Two-stage low-complexity max-log bit-level LLR calculator and method

1. A demodulator comprising:

a bit/symbol hard demodulator configured to obtain hard bit or symbol information from a received signal;

at least one lookup table configured to reference coefficients for computation of log-likelihood ratios (LLRs) from the hard bit or symbol information; and

a log-likelihood ratio calculation module configured to compute bit-level LLRs from the referenced-coefficients and the received signal; said log-likelihood ratio calculation module computing the LLR based upon coefficients obtained from the at least one lookup table and an additive noise coefficient computed from the received signal, said received signal including in-phase and quadrature components and the hard demodulators further comprising a 2 2N quadrature amplitude modulation (QAM) constellation for mapping the incoming information to hard bits with N being number of bits.

2. The demodulator as recited in claim 1 , wherein the QAM constellation includes two branches, and the two branches each include a pulse amplitude modulation (PAM) constellation.

3. The demodulator as recited in claim 2 , wherein each branch is labeled in accordance with a binary reflected Gray code (BRGC).

4. The demodulator as recited in claim 1 , wherein the coefficients are indexed by bit and symbol estimates and bit position.

5. The demodulator as recited in claim 1 , wherein the received signal includes in-phase and quadrature components and the hard demodulator further comprising a 2 M pulse shift keying modulation (PSK) constellation with M being incoming bits for mapping the incoming information to hard bits.

6. The demodulator as recited in claim 5 , wherein PSK constellation is labeled in accordance with an inverse regular binary reflected Gray code (BRGC).

7. The demodulator as recited in claim 5 , wherein log-likelihood ratio calculation module computes the LLR based upon coefficients obtained from the at least one lookup table and an additive noise coefficient computed from the received signal.

8. The demodulator as recited in claim 7 , wherein the coefficients are indexed by hard modulated bits and bit position.

9. The demodulator as recited in claim 8 , wherein the hard modulated bits provide a quadrature sign (S) and a value which are employed to lookup at least one coefficient.

10. A method for demodulation, comprising:

demodulating a received signal to obtain hard bit or symbol information and mapping the incoming information to hard bits in accordance with a 2 2N quadrature amplitude modulation (QAM) constellation with N being number of bits;

referencing coefficients from at least one lookup table to compute log-likelihood ratios (LLRs) from the hard bit or symbol information;

computing bit-level log-likelihood ratios LLRs from the referenced coefficients and the received signal and computing bit-level log-likelihood ratios includes computing the LLRs based upon coefficients obtained from the at least one lookup table and an additive noise coefficient computed from the received signal, wherein the coefficients are indexed by bit/symbol estimates and bit position.

11. The method as recited in claim 10 , wherein the QAM constellation includes two branches, and the two branches each employ a pulse amplitude modulation (PAM) constellation for mapping the hard bits.

12. The method as recited in claim 11 , further comprising labeling each branch in accordance with a binary reflected Gray code (BRGC).

13. The method as recited in claim 10 , wherein demodulating includes mapping the incoming information to hard bits in accordance with a 2 M pulse shift keying modulation (PSK) constellation with M being incoming bits.

14. The method as recited in claim 13 , further comprising labeling the PSK constellation in accordance with an inverse regular binary reflected Gray code (BRGC).

15. The method as recited in claim 13 , wherein computing bit-level log-likelihood ratios includes computing the LLRs based upon coefficients obtained from the at least one lookup table and an additive noise coefficient computed from the received signal, wherein the coefficients are indexed by hard modulated bits and bit position.

16. The method as recited in claim 15 , wherein the hard modulated bits provide a quadrature sign (S) and a value which are employed to lookup at least one coefficient.