Multi-symbol phase offset estimation

Abstract

Receivers typically detect the presence of a pilot tone, transmitted as part of an RF signal, and use the pilot tone as a reference to detect symbols in the received RF signal. However, improper synchronization between the transmitter and the receiver units can result in timing offset and carrier frequency offset in the digitized received RF signal, impair the orthogonality between OFDM sub-carriers, and cause inter-carrier interference. Phase offsets caused by carrier frequency offset and timing offset can also degrade receiver performance. Functionality can be incorporated to estimate the phase offset over multiple symbols. Estimating the phase offset over multiple symbols in the received RF signal can lower the error rate. Correcting the phase offset in the received RF signal can ensure accurate sampling of the received signal, accurate channel estimates, and accurate decoding of the digitized received signal. This can minimize receiver performance degradation.

1 . A method comprising:
 computing a first phase offset estimate based, at least in part, on a first plurality of phase offset compensated symbols of a first receive chain and a second plurality of phase offset compensated symbols of a second receive chain;   applying the first phase offset to each of a first plurality of symbols of the first receive chain and to each of a second plurality of symbols of the second receive chain,
 wherein said applying the first phase offset to each of the first plurality of symbols generates a third plurality of phase compensated symbols and said applying the first phase offset to each of the second plurality of symbols generates a fourth plurality of phase offset compensated symbols, 
 wherein the first plurality of phase offset compensated symbols precedes the third plurality of phase offset compensated symbols and the second plurality of phase offset compensated symbols precedes the fourth plurality of phase offset compensated symbols; 
   computing a second phase offset estimate based, at least in part, on the third plurality of phase offset compensated symbols and the fourth plurality of phase offset compensated symbols; and   generating an estimate of a plurality of transmitted symbols based, at least in part, on the third and fourth pluralities of phase offset compensated symbols.   
     
     
         2 . The method of  claim 1 , wherein said computing the first phase offset estimate based, at least in part, on the first plurality of phase offset compensated symbols and the second plurality of phase offset compensated symbols comprises computing an angle of a sum of the first plurality of phase offset compensated symbols and the second plurality of phase offset compensated symbols. 
     
     
         3 . The method of  claim 1 , wherein said generating the estimate of the plurality of transmitted symbols based, at least in part, on the third and fourth pluralities of phase offset compensated symbols comprises combining the third and fourth pluralities of phase offset compensated symbols. 
     
     
         4 . The method of  claim 3 , wherein said combining is in accordance with space-time block coding. 
     
     
         5 . The method of  claim 1  further comprising:
 receiving a first digitized symbol of the first receive chain and a second digitized symbols of the second receive chain; and 
 weighting the first and second digitized symbols in accordance with proportional strengths of signals corresponding to the first and the second digitized symbols, wherein said weighting generates a first symbol of the first plurality of symbols and a first symbols of the second plurality of symbols. 
 
     
     
         6 . The method of  claim 5  further comprising one of:
 dividing each of the first plurality of symbols and each of the second plurality of symbols by a power value; and 
 dividing each of the third plurality of phase offset compensated symbols and each of the fourth plurality of phase offset compensated symbols by the power value, 
 wherein the power value is computed based on a magnitude of channel estimates, noise variance, and data variance. 
 
     
     
         7 . The method of  claim 1 , wherein a number of the first plurality of phase compensated symbols is based on a rate at which noise changes over time. 
     
     
         8 . A device comprising:
 a phase offset estimation unit adapted to compute a phase offset with n consecutive phase offset compensated symbols of each of j receive chains, wherein n and j are positive integers greater than 1;   a decoding unit coupled with the phase offset estimation unit, the decoding unit adapted to,
 apply the phase offset to each of n consecutive symbols, which succeed the n consecutive phase offset compensated symbols used to compute the phase offset, of each of the j receive chains to generate a succeeding n consecutive phase offset compensated symbols of each of the j receive chains; and 
 supply the succeeding n consecutive phase offset compensated symbols of each of the j receive chains to the phase offset estimation unit. 
   
     
     
         9 . The device of  claim 8  further comprising the decoding unit operable to synchronously supply the succeeding n consecutive phase offset compensated symbols of each of the j receive chains to the phase offset estimation unit. 
     
     
         10 . The device of  claim 8  further comprising a maximum ratio combining unit adapted to receive a digitized symbol from each of the j receive chains, and to weight a combination of the digitized symbols from the j receive chains in proportion with a strength of a signal received by a corresponding one of the j receive chains to output the n consecutive symbols of each of the j receive chains. 
     
     
         11 . The device of  claim 10  further comprising a power calculator adapted to receive channel estimates of the j receive chains and adapted to compute a power value with the channel estimates, data variance, and noise variance, the decoding unit adapted to apply the power value to each of the n consecutive symbols of each of the j receive chains or to each of the n consecutive phase offset compensated symbols of the j receive chains. 
     
     
         12 . The device of  claim 8  further comprising a space-time block coding unit adapted to combine the n consecutive phase offset compensated symbols of each of the j receive chains in accordance with space-time block coding applied to n consecutive transmitted symbols corresponding to the n consecutive phase offset compensated symbols to output estimates of the n consecutive transmitted symbols. 
     
     
         13 . The device of  claim 8 , wherein the phase offset estimation unit adapted to compute the phase offset with n consecutive phase offset compensated symbols over the j receive chains comprises the phase offset estimation unit adapted to compute an angle of a sum of the n consecutive phase offset compensated symbols over the j receive chains. 
     
     
         14 . A system comprising:
 a processor;   j receive chains, each of the receive chains adapted to receive and process wireless signals that carry symbols;   a phase offset estimation unit adapted to compute a phase offset with n consecutive phase offset compensated symbols over the j receive chains, wherein n and j are positive integers greater than 1;   a decoding unit coupled with the phase offset estimation unit, the decoding unit adapted to,
 apply the phase offset to each of n consecutive symbols, which succeed the n consecutive phase offset compensated symbols used to compute the phase offset, of each of the j receive chains to generate a succeeding n consecutive phase offset compensated symbols of each of the j receive chains; and 
 supply the succeeding n consecutive phase offset compensated symbols of each of the j receive chains to the phase offset estimation unit. 
   
     
     
         15 . The system of  claim 14  further comprising the decoding unit operable to synchronously supply the succeeding n consecutive phase offset compensated symbols of each of the j receive chains to the phase offset estimation unit. 
     
     
         16 . The system of  claim 14 , wherein the decoding unit further comprises a maximum ratio combining unit adapted to receive a digitized symbol from each of the j receive chains, and to weight a combination of the digitized symbols from the j receive chains in proportion with a strength of a signal received by a corresponding one of the j receive chains to output the n consecutive symbols of each of the j receive chains. 
     
     
         17 . The system of  claim 17 , wherein the decoding unit further comprises a power calculator adapted to receive channel estimates of the j receive chains and adapted to compute a power value with the channel estimates, data variance, and noise variance, the decoding unit adapted to apply the power value to each of the n consecutive symbols of each of the j receive chains or to each of the n consecutive phase offset compensated symbols of the j receive chains. 
     
     
         18 . The system of  claim 14 , wherein the decoding unit further comprises a space-time block coding unit adapted to combine the n consecutive phase offset compensated symbols of each of the j receive chains in accordance with space-time block coding applied to n consecutive transmitted symbols corresponding to the n consecutive phase offset compensated symbols to output estimates of the n consecutive transmitted symbols. 
     
     
         19 . The system of  claim 14 , wherein the phase offset estimation unit adapted to compute the phase offset with n consecutive phase offset compensated symbols over the j receive chains comprises the phase offset estimation unit adapted to compute an angle of a sum of the n consecutive phase offset compensated symbols over the j receive chains.