Method and apparatus for estimating frequency offset and timing offset of one or more mobile stations
View Patent ↗A method and apparatus for estimating frequency offset and timing offset of a first Mobile Station (MS) in a communication system is provided. The method includes receiving a composite signal at a plurality of receiver antennas of a Base Transceiver Station (BTS). The composite signal includes a first signal transmitted from a first MS and a second signal transmitted from a second MS. The composite signal includes one or more tiles. Each tile includes a plurality of data sub-carriers, a plurality of first pilot sub-carriers, and a plurality of second pilot sub-carriers. A total phase offset of the first MS is estimated based on a complex conjugate product of pilot symbols of the plurality of first pilot sub-carriers. Thereafter, a first phase offset corresponding to the timing offset of the first MS is estimated based on a Power Delay Profile (PDP) of one or more first pilot sub-carriers. Finally, a second phase offset corresponding to the frequency offset of the first MS is determined based on the total phase offset and the first phase offset.
1. A method for estimating a channel in a collaborative spatial multiplexing system, the method comprising:
receiving a composite signal comprising a first signal of a first mobile station and a second signal of a second mobile station, the composite signal comprising a tile having a plurality of data sub-carriers, a plurality of first pilot sub-carriers of the first mobile station, and a plurality of second pilot sub-carriers of the second mobile station;
estimating a total phase offset of the first mobile station based on a complex conjugate product of pilot symbols of the plurality of first pilot sub-carriers of the first mobile station;
estimating a first phase offset of the first mobile station based on a power delay profile (PDP) of at least one of the plurality of first pilot sub-carriers of the first mobile station;
estimating a second phase offset of the first mobile station based on the difference between the total phase offset and the first phase offset;
determining a combined phase offset for a plurality of data sub-carriers for the first mobile station and the plurality of first pilot sub-carriers of the first mobile station based on a weighted sum of the first phase offset and the second phase offset; and
determining a channel estimate of the tile for the first mobile station based on the combined phase offset and the first pilot sub-carriers of the first mobile station.
2. The method of claim 1 , further comprising estimating the PDP, comprising:
calculating an impulse response using at least one of the plurality of first pilot sub-carriers; and squaring the absolute value of the impulse response.
3. The method of claim 2 , further comprising averaging a square of the absolute value of the impulse response over time.
4. The method of claim 2 , wherein the PDP further comprises an average of PDPs across multiple receiver antennas.
5. The method of claim 1 , wherein estimating the first phase offset corresponding to the timing offset of the first MS based on the PDP comprises identifying a first tap of the PDP that exceeds a predetermined threshold.
6. The method of claim 1 , wherein estimating the total phase offset comprises summing complex conjugate products of pilot symbols of the plurality of first pilot sub-carriers of the first mobile station over a plurality of tiles.
7. The method of claim 1 , wherein estimating the total phase offset comprises summing complex conjugate products of pilot symbols of the plurality of first pilot sub-carriers of the first mobile station over multiple receiver antennas.
8. The method of claim 1 , further comprising estimating a channel for the second mobile station, comprising:
estimating a second total phase offset of the second mobile station based on a complex conjugate product of pilot symbols of the plurality of second pilot sub-carriers of the second mobile station;
estimating a second first phase offset of the second mobile station based on a power delay profile (PDP) of at least one of the plurality of second pilot sub-carriers of the second mobile station;
estimating a second second phase offset of the second mobile station based on the difference between the second total phase offset and the second first phase offset;
determining, a second combined phase offset for a plurality of data sub-carriers for the second mobile station and, the plurality of second pilot sub-carriers of the second mobile station based on a weighted sum of the second first phase offset and the second phase offset; and
determining a channel estimate of the tile for the second mobile station based on the second combined phase offset and the second pilot sub-carriers of the second mobile station.
9. A Base Transceiver Station (BTS) for estimating a channel in a collaborative spatial multiplexing system, the BTS comprises:
a receiver antenna for receiving a composite signal comprising a first signal of a first mobile station and a second signal of a second mobile station, the composite signal comprising a tile having a plurality of data sub-carriers, a plurality of first pilot sub-carriers of the first mobile station, and a plurality of second pilot sub-carriers of the second mobile station; and
a processor configured to:
estimate a total phase offset of the first mobile station based on a complex conjugate product of pilot symbols of the plurality of first pilot sub-carriers of the first mobile station;
estimate a first phase offset of the first mobile station based on a power delay profile (PDP) of at least one of the plurality of first pilot sub-carriers of the first mobile station;
estimate a second phase offset of the first mobile station based on the difference between the total phase offset and the first phase offset;
determine a combined phase offset for a pluralityy of data sub-carriers for the first mobile station and the plurality of first pilot sub-carriers of the first mobile station based on a weighted sum of the first phase offset and the second phase offset; and
determine a channel estimate of the tile for the first mobile station based on the combined phase offset and the first pilot sub-carriers of the first mobile station.
10. The BTS of claim 9 , wherein the processor is further configured to estimate the PDP by calculating an impulse response using at least one of the plurality of first pilot sub-carriers and squaring the absolute value of the impulse response.
11. The BTS of claim 9 , wherein the first phase offset corresponding to the timing offset is estimated by identifying a first tap of the PDP that exceeds a predetermined threshold.
12. The BTS of claim 9 , wherein the total phase offset is estimated by summing complex conjugate products of pilot symbols of the plurality of first pilot sub-carriers of the first mobile station over a plurality of tiles.
13. The BTS of claim 9 , wherein the total phase offset is estimated by summing complex conjugate products of pilot symbols of the plurality of first pilot sub-carriers of the first mobile station over multiple receiver antennas.