Reduced dimension channel estimation in a wireless communication network
Methods and systems for obtaining improved joint channel estimates for a multi-user, frequency-multiplexed data transmission such as SC-FDMA or OFDM begins by estimating separate contributions of users (and/or other signal sources) to the received signal based on joint frequency domain channel estimates. A reduced data set is obtained by subtracting contributions of one or more users from the received data, leaving only the estimated contributions of the remaining users, with noise and residual estimation error signal. Time domain joint channel estimation is then performed on the reduced data set, which is feasible because the number of users has been reduced. In exemplary embodiments, the reduced data set includes only one estimated user contribution. This process is repeated to obtain channel estimates for all of the users. The method can be repeated by using the channel estimates to re-estimate the user contributions and calculate revised channel estimates.
1. A method of obtaining channel estimates for a frequency-multiplexed data transmission, the method comprising:
receiving, by a receiver unit in wireless communication network, raw time domain data representing a plurality of known reference symbols transmitted over a plurality of frequency-separated subcarriers by a plurality of signal sources;
by a signal processing unit:
jointly calculating frequency domain channel estimates for the frequency-separated subcarriers;
generating a reduced data set by subtracting from representative data derived from said raw time domain data an estimated contribution arising from at least one of the signal sources according to the jointly calculated frequency domain channel estimates for the frequency-separated subcarriers; and
calculating channel estimates from the reduced data set.
2. The method of claim 1 , comprising grouping said subcarriers into subcarrier groups, each subcarrier group including K subcarriers, where K is an integer greater than or equal to 1.
3. The method of claim 2 , wherein the K subcarriers in each subcarrier group are frequency contiguous.
4. The method of claim 2 , wherein the method further comprises applying at least one of interpolation and filtering to the frequency domain channel estimates to obtain frequency domain channel estimates for groups of J subcarriers, where J is an integer less than K.
5. The method of claim 1 , wherein calculating the joint frequency domain channel estimates includes applying at least one of a least squares algorithm, a minimum mean square error algorithm, a recursive least squares algorithm, a Kalman filter, and an extended Kalman filter.
6. The method of claim 1 , comprising calculating time domain channel estimates by applying at least one of a least squares algorithm, a minimum mean square error algorithm, a recursive least squares algorithm, a Kalman filter, and an extended Kalman filter.
7. The method of claim 6 , wherein the time domain channel estimates are calculated across the entire bandwidth of the frequency-multiplexed transmission.
8. The method of claim 1 , wherein generating the reduced data set includes subtracting from the representative data the estimated contributions arising from all of the signal sources, so that only a residual signal and noise remains, and then re-adding at least one of the estimated contributions to the residual signal and noise.
9. The method of claim 1 , wherein the reduced data set is generated by subtracting from said frequency domain data an estimated contribution arising from at least one of the signal sources according to the frequency domain channel estimates to create a reduced frequency domain data set, and then converting the reduced frequency domain data set into the reduced data set.
10. The method of claim 1 , wherein the reduced data set is generated by subtracting from said raw time domain data an estimated time domain contribution arising from at least one of the signal sources according to the frequency domain channel estimates.
11. The method of claim 1 , further comprising:
generating a revised reduced data set by subtracting from said representative data an estimated contribution arising from at least one of the signal sources according to the time domain channel estimates; and
calculating revised time domain or frequency domain channel estimates from the revised reduced data set.
12. The method of claim 1 , wherein the raw time domain data spans an entire bandwidth of a plurality of known reference symbols.
13. The method of claim 1 , wherein the signal sources communicate according to LTE protocols.
14. The method of claim 1 , wherein the raw time domain data is encoded as OFDM or SC-FDMA data.
15. The method of claim 1 , wherein subtracting an estimated contribution arising from at least one of the signal sources includes subtracting a fractional contribution arising from at least one of the signal sources from said raw time domain data.
16. A system for obtaining channel estimates for a frequency-multiplexed data transmission, the system comprising:
a receiver unit configured to receive raw time domain data representing a plurality of known reference symbols transmitted over a plurality of frequency-separated subcarriers by a plurality of signal sources; and
a signal processing unit configured to jointly calculating frequency domain channel estimates for the frequency-separated subcarriers, generate a reduced data set by subtracting from representative data derived from said raw time domain data an estimated contribution arising from at least one of the signal sources according to the jointly calculated frequency domain channel estimates for the frequency-separated subcarriers, and calculate channel estimates from the reduced data set.
17. The system of claim 16 , wherein the signal processing unit is configured to group said subcarriers into subcarrier groups, each subcarrier group including K subcarriers, where K is an integer greater than or equal to 1.
18. The system of claim 17 , wherein the K subcarriers in each subcarrier group are frequency contiguous.
19. The system of claim 17 , wherein the signal processing unit is configured to apply at least one of interpolation and filtering to the frequency domain channel estimates to obtain frequency domain channel estimates for groups of J subcarriers, where J is an integer less than K.
20. The system of claim 16 , wherein the signal processing unit is configured to calculate the joint frequency domain channel estimates by applying at least one of a least squares algorithm, a minimum mean square error algorithm, a recursive least squares algorithm, a Kalman filter, and an extended Kalman filter.
21. The system of claim 16 , wherein the signal processing unit is configured to calculate the time domain channel estimates by applying at least one of a least squares algorithm, a minimum mean square error algorithm, a recursive least squares algorithm, a Kalman filter, and an extended Kalman filter.
22. The system of claim 21 , wherein the signal processing unit is configured to calculate the time domain channel estimates across the entire bandwidth of the frequency-multiplexed transmission.
23. The system of claim 16 , wherein the signal processing unit is configured to subtract from the representative data the estimated contributions arising from all of the signal sources, so that only a residual signal and noise remains, and then re-add at least one of the estimated contributions to the residual signal and noise so as to generate the reduced data set.
24. The system of claim 16 , wherein the signal processing unit is configured to generate the reduced data set by subtracting from said frequency domain data an estimated contribution arising from at least one of the signal sources according to the frequency domain channel estimates to create a reduced frequency domain data set, and then converting the reduced frequency domain data set into the reduced data set.
25. The system of claim 16 , wherein the signal processing unit is configured to generate the reduced data set by subtracting from said raw time domain data an
estimated contribution arising from at least one of the signal sources according to the frequency domain channel estimates.
26. The system of claim 16 , wherein the signal processing unit is further configured to:
generate a revised reduced data set by subtracting from said representative data an estimated contribution arising from at least one of the signal sources according to the time domain channel estimates; and
calculate revised time domain or frequency domain channel estimates from the revised reduced data set.
27. The system of claim 16 , wherein the receiver unit is configured to receive raw time domain data that spans an entire bandwidth of a plurality of known reference symbols.
28. The system of claim 16 , wherein the receiver unit is configured to receive raw time domain data from signal sources that communicate according to LTE protocols.
29. The system of claim 16 , wherein the receiver unit is configured to receive raw time domain data that is encoded as OFDM or SC-FDMA data.
30. A non-transitory computer readable medium storing a computer program, executable by a machine, for obtaining channel estimates for a frequency-multiplexed data transmission, the computer program comprising executable instructions for:
receiving, by a receiver unit in wireless communication network, raw time domain data representing a plurality of known reference symbols transmitted over a plurality of frequency-separated subcarriers by a plurality of signal sources;
jointly calculating frequency domain channel estimates for the frequency-separated subcarriers;
generating a reduced data set by subtracting from representative data derived from said raw time domain data an estimated contribution arising from at least one of the signal sources according to the jointly calculated frequency domain channel estimates for the frequency-separated subcarriers; and
calculating channel estimates from the reduced data set.