Decoding of the overhead channels of the geosynchronous (GEO) satellite reverse link

1. A method to determine a codeword conveyed in an overhead channel in a coherent receiver used in a wireless communication system, the method comprising:

using an antenna for receiving the codeword;

correlating the received codeword with at least a subset of a set of valid codewords to establish a set of cross-correlations for the received codeword corresponding to each member of the at least the subset of the set of valid codewords;

extracting pilot symbols from a received pilot signal;

forming a channel estimate from the extracted pilot symbols;

forming a set of metrics from the set of cross-correlations and from the channel estimate, wherein each of the set of metrics is formed by summing a coherent detection metric and a non-coherent detection metric; and

selecting an estimated codeword corresponding to a maximum metric from the set of metrics.

2. The method of claim 1 , further comprising

scaling each of the set of cross-correlations by a function of a ratio of an overhead channel power to a pilot channel power to obtain a scaled correlation result.

3. The method of claim 2 , wherein the function comprises a square root.

4. The method of claim 1 , further comprising:

scaling the cross-correlations of the received codewords with the subset of the set of valid codewords, said scaling performed at least in part as a function of a ratio of overhead channel power to pilot channel power; and

using the scaled cross-correlations in the forming of the set of metrics by one of

adding the channel estimate formed from the received pilot signal, or

computing an absolute value of a sum of the scaled cross-correlation result and the channel estimate formed from the received pilot signal.

5. The method of claim 1 , further comprising:

determining a correspondence of the received codeword by multiplying a result of the correlation by a complex conjugate of the channel estimate, and taking the real part of the multiplication;

repeating the determination for a predetermined number of repetitions;

summing the determinations, forming the coherent detection metric;

computing the energy of the correlation result;

repeating the computation of the energy of the correlation result;

summing the computations; and

scaling a sum of the computations by a function of a ratio of overhead channel power to pilot channel power, forming the non-coherent detection metric.

6. The method of claim 5 , further comprising:

using the receiver in a geosynchronous (GEO) satellite reverse link using maximum likelihood decoding.

7. The method of claim 5 , further comprising:

employing a small block code selected from one of orthogonal, bi orthogonal and simplex codes.

8. The method of claim 5 , further comprising:

employing a Walsh-Hadamard transformation to establish the set of valid codewords from a small block code selected from one of orthogonal, bi orthogonal and simplex codes.

9. A coherent receiver used in a wireless communication system, comprising:

means for receiving a codeword conveyed in an overhead channel;

means for correlating the received codeword with at least a subset of a set of valid codewords to establish a set of cross-correlations for the received codeword corresponding to each member of the at least the subset of the set of valid codewords;

means for extracting pilot symbols from a received pilot signal;

means for forming a channel estimate from the extracted pilot symbols;

means for forming a set of metrics from the set of cross-correlations and from the channel estimate, wherein each of the set of metrics is formed by summing a coherent detection metric and a non-coherent detection metric; and

means for selecting an estimated codeword corresponding to a maximum metric from the set of metrics.

10. The coherent receiver of claim 9 , further comprising:

means for scaling each of the set of cross-correlations by a function of a ratio of an overhead channel power to a pilot channel power to obtain a scaled correlation result.

11. The coherent receiver of claim 9 , further comprising:

means for scaling the cross-correlations of the received codewords with the subset of the set of valid codewords, said scaling performed at least in part as a function of a ratio of overhead channel power to pilot channel power, and using the scaled cross-correlations in the forming of the set of metrics.

12. The coherent receiver of claim 9 , further comprising:

means for scaling the cross-correlations of the received codewords with the subset of the set of valid codewords, said scaling performed at least in part as a function of a ratio of overhead channel power to pilot channel power, and using the scaled cross-correlations in the forming of the set of metrics by adding the channel estimate formed from the received pilot signal.

13. The coherent receiver of claim 9 , further comprising:

means for scaling the cross-correlations of the received codewords with the subset of the set of valid codewords, said scaling performed at least in part as a function of a ratio of overhead channel power to pilot channel power, to provide a scaled cross-correlation result, and using the scaled cross-correlations in the forming of the set of metrics by computing an absolute value of a sum of the scaled cross-correlation result and the channel estimate formed from the received pilot signal.

14. The coherent receiver of claim 9 , further comprising:

means for determining a correspondence of the received codeword by multiplying a result of the correlation by a complex conjugate of the channel estimate, and taking the real part of the multiplication;

means for repeating the determination for a predetermined number of repetitions;

means for summing the determinations, forming the coherent detection metric;

means for computing the energy of the correlation result;

means for repeating the computation of the energy of the correlation result;

means for summing the computations; and

means for scaling a sum of the computations by a function of a ratio of overhead channel power to pilot channel power, forming the non-coherent detection metric.

15. The coherent receiver of claim 14 , further comprising:

means for employing a small block code selected from one of orthogonal, bi orthogonal and simplex codes.

16. A coherent receiver used in a wireless communication system, the coherent receiver comprising a processor coupled to a memory, the memory storing program codes executable by the processor for performing the following:

receiving a codeword conveyed in an overhead channel;

correlating the received codeword with at least a subset of a set of valid codewords to establish a set of cross-correlations for the received codeword corresponding to each member of the at least the subset of the set of valid codewords;

extracting pilot symbols from a received pilot signal;

forming a channel estimate from the extracted pilot symbols;

forming a set of metrics from the set of cross-correlations and from the channel estimate, wherein each of the set of metrics is formed by summing a coherent detection metric and a non-coherent detection metric; and

selecting an estimated codeword corresponding to a maximum metric from the set of metrics.

17. The coherent receiver of claim 16 , further comprising wherein the processor is further configured to performing the following:

scaling the cross-correlations of the received codewords with the subset of the set of valid codewords, said scaling performed at least in part as a function of a ratio of overhead channel power to pilot channel power, and

using the scaled cross-correlations in the forming of the set of metrics by one of:

adding the channel estimate formed from the received pilot signal, or

computing an absolute value of a sum of the scaled cross-correlation result and the channel estimate formed from the received pilot signal.

18. The coherent receiver of claim 16 , wherein the processor is further configured to performing the following:

determining a correspondence of the received codeword by multiplying a result of the correlation by a complex conjugate of the channel estimate, and taking the real part of the multiplication;

repeating the determination for a predetermined number of repetitions;

summing the determinations, forming a first partial the coherent detection metric;

computing the energy of the correlation result;

repeating the computation of the energy of the correlation result;

summing the computations; and

scaling a sum of the computations by a function of a ratio of overhead channel power to pilot channel power, forming the non-coherent detection metric.

19. The coherent receiver of claim 18 , wherein the processor is further configured to performing the following:

using the receiver in a GEO satellite reverse link using maximum likelihood decoding.

20. The coherent receiver of claim 18 , wherein the processor is further configured to performing the following:

employing a small block code selected from one of orthogonal, bi orthogonal and simplex codes.

21. The coherent receiver of claim 18 , wherein the processor is further configured to performing the following:

employing a Walsh-Hadamard transformation to establish the set of valid codewords from a small block code selected from one of orthogonal, bi orthogonal and simplex codes.

22. A non-transitory computer-readable medium encoded with a computer program, the non-transitory computer-readable medium comprising:

a first instruction for causing a computer to receive a codeword;

a second instruction for causing the computer to establish a set of valid codewords;

a third instruction for causing the computer to receive a pilot signal;

a fourth instruction for causing the computer to extract pilot symbols from the pilot signal;

a fifth instruction for causing the computer to create a channel estimate from the pilot symbol;

a sixth instruction for causing the computer to determine a set of metrics corresponding to correlations between the received codeword and each codeword in the set of valid codewords, wherein each of the set of metrics is determined by summing a coherent detection metric and a non-coherent detection metric;

a seventh instruction for causing the computer to remove a channel induced phase ambiguity using a channel estimate obtained from the pilot symbols;

an eighth instruction for causing the computer to choose a codeword with the largest correlation; and

a ninth instruction for causing the computer to create a revised channel estimate from a received signal carrying the chosen codeword.