Methods and systems for soft-bit demapping

1. A method for soft-bit output demapping, comprising:

receiving a data stream at a receiver;

equalizing said received data stream to remove channel and noise effects from said received data stream, thereby generating an equalized data stream;

soft-bit slicing said equalized data stream to generate one or more preliminary soft-bit values, said preliminary soft-bit values corresponding to one or more bits of a data symbol contained in said received data streams, wherein said soft-bit slicing step comprises:

iteratively generating said one or more preliminary soft-bit values, whereby a soft-bit value corresponding to a first bit of the data symbol is used to generate preliminary soft-bit values corresponding to subsequent bits of the data symbol; and

scaling said preliminary soft-bit values to generate final soft-bit values.

2. The method of claim 1 , further comprising:

generating a plurality of configuration parameters for configuring said equalizing, soft-bit slicing, and scaling steps.

3. The method of claim 1 , wherein said equalizing step comprises multiplying said received data stream by a weight matrix, said weight matrix including weight coefficients computed according to channel response and noise estimates.

4. The method of claim 1 , wherein said equalizing step is configurable to accommodate a plurality of the following transmit/receive antenna modes of operations:

a single transmit antenna and a single receive antenna;

a single transmit antenna and multiple receive antennas; and

multiple transmit antennas and multiple receive antennas.

5. The method of claim 1 , wherein said soft-bit slicing step comprises performing maximum likelihood soft-bit slicing.

6. The method of claim 1 , wherein said soft-bit slicing step comprises implementing the following equation for BPSK modulation:

Λ R,0 =y R ,

where Λ R,0 is a preliminary soft-bit value for a BPSK-modulated transmitted data symbol and y R is the real part of a received equalized stream corresponding to said transmitted data symbol.

7. The method of claim 1 , wherein said soft-bit slicing step comprises implementing the following equations for QPSK modulation:

Λ R,0 =y R

Λ I,0 =y I ,

where Λ R,0 and Λ I,0 are respectively preliminary soft-bit values for the first and second bits in a QPSK-modulated transmitted data symbol and y R and y I are respectively the real and imaginary parts of a received equalized stream corresponding to said transmitted data symbol.

8. The method of claim 1 , wherein said soft-bit slicing step comprises implementing the following equations for 16-QAM modulation:

Λ R,0 =y R

Λ R,1 =2.(REF*K)−|Λ R,0 |

Λ I,0 =y I

Λ I,1 =2.(REF*K)−|Λ I,0 |

where Λ R,0 , Λ R,1 , Λ I,0 , Λ I,1 are respectively preliminary soft-bit values for the first, second, third, and fourth bits in a 16-QAM-modulated transmitted data symbol, y R and y I are respectively the real and imaginary parts of a receive equalized stream corresponding to said transmitted data symbol, REF is a mode-dependent constant, and K a modulation-dependent constant.

9. The method of claim 1 , wherein said soft-bit slicing step comprises implementing the following equations for 64-QAM modulation:

Λ R,0 =y R

Λ R,1 =4.(REF*K)−|Λ R,0 |

Λ R,2 =2.(REF*K)−|Λ R,1 |

Λ I,0 =y I

Λ I,1 =4.(REF*K)−|Λ I,0 |

Λ I,2 =2.(REF*K)−|Λ I,1 |

where Λ R,0 , Λ R,1 , Λ R,2 , Λ I,0 , Λ I,1 , Λ I,2 are respectively preliminary soft-bit values for the first, second, third, fourth, fifth, and sixth bits in a 64-QAM-modulated transmitted data symbol, y R and y I are respectively the real and imaginary parts of a receive equalized stream corresponding to said transmitted data symbol, REF is a mode-dependent constant, and K a modulation-dependent constant.

10. The method of claim 1 , wherein said soft-bit slicing step comprises implementing the following equations following for 256-QAM modulation:

Λ R,0 =y R

Λ R,1 =8.(REF*K)−|Λ R,0 |

Λ R,2 =4.(REF*K)−|Λ R,1 |

Λ R,3 =2.(REF*K)−|Λ R,2 |

Λ I,0 =y I

Λ I,1 =8.(REF*K)−|Λ I,0 |

Λ I,2 =4.(REF*K)−|Λ I,1 |

Λ I,3 =2.(REF*K)−|Λ I,2 |

where Λ R,0 , Λ R,1 , Λ R,2 , Λ R,3 , Λ I,0 , Λ I,1 , Λ I,2 , Λ I,3 are respectively preliminary soft-bit values for the first, second, third, fourth, fifth, sixth, seventh, and eighth bits in a 256-QAM-modulated transmitted data symbol, y R and y I are respectively the real and imaginary parts of a receive equalized stream corresponding to said transmitted data symbol, REF is a mode-dependent constant, and K a modulation-dependent constant.

11. The method of claim 1 , wherein said soft-slicing step is configurable to accommodate one or more of the following modulation schemes:

BPSK,

QPSK, and

QAM.

12. The method of claim 1 , wherein said scaling step comprises scaling said preliminary soft-bit values using scaling factors, thereby ensuring said generated final soft-bit values have uniform dynamic ranges for all modes of operation and all signal-to-noise ratio (SNR) conditions at receiver branches.

13. The method of claim 1 , wherein said scaling factors are generated using received noise variance information.

14. The method of claim 1 , wherein said scaling step comprises multiplying each of said preliminary soft-bit values by a scaling factor and a modulation-dependent constant.

15. The method of claim 1 , wherein said scaling step comprises implementing the following equation:

L=Λ*SCALE*4*K,

where L is a final soft-bit value corresponding to a bit in said one or more modulated data symbol bits, Λ is a preliminary L-value generated by said soft-slicing step, SCALE is a scaling factor, and K is a modulation-dependent constant.

16. The method of claim 12 , wherein at least a portion of the equation implemented by said scaling step is performed in a logarithmic domain.