Linear minimum mean square error equalization with interference cancellation for mobile communication forward links utilizing orthogonal codes covered by long pseudorandom spreading codes

An apparatus for symbol determination in a direct sequence spread spectrum multiple access communication system having a plurality of code channels in use, the apparatus comprising:

• first means for linearly filtering a received signal to form a first filtered signal;
• means for despreading the first filtered signal and providing a plurality of symbol estimates for all corresponding code channels of the plurality of code channels;
• means for generating an estimated transmitted signal from the plurality of symbol estimates;
• means for generating an estimated received signal from the estimated transmitted signal and a channel estimate;
• means for producing a residual signal as a difference between the received signal and the estimated received signal;
• second means for linearly filtering the residual signal to form a second filtered signal;
• means for combining the second filtered signal with the estimated transmitted signal to form a next estimated transmitted signal;
• and
• means for despreading the next estimated transmitted signal and providing a next plurality of symbol estimates for a selected code channel of the plurality of code channels.

An apparatus for symbol determination in a direct sequence spread spectrum multiple access communication system having a plurality of code channels in use, the apparatus comprising:

• a network interface for communication with a serving base station;
• a memory;
• and
• a processor coupled to the network interface and to the memory,
• wherein the processor when operative is configured to linearly filter a received signal to form a first filtered signal, to despread the first filtered signal and provide a plurality of symbol estimates for all corresponding code channels of the plurality of code channels;
• to generate an estimated transmitted signal from the plurality of symbol estimates, to generate an estimated received signal from the estimated transmitted signal and a channel estimate and to produce a residual signal as a difference between the received signal and the estimated received signal;
• and the processor further configured to linearly filter the residual signal to form a second filtered signal, to combine the second filtered signal with the estimated transmitted signal to form a next estimated transmitted signal, and to despread the next estimated transmitted signal and provide a next plurality of symbol estimates for a selected code channel of the plurality of code channels.

A method of symbol determination in a code division multiple access communication system having a plurality of code channels in use, the method comprising:

• equalizing a received signal, using minimum mean square error equalization, to form a first filtered signal;
• despreading the first filtered signal and providing a plurality of symbol estimates for all corresponding code channels of the plurality of code channels;
• generating an amplitude estimate for all corresponding code channels of the plurality of code channels and generating a confidence measure for each symbol estimate of the plurality of symbol estimates;
• generating an estimated transmitted signal from the plurality of symbol estimates by weighting each symbol estimate by its corresponding confidence measure to form a plurality of weighted symbols, and spreading the plurality of weighted symbols using a corresponding plurality of orthogonal codes, a corresponding plurality of amplitude estimates, and a sector spreading code;
• generating an estimated received signal from the estimated transmitted signal and a channel estimate determined by correlation of the received signal with a known pilot signal;
• producing a residual signal as a difference between the received signal and the estimated received signal;
• equalizing the residual signal, using minimum mean square error equalization, to form a second filtered signal;
• combining the second filtered signal with the estimated transmitted signal to form a next estimated transmitted signal;
• and
• despreading the next estimated transmitted signal to form a next despread signal and, using the next despread signal, providing a next plurality of symbol estimates for a selected code channel of the plurality of code channels.

An apparatus for symbol determination in a code division multiple access communication system having a plurality of code channels in use, the apparatus comprising:

• a first linear equalizer, the first linear equalizer operative to equalize a received signal, using minimum mean square error equalization, to form a first filtered signal;
• a code despreader coupled to the first linear equalizer, the code despreader operative to despread the first filtered signal to produce a despread signal;
• an amplitude estimator coupled to the code despreader, the amplitude estimator operative to generate an amplitude estimate for all corresponding code channels of the plurality of code channels;
• a symbol decider coupled to the code despreader, the symbol decider operative to provide a plurality of symbol estimates from the despread signal for all corresponding code channels of the plurality of code channels and to generate a confidence measure for each symbol estimate of the plurality of symbol estimates;
• a transmitted signal estimator coupled to the symbol decider and to the amplitude estimator, the transmitted signal estimator operative to generate an estimated transmitted signal from the plurality of symbol estimates by weighting each symbol estimate by its corresponding confidence measure to form a plurality of weighted symbols, and to spread the plurality of weighted symbols using a corresponding plurality of orthogonal codes, a corresponding plurality of amplitude estimates, and a sector scrambling code;
• a channel estimator operative to determine a channel estimate by correlation of the received signal with a known pilot signal;
• a received signal estimator coupled to the transmitted signal estimator and to the channel estimator, the received signal estimator operative to generate an estimated received signal from the estimated transmitted signal and the channel estimate;
• a summer coupled to the received signal estimator, the summer operative to produce a residual signal as a difference between the received signal and the estimated received signal;
• a second linear equalizer coupled to the summer, the second linear equalizer operative to equalize the residual signal, using minimum mean square error equalization, to form a second filtered signal;
• a combiner coupled to the second linear equalizer, to the transmitted signal estimator, and to the code despreader, the combiner operative to combine the second filtered signal with the estimated transmitted signal to form a next estimated transmitted signal;
• and
• wherein the code despreader is further operative to despread the next estimated transmitted signal to form a next despread signal and, using the next despread signal, the symbol decider is further operative to provide a next plurality of symbol estimates for a selected channel of the plurality of channels.