Modulation-type discrimination in a wireless communication network

1. A method of discriminating a modulation type for decoding a signal field of an encoded signal in a wireless communication system, the method comprises:

receiving, via a receiver, the encoded signal having a preamble training sequence associated with a frame, the preamble training sequence including the signal field;

generating at least a first log-likelihood ratio (LLR) stream and a second LLR stream for each of a plurality of sub-symbols for a predetermined portion of the received encoded signal based upon an m-bit wide modulation reference, wherein m represents the bit width of the modulation reference, the first LLR stream and the second LLR stream includes a plurality of LLR values;

summing the plurality of LLR values of the first LLR stream to produce a first cumulative LLR;

summing the plurality of LLR values of the second LLR stream to produce a second cumulative LLR;

discriminating the first cumulative LLR with the second cumulative LLR to produce a discriminated modulation type output by:

comparing the first cumulative LLR with the second cumulative LLR;

upon a favorable comparison of the first cumulative LLR with the second cumulative LLR, setting the discriminated modulation type to a first specified modulation type of a plurality of specified modulation types; and

upon an unfavorable comparison of the first cumulative LLR with the second cumulative LLR, setting the modulation type to one of a second or a third specified modulation type by:

when the first cumulative LLR is greater than the second cumulative LLR, setting the discriminated modulation type to the second specified modulation type; and

when the first cumulative LLR is less than the second cumulative LLR, setting the discriminated modulation type to the third specified modulation type; and

decoding the signal field of the preamble training sequence based on the discriminated modulation type output.

2. The method of claim 1 wherein the third specified modulation type is a rotated second specified modulation type.

3. The method of claim 1 wherein the modulation reference is a QPSK modulation type.

4. The method of claim 1 wherein the second specified modulation type is a BPSK modulation type.

5. The method of claim 1 wherein the third specified modulation type is a rotated BPSK modulation type.

6. The method of claim 1 wherein the predetermined portion is a signal field.

7. The method claim 1 wherein the generating step further comprises:

selecting the predetermined portion based on a format from a plurality of formats of the frame.

8. A modulation-type discriminator for a radio frequency receiver comprises:

a log-likelihood ratio (LLR) module operable to receive a signal field of an encoded signal having a preamble training sequence associated with a frame, the LLR module operable to generate a first and a second LLR stream for each of a plurality of sub-symbols for a predetermined portion of the received encoded signal based on a two-bit wide modulation reference;

a summing module disposed to receive the first and the second LLR streams and operable to cumulate the first LLR stream to produce a first cumulative LLR and the second LLR stream to produce a second cumulative LLR; and

a discriminator module operable to receive the first and the second cumulative LLR, and further operable to compare each of the first and the second cumulative LLR to provide a discriminated modulation type from a plurality of specified modulation types by:

comparing the first cumulative LLR with the second cumulative LLR;

upon a favorable comparison result that discriminates the received signal field as substantially equivalent to the modulation reference, setting the discriminated modulation type to a first specified modulation type of the plurality of specified modulation types; and

upon an unfavorable comparison result that discriminates the received signal field as being non-equivalent to the modulation reference, setting the discriminated modulation type to one of a second or a third specified modulation type of the plurality of specified modulation types by:

when the first cumulative LLR is greater than the second cumulative LLR, setting the discriminated modulation type to the second specified modulation type; and

when the first cumulative LLR is less than the second cumulative LLR, setting the discriminated modulation type to the third specified modulation type.

9. The modulation-type discriminator of claim 8 wherein the modulation reference is a QPSK modulation type.

10. The modulation-type discriminator of claim 8 wherein the first specified modulation type of the plurality of specified modulation types is a QPSK modulation type.

11. The modulation-type discriminator of claim 8 wherein the second specified modulation type of the plurality of specified modulation types is a BPSK modulation type.

12. The modulation-type discriminator of claim 8 wherein the third specified modulation type of the plurality of specified modulation types is a rotated-BPSK modulation type.

13. The modulation-type discriminator of claim 8 wherein the predetermined portion is a signal field.

14. The modulation-type discriminator of claim 8 wherein the predetermined portion is based on a format from a plurality of formats for the frame.

15. An integrated circuit radio transceiver comprises:

transmit signal path circuitry operable to transmit radio-frequency signals;

receive signal path circuitry operable to receive radio-frequency signals having a preamble associated with a frame, the preamble having a signal field, the receive signal path circuitry includes modulation-type discriminator circuitry coupled to discriminate a signal field modulation type from a predetermined portion of a received radio-frequency signal, the modulation-type discriminator circuitry includes logic circuitry that comprises:

a digital receiver processing module; and

memory coupled to the digital receiver processing module, wherein the memory stores operational instructions that prompts the digital receiver processing module to:

generate at least a first log-likelihood ratio (LLR) stream and a second LLR stream for each of a plurality of sub-symbols for a predetermined portion of the received encoded signal based upon an m-bit wide modulation reference, wherein m represents the bit width of the modulation reference, the first LLR stream and the second LLR stream includes a plurality of LLR values;

sum the plurality of LLR values of the first LLR stream to produce a first cumulative LLR;

sum the plurality of LLR values of the second LLR stream to produce a second cumulative LLR;

discriminate the first cumulative LLR with the second cumulative LLR to produce a discriminated modulation type output by:

upon a favorable comparison result that discriminates the signal field of the received radio-frequency signal as substantially equivalent to a two-bit wide modulation reference, setting the discriminated modulation type to a first specified modulation type of a plurality of specified modulation types; and

upon an unfavorable comparison result that discriminates the signal field of the received radio-frequency signal as being non-equivalent to the two-bit wide modulation reference, setting the discriminated modulation type to one of a second or a third specified modulation type of the plurality of specified modulation types by:

 when the first cumulative log likelihood ratio is greater than the second cumulative log likelihood ratio, setting the discriminated modulation type to the second specified modulation type; and

 when the first cumulative log likelihood ratio is less than the second cumulative log likelihood ratio, setting the discriminated modulation type to the third specified modulation type; and

decode the signal field based upon the discriminated modulation type output.

16. The integrated circuit radio transceiver of claim 15 wherein the modulation reference is a QPSK modulation type.

17. The integrated circuit radio transceiver of claim 15 wherein the first specified modulation type of the plurality of specified modulation types is a QPSK modulation type.

18. The integrated circuit radio transceiver of claim 15 wherein the second specified modulation type of the plurality of specified modulation types is a BPSK modulation type.

19. The modulation-type discriminator of claim 15 wherein the predetermined portion is a signal field.

20. A method of discriminating a modulation type for decoding a signal field of an encoded signal in a wireless communication system, the method comprises:

receiving, via a receiver, the encoded signal having a preamble training sequence associated with a frame, the preamble training sequence including the signal field;

processing a plurality of sub-symbols of the received encoded signal associated with the signal field to produce a stream having a real portion and an imaginary portion for each of the sub-symbols, each of the portions having a magnitude;

for each sub-symbol, discriminating the magnitude of the real portion with the magnitude of the imaginary portion to produce a discriminated modulation type output, wherein:

when the magnitude of the real portion and the imaginary portion approximate each other, the discriminated modulation type output is a first modulation type;

when the magnitude of the real portion and the imaginary portion are not approximate to each other, the discriminated modulation type output is one of a second or a third modulation type, such that:

when the magnitude of the real portion is greater than that of the imaginary portion, the discriminated modulation type output is the second specified modulation type; and

when the magnitude of the real portion is less than that of the imaginary portion, the discriminated modulation type output is the third specified modulation type; and

decoding the signal field of the preamble training sequence based on the discriminated modulation type output.

21. The method of claim 20 wherein processing the plurality of sub-symbols further comprises:

multiplying the received encoded signal with the conjugate of a channel estimate.

22. The method of claim 20 wherein the first modulation type is a QPSK modulation type.

23. The method of claim 22 wherein the second modulation type is a BPSK modulation type.

24. The method of claim 23 wherein the third specified modulation type is a rotated BPSK modulation type.