Multiple channel joint decoding at mobile handset
A system and method suppresses the interference caused by non-orthogonal signals on multiple channels of the same receiver by applying an inverse of the correlation among the non-orthogonal signals to the decoded signals. In a multi-channel receiver, the receiver is aware of the codes that are allocated to each of the channels, and thus, can be configured to determine the correlation among the multiple codes that are allocated to a receiver. The inverse of this correlation is applied to the output of the correlators assigned to each code, thereby suppressing the effects of using non-orthogonal codes for transmissions to the same receiver. If different sized codes are allocated to the same receiver, the correlation of the shorter code and a corresponding segment of the longer code is computed. The inverse of the correlation for the segment is applied to the output of the correlators, corresponding in time to the processing of the shorter code and this segment of the longer code. The correlation of the shorter code and each shorter-code-length segment of the longer code is similarly determined and its inverse applied to the outputs of the correlators. An output corresponding to the entire longer-length code is determined by combining the intermediate outputs corresponding to each shorter-code-length segment.
1. A CDMA receiving system comprising:
a receiver that is configured to receive a composite signal that includes a plurality of information, signals;
a first decoder, operably coupled to the receiver, that is configured to decode a first information signal of the plurality of information signals, wherein the decoder decodes the information signal by separately decoding segments of the information signal using segments of a first CDMA code that are shorter in length than the first CDMA code, to produce an intermediate value corresponding to the information signal associated with each segment;
a second decoder, operable coupled to the receiver, that is configured to decode a second information signal of the plurality of information signals based on a second CDMA code; and
a decorrelator configured to provide an output value based on the intermediate values, an output of the second decoder, and a correlation among a segment of the first CDMA code and the second CDMA code.
2. The system of claim 1 , wherein
the first decoder is further configured to form a composite of the intermediate values corresponding to each segment.
3. The system of claim 2 , further including:
at least one other decoder that is configured to decode at least one other information signal using at least one other CDMA code.
4. The system of claim 3 , wherein
the second CDMA code and the at least one other CDMA code have a length corresponding to the segments of the first CDMA code.
5. The system of claim 3 , wherein the decorrelator is configured to provide the output value based on the intermediate values, an output of the second decoder, an output of each of the at least one other decoder, and a correlation among the segment of the first CDMA code, the second CDMA code and each of the at least one other CDMA codes.
6. A method of decoding an information symbol from a composite signal, the method comprising, under control of a CDMA receiving system:
partitioning the composite signal into a plurality of segments, each segment of the plurality of segments being shorter in length than the information symbol;
determining a first output value corresponding to a segment, based on a correlation between the segment and a corresponding segment of a first CDMA code having a same length as the information symbol; and
determining a second output value from the composite signal based on a second CDMA code, and
modifying the first output value and the second output value, based on a correlation between the first CDMA code and the second CDMA code.
7. The method of claim 6 , further including
forming a composite of output values of each segment, to determine an output symbol corresponding to the information symbol.
8. The method of claim 6 , wherein modifying the first output value and the second output value based on a correlation between the first CDMA code and the second CDMA code comprises:
determining an inverse of the correlation between the first CDMA code and the second CDMA code.
9. The system of claim 1 , wherein the decorrelator is configured to compute an inverse of the correlation.
10. A CDMA receiving system comprising:
a receiver that is configured to receive a composite signal that includes a plurality of information signals;
a decoder, operably coupled to the receiver, that is configured to decode an information signal of the plurality of information signals, wherein the decoder decodes the information signal by separately decoding segments of the information signal using segments of a CDMA code that are shorter in length than the CDMA code, to produce an intermediate value corresponding to the information signal associated with each segment, and the decoder is further configured to form a composite of the intermediate values corresponding to each segment;
at least one other decoder that is configured to decode at least one other information signal using at least one other CDMA code; and
a decorrelator that is configured to provide an output value based on the intermediate values, an output of each of the at least one other decoder, and a correlation among the corresponding segment of the first CDMA code and each of the at least one other CDMA codes.