Code-division multiple-access demodulator with interference cancellation

Claim 1

A demodulator for code-division multiple-access spread-spectrum communications, comprising: a memory (13) divided into separate memory areas for different transmitting stations, each memory area storing received chip data and updated chip data for a plurality of symbols including at least a newest symbol and an oldest symbol; a spreading-code generator (15) for generating spreading codes used by respective transmitting stations; a correlator (14) coupled to correlate all data in a designated memory area among said memory areas with a corresponding spreading code generated by said spreading-code generator (15), thereby generating correlated values for a plurality of symbols; an estimator (16) coupled to receive said correlated values, calculate therefrom a plurality of estimated symbol values, and temporarily store said estimated symbol values; a respreader (17) coupled to calculate differences between said estimated symbol values and previously stored estimated symbol values, and multiply said differences by said corresponding spreading code to create remaining interference values; an interference subtractor (18) coupled to update all data stored in said memory (13), except data stored in said designated memory area, by subtracting said remaining interference values; a controller (19) for recognizing symbol boundaries and designating a memory area in said memory whenever its corresponding transmitting station completes transmission of a symbol; and an output port (20) coupled to output, for the oldest symbol stored in said designated memory area, a demodulated value that has at least been correlated by said correlator (14).

Claim 8

A method of demodulating a code-division multiple-access spread-spectrum signal, comprising the steps of: storing received chip data and updated chip data in a memory divided into separate memory areas, each memory area corresponding to a different transmitting station, and each memory area storing data for a plurality of symbols including at least a newest symbol and an oldest symbol; designating a transmitting station and its corresponding memory area whenever said transmitting station finishes transmitting a symbol, thus obtaining a designated transmitting station and designated memory area; correlating all data stored in the designated memory area with a spreading code employed by the designated transmitting station, thereby generating correlated values for a plurality of symbols; estimating symbol values from said correlated values, thereby generating estimated symbol values; storing said estimated symbol values temporarily, so that current estimated symbol values and previous estimated symbol values are available simultaneously; calculating difference values between said current estimated symbol values and said previous estimated symbol values; multiplying said difference values by the spreading code employed by said designated transmitting station, thereby generating remaining interference values; updating all data stored in said memory, except data stored in said designated memory area, by subtracting said remaining interference values; and outputting a demodulated value for the oldest symbol stored in said designated memory area, said demodulated value having at least been correlated in said step of correlating all data.