Turbo channel estimation for OFDM systems
View Patent ↗A system and method for estimating a channel in a wireless receiver is disclosed. The method preferably applies to a communication system using the OFDM standard. The method comprises receiving a block of “n” transmitted symbols, the symbols including pilot symbols and “d” data symbols, estimating a channel using the pilot symbols to create a channel estimate, choosing a group of “m” strongest symbols from the “d” received symbols, compensating the “m” strongest symbols using the channel estimate to create a group of “m” compensated symbols, re-estimating the channel using the group of “m” compensated symbols and pilot symbols; and either (1) repeating the steps of choosing a group of “m” strongest symbols, compensating the group of “m” strongest symbols and re-estimating the channel, or (2) using a latest channel estimate to compensate all symbols within the block. The system comprises a wireless receiver having an estimator programmed, for example, using DSP or ASIC and imbedded into the wireless system design software for accomplishing the steps set forth according to the method.
1. A method comprising:
estimating a channel estimate associated with a wireless communications system including a plurality of receiver paths, wherein the channel estimate is at least partially based on a compensated symbol recovered from a plurality of signals received over the plurality of receiver paths, wherein the compensated symbol is recovered based on a first selected group of data symbols recovered from the plurality of signals and a plurality of first channel estimates corresponding to respective signals of the plurality of signals;
selecting the first selected group of data symbols from data symbols of the plurality of signals based on signal strength of the data symbols of the plurality of signals, wherein the selecting comprises:
selecting a selected signal of individual signals of the plurality of signals having a strongest signal strength;
selecting into the first selected group of data symbols at least one strongest data symbol from the selected signal according to individual data symbol strength; and
selecting into the first selected group of data symbols from another signal not selected from the plurality of signals, at least one data symbol at frequency tone positions corresponding to the frequency tone positions of the at least one strongest data symbol; and
recovering a data symbol from delayed versions of the plurality of signals and based on the channel estimate.
2. The method, as recited in claim 1 , further comprising:
receiving the plurality of signals over corresponding receiver paths of a plurality of receiver paths, wherein individual signals of the plurality of signals correspond to respective antennas of a plurality of antennas of the communications system.
3. The method, as recited in claim 1 , further comprising:
estimating the plurality of first channel estimates based on respective pilot symbols of the plurality of signals.
4. The method, as recited in claim 1 , wherein the channel estimate is based on the compensated symbol and a pilot symbol.
5. A method comprising:
estimating a channel estimate associated with a wireless communications system including a plurality of receiver paths, wherein the channel estimate is at least partially based on a compensated symbol recovered from a plurality of signals received over the plurality of receiver paths, wherein the compensated symbol is recovered based on a first selected group of data symbols recovered from the plurality of signals and a plurality of first channel estimates corresponding to respective signals of the plurality of signals; and
recovering a data symbol from delayed versions of the plurality of signals based on the channel estimate,
wherein estimating the channel estimate comprises updating the channel estimate based on at least one additional selected group of data symbols recovered from the plurality of signals, and
wherein the at least one additional selected group of data symbols includes a second number of data symbols different from a first number of symbols included in the first selected group of data symbols.
6. An apparatus comprising:
a first channel estimator configured to estimate a first channel estimate associated with a wireless communications system including a plurality of receiver paths, wherein the channel estimate is at least partially based on a compensated symbol recovered from a plurality of signals received over the plurality of receiver paths, wherein the compensated symbol is recovered based on a first selected group of data symbols recovered from the plurality of signals and a plurality of second channel estimates corresponding to respective signals of the plurality of signals;
a select circuit configured to select the first selected group of data symbols from data symbols of the plurality of signals based on signal strength of the data symbols of the plurality of signals; and
a data symbol compensator configured to recover a data symbol from delayed versions of the plurality of signals based on the first channel estimate,
wherein the select circuit is configured to select a selected signal of individual signals of the plurality of signals having a strongest signal strength, and
wherein the select circuit is configured to select into the first selected group of data symbols at least one strongest data symbol from the selected signal according to individual data symbol strength, and configured to select into the first selected group of data symbols from another signal not selected from the plurality of signals, at least one data symbol at frequency tone positions corresponding to the frequency tone positions of the at least one strongest data symbol.
7. The apparatus, as recited in claim 6 , wherein the first channel estimator is configured to update the first channel estimate based on at least one additional selected group of data symbols recovered from the plurality of signals.
8. The apparatus, as recited in claim 6 , further comprising:
a plurality of antennas coupled to respective receiver paths of the plurality of receiver paths.
9. The apparatus, as recited in claim 6 , further comprising:
a symbol compensator configured to recover symbols based on the first selected group of data symbols and the plurality of second channel estimates.
10. An apparatus comprising:
a first channel estimator configured to estimate a first channel estimate associated with a wireless communications system including a plurality of receiver paths, wherein the channel estimate is at least partially based on a compensated symbol recovered from a plurality of signals received over the plurality of receiver paths, wherein the compensated symbol is recovered based on a first selected group of data symbols recovered from the plurality of signals and a plurality of second channel estimates corresponding to respective signals of the plurality of signals;
a data symbol compensator configured to recover a data symbol from delayed versions of the plurality of signals based on the first channel estimate; and
a plurality of second channel estimators configured to estimate the plurality of second channel estimates corresponding to respective signals of the plurality of signals.
11. A method comprising:
estimating a channel estimate associated with a wireless communications system including a plurality of receiver paths, wherein the channel estimate is at least partially based on a compensated symbol recovered from a plurality of signals received over the plurality of receiver paths, wherein the compensated symbol is recovered based on a first selected group of data symbols recovered from the plurality of signals and a plurality of first channel estimates corresponding to respective signals of the plurality of signals;
recovering a data symbol from delayed versions of the plurality of signals based on the channel estimate,
selecting, into the first selected group of data symbols according to individual data symbol strength, at least one strongest data symbol of a selected signal selected from the plurality of signals; and
selecting into the first selected group of data symbols from another signal not selected from the plurality of signals, at least one data symbol at frequency tone positions corresponding to the frequency tone positions of the at least one strongest data symbol.