Method and apparatus for simple and efficient interference cancellation for chip synchronized CDMA
First Claim
Patent Images
1. In a Code Division Multiple Access (CDMA) spread spectrum receiver, apparatus for cancelling interference from other CDMA spread spectrum transmitters, said apparatus comprising:
- first correlating means for receiving a composite signal of plural, overlapping spread-coded signals, and applying a first spreading sequence to said composite signal to produce a first output, said first output comprising an intended signal and first interference components;
second correlating means for receiving and decoding said composite signal with a reference sequence whose cross correlation with code sequences of said other CDMA spread spectrum transmitters is substantially a constant and producing a second output with second interference components, said second interference components being substantially equivalent to said first interference components; and
combining means for combining said first and second outputs such that said first and second interference components substantially cancel each other and produce a third output representing said intended signal.
1 Assignment
0 Petitions
Accused Products
Abstract
Interference from other users in a CDMA Spread Spectrum system is cancelled by constructing a single reference sequence which is representative of the spreading sequences of all users in the system. Interference from the other users can be cancelled without each receiver employing a separate decorrelator for every other user in the system and having an accurate estimate of the received power level of every transmitted signal.
-
Citations
10 Claims
-
1. In a Code Division Multiple Access (CDMA) spread spectrum receiver, apparatus for cancelling interference from other CDMA spread spectrum transmitters, said apparatus comprising:
-
first correlating means for receiving a composite signal of plural, overlapping spread-coded signals, and applying a first spreading sequence to said composite signal to produce a first output, said first output comprising an intended signal and first interference components; second correlating means for receiving and decoding said composite signal with a reference sequence whose cross correlation with code sequences of said other CDMA spread spectrum transmitters is substantially a constant and producing a second output with second interference components, said second interference components being substantially equivalent to said first interference components; and combining means for combining said first and second outputs such that said first and second interference components substantially cancel each other and produce a third output representing said intended signal. - View Dependent Claims (2, 3, 4, 5)
-
-
6. A method of cancelling interference from other transmitters in a CDMA spread spectrum receiver, comprising the steps of:
-
receiving a composite signal of plural, overlapping spread-coded signals; extracting an intended signal having interference components from said composite signal by applying a first spreading sequence to said composite signal; decoding said composite signal with a reference sequence whose cross correlation with code sequences of said other CDMA spread spectrum transmitters is substantially a constant, to generate a decoded signal; and combining said intended signal with said decoded signal to substantially cancel said interference components in said intended signal. - View Dependent Claims (7, 8)
-
-
9. A method of processing a Code Division Multiple Access (CDMA) signal to cancel interference in said CDMA signal from other transmitters in a CDMA spread spectrum receiver, comprising the steps of:
-
constructing an m row by L=2m -1 column generator matrix G for a maximal length code, where m is a positive integer ≧
2;obtaining a matrix Ge by expurgating e rows of said generator matrix G, where e is an integer, 1<
e<
m;generating nonzero codewords with said matrix Ge ; selecting 2m-e -1 of said nonzero codewords as bandwidth spreading codes; identifying a set Γ
of 2e -1 locations for any zero columns in Ge ;creating a reference sequence of length L=2m -1 wherein locations identified by said set Γ
are 1, and the remaining 2m -2e locations are 0; andapplying a signal which comprises said reference sequence to said CDMA signal to substantially cancel interference from said other transmitters. - View Dependent Claims (10)
-
Specification