Method and apparatus for interference rejection combining and detection
A multi-branch OFDM receiver combines diversity signals received over different receiver branches using interference rejection combining. The receiver generates first channel estimates associated with a serving base station, second channel estimates associated with at least one non-serving base station, and a time offset between the serving base station and non-serving base station. The receiver computes a noise covariance matrix based on the second channel estimates and the time offset, and then combines the diversity signals received over different branches using the first channel estimates and the noise covariance matrix.
1. A method of combining diversity signals received over different branches of a multi-branch OFDM receiver, said method comprising:
generating first channel estimates associated with a serving base station;
generating second channel estimates associated with at least one non-serving base station;
determining a time offset between said serving base station and said non-serving base station;
computing a noise covariance matrix based on the second channel estimates and said time offset; and
combining said diversity signals using said first channel estimates and said noise covariance matrix to generate an estimate of a transmitted symbol.
2. The method of claim 1 wherein computing a noise covariance based on said second channel estimates and said time offset further comprises computing said noise covariance matrix based on a power offset between pilot and data symbols.
3. The method of claim 1 wherein a noise covariance matrix is computed for each one of a plurality of subcarriers in an OFDM signal and wherein said diversity signals received on each subcarrier are combined using a respective noise covariance matrix.
4. The method of claim 1 further comprising computing a total noise covariance matrix representing the total noise covariance between a serving base station and a plurality of non-serving base stations, and wherein said total noise covariance is used to combine said diversity signals.
5. The method of claim 4 wherein computing a total noise covariance matrix comprises computing a separate noise covariance for each one of a plurality of non-serving base stations, and combining said separate noise covariance matrices to generate said total noise covariance matrix.
6. The method of claim 1 wherein computing a noise covariance matrix further includes computing a white noise coefficient and computing the noise covariance matrix based on the white noise coefficient.
7. The method of claim 1 wherein the generating of first channel estimates for a channel from a serving base station to said multi-branch receiver comprises synchronizing with the serving base station, demodulating first pilot symbols transmitted by the serving base station, and generating said first channel estimates based on the first pilot symbols.
8. The method of claim 7 wherein the generating of second channel estimates for a channel from at least one non-serving base station to said multi-branch receiver comprises synchronizing with the non-serving base station, demodulating second pilot symbols transmitted by the at least one non-serving base station, and generating said second channel estimates based on the second pilot symbols.
9. A receiver comprising:
a channel estimator to generate first channel estimates associated with a serving base station and second channel estimates associated with a non-serving base station;
a cell search unit to determine a time offset between said serving base station and said non-serving base station;
a covariance estimator to compute a noise covariance matrix based on the second channel estimates and said time offset; and
a detector to combine diversity signals received from the serving base station using said first channel estimates and said noise covariance matrix to generate an estimate of a transmitted symbol.
10. The receiver of claim 9 wherein the covariance estimator is configured to compute a noise covariance based on said second channel estimates, said time offset and a power offset between pilot and data symbols.
11. The receiver of claim 9 wherein the covariance estimator is configured to compute a noise covariance matrix for each one of a plurality of subcarriers in an OFDM signal and wherein the detector combines the diversity signals received on each subcarrier using a respective noise covariance matrix.
12. The receiver of claim 9 wherein the covariance estimator is configured to compute a total noise covariance matrix representing the total noise covariance between a serving base station and a plurality of non-serving base stations, and wherein the detector uses the total noise covariance to combine said diversity signals.
13. The receiver of claim 12 wherein the covariance estimator is configured to compute a total noise covariance matrix by computing a separate noise covariance for each one of a plurality of non-serving base stations, and combining said separate noise covariance matrices to generate said total noise covariance matrix.
14. The receiver of claim 9 wherein the covariance estimator is configured to compute a total noise covariance matrix by computing a white noise coefficient and then compute the total noise covariance based on the white noise coefficient.
15. The receiver of claim 9 further comprising an FFT processor configured to demodulate first pilot symbols from the serving base station, and wherein said channel estimator generates said first channel estimates based on the first pilot symbols.
16. The receiver of claim 15 further comprising an FFT processor configured to demodulate second pilot symbols from at least one non-serving base station, and wherein said channel estimator generates said second channel estimates based on the second pilot symbols.