Communication unit for soft-decision demodulation and method therefor

1 . A communication unit for performing soft-decision demodulation comprising a receiver, wherein the receiver is arranged to receive a transmitted signal having a first set of bits comprising k bits that has been selected from a set of 2 k possible signals according to values of the k bits, and includes a second set of bits comprising Q m bits based on a phase rotation of the transmitted signal selected from a set of 2 Qm possible rotations, wherein the receiver comprises:

a demodulator comprising a bank of 2 k correlators and configured to:

detect a transmission of each possible transmitted signal, and

output 2 k phases of the correlator outputs as a third set of inputs;

a de-mapper circuit coupled to the demodulator and configured to:

receive the third set of inputs;

determine statistics derived from one aggregated correlator output phase distribution of the third set of inputs that approximates an aggregation of a 2 k distributions of the output phases of the bank of 2 k correlators when the corresponding one of the set of 2 k possible signals was selected as the transmission signal; and

output a second set of aposteriori soft bits comprising Q m soft bits.

2 . The communication unit of claim 1 , wherein the aggregated correlator output phase distribution is represented by a second set of distribution parameters.

3 . The communication unit of claim 2 , wherein the second set of distribution parameters comprises a spreading parameter, sigma phase .

4 . The communication unit of claim 1 , wherein the demodulator is further configured to output 2 k magnitudes of correlator outputs, based on the detected possible transmitted signals, by the bank of 2 k correlators as a first set of inputs.

5 . The communication unit of claim 4 , wherein the de-mapper circuit is configured to perform at least one of the following:

estimate the second set of distribution parameters of the aggregated correlator output phase distribution by fitting a fifth probability distribution to phase errors of correlator outputs obtained by correlating received synchronisation signals with correlators corresponding to known synchronisation signals;

estimate the second set of distribution parameters of the aggregated correlator output phase distribution by fitting a sixth probability distribution to phase errors of correlator outputs having the greatest magnitude among sets of 2 k correlator outputs obtained by the bank of 2 k correlators;

select the second set of distribution parameters of the aggregated correlator output phase distribution from a look-up-table coupled to the de-mapper circuit.

6 . The communication unit of claim 5 , wherein at least one of the fifth or sixth probability distributions is a Gaussian distribution.

7 . The communication unit of claim 2 , wherein the de-mapper circuit is configured to accept a fourth set of apriori soft signals comprising Q m soft bits as a fourth set of inputs.

8 . The communication unit of claim 7 , wherein the second set of aposteriori soft bits is combined with soft bits of the fourth set of apriori soft signals to obtain a second set of extrinsic soft bits comprising Q m soft bits.

9 . The communication unit of claim 2 , wherein the output phases of the 2 k correlators are combined with the second set of distribution parameters of the aggregated correlator output phase distribution to obtain a third set of apriori soft signals comprising 2 k+Qm soft phases.

10 . The communication unit of claim 9 , wherein the communication unit combines all apriori soft signals to generate a set of 2 k+Qm aposteriori soft signals and wherein the set of 2 k+Qm aposteriori soft signals is combined to obtain the second set of aposteriori soft bits.

11 . A method for performing soft-decision demodulation comprising a communication unit having a receiver, the receiver having a de-mapper circuit coupled to a demodulator that comprises a bank of 2 k correlators, the method at the receiver comprising:

receiving a transmitted signal having a first set of bits comprising k bits that has been selected from a set of 2 k possible signals according to values of the k bits and having a second set of bits comprising Q m bits based on a phase rotation of the transmitted signal selected from a set of 2 Qm possible rotations,

detecting a transmission of each possible transmitted signal, and

outputting 2 k phases of the correlator outputs as a third set of inputs;

receiving the third set of inputs;

determining statistics derived from one aggregated correlator output phase distribution of the third set of inputs that approximates an aggregation of a 2 k distributions of the output phases of the bank of 2 k correlators when the corresponding one of the set of 2 k possible signals was selected as the transmission signal; and

outputting a second set of aposteriori soft bits comprising Q m soft bits.

12 . The method of claim 11 , further comprising representing the aggregated correlator output phase distribution by a second set of distribution parameters.

13 . The method of claim 12 , wherein the second set of distribution parameters comprises a spreading parameter, sigma phase .

14 . The method of claim 11 , further comprising outputting 2 k magnitudes of correlator outputs by the demodulator, based on the detected possible transmitted signals, by the bank of 2 k correlators as a first set of inputs.

15 . The method of claim 14 , further comprising performing by the de-mapper circuit at least one of the following:

estimating the second set of distribution parameters of the aggregated correlator output phase distribution by fitting a fifth probability distribution to phase errors of correlator outputs obtained by correlating received synchronisation signals with correlators corresponding to known synchronisation signals;

estimating the second set of distribution parameters of the aggregated correlator output phase distribution by fitting a sixth probability distribution to phase errors of correlator outputs having the greatest magnitude among sets of 2 k correlator outputs obtained by the bank of 2 k correlators;

selecting the second set of distribution parameters of the aggregated correlator output phase distribution from a look-up-table coupled to the de-mapper circuit.

16 . The method of claim 15 , wherein at least one of the fifth or sixth probability distributions is a Gaussian distribution.

17 . The method of claim 12 , further comprising accepting, by the de-mapper circuit, a fourth set of apriori soft signals comprising Q m soft bits as a fourth set of inputs.

18 . The method of claim 17 , further comprising combining the second set of aposteriori soft bits with soft bits of the fourth set of apriori soft signals thereby obtaining a second set of extrinsic soft bits comprising Q m soft bits.

19 . The method of claim 12 , further comprising combining the output phases of the 2 k correlators with the second set of distribution parameters of the aggregated correlator output phase distribution thereby obtaining a third set of apriori soft signals comprising 2 k+Qm soft phases.

20 . The method of claim 19 , further comprising combining all apriori soft signals to generate a set of 2 k+Qm aposteriori soft signals and combining the set of 2 k+Qm aposteriori soft signals thereby obtaining the second set of aposteriori soft bits.