Method and apparatus for compensating for phase noise of symbols spread with a long spreading code

Abstract

A method and apparatus for compensating for phase noise of symbols spread with a long spreading code are disclosed. To compensate for the phase noise, a phase error estimate is generated from despread symbols with a short spreading code. A phase correcting phasor is applied to chip rate data before despreading the data with a long spreading code. A signal-to-interference ratio (SIR) on a common pilot channel (CPICH) may be calculated by spreading the data with a parent spreading code in an orthogonal variable spreading factor (OVSF) code tree and by combining symbols. Alternatively, a magnitude of the symbols may be used in estimating the SIR. The SIR of a channel using a short spreading code and an SIR of a channel using a long spreading code are measured. The SIR of the channel with the long spreading code may be compensated in accordance with a difference between degradation of the SIRs.

1 . A receiver that receives data with a short spreading code transmitted over a first channel and data with a long spreading code transmitted over a second channel, comprising:
 a despreader that receives transmitted data that has been processed as chip rate data, and that despreads chip rate data generated from received signals with a short spreading code to generate symbols;   a constellation correction unit that generates a phase error estimate based on the symbols;   a phasor generator that generates a phase correcting phasor based on the phase error estimate;   a multiplier that multiplies the phase correcting phasor with the chip data rate to generate phase corrected chip rate data; and   a second despreader that receives the phase corrected chip rate data and despreads the corrected chip rate data with a long spreading code.   
   
   
       2 . The receiver of  claim 1  wherein the first channel is a high speed physical downlink shared channel (HS-PDSCH) and the second channel is a common pilot channel (CPICH). 
   
   
       3 . The receiver of  claim 2  further comprising a signal-to-interference ratio (SIR) estimator for estimating an SIR from the second channel symbols on the CPICH channel. 
   
   
       4 . The receiver of  claim 3 , further comprising a channel quality indicator (CQI) mapping unit for generating a CQI from the SIR on the CPICH. 
   
   
       5 . The receiver of  claim 2 , wherein the despreader is an HS-PDSCH despreader that uses a spreading factor of 16. 
   
   
       6 . The receiver of  claim 1 , wherein the constellation correction unit corrects gain and phase errors. 
   
   
       7 . The receiver of  claim 1 , wherein the phase error estimate is an average of multiple phase error estimates generated by the constellation correction unit. 
   
   
       8 . The receiver of  claim 1 , further comprising a magnitude calculator that calculates a magnitude of the symbols. 
   
   
       9 . The receiver of  claim 1 , further comprising an SIR estimator that estimates a signal to interference ratio (SIR) SIR using the magnitude of the symbols. 
   
   
       10 . A receiver that receives data with a short spreading code transmitted over a first channel and data with a long spreading code transmitted over a second channel, comprising:
 a first despreader that receives transmitted data that has been processed as chip rate data, and that despreads chip rate data generated from received signals with a short spreading code to generate symbols;   a buffer that receives and stores the chip rate data;   a constellation correction unit that generates phase corrected symbols based on the generated symbols;   a phasor generator that generates a unit magnitude phasor from phase error estimates received from the constellation correction unit;   a multiplier that multiplies the unit magnitude phasor and chip rate data to generate phase-corrected chip rate data;   a second despreader that receives the phase-corrected chip rate data and despreads the corrected chip rate data with a long spreading code.   
   
   
       11 . The receiver of  claim 10  wherein the first channel is a high speed physical downlink shared channel (HS-PDSCH) and the second channel is a common pilot channel (CPICH). 
   
   
       12 . The receiver of  claim 11  wherein the second despreader generates dedicated channel (DCH) high speed control channel (HS-PDSCH) symbols. 
   
   
       13 . The receiver of  claim 10  wherein the second despreader generates common pilot channel (CPICH) symbols. 
   
   
       14 . The receiver of  claim 13  further comprising a signal to interference ratio (SIR) estimator generates an SIR estimate from the CPICH symbols. 
   
   
       15 . The receiver of  claim 14  further comprising a channel quality indicator (CQI) generator that generates a channel quality indication from the SIR estimate.