Ofdm channel estimation method and apparatus

Abstract

Smaller patterns of regularly-spaced pilot symbols are discerned from a larger pattern of irregularly-spaced pilot symbols transmitted in the time-frequency domain. Accordingly, the irregularly-spaced pilot symbols can be partitioned into at least two different groups of regularly-spaced pilot symbols in the time-frequency domain. Each group of regularly-spaced pilot symbols is individually processed with lower complexity and the results combined to generate an accurate time-frequency channel response estimate. According to an embodiment, a set of irregularly-spaced pilot symbols is transmitted over a time-frequency window. Channel response is estimated based on the pilot symbols by grouping the pilot symbols into subsets of regularly-spaced pilot symbols. An intermediate quantity is generated for each subset of regularly-spaced pilot symbols as a function of the pilot symbols included in the subset. The channel response is estimated over the time-frequency window as a function of the intermediate quantities.

1 . A method of estimating channel response based on a set of irregularly-spaced pilot symbols transmitted over a time-frequency window, the method comprising:
 grouping the pilot symbols into subsets of regularly-spaced pilot symbols;   generating an intermediate quantity for each subset of regularly-spaced pilot symbols as a function of the pilot symbols included in the subset; and   estimating the channel response over the time-frequency window as a function of the intermediate quantities.   
     
     
         2 . The method of  claim 1 , comprising grouping the pilot symbols into subsets of regularly-spaced pilot symbols based on a priori pilot spacing information. 
     
     
         3 . The method of  claim 1 , wherein grouping the pilot symbols into subsets of regularly-spaced pilot symbols comprises:
 blindly detecting a communication mode used to transmit the pilot symbols; and   grouping the pilot symbols into the subsets of regularly-spaced pilot symbols based on the communication mode.   
     
     
         4 . The method of  claim 1 , wherein grouping the pilot symbols into subsets of regularly-spaced pilot symbols comprises:
 partitioning an irregularly-spaced pilot symbol pattern into a plurality of regularly-spaced pilot symbol patterns over the time-frequency window; and   identifying the pilot symbols associated with each regularly-spaced pilot symbol pattern.   
     
     
         5 . The method of  claim 4 , comprising partitioning the irregularly-spaced pilot symbol pattern into at least four regularly-spaced WiMax pilot symbol patterns over the time-frequency window. 
     
     
         6 . The method of  claim 4 , comprising partitioning the irregularly-spaced pilot symbol pattern into at least two regularly-spaced LTE pilot symbol patterns over the time-frequency window. 
     
     
         7 . The method of  claim 1 , wherein generating an intermediate quantity for each subset of regularly-spaced pilot symbols as a function of the pilot symbols included in the subset comprises generating an intermediate minimum mean-square error channel estimate for each subset. 
     
     
         8 . The method of  claim 7 , wherein estimating the channel response as a function of the intermediate quantities comprises combining the intermediate minimum mean-square error channel estimates to form a composite minimum mean-square error channel estimate. 
     
     
         9 . The method of  claim 1 , wherein generating an intermediate quantity for each subset of regularly-spaced pilot symbols as a function of the pilot symbols included in the subset comprises generating an intermediate delay-Doppler image for each subset. 
     
     
         10 . The method of  claim 9 , wherein estimating the channel response as a function of the intermediate quantities comprises:
 combining the intermediate delay-Doppler images to form a composite delay-Doppler image; and   converting the composite delay-Doppler image from the delay-Doppler domain to the time-frequency domain.   
     
     
         11 . The method of  claim 10 , further comprising filtering the composite delay-Doppler image before conversion to the time-frequency domain. 
     
     
         12 . The method of  claim 11 , wherein filtering the composite delay-Doppler image before conversion to the time-frequency domain comprises reducing non-zero elements of the composite delay-Doppler image outside a predetermined delay-Doppler spread. 
     
     
         13 . A receiver comprising a baseband processor configured to:
 group a set of irregularly-spaced pilot symbols transmitted over a time-frequency window into subsets of regularly-spaced pilot symbols;   generate an intermediate quantity for each subset of regularly-spaced pilot symbols as a function of the pilot symbols included in the subset; and   estimate channel response over the time-frequency window as a function of the intermediate quantities.   
     
     
         14 . The receiver of  claim 13 , wherein the baseband processor is configured to group the pilot symbols into subsets of regularly-spaced pilot symbols based on a priori pilot spacing information. 
     
     
         15 . The receiver of  claim 13 , wherein the baseband processor is configured to blindly detect a communication mode used to transmit the pilot symbols and group the pilot symbols into the subsets of regularly-spaced pilot symbols based on the communication mode. 
     
     
         16 . The receiver of  claim 13 , wherein the baseband processor is configured to partition an irregularly-spaced pilot symbol pattern into a plurality of regularly-spaced pilot symbol patterns over the time-frequency window and identify the pilot symbols associated with each regularly-spaced pilot symbol pattern. 
     
     
         17 . The receiver of  claim 16 , wherein the baseband processor is configured to partition the irregularly-spaced pilot symbol pattern into at least four regularly-spaced WiMax pilot symbol patterns over the time-frequency window. 
     
     
         18 . The receiver of  claim 16 , wherein the baseband processor is configured to partition the irregularly-spaced pilot symbol pattern into at least two regularly-spaced LTE pilot symbol patterns over the time-frequency window. 
     
     
         19 . The receiver of  claim 13 , wherein the baseband processor is configured to generate an intermediate minimum mean-square error channel estimate for each subset of regularly-spaced pilot symbols as a function of the pilot symbols included in the subset. 
     
     
         20 . The receiver of  claim 19 , wherein the baseband processor is configured to combine the intermediate minimum mean-square error channel estimates to form a composite minimum mean-square error channel estimate. 
     
     
         21 . The receiver of  claim 13 , wherein the baseband processor is configured to generate an intermediate delay-Doppler image for each subset of regularly-spaced pilot symbols as a function of the pilot symbols included in the subset. 
     
     
         22 . The receiver of  claim 21 , wherein the baseband processor is configured to combine the intermediate delay-Doppler images to form a composite delay-Doppler image and convert the composite delay-Doppler image from the delay-Doppler domain to the time-frequency domain.