System and method for communicating data using weighted bit soft decisions for differentially encoded phase shift keying
View Patent ↗A receiver includes a signal input for receiving a differentially-encoded quadrature phase-shift keyed (DEQPSK) communication signal. A demodulator performs bit decisions on a received coherent symbol and bit decisions on a received differential symbol. A processor is operative with the demodulator and scales a soft decision by a factor from 0 to 1 when the results of the bit decisions on the received coherent branch and differential branch are different.
1. A receiver, comprising:
a signal input for receiving a differentially-encoded quadrature phase-shift keyed (DEQPSK) communications signal; and
a coherent demodulator circuit that performs hard bit decisions on a received coherent phase and a differential demodulator circuit that performs hard bit decisions and soft bit decisions on a received differential phase; and
a processor operative with the coherent and differential demodulator circuits that receives hard bit decisions from both of the coherent and differential demodulator circuits and compares the hard bit decisions and scales any soft bit decisions by a factor from 0 to 1 when the results of the hard bit decisions on the received coherent phase after re-mapping and differential phase are different.
2. The receiver according to claim 1 , wherein said processor is operative for obtaining a last received symbol, conjugating the symbol and multiplying it by a current symbol such that the change corresponds to an estimate of the data.
3. The receiver according to claim 1 , and further comprising a phase tracker operative with the coherent demodulator circuit for coherently tracking phase and frequency.
4. The receiver according to claim 3 , wherein said processor is operative with the coherent demodulator circuit for obtaining a coherent estimate of data using the phase tracker.
5. The receiver according to claim 1 , wherein said processor is operative for obtaining a differential data estimate and a coherent data estimate such that two separate sets of data decisions can be compared.
6. The receiver according to claim 1 , wherein said scaling for soft decisions can vary as a function of received signal-to-noise ratio.
7. The receiver according to claim 1 , and further comprising a look-up table used to determine the current differential data received for coherent branch based on the current coherently demodulated symbol and a previous one.
8. A method of demodulating a differentially-encoded quadrature phase-shift keyed (DEQPSK) communications signal, comprising:
receiving the DEQPSK communications signal within a receiver;
demodulating the received communications signal in a coherent demodulator circuit by performing hard bit decisions on received coherent symbols and re-mapping to differential data,
demodulating the received communications signal in a differential demodulator circuit by performing hard bit decisions and soft bit decisions on received differential symbols; and
receiving hard bit decisions from both of the coherent and differential demodulators and scaling any soft bit decisions by a factor from 0 to 1 when the results of the hard bit decisions on the coherent demodulator circuit and the differential demodulator circuit are different.
9. The method according to claim 8 , which further comprises obtaining a last received symbol, conjugating the symbol and multiplying it by a current symbol such that the change corresponds to the data.
10. The method according to claim 8 , which further comprises coherently demodulating the communications signal using a phase/frequency tracker.
11. The method according to claim 10 , which further comprises tracking the phase and frequency of received signal.
12. The method according to claim 10 , which further comprises obtaining a coherent estimate of data using the phase/frequency tracker.
13. The method according to claim 8 , which further comprises obtaining a differential data estimate and a coherent data estimate such that two separate sets of data decisions can be compared.
14. The method according to claim 8 , which further comprises sampling the received signal to obtain in-phase (I) and quadrature (Q) values for calculating a distance equation.
15. The method according to claim 8 , which further comprises querying a look-up table for obtaining differential data based on last received coherent data and current received coherent data.
16. A method of demodulating a differentially-encoded quadrature phase-shift keyed (DEQPSK) communications signal, comprising:
receiving the DEQPSK communications signal within a modem;
demodulating the received communications signal by performing hard bit decisions in a coherent demodulator circuit on received coherent symbols and performing hard bit decisions and soft bit decisions in a differential demodulator circuit on a received differential symbols; and
using a fixed point conversion table obtained by calculating two soft decision values for a quantized set of x and y coordinates and receiving bit decisions from both of the coherent and differential demodulators and scaling soft bit decision values by a factor from 0 to 1 when the results of hard bit decisions on the coherent demodulator circuit and the differential demodulator circuit are different.
17. The method according to claim 16 , which further comprises obtaining a last received symbol, conjugating the symbol and multiplying it by a current symbol such that the change corresponds to the data.
18. The method according to claim 16 , which further comprises coherently demodulating using a phase tracker.
19. The method according to claim 18 , which further comprises tracking the phase and frequency using the phase tracker.
20. The method according to claim 18 , which further comprise obtaining a coherent estimate of data using the phase tracker.
21. The method according to claim 16 , which further comprises obtaining a differential data estimate and a coherent data estimate such that two separate sets of data decisions can be compared.
22. The method according to claim 16 , which further comprises sampling the received signal to obtain in-phase (I) and quadrature (Q) values for calculating a distance equation.
23. The method according to claim 16 , which further comprises querying a look-up table for obtaining differential data based on last received coherent data and current received coherent data.
24. The method according to claim 16 , which further comprises querying a pre-computed table to generate soft decisions based on received demodulated symbol.
25. The method according to claim 16 , which further comprises scaling soft decisions obtained from pre-computed table by a factor from 0 to 1 when the hard bit decisions on the coherent demodulator circuit and the differential demodulation circuit are different.