Post detection selection combining diversity receivers for mobile and indoor radio channels

A method of determining channel quality of a carrier modulated signal encoding digital information as symbol phase angles each selected from a set of symbol constellation phase points {.theta.} transmitted through a AWGN channel comprising the steps of:

• a) receiving, heterodyning, and sampling the carrier modulated signal to produce a plurality of baseband received samples r.sub.k ;
• b) decoding the received samples r.sub.k into a plurality of phase angles .phi..sub.k ;
• c) computing SIR value .gamma..sub.k from phase angles .phi..sub.k according to the equation:
• ##EQU28## where .theta..sub.k is a transmitted phase angle from the set of symbol constellation phase points {.theta.} which is closest to .phi..sub.k ;
• and
• d) computing a channel quality from the SIR values.

A method of decoding digital information redundantly encoded as symbols from a signal constellation in a signal transmitted through a channel comprising the steps of:

• a) receiving, heterodyning, and sampling the transmitted signal to produce a plurality of baseband received samples r.sub.k, with `k` being an index applying to a kth sampling instant;
• b) determining phase angles .phi..sub.k ;
• c) identifying each phase angle .phi..sub.k as not marked;
• d) calculating signal-to-impairment ratio (SIR) values from the determined phase angles .phi..sub.k indicating channel quality according to the equation:
• ##EQU36## where .theta..sub.k is a transmitted phase angle from the set of symbol constellation phase points {.theta.} which is closest to .phi..sub.k ;
• and
• e) computing a channel quality from the SIR values;
• f) decoding phase angles .phi..sub.k which have not been marked into a block of message data employing an error correction scheme which takes advantage of the redundancy in the encoding;
• g) determining if data block is acceptable, and
• i. if it is acceptable, providing the message data block to a digital output device, and
• ii. if it is not accentable, identifying a phase angle .phi..sub.k pertaining to a lowest SIR value which has not yet been marked as marked;
• and
• h) repeating steps "f"-"g" until the data block is acceptable for a predetermined maximum number of repetitions.

A method of decoding digital information redundantly encoded as symbols from a signal constellation in a signal transmitted through a channel comprising the steps of:

• a) receiving, heterodyning, and sampling the transmitted signal to produce a plurality of baseband received:
• samples r.sub.k ;
• b) determining phase angles .phi..sub.k from the samples r.sub.k, with `k` being an index applying to a kth sampling instant;
• c) estimating which symbol from the signal constellation transmitted corresponds to phase angles .phi..sub.k ;
• d) calculating signal-to-impairment ratio (SIR) values for estimated phase angles .phi..sub.k indicating channel quality according to the equation:
• ##EQU37## where .theta..sub.k is a transmitted phase angle from the set of symbol constellation phase points {.theta.} which is closest to .phi..sub.k ;
• and
• e) computing a channel quality from the SIR values;
• f) determining for each of the SIR values, if the SIR value exceeds a predetermined value, then erasing the symbol corresponding to the SIR value;
• g) decoding each symbol which has not been erased by reverse mapping each phase angle .phi..sub.k to a bit string according to the signal constellation employed in encoding the digital information;
• h) employing an error correction scheme which takes advantage of the redundancy in the encoding and provides bit strings originally encoded in the phase angle .phi..sub.k that have been marked, from the remaining bit strings;
• and
• i) repeating steps "a"-"h" for subsequent signal transmissions.

A system for decoding digital information redundantly encoded as symbols from a set of signal constellation points {.theta.} in a signal transmitted through a channel comprising:

• a) a front end capable of receiving, heterodyning, and sampling the transmitted signal to produce a plurality of baseband received samples r.sub.k, with `k` being an index applying to a kth sampling instant;
• b) a buffer capable of retaining a plurality of phase angles;
• c) a phase detector coupled to the front end adapted for providing a plurality of phase angles .phi..sub.k from the baseband received samples r.sub.k and storing the phase angles .phi..sub.k in the buffer;
• d) an SIR calculation unit capable of calculating a signal-to-impairment ratio (SIR), .gamma..sub.k, for each phase angle .phi..sub.k indicating channel quality according to the equation:
• ##EQU41## where .theta..sub.k is a transmitted phase angle from the set of symbol constellation phase points {.theta.} which is closest to .phi..sub.k ;
• and
• d) computing a channel quality from the SIR value;
• e) an error correction decoder capable of estimating a block of message dam, e.sub.k, corresponding to the transmitted signal constellation points {.theta.} from phase angles .phi..sub.k which have not been marked as corrupted, and adapted for employing the redundancy inherent in the encoding scheme to calculate message data pertaining to phase angles marked, as corrupted;
• f) erasure control unit coupled to the SIR calculation unit, for sequentially marking a phase angles .phi..sub.k having the lowest SIR value of remaining unmarked phase angles as a corrupted phase angle in the, buffer;
• and
• g) an output device capable of utilizing the message data, e.sub.k ;
• h) an error detection unit capable of determining if the block of message data, e.sub.k, is acceptable, and
• i. if acceptable providing the block of message data bit to the output device, and
• ii. if the block of message data is not acceptable, then iteratively for a predetermined maximum number of repetitions, causing the erasure control unit to mark a phase angle having the lowest SIR of all phase angles which have not been marked, and causing then causing the error correction decoder to estimate an updated block of message data, e.sub.k from the remaining phase angles which have not been marked.