Patent ID: 7248647

Claim:
A system operative to communicate digital data symbols with higher than quadrature phase shift keying (QPSK) modulation, the system comprising a transmitter and a receiver comprising: the transmitter comprising a modulator and means to split and encode the data into a first block of more significant bits of symbols and a second block of less significant bits of the symbols for modulating by the modulator; the receiver being operative to receive digital data bits by iterative determination of soft estimates of bits followed by a hard decision as to what bit was intended, the receiver comprising: a first processor operative to provide first soft estimates of bits of the received signal; a second processor operative to decode the first soft estimates and to provide second soft estimates of the bits; a first combiner operative to provide adapted first soft estimates to the second processor, the adapted first soft estimates of each bit being dependent upon a respective first soft estimate and a respective previous first soft estimate; and a second combiner operative to provide third soft estimates back to the first processor for subsequent further decoding, the third soft estimates of each bit being dependent upon a respective second soft estimate and a respective previous second soft estimate; wherein the more significant bits are detected in the received signal in a first series of iterations, their estimated contribution to the received signal being subtracted to provide a modified received signal from which the less significant bits are detected by a second series of iterations.