Joint multi-code detectors in CDMA communications system

A CDMA communication system for jointly detecting symbols in two or more received signals contained within a composite signal, the receiver comprising:

• a multi-code RAKE receiver for separating said composite signal into two or more RAKE output signals by despreading said composite signal using two or more selected spreading codes and for determining RAKE combining weights based on a noise covariance matrix;
• a code correlator for generating cross-correlations between said two or more spreading codes;
• and
• a multi-code joint detector for jointly detecting symbols in said received signals based on said RAKE output signals and said RAKE combining weights from said RAKE receiver and said cross-correlations from said code correlator.

A method of generating branch metrics for a multi-code joint detector in a CDMA receiver that jointly detects received signals encoded with different spreading codes, the method comprising:

• forming a trellis representing possible states and state transitions for said multi-code joint detector;
• determining cross-correlations between said spreading codes;
• determining a noise covariance matrix;
• determining RAKE combining weights based on said noise covariance matrix;
• and
• generating branch metrics associated with said state transitions based on said cross-correlations and said RAKE combining weights.

A multi-code joint detector for jointly detecting symbols in two or more received signals contained within a composite signal, the detector comprising:

• a multi-code RAKE receiver for determining RAKE receiver output signals and for determining RAKE combining weights based on a noise covariance matrix;
• a trellis representing possible states and state transitions;
• and
• a branch metric calculator for calculating branch metrics associated with said state transitions and based on cross-correlations between said two or more spreading codes and on said RAKE combining weights.

A method of generating a received signal soft value for a decoder in a CDMA receiver, comprising:

• generating forward state metrics based on branch metrics leading into a decoder sequence estimation state;
• selecting branch metrics leading out of said state to use as backward state metrics;
• and
• generating a soft value of said received signal based on said forward state metrics and said selected branch metrics.

A detector for generating soft values comprising:

• a forward state metric calculator to calculate forward or state metrics for a current state based on a set of previous state metrics for possible previous states and branch metrics for branches connecting said previous states to said current state;
• a soft value generator to generate a soft value for said current state based on said forward state metric and branch metrics for branches connecting said current state to possible next states;
• and
• a branch metric calculator to compute said branch metrics.