Coarse bin frequency synchronization in a communication system

Abstract

For frequency bin error estimation, multiple hypotheses are formed for different frequency bin errors, pilot offsets, or combinations of frequency bin error and pilot offset. For each hypothesis, received symbols are extracted from the proper subbands determined by the hypothesis. In one scheme, the extracted received symbols for each hypothesis are despread with a scrambling sequence to obtain despread symbols for that hypothesis. A metric is derived for each hypothesis based on the despread symbols, e.g., by deriving a channel impulse response estimate based on the despread symbols and then deriving the metric based on the channel impulse response estimate. In another scheme, the extracted received symbols for each hypothesis are correlated, and a metric is derived based on the correlation results. For both schemes, the frequency bin error and/or the pilot offset are determined based on the metrics for all hypotheses evaluated.

1 . An apparatus comprising:
 a wireless receiver, wherein the wireless receiver comprises:
 a processor configured to perform despreading of received symbols with a scrambling sequence for each of a plurality of hypotheses, to derive a metric for each hypothesis based on despread symbols for the hypothesis, and to determine a frequency error based on metrics derived for the plurality of hypotheses; and 
 a memory coupled to the processor; 
   wherein the processor is configured to derive a channel impulse response estimate for each hypothesis based on the despread symbols for the hypothesis, and to derive the metric for each hypothesis based on the channel impulse response estimate for the hypothesis.   
     
     
         2 . The apparatus of  claim 1 , wherein the processor is configured to form the plurality of hypotheses for a range of frequency errors, wherein each hypothesis corresponds to a different hypothesized frequency error. 
     
     
         3 . The apparatus of  claim 1 , wherein the processor is configured to form the plurality of hypotheses for a range of frequency errors and for multiple pilot offsets, wherein each hypothesis corresponds to a different combination of frequency error and pilot offset. 
     
     
         4 . The apparatus of  claim 1 , wherein for each hypothesis the processor is configured to extract the received symbols for subbands determined by the hypothesis, and to perform despreading of the extracted received symbols with the scrambling sequence. 
     
     
         5 . The apparatus of  claim 4 , wherein the extracted received symbols are hypothesized to be for a scattered pilot sent on different sets of subbands in different symbol periods. 
     
     
         6 . The apparatus of  claim 4 , wherein the extracted received symbols are hypothesized to be for a continual pilot sent on a predetermined set of subbands. 
     
     
         7 . The apparatus of  claim 1 , wherein the processor is configured to derive the metric for each hypothesis based on energy of a largest channel tap in the channel impulse response estimate for the hypothesis. 
     
     
         8 . The apparatus of  claim 1 , wherein the processor is configured to identify large channel taps in the channel impulse response estimate for each hypothesis based on a threshold, and to derive the metric for each hypothesis based on energy of the large channel taps for the hypothesis. 
     
     
         9 . The apparatus of  claim 1 , wherein the received symbols are for data and pilot transmitted using orthogonal frequency division multiplexing (OFDM). 
     
     
         10 . The apparatus of  claim 1 , wherein the received symbols are for data and pilot transmitted using single-carrier frequency division multiple access (SC-FDMA). 
     
     
         11 . A method comprising:
 performing despreading of received symbols with a scrambling sequence for each of a plurality of hypotheses;   deriving a metric for each hypothesis based on despread symbols for the hypothesis; and   determining a frequency error based on metrics derived for the plurality of hypotheses.   wherein the deriving the metric for each hypothesis comprises:
 deriving a channel impulse response estimate for each hypothesis based on the despread symbols for the hypothesis; and 
 deriving the metric for each hypothesis based on the channel impulse response estimate for the hypothesis. 
   
     
     
         12 . The method of  claim 11 , further comprising:
 forming the plurality of hypotheses for a range of frequency errors and for multiple pilot offsets, wherein each hypothesis corresponds to a different combination of frequency error and pilot offset.   
     
     
         13 . The method of  claim 11 , further comprising:
 forming the plurality of hypotheses for a range of frequency errors, wherein each hypothesis corresponds to a different hypothesized frequency error.   
     
     
         14 . The method of  claim 11 , further comprising:
 extracting the received symbols for subbands determined by the hypothesis; and   performing despreading of the extracted received symbols with the scrambling sequence.   
     
     
         15 . An apparatus comprising:
 means for performing despreading of received symbols with a scrambling sequence for each of a plurality of hypotheses;   means for deriving a metric for each hypothesis based on despread symbols for the hypothesis; and   means for determining a frequency error based on metrics derived for the plurality of hypotheses.   wherein the means for deriving the metric for each hypothesis comprises:
 means for deriving a channel impulse response estimate for each hypothesis based on the despread symbols for the hypothesis; and 
 means for deriving the metric for each hypothesis based on the channel impulse response estimate for the hypothesis. 
   
     
     
         16 . The apparatus of  claim 15 , further comprising:
 means for forming the plurality of hypotheses for a range of frequency errors and for multiple pilot offsets, wherein each hypothesis corresponds to a different combination of frequency error and pilot offset.   
     
     
         17 . The apparatus of  claim 15 , further comprising:
 means for forming the plurality of hypotheses for a range of frequency errors, wherein each hypothesis corresponds to a different hypothesized frequency error.   
     
     
         18 . The apparatus of  claim 15 , further comprising:
 means for extracting the received symbols for subbands determined by the hypothesis; and   means for performing despreading of the extracted received symbols with the scrambling sequence.   
     
     
         19 . A non-transitory computer readable medium containing software that, when executed, causes the computer to perform the acts of:
 performing despreading of received symbols with a scrambling sequence for each of a plurality of hypotheses;   deriving a metric for each hypothesis based on despread symbols for the hypothesis; and   determining a frequency error based on metrics derived for the plurality of hypotheses.   wherein the deriving the metric for each hypothesis comprises:
 deriving a channel impulse response estimate for each hypothesis based on the despread symbols for the hypothesis; and 
 deriving the metric for each hypothesis based on the channel impulse response estimate for the hypothesis.