Patent ID: 7636399

Claim:
In a communication system comprising a transmitter and a receiver, wherein the transmitter comprises an outer encoder followed by a transmitter interleaver and an M c -ary continuous phase modulation (CPM) modulator for transmitting a CPM signal modulated with a sequence of M c -ary symbols, a method for non-coherent decoding of the CPM signal received by the receiver via a communication channel, the method comprising: a) identifying CPM symbol positions in the received CPM signal; b) selecting a portion of the received CPM signal comprising N consecutive CPM symbol positions; c) generating a sequence of N b =N*log 2 (M c ) inner extrinsic information values for the selected portion of the received CPM signal from N b a-priori information values and a plurality of complex branch metrics using a recursive tree search algorithm, wherein at each step of said algorithm at most M tree paths are retained, 1<M<M c N , wherein each tree path corresponds to a sequence of up to N M c -ary symbols, and wherein the tree paths to be retained are selected based on absolute values of cumulative metrics associated therewith and accounting for the a-priori information values, and wherein the cumulative metrics are complex-valued and are recursively obtained from the complex branch metrics; d) providing the sequence of N b inner extrinsic information values to an inverse interleaver to form a de-interleaved sequence of inner information values, and sending said de-interleaved sequence to an outer SISO decoder; e) generating a sequence of N b encoded outer extrinsic information values using the outer SISO decoder from said de-interleaved sequence; f) interleaving the sequence of N b encoded outer extrinsic information values to generate the set of N b a-priori information values, and providing said set of N b a-priori information values to the inner CPM decoder; g) iteratively repeating the sequence of steps (c)-(f); and, h) generating a decoded sequence of N b soft outer extrinsic values obtained by the outer SISO decoder from the N b de-interleaved inner extrinsic information values.