Method and apparatus for automatic frequency control in a CDMA receiver

A transceiver for processing code division multiple access signals received through at least two multipath propagation channels to produce at least two combined frequency error estimates, comprising:

• a processor for receiving and processing the signals using a local frequency reference oscillator to obtain representative complex numerical samples for processing;
• channel estimators for correlating the complex numerical samples with shifts of a locally generated despreading code and producing a number of complex channel estimates, each corresponding to a different delayed ray of the at least two multipath propagation channels;
• frequency error estimators for computing a frequency error estimate for each ray based on successive values of a respective one of the channel estimates;
• and
• at least two summers for performing weighted summations of groups of the frequency error estimates to provide at least two combined frequency error estimates,
• wherein:
• each of the combined frequency error estimates is a combined frequency error estimate of only those rays associated with a same one of the at least two base station transmitters, the one of the at least two base station transmitters being different for each of the combined frequency error estimates.

A method for processing code division multiple access signals received through at least one multipath propagation channel to produce at least one relative frequency error estimate, comprising the steps of:

• receiving and processing the signals using the local frequency reference oscillator to obtain representative complex numerical samples for processing;
• correlating the complex numerical samples with shifts of a locally generated despreading code and producing a number of complex channel estimates, each corresponding to a different delayed ray of the at least one multipath propagation channel;
• computing a frequency error estimate for each ray based on successive values of a respective one of the channel estimates;
• performing at least one weighted summation of the frequency error estimates to provide at least one relative frequency error estimate;
• using the at least one relative frequency error estimate to control the frequency of a local frequency reference oscillator;
• despreading a desired signal with a rake combiner using shifts of a locally generated wanted signal despreading code to produce one complex sample per data symbol per shift and performing a weighted summation of the complex samples per shift using weighting factors based on the channel estimates to produce a rake-combined value for each data symbol;
• decoding the per-symbol rake-combined values using a soft error correction decoder to reproduce wanted information bits;
• and
• performing an error check on the decoded information bits and to generate an error or no-error indication, wherein the relative frequency error estimate is only used to control the local reference oscillator when a no-error indication is generated.

A method for processing code division multiple access signals received through at least two multipath propagation channels to produce at least two combined frequency error estimates, comprising the steps of:

• receiving and processing the signals using the local frequency reference oscillator to obtain representative complex numerical samples for processing;
• correlating the complex numerical samples with shifts of a locally generated despreading code and producing a number of complex channel estimates, each corresponding to a different delayed ray of the at least two multipath propagation channels;
• computing a frequency error estimate for each ray based on successive values of a respective one of the channel estimates;
• and
• performing at least two weighted summations of groups of the frequency error estimates to provide at least two combined frequency error estimates,
• wherein each of the combined frequency error estimates is a combined frequency error estimate of only those rays associated with a same one of the at least two base station transmitters, the one of the at least two base station transmitters being different for each of the combined frequency error estimates.

A transceiver for processing code division multiple access signals received through at least one multipath propagation channel to produce at least one relative frequency error estimate, comprising:

• a processor for receiving and processing the signals using the local frequency reference oscillator to obtain representative complex numerical samples for processing;
• despreaders for different delayed rays of the multipath channel for correlating the numerical samples with different shifts of a locally generated despreading code over symbol intervals to produce streams of complex despread values corresponding to each ray and successive symbol interval;
• frequency error correctors for correcting frequency errors on each of the despread value streams by, for each of the despread value streams, progressively rotating the phase angle of successive despread values at a rate given by an associated frequency error integral;
• channel estimators for processing the frequency-corrected despread value streams to produce complex channel estimates for each ray;
• frequency error estimators for determining a frequency error estimate for each ray by processing successive values of the channel estimates for the corresponding ray;
• and
• at least one combiner for combining the associated frequency error integrals to produce at least one relative frequency error estimate.

A method for processing code division multiple access signals received through at least one multipath propagation channel to produce at least one relative frequency error estimate, comprising the steps of:

• receiving and processing the signals using the local frequency reference oscillator to obtain representative complex numerical samples for processing;
• correlating the numerical samples with different shifts of a locally generated despreading code over symbol intervals to produce streams of complex despread values corresponding to each ray and successive symbol interval;
• correcting frequency errors on each of the despread value streams by, for each of the despread value streams, progressively rotating the phase angle of successive despread values at a rate given by an associated frequency error integral;
• processing the frequency-corrected despread value streams to produce complex channel estimates for each ray;
• determining a frequency error estimate for each ray by processing successive values of the channel estimates for the corresponding ray;
• and
• combining the associated frequency error integrals to produce at least one relative frequency error estimate.

A transceiver for processing code division multiple access signals received through at least one multipath propagation channel to produce at least one relative frequency error estimate, comprising:

• a processor for receiving and processing the signals using a local frequency reference oscillator to obtain representative complex numerical samples for processing;
• channel estimators for correlating the complex numerical samples with shifts of a locally generated despreading code and producing a number of complex channel estimates, each corresponding to a different delayed ray of the at least one multipath propagation channel;
• frequency error estimators for computing a frequency error estimate for each ray based on successive values of a respective one of the channel estimates;
• and
• at least one summer for performing a weighted summation of the frequency error estimates to provide at least one relative frequency error estimate,
• wherein the relative frequency error estimate is used to control the frequency of a local frequency reference oscillator, and
• further comprising an outer loop integrator for integrating the frequency estimates to produce a control signal to control the local frequency reference oscillator to a value based on the received signal,
• wherein the at least one summer adds the real parts of the per-ray frequency error estimates to obtain a real sum and adding the imaginary parts to produce an imaginary sum and computing the two-argument arctangent of the real and imaginary sum.

A method for processing code division multiple access signals received through at least one multipath propagation channel to produce at least one relative frequency error estimate, comprising the steps of:

• receiving and processing the signals using the local frequency reference oscillator to obtain representative complex numerical samples for processing;
• correlating the complex numerical samples with shifts of a locally generated despreading code and producing a number of complex channel estimates, each corresponding to a different delayed ray of the at least one multipath propagation channel;
• computing a frequency error estimate for each ray based on successive values of a respective one of the channel estimates;
• performing at least one weighted summation of the frequency error estimates to provide at least one relative frequency error estimate;
• using the at least one relative frequency error estimate to control the frequency of a local frequency reference oscillator;
• integrating the relative frequency error estimate using an outer loop integrator to produce a control signal;
• and
• controlling the frequency of the local frequency reference oscillator using the control signal,
• wherein the step of performing at least one weighted summation includes adding the real parts of the per-ray frequency error estimates to obtain a real sum and adding the imaginary parts to produce an imaginary sum and computing the two-argument arctangent of the real and imaginary sum.

An apparatus for estimating at least two frequency errors between a local frequency reference of a receiver and carrier frequencies of two or more transmitters, comprising:

• frequency error estimators for estimating frequency errors separately for different signal paths;
• and
• combiners for combining groups of the frequency error estimates to produce at least two combined frequency error estimates,
• wherein:
• each of the combined frequency error estimates is a combined frequency error estimate of only those rays associated with a same one of the two or more transmitters, the one of the two or more transmitters being different for each of the combined frequency error estimates.

A method for estimating at least two frequency errors between a local frequency reference of a receiver and carrier frequencies of two or more transmitters, comprising the steps of:

• estimating frequency errors separately for different signal paths;
• and
• combining groups of the frequency error estimates to produce at least two combined frequency error estimates,
• wherein each of the combined frequency error estimates is a combined frequency error estimate of only those rays associated with a same one of the two or more transmitters, the one of the two or more transmitters being different for each of the combined frequency error estimates.