A programmable codec design for trellis coded modulation

The programmable trellis codec (PTC) is a trellis coded modulation (TCM) encoder-decoder circuit that is designed to provide the flexibility of implementing a variety of TCM codes with both quadrature amplitude modulation (QAM) and phase shift keying (PSK) constellations. It can also be used to perform maximum-likelihood sequence estimation for partial-response channels. PTC has the necessary computational power to achieve the required throughput for applications including digital subscriber lines, digital audio broadcast, and voice-band modems. The circuit implements both the TCM encoder and the TCM decoder for full-duplex operation. Given the register and memory sizes allocated and the bus widths specified for the PTC circuit described in this paper, the chip can handle trellis codes with up to 32 states, 4 branches per state, 8 cosets, 4 dimensions per symbol, 11 coded bits per two-dimensional sample, and the survivor trace back depth of 63 symbols.