EP0641102A2
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EP
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Direct sequence - Code division multiple access receiver with multiuser interference canceller
Assignee: Philips Electronics UK Ltd
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Filing: 1994-08-18
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Granted: —
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Expires: 2014-08-18
Abstract
Abstract A DS-CDMA system comprises at least one transmitter and at least one receiver operating on a dedicated signal channel which is used by other DS-CDMA operators in a non-synchronous way. A receiver for use in such a DS-CDMA system includes a data aided multiuser interference canceller (38) comprising a feedforward filter (48) connected to a subtracting stage (50). A decision stage (52) is connected to an output of the subtracting stage (50). Decisions from the decision stage (52) are stored in a memory which also stores preliminary decisions made on the signal applied to the feedforward filter (48) by a simple receiver (46). These decisions are applied to a feedback filter (58) the output of which is connected to the subtracting stage (50) thereby removing the effects of pre-cursive and post-cursive interference. The input to, and output from, the decision stage 52 are compared and the difference is used for adjusting the tap weights of the feedforward and feedback filters (48,58). In the case of a single input, single output, the feedforward filter (48) comprises a fractionally spaced equalizer which despreads and filters the DS-CDMA signal. In the case of multiple input, multiple output, the received signal is despread in a bank of code matched filters and the output is applied to the canceller (38) in which the feedforward filter (48) comprises a linear synchronous equalizer.
Inventors
- 👤 Pantelis C/O Dept. Of Elec. & El. Monogioudis
- 👤 John Mark C/O Philips Res. Lab. Edmonds
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 11:32
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/69; H04B1/707; H04B1/7097; H04B1/7103; H04B1/7107
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
142 words
A direct sequence-code division multiple access (DS-CDMA) system comprising a transmitter and a receiver, the transmitter having means for multiplying a modulating signal with a spreading sequence in order to form a spread spectrum signal and for transmitting the spread spectrum signal on a CDMA channel, and the receiver comprising means for receiving signals on said CDMA channel, means for cancelling multiple access interference, said means including feedforward filtering means, feedback filtering means, quantizing means for producing quantized decisions from information derived from the feedforward filtering means, means for making tentative decisions on received information, means for producing an inversion of the equivalent CDMA channel in dependence on the cross correlation values of all the contemporaneous users and means responsive to the production of the inversion of the equivalent CDMA channel for adjusting tap weights of at least the feedforward filtering means.
Claim 2
Dependent Claim
29 words
A DS-CDMA system as claimed in Claim 1, characterised in that the equivalent CDMA channel is described in the frequency (D-transform) or time domain by a matrix C(D), where
Claim 3
Dependent Claim
265 words
A direct sequence-code division multiple access (DS-CDMA) system comprising a transmitter and a receiver, the transmitter having means for multiplying a modulating signal with a spreading sequence in order to form a spread spectrum signal and for transmitting the spread spectrum signal on a CDMA channel, and the receiver comprising an interference canceller having a signal input, delay means coupled to the input, an equalizer having an input coupled to the delay means, first subtracting means having first and second inputs and an output, the first input being connected to an output of the equalizer, a quantizing stage having an input coupled to the output of the subtractor and a signal output, second subtracting means having a first input coupled to the input of the quantizing stage and a second input coupled to the output of the quantizing stage and an output, means for producing preliminary decisions having an input coupled to the signal input and an output, memory means having first input means coupled to the output of the quantizing stage, second input means coupled to the output of the means for producing preliminary decisions and output means, signal cancelling means having first input means coupled to the output means of the memory means, and an output coupled to the first subtracting means, wherein the output of the second subtracting means is coupled to means for adjusting the tap weights of the equalizer and the signal cancelling means and wherein the length of the equalizer is substantially equal to or greater than the length of a spreading sequence used to form the DS-CDMA signal.
Claim 4
Dependent Claim
86 words
A receiver for a DS-CDMA signal, comprising means for cancelling multiple access interference, said means including feedforward filtering means, feedback filtering means, quantizing means for producing quantized decisions from information derived from the feedforward filtering means, means for making tentative decisions on received information, means for producing an inversion of the equivalent CDMA channel in dependence on the cross correlation values of all the contemporaneous users and means responsive to the production of the inversion for adjusting tap weights of at least the feedforward filtering means.
Claim 5
Dependent Claim
222 words
A receiver for a DS-CDMA signal, comprising an interference canceller having a signal input, delay means coupled to the input, an equalizer having an input coupled to the delay means, first subtracting means having first and second inputs and an output, the first input being connected to an output of the equalizer, a quantizing stage having an input coupled to the output of the subtractor and a signal output, second subtracting means having a first input coupled to the input of the quantizing stage and a second input coupled to the output of the quantizing stage and an output, means for producing preliminary decisions having an input coupled to the signal input and an output, memory means having first input means coupled to the output of the quantizing stage, second input means coupled to the output of the means for producing preliminary decisions and outputs means, signal cancelling means having first input means coupled to the output means of the memory means, and an output coupled to the first subtracting means, wherein the output of the second subtracting means is coupled to means for adjusting the tap weights of the equalizer and the signal cancelling means and wherein the length of the equalizer is substantially equal to or greater than the length of a spreading sequence used to form the DS-CDMA signal.
Claim 6
Dependent Claim
68 words
A receiver as claimed in Claim 5, wherein the signal cancelling means has a plurality of shift register stages for receiving preliminary decisions derived in operation and stored in the memory and past decisions derived in operation and stored in the memory, characterised in that the number of shift register stages required for past decisions is less than the number of shift register stages required for preliminary decisions.
Claim 7
Dependent Claim
27 words
A receiver as claimed in Claim 5 or 6, characterised in that the equalizer comprises a fractionally spaced equalizer which despreads and equalizes a received DS-CDMA signal.
Claim 8
Dependent Claim
32 words
A receiver as claimed in Claim 5 or 6, characterised in that the equalizer comprises a linear synchronous equalizer and in that a signal despreading means is coupled to said signal input
Claim 9
Dependent Claim
39 words
A receiver as claimed in any one of Claims 5 to 8, characterised by the or each interference canceller having decoding means coupled between the signal output of the decision stage and the first input to the memory means.
Claim 10
Dependent Claim
114 words
A receiver as claimed in Claim 5 or 6, wherein for a multiple input single output, the receiver is characterised by a plurality of code matched filters having a common input for receiving an input signal, means for applying a different user's spreading code to each of the code matched filters, means for sampling the output of each code matched filter at the bit rate, a corresponding plurality of interference cancellers having inputs coupled to a respective one of the sampling means, means coupled to outputs of the interference cancellers for subtracting unwanted signals from a wanted signal and producing a difference signal and quantizing means having an input for receiving the difference signal.
References Cited (Backward Citations)
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