International Business Machines Corporation

Jacob Sheinvald

Ehud Dov Karnin

Shay Ben-David

A method for channel estimation, includes receiving an input signal due to a superposition of waveforms encoding symbols transmitted respectively by a plurality of transmitters in a common frequency band. Each transmitter among the plurality of transmitters modulates the symbols with a respective spreading code. The input signal is sampled at sampling intervals over the duration of an observation period, thus providing a sequence of samples. The sequence of complex samples is processed to estimate a channel response for each of the transmitters by maximizing, individually for each of the transmitters and based on the respective spreading code of the transmitter, a likelihood of correctly decoding the transmitted symbols using the estimated channel response.

Code-division-multiple-access (DS-CDMA) channels with aperiodic codes

A method for multi-user detection includes receiving a complex input signal due to a superposition of waveforms encoding symbols in a constellation of fixed magnitude and variable phase, which symbols are transmitted respectively by a plurality of transmitters in a common frequency band. The complex input signal is sampled at sampling intervals over the duration of an observation period to provide a sequence of complex samples. The sequence of complex samples is processed to determine soft decision values corresponding to the symbols transmitted by the plurality of the transmitters in the observation period, while constraining the soft decision values to a circle in a complex plane. The soft decision values are projected onto the constellation to estimate the transmitted symbols.

Enhancing CDMA multiuser detection by constraining soft decisions

A method for multi-user detection includes receiving a complex input signal due to a superposition of waveforms encoding symbols in a real-valued constellation, which are transmitted respectively by a plurality of transmitters in a common frequency band. The complex input signal is sampled at sampling intervals over the duration of an observation period to provide a sequence of complex samples. The sequence of complex samples is processed to determine soft decision values corresponding to the symbols transmitted by the plurality of the transmitters in the observation period, while constraining the soft decision values to be real values. The soft decision values are then projected onto the constellation to estimate the transmitted symbols.

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Nofit, Israel

Jacob Sheinvald