US5568473A
Expired / Lapsed
US
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Method and apparatus for simple and efficient interference cancellation for chip synchronized CDMA
Assignee: Comsat Corp
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Filing: 1994-12-08
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Granted: 1996-10-22
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Expires: 2014-12-08
Abstract
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.
Inventors
- 👤 Farhad Hemmati
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 15:57
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/69; H04B1/707; H04B1/7097; H04B1/7103; H04B1/7107
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
145 words
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.
Claim 2
Dependent Claim
145 words
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.
Claim 3
Dependent Claim
18 words
An apparatus in accordance with claim 1, further comprising: reference sequence generating means for generating said reference sequence.
Claim 4
Dependent Claim
22 words
An apparatus in accordance with claim 1, further comprising signal receiving means for receiving said composite signal of plural, overlapping spread-coded signals.
Claim 5
Dependent Claim
25 words
An apparatus in accordance with claim 1, wherein said second correlating means further comprises adjuster means for adjusting the signal level of said second output.
Claim 6
Dependent Claim
48 words
An apparatus in accordance with claim 1, further comprising: decision making means for receiving said third output and producing a first final signal when said third output is less than a predetermined threshold, and a second final signal when said third output is not less said predetermined threshold.
Claim 7
Independent Claim
97 words
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.
Claim 8
Independent Claim
97 words
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.
Claim 9
Dependent Claim
31 words
A method in accordance with claim 6, further comprising the step of: generating said reference sequence whose cross correlation with code sequences of said other CDMA transmitters is substantially a constant.
Claim 10
Dependent Claim
28 words
A method in accordance with claim 6, further comprising the step of: adjusting the level of said decoded signal before combining said decoded signal with said intended signal.
Claim 11
Independent Claim
162 words
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=2 m -1 column generator matrix G for a maximal length code, where m is a positive integer ≧2; obtaining a matrix G e by expurgating e rows of said generator matrix G, where e is an integer, 1<e<m; generating nonzero codewords with said matrix G e ; selecting 2 m-e -1 of said nonzero codewords as bandwidth spreading codes; identifying a set Γ of 2 e -1 locations for any zero columns in G e ; creating a reference sequence of length L=2 m -1 wherein locations identified by said set Γ are 1, and the remaining 2 m -2 e locations are 0; and applying a signal which comprises said reference sequence to said CDMA signal to substantially cancel interference from said other transmitters.
Claim 12
Independent Claim
162 words
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=2 m -1 column generator matrix G for a maximal length code, where m is a positive integer ≧2; obtaining a matrix G e by expurgating e rows of said generator matrix G, where e is an integer, 1<e<m; generating nonzero codewords with said matrix G e ; selecting 2 m-e -1 of said nonzero codewords as bandwidth spreading codes; identifying a set Γ of 2 e -1 locations for any zero columns in G e ; creating a reference sequence of length L=2 m -1 wherein locations identified by said set Γ are 1, and the remaining 2 m -2 e locations are 0; and applying a signal which comprises said reference sequence to said CDMA signal to substantially cancel interference from said other transmitters.
Claim 13
Dependent Claim
44 words
A method of processing a Code Division Multiple Access (CDMA) signal as defined in claim 9, wherein said step of applying a signal further comprises the step of generating an estimate for components of said interference in said CDMA signal from said other transmitters.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1999-10-22 | 2000-04-22 | 2000-10-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2003-10-22 | 2004-04-22 | 2004-10-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2007-10-22 | 2008-04-22 | 2008-10-22 | $7700.00 | Window Closed / Lapsed |