Estimating frequency offset at a subscriber station receiver
View Patent ↗A method and system of estimating frequency offset at a subscriber station is disclosed. One method includes the subscriber station receiving a composite signal, wherein the composite signal includes multi-carrier signals transmitted from a plurality of base stations. The subscriber station selects a first pair of multi-carrier symbols of the composite signal, wherein each multi-carrier symbol of the first pair of multi-carrier symbols includes a pilot sub-carrier having a common sub-carrier index. The subscriber station selects a second pair of multi-carrier symbols of the composite signal, the second pair having different symbol indices than the first pair, but having a same symbol index separation, wherein each of the multi-carrier symbols of the second pair of multi-carrier symbols includes a pilot sub-carrier having a second common sub-carrier index. The subscriber station estimates a phase based on a first sum of complex conjugate products between received symbols on the pilot sub-carriers of the first pair of multi-carrier symbols, and/or based on a second sum of complex conjugate products between received symbols on the pilot sub-carriers of the second pair of multi-carrier symbols. The subscriber station provides the phase to a filter of a frequency tracking loop of the subscriber station.
1. A method of estimating frequency offset at a subscriber station, comprising:
the subscriber station receiving a signal;
the subscriber station selecting a first pair of multi-carrier symbols of the signal, each multi-carrier symbol of the first pair of multi-carrier symbols comprising at least a pilot sub-carrier;
the subscriber station selecting a second pair of multi-carrier symbols of the composite signal, the second pair having at least one different symbol index than the first pair,
estimating at least one phase based on a complex conjugate product between channel estimates of at least one of the first pair multi-carrier symbols and the second pair of multi-carrier symbols, wherein each of the multi-carrier symbols of the second pair of multi-carrier symbols comprising at least a pilot sub-carrier;
the subscriber station providing the at least one phase to a filter of a frequency tracking loop.
2. The method of claim 1 , wherein the channel estimates are frequency domain channel estimates, and the frequency domain channel estimates on pilot sub-carriers are obtained by removing transmit pilot symbols of a serving base station from received symbols on the pilot sub-carriers; and
the subscriber station estimating at least one phase based on a first sum of complex conjugate products between frequency domain channel estimates on the pilot sub-carriers of the first pair of multi-carrier symbols, and based on a second sum of complex conjugate products between frequency domain channel estimates on the pilot sub-carriers of the second pair of multi-carrier symbols.
3. The method of claim 1 , wherein the channel estimates are time domain channel estimates, and the subscriber station estimating at least one phase based on a first sum of complex conjugate products between taps of time domain channel estimates of the first pair of multi-carrier symbols, and based on a second sum of complex conjugate products between taps of time domain channel estimates of the second pair of multi-carrier symbols.
4. The method of claim 1 , wherein the signal comprises a composite signal, the composite signal comprising multi-carrier signals transmitted from a plurality of base stations.
5. The method of claim 1 , comprising:
estimating a phase of a total sum, wherein the total sum comprises the first sum and the second sum.
6. The method of claim 1 , wherein the first pair of multi-carrier symbols and the second pair of multi-carrier symbols are from a same frame.
7. The method of claim 6 , wherein the phase is provided to the filter once every frame.
8. The method of claim 5 , wherein the first pair of multi-carrier symbols is from a first frame, and the second pair of multi-carrier symbols is from a second frame.
9. The method of claim 8 , wherein the at least one phase is provided to the filter once every frame of the composite signal.
10. The method of claim 1 , wherein the at least one phase comprises obtaining a linear combination of complex conjugate products obtained across N frames is provided to the filter once every frame.
11. The method of claim 1 , wherein estimating the at least one phase comprises obtaining a linear combination of complex conjugate products obtained across N frames, determining the at least one phase from the linear combination, and providing the phase to the filter once every N frames.
12. The method of claim 1 , further comprising the subscriber station obtaining a first phase based on a sum of complex conjugate products between received symbols on corresponding pilot sub-carriers of the multi-carrier symbols of the first pair of multi-carrier symbols; and
the subscriber station providing the first phase to a filter of a frequency tracking loop.
13. The method of claim 1 , further comprising the subscriber station obtaining a second phase based on a sum of complex conjugate products between received symbols on corresponding pilot sub-carriers of the multi-carrier symbols of the second pair of multi-carrier symbols;
the subscriber station providing the second phase to the filter of the frequency tracking loop.
14. The method of claim 1 , further comprising:
the subscriber station selecting a third pair of multi-carrier symbols of the composite signal, the third pair having different symbol indices than the first pair, each of the multi-carrier symbols of the third pair of multi-carrier symbols comprising at least a pilot sub-carrier having a third common sub-carrier index.
15. The method of claim 1 , wherein a symbol index separation of at least one of the first pair of multi-carrier symbols and the second pair of multi-carrier symbols is selected based upon a delay spread.
16. The method of claim 1 , wherein a symbol index separation of at least one of the first pair of multi-carrier symbols and the second pair of multi-carrier symbols is selected based upon a maximal frequency offset.
17. The method of claim 10 , wherein a separation in time between multi-carrier symbols of at least one of the first pair of multi-carrier symbols and the second pair of multi-carrier symbols is inversely proportional to the Doppler spread.
18. The method of claim 1 , further comprising the first pair of multi-carrier symbols and the second pair of multi-carrier symbols having a same symbol index separation.
19. The method of claim 1 , wherein if a symbol index separation of the first pair of multi-carrier symbols is different than a symbol index separation of the second pair of multi-carrier symbols.
20. A method of estimating frequency offset at a subscriber station, comprising:
the subscriber station receiving a composite signal, the composite signal comprising multi-carrier signals transmitted from a plurality of base stations;
the subscriber station selecting a first pair of multi-carrier symbols of the composite signal, each multi-carrier symbol of the first pair of multi-carrier symbols comprising at least a pilot sub-carrier having a common sub-carrier index;
the subscriber station selecting a second pair of multi-carrier symbols of the composite signal, the second pair having at least one different symbol index than the first pair, each of the multi-carrier symbols of the second pair of multi-carrier symbols comprising at least a pilot sub-carrier having a second common sub-carrier index;
the subscriber station estimating at least one phase based on a first sum of complex conjugate products between received symbols on the pilot sub-carriers of the first pair of multi-carrier symbols, and based on a second sum of complex conjugate products between received symbols on the pilot sub-carriers of the second pair of multi-carrier symbols;
the subscriber station providing the phase to a filter of a frequency tracking loop.
21. The method of claim 20 , comprising:
estimating a phase of a total sum, wherein the total sum comprises the first sum and the second sum.
22. The method of claim 20 , wherein the first pair of multi-carrier symbols and the second pair of multi-carrier symbols are from a same frame.
23. The method of claim 22 , wherein the phase is provided to the filter once every frame of the composite signal.
24. The method of claim 21 , wherein the first pair of multi-carrier symbols is from a first frame, and the second pair of multi-carrier symbols is from a second frame.
25. The method of claim 24 , wherein the at least one phase is provided to the filter once every frame of the composite signal.
26. A method of estimating frequency offset at a subscriber station, comprising:
the subscriber station receiving a signal;
the subscriber station selecting a first pair of multi-carrier symbols of the signal, each multi-carrier symbol of the first pair of multi-carrier symbols comprising at least a pilot sub-carrier having a common sub-carrier index;
the subscriber station selecting a second pair of multi-carrier symbols of the composite signal, the second pair having at least one different sub-carrier index than the first pair, and selected from a different frame;
estimating at least one phase based on a complex conjugate product between channel estimates of at least one of the first pair multi-carrier symbols and the second pair of multi-carrier symbols, wherein each of the multi-carrier symbols of the second pair of multi-carrier symbols comprising at least a pilot sub-carrier having a second common sub-carrier index, and wherein the channel estimates comprise at least one of time domain channel estimates and frequency domain channel estimates;
the subscriber station providing the at least one phase to a filter of a frequency tracking loop.
27. The method of claim 26 , further comprising:
the second pair having at least one different symbol index than the first pair.
28. A subscriber station that receives a signal, comprising:
means for selecting a first pair of multi-carrier symbols of the signal, each multi-carrier symbol of the first pair of multi-carrier symbols comprising at least a pilot sub-carrier;
means for selecting a second pair of multi-carrier symbols of the composite signal, the second pair having at least one different symbol index than the fist pair,
means for estimating at least one phase based on a complex conjugate product between channel estimates of at least one of the first pair multi-carrier symbols and the second pair of multi-carrier symbols, wherein each of the multi-carrier symbols of the second pair of multi-carrier symbols comprising at least a pilot sub-carrier;
means for providing the at least one phase to a filter of a frequency tracking loop.