Cyclic trellis coded modulation
A universal method of trellis encoding signals mapped according to any signal constellation format involves constructing an encoder output table and a state transition table. The encoder output table defines the output symbol of an encoder given the input symbol and the present state of the encoder, while the state transition table defines the next state of the encoder given the present state of the encoder and the input applied to the encoder. The output table and the next state table are constructed with the objective of providing maximal distances between the branches of the trellis diagram without any regards for the shift register implementation of the code. Cyclic trellis-coded modulation is an example of such codes without feed-forward or feed-back shift register implementations, and with equal or better performance than “optimal” shift register trellis codes with 16 states or less. The cyclic trellis codes for both AWGN and Rayleigh fading applications can be constructed for any signal constellation without resorting to exhaustive searches.
1. An apparatus for trellis encoding, comprising:
means for trellis encoding an input signal via a signal constellation having an even number of constellation points, and
wherein the means for trellis encoding includes means for providing paths in the trellis, wherein all the paths merging out of a state and into the same state are defined so as to provide maximal or near maximal spacing between outputs on state transition paths for all signal constellations having an even number of constellation points.
2. A wireless data transmitter, comprising:
a data input portion;
a state machine encoder, coupled to the data input portion, wherein the state machine encoder is programmed with limited state transition paths wherein the state transition paths are defined to provide a minimum number of two branch state transition paths between states out of all possible state transition paths between the same state; and
a transmitter coupled to the state machine encoder.