Methods and apparatus for providing a maximum likelihood (ML) decoding pipeline for quadrature phase-shift keying (QPSK) multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) receivers
View Patent ↗Methods and apparatus are provided for performing log-likelihood ratio (LLR) computations in a pipeline. Portions of a metric used to compute LLR values are computed in one pipeline part. The portions correspond to all permutations of some received signal streams. The portions are combined with one permutation x 2 of the received signal stream that was not included in the previous pipeline computation in a subsequent pipeline part to produce M values associated with a particular bit position. At each subsequent clock cycle, a different permutation of x 2 is combined with the previously computed portions producing different M values. State values corresponding to different values of bit positions of the received stream are computed by finding the minimum among the M values, in each clock cycle, that affect a particular bit position. The state values are combined to compute the LLR values for the bit position in a final pipeline part.
1. A method comprising:
generating, with control circuitry in a first pipeline stage, a first plurality of differences between a received input signal value and a first set of predetermined signal values;
generating, in a second pipeline stage following the first pipeline stage, a first plurality of reliability values based on the first plurality of differences while a second plurality of differences between the received input signal value and a second set of predetermined signal values is generated in the first pipeline stage; and
comparing the first plurality of reliability values with a second plurality of reliability values based at least in part on the second set of predetermined signal values.
2. The method of claim 1 , wherein the first set of predetermined signal values corresponds to all permutations of a subset of a plurality of input streams and a first permutation of a remainder of the plurality of input streams.
3. The method of claim 1 , wherein the comparing comprises comparing a first minimum of the first plurality of reliability values with a second minimum of the second plurality of minimum values.
4. The method of claim 1 , wherein the control circuitry is in a QPSK receiver.
5. The method of claim 1 , wherein the first plurality of reliability values corresponds to a first tone of the input signal.
6. The method of claim 2 , wherein the second set of predetermined signal values corresponds to all permutations of the subset of the plurality of input streams and a second permutation of the remainder of the plurality of input streams.
7. The method of claim 3 , further comprising storing the minimum of the first and second minima.
8. The method of claim 5 , wherein the control circuitry is in an OFDM receiver.
9. The method of claim 7 , wherein the stored minimum is associated with a first value of a symbol position of the input signal.
10. The method of claim 9 , further comprising:
generating a second stored minimum associated with a second value of the symbol position of the input signal;
comparing the stored minima; and
determining whether the first value or the second value is more likely based on the comparison.
11. A system comprising control circuitry configured to:
generate, in a first pipeline stage, a first plurality of differences between a received input signal value and a first set of predetermined signal values;
generate, in a second pipeline stage following the first pipeline stage, a first plurality of reliability values based on the differences while a second plurality of differences between the received input signal value and a second set of predetermined signal values is generated in the first pipeline stage; and
compare the first plurality of reliability values with a second plurality of reliability values based at least in part on the second set of predetermined signal values.
12. The system of claim 11 , wherein the first set of predetermined signal values corresponds to all permutations of a subset of a plurality of input streams and a first permutation of a remainder of the plurality of input streams.
13. The system of claim 11 , wherein the comparing comprises comparing a first minimum of the first plurality of reliability values with a second minimum of the second plurality of minimum values.
14. The system of claim 11 , wherein the control circuitry is in a QPSK receiver.
15. The system of claim 11 , wherein the first plurality of reliability values corresponds to a first tone of the input signal.
16. The system of claim 12 , wherein the second set of predetermined signal values corresponds to all permutations of the subset of the plurality of input streams and a second permutation of the remainder of the plurality of input streams.
17. The system of claim 13 , wherein the control circuitry is further configured to store the minimum of the first and second minima.
18. The system of claim 15 , wherein the control circuitry is in an OFDM receiver.
19. The system of claim 17 , wherein the stored minimum is associated with a first value of a symbol position of the input signal.
20. The system of claim 19 , wherein the control circuitry is further configured to:
generate a second stored minimum associated with a second value of the symbol position of the input signal;
compare the stored minima; and
determine whether the first value or the second value is more likely based on the comparison.