Radio telecommunications system operative by interactive determination of soft estimates, and a corresponding method

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.