are kept in the survivor memory so as to further improve on the bit error performance. Results on simulated bit error rates give an insight into the effect of various channel and receiver parameters, in particular, interleaver length (thus latency), number of equalizer states, and the choice of trellis codes. The entire digital receiver with feedforward sync, appropriate prefiltering and M-CED equalization/decoding is shown to combine the advantages of being robust against fading and yielding good BER performance also at low delay.