Parallel interference cancellation for CDMA applications

A method of decoding a spread spectrum composite signal in successive stages, said composite signal comprising plural user signals that have been spread with plural respective codes, wherein in each of said stages each user signal is despread, filtered to produce a signal value, analyzed to produce a tentative decision value, respread, summed with other respread signals to produce combined interference signals, said method carried out in each of said successive stages comprising:

• scaling one of said combined interference signals with a weighting factor to produce a scaled combined interference signal;
• scaling said composite signal with said weighting factor to produce a scaled composite signal;
• scaling one of said signal values by the complement of said weighting factor to produce a leakage signal;
• and
• combining said scaled composite signal with a scaled combined interference signal and a corresponding leakage signal to produce an estimate of a respective user signal.

A method of decoding a spread spectrum composite signal, said composite signal comprising plural user signals that have been spread with plural respective codes, said method comprising a plurality of interference cancellation steps performed in succession, wherein each step comprises the performance for each one of said user signals of the following substeps:

• despreading said composite signal to produce a despread signal corresponding to each user signal;
• filtering each despread signal to produce a signal value for each user signal;
• analyzing each signal value to produce an information signal for each user signal;
• respreading each information signal to produce an interference signal for each user signal;
• summing at least the interference signals corresponding to user signals other than said one user signal to produce a combined interference signal;
• scaling said combined interference signal with a weighting factor to produce a scaled combined interference signal;
• scaling said composite signal with said weighting factor to produce a scaled composite signal;
• scaling said signal value by the complement of said weighting factor to produce a leakage signal;
• and
• combining said scaled composite signal, said scaled combined interference signal and said leakage signal to produce an estimate of said one user signal.

An apparatus for decoding a spread spectrum composite signal, said composite signal comprising plural user signals that have been spread with plural respective codes, wherein each user signal is despread, filtered to produce a signal value, analyzed to produce a tentative decision value, respread, summed with other respread signals to produce combined interference signals, comprising:

• means for scaling one of said combined interference signals with a weighting factor to produce a scaled combined interference signal;
• means for scaling said composite signal with said weighting factor to produce a scaled composite signal;
• means for scaling one of said signal value by the complement of said weighting factor to produce a leakage signal;
• and
• means for combining said scaled composite signal with scaled combined interference signal and a corresponding leakage signal to produce an estimate of a respective user signal.

An apparatus for decoding a spread spectrum composite signal in successive stages, said composite signal comprising plural user signals that have been spread with plural respective codes, wherein in each of said stages each user signal is despread, filtered to produce a signal value, analyzed to produce a tentative decision value, respread, summed with other respread signals to produce combined interference signals, each of said successive stages comprising:

• means for scaling one of said combined interference signals with a weighting factor to produce a scaled combined interference signal;
• means for scaling said composite signal with said weighting factor to produce a scaled composite signal;
• means for scaling one of said signal value by the complement of said weighting factor to produce a leakage signal;
• and
• means for combining said scaled composite signal with a scaled combined interference signal and a corresponding leakage signal to produce an estimate of a respective user signal.

An apparatus for decoding a spread spectrum composite signal, said composite signal comprising plural user signals that have been spread with plural respective codes, said apparatus comprising a plurality of successive interference cancellation stages, wherein each stage comprises for each one of said user signals:

• means for despreading said composite signal to produce a despread signal corresponding to each user signal;
• means for filtering said despread signal to produce a signal value for each user signal;
• means for analyzing each signal value to produce an information signal for each user signal;
• means for respreading each information signal to produce an interference signal for each user signal;
• means for summing at least the interference signals corresponding to user signals other than said one user signal to produce a combined interference signal;
• means for scaling said combined interference signal with a weighting factor to produce a scaled combined interference signal;
• means for scaling said composite signal with said weighting factor to produce a scaled composite signal;
• means for scaling said signal value by the complement of said weighting factor to produce a leakage signal;
• and
• means for combining said scaled composite signal, said scaled combined interference signal and said leakage signal to produce an estimate of said one user signal.