EP0157692A2
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EP
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Code division multiplexer using direct sequence spread spectrum signal processing
Assignee: Atos Origin IT Services Inc
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Filing: 1985-03-22
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Granted: —
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Expires: 2005-03-22
Abstract
Abstract A plurality of transmitters synchronized to a common clock each transmit a data signal spread by a common bi- polar pseudo-random code having a different assigned code sequence shift. A receiver, synchronized to the clock, discriminates the signals transmitted by a predetermined transmitter from signals transmitted by the others by generating a first pseudo-random code that is a replica of the common bipolar pseudo-random code and has a code sequence shift corresponding to that of the predetermined transmitter, and a second bipolar pseudo-random code that is a replica of the common bipolar pseudo-random code and has an unassigned code sequence shift. The difference between the first and second bipolar pseudo-random code sequences, which is a trinary code sequence, is cross-correlated with the incoming signals. The cross-correlation despreads only the signal having the predetermined code sequence shift. Each receiver includes a number of correlation detectors offset from each other by a fraction of a code chip, together with decision circuitry to identify cross-correlation peaks. The cross-correlation output of a primary correlation detector generates in-phase and quadrature-phase correlation signals, with the quadrature-phase signal being at a minimum when the receiver and predetermined transmitter are perfectly synchronized with each other. The ratio of the in-phase and quadrature-phase signals are processed to identify the presence of a data signal within a background of noise and to improve synchronization lock between the receiver and predetermined transmitter. The output of eacu sub-receiver is processed to extract data using weighting factors selected . according to the particular distortion present, to improve signal-to-noise ratio. Analog and digital implementations of the correlation detectors are disclosed.
Inventors
- 👤 Lawrence Bertram Horowitz
- 👤 Eugene Thomas Wiggins
- 👤 Donald Wallace Rouse
- 👤 John Walter Jerrim
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 00:59
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/69; H04B1/707; H04B1/7073; H04B1/7075; H04B1/7085; H04J; H04J13/00; G; G03; G03G; G03G2215/00; G03G2215/00135; G03G2215/00139; G03G2215/00143; G03G2215/00156; G03G2215/01; G03G2215/0167; G03G2215/017
Claims Analysis
Total Claims: 30
Claim 1
Independent Claim
173 words
A direct sequence spread spectrum code division multiplex system, comprising: a timing source; a plurality of transmitters synchronized to the timing signal source and each transmitting data spread by a bipolar pseudo-random code which is a different assigned shift of a common bipolar code sequence; and characterized by: a receiver synchronized to said timing signal source for receiving said data signals and discriminating the signal transmitted by a predetermined transmitter spread by a bipolar pseudo-random code having a predetermined assigned code sequence shift from signals transmitted by the other transmitter, the receiver including means for generating a first bipolar pseudo-random code that is a replica of the tranmitted common bipolar pseudo-random code and has the predetermined assigned code sequence shift, means for generating a second bipolar pseudo-random code that is a replica of the transmitted common bipolar pseudo-random code and has an unassigned code sequence shift, means for processing said first and second bipolar pseudo-random codes to obtain a trinary code sequence and means for cross-correlating said transmitted signals and said trinary sequence.
Claim 2
Dependent Claim
173 words
A direct sequence spread spectrum code division multiplex system, comprising: a timing source; a plurality of transmitters synchronized to the timing signal source and each transmitting data spread by a bipolar pseudo-random code which is a different assigned shift of a common bipolar code sequence; and characterized by: a receiver synchronized to said timing signal source for receiving said data signals and discriminating the signal transmitted by a predetermined transmitter spread by a bipolar pseudo-random code having a predetermined assigned code sequence shift from signals transmitted by the other transmitter, the receiver including means for generating a first bipolar pseudo-random code that is a replica of the tranmitted common bipolar pseudo-random code and has the predetermined assigned code sequence shift, means for generating a second bipolar pseudo-random code that is a replica of the transmitted common bipolar pseudo-random code and has an unassigned code sequence shift, means for processing said first and second bipolar pseudo-random codes to obtain a trinary code sequence and means for cross-correlating said transmitted signals and said trinary sequence.
Claim 3
Dependent Claim
17 words
The system of Claim 1, wherein said bipolar code sequence is a maximal length - (ML) sequence.
Claim 4
Dependent Claim
19 words
The system of Claim 1 or 2, wherein said bipolar code sequence is a phase shift keyed (PSK) signal.
Claim 5
Dependent Claim
152 words
In a direct sequence spread spectrum code division multiplex system including a plurality of transmitters synchronized to a common timing signal and each transmitting a data signal s(t) spread by a bipolar pseudo-random code which is a different assigned shift of a common code sequence: a receiver synchronized to said timing signal for receiving said transmitted signal spread by a bipolar pseudo-random code having a predetermined assigned code sequence shift, and characterized by: means for generating a first bipolar pseudo-random code that is a replica of the transmitted common bipolar pseudo-random code and has the predetermined assigned code sequence shift, means for generating a second bipolar pseudo-random code that is a replica of the transmitted common bipolar pseudo-random code and has an unassigned code sequence shift, means for processing said first and second bipolar pseudo-random codes to obtain a trinary sequence and means for cross-correlating said transmitted signals and said trinary sequence.
Claim 6
Dependent Claim
152 words
In a direct sequence spread spectrum code division multiplex system including a plurality of transmitters synchronized to a common timing signal and each transmitting a data signal s(t) spread by a bipolar pseudo-random code which is a different assigned shift of a common code sequence: a receiver synchronized to said timing signal for receiving said transmitted signal spread by a bipolar pseudo-random code having a predetermined assigned code sequence shift, and characterized by: means for generating a first bipolar pseudo-random code that is a replica of the transmitted common bipolar pseudo-random code and has the predetermined assigned code sequence shift, means for generating a second bipolar pseudo-random code that is a replica of the transmitted common bipolar pseudo-random code and has an unassigned code sequence shift, means for processing said first and second bipolar pseudo-random codes to obtain a trinary sequence and means for cross-correlating said transmitted signals and said trinary sequence.
Claim 7
Dependent Claim
201 words
A receiver as in Claim 4, characterized in that: said receiver includes a plurality of correlation detectors and means for developing (1) a first reference bipolar sequence r(t) that is a replica of the common bipolar sequence and has a code shift that is within one code chip of the assigned shift of the predetermined transmitter and is displaced from the common bipolar code sequence applied to the other correlation detectors by a common fraction of a code chip less than unity, and (2) a second reference bipolar sequence e(t) that is a replica of the common bipolar sequence and has an unassigned code sequence shift, each of said correlation detectors including first means for obtaining the product of the transmitted sequences s(t) and the first reference bipolar sequence r(t); second means for obtaining the product of the transmitted sequences s(t) and the second reference bipolar sequence e(t) and third means for obtaining a difference between the products obtained by the first and second means; synchronous integrator means for integrating the difference; means for synchronously sampling an output of the integrator means and signal processor means responsive to outputs of said correlation detectors to synchronize said receiver to said predetermined transmitter.
Claim 8
Dependent Claim
143 words
The receiver of Claim 5, characterized in that each of said first and second means includes first and second analog multiplexers, each of said multiplexers having two input terminals and an output terminal; means for controlling said first and second multiplexers in response, respectively, to the first and second reference bipolar sequences r(t) and e(t); and a difference circuit connected to the outputs of the two multiplexers; said transmitted sequences s(t) being applied to one of the input terminals of the multiplexers and being applied, through an inverter, to the second input terminals of the multiplexers; each of said multiplexers being connected to its first input terminal when its respective referece sequence has one value applied thereto and to its second input terminal when its respective reference sequence has a second value, the output v(t) of the difference circuit having the following values:
Claim 9
Dependent Claim
94 words
The receiver of Claim 5 or 6, characterized in that each of said first and second means comprises an analog multiplexer having three input terminals and an output terminal, said transmitted sequences s(t) being applied to the first input terminal of said multiplexer and being applied through an inverter to the second input terminal of said multiplexer and the third input terminal receiving a ground; and digital logic means for connecting the multiplexer to its third input when r(t) = e(t) and to one of its first and second inputs, selectively, when r(t) e(t).
Claim 10
Dependent Claim
99 words
The receiver of any Claims 5, 6 or 7, characterized in that each of said first and second means comprises a pair of two-input analog multiplexers connected in tandem, the first multiplexer having its two inputs connected, respectively, to receive said transmitted sequences s(t) and to an inversion s(t) of said transmitted sequences; said second multiplexer having its two inputs connected respectively to a ground and to an output of said first analog multiplexer, and digital logic means for controlling said first and second multiplexers in response to said two reference sequences r(t), e(t) to generate an output v(t):
Claim 11
Dependent Claim
72 words
The receiver of any of Claims 5 to 8, characterized in that each of said product detectors includes an analog multiplexer having four inputs and an output; two of said inputs being connected to a ground and the remaining two inputs being connected respectively to receive said input sequences s(t) and to an inversion s(t) of said input sequences, and means for controlling said multiplexer to develop the following output signal v(t):
Claim 12
Dependent Claim
113 words
The receiver of any of Claims 5 to 9, characterized in that each of said first and second means includes an analog-to-digital converter for digitizing the transmitted sequences s(t); an accumulator responsive to the output of the converter and logic means responsive to the reference sequences r(t), e(t) to maintain constant the count in the accumulator when r(t) = e(t) and to increment or decrement the count in accumulator when r(t) e(t); an output register; means for periodically transferring the contents of the accumulator to the output register; and means for processing the contents of the output register to develop a receiver timing error signal to synchronize the receiver to the predetermined transmitter.
Claim 13
Dependent Claim
102 words
The receiver of any of Claims 5 to 10, characterized in that each of said first and second means comprises: a voltage-to-frequency converter; means for obtaining the absolute value of the transmitted sequences s(t); a reversible counter responsive to the output of the voltage-to-frequency converter means and; digital logic means for controlling said reversible counter means whereby the counter (a) is disabled when r(t) = e(t) (b) upcounts when s(t) is positive and downcounts when s(t) is negative, when r(t) = 0, e(t) =1 (c) downcounts when s(t) is positive and upcounts when s(t) is positive, when r(t) =1, e(t) = 0.
Claim 14
Dependent Claim
27 words
The receiver as in Claim 5, characterized by: means responsive to the output of each of the correlation detectors for recovering data transmitted by said preselected transmitter.
Claim 15
Dependent Claim
45 words
The receiver of Claim 12, characterized in that said data recovering means includes means for storing weighting factors depending upon a particular form of distortion present and means for applying said weighting factors to amplify the respective outputs of said sub-receivers, to optimize signal-to-noise ratio.
Claim 16
Dependent Claim
59 words
The system as in Claim 5, characterized by: a method of improving signal-to-noise ratio comprising the steps of storing weighting factors corresponding to the output of each of said correlation detectors and selected depending upon the particular form of distortion present; amplifying the outputs from said correlation detectors as functions of said weighting factors; and combining said amplified outputs.
Claim 17
Dependent Claim
94 words
The receiver as in Claim 5, characterized in that each of said correlation detectors includes means for generating an in-phase correlation signal that is at a maximum and a quadrature-phase correlation signal that is at a minimum when said receiver and said predetermined transmitter are synchronized to each other, and said processor means includes means for obtaining an absolute value of the ratio of said in-phase and quadrature-phase correlation signals, and means for shifting receiver timing by a predetermined amount depending upon the magnitude of said ration to achieve synchronization with said predetermined transmitter.
Claim 18
Dependent Claim
34 words
The receiver of Claim 15, characterized in that receiver timing is maintained constant in response to a measured ratio greater than a predetermined ratio, to establish a synchronization deadband about an optimal synchronization point.
Claim 19
Dependent Claim
33 words
The receiver of Claim 15 or 16, characterized in that said processor means includes memory means containing tabulated data defining synchronization timing shifts as a function of different values of said correlation ratio.
Claim 20
Dependent Claim
103 words
The receiver as in Claim 5, characterized in that each of said correlation detectors includes means for generating an in-phase correlation signal that is at a maximum and quadrature-phase correlation signal that is at a minimum when said receiver and said predetermined transmitter are synchronized to each other, and said processor means includes means for determining an absolute value of the ratio of said in-phase correlation signal and said quadrature-phase correlation signal; means for comparing the magnitude of said ratio with a predetermined magnitude and means responsive to said comparing means for identifying the presence of a signal within a background of noise.
Claim 21
Dependent Claim
46 words
The receiver of Claim 18, characterized in that said processor means further includes means for synchronizing said receiver to incoming signals only when said ratio magnitude is greater than said predetermined value, to cause said receiver to lock to said predetermined transmitter and not to noise.
Claim 22
Dependent Claim
183 words
In a direct sequence spread spectrum code division multiplex system comprising: a timing source; a plurality of transmitters synchronized to the timing signal source and each transmitting a data signal spread by common bipolar pseudo-random code which is a different assigned shift of a common bipolar pseudo-random code sequence; and a receiver synchronized to the timing signal source for receiving said transmitted bipolar pseudo-random code having a predetermined assigned code sequence shift: a method of synchronizing the receiver to a predetermined one of said transmitters transmitting a data signal spread by the bipolar pseudo-random code having said predetermined assigned code sequence, characterized by the steps of: generating a first bipolar pseudo-random code that is a replica of the transmitted bipolar pseudo-random code having said predetermined assigned code sequence shift; generating a second bipolar pseudo-random code that is a replica of the transmitted bipolar pseudo-random code having an unassigned code sequence shift; combining said first and second bipolar pseudo-random codes to obtain a trinary sequence; cross-correlating said transmitted binary pseudo-random codes and said trinary code sequence; and in response, generating a receiver timing signal.
Claim 23
Dependent Claim
183 words
In a direct sequence spread spectrum code division multiplex system comprising: a timing source; a plurality of transmitters synchronized to the timing signal source and each transmitting a data signal spread by common bipolar pseudo-random code which is a different assigned shift of a common bipolar pseudo-random code sequence; and a receiver synchronized to the timing signal source for receiving said transmitted bipolar pseudo-random code having a predetermined assigned code sequence shift: a method of synchronizing the receiver to a predetermined one of said transmitters transmitting a data signal spread by the bipolar pseudo-random code having said predetermined assigned code sequence, characterized by the steps of: generating a first bipolar pseudo-random code that is a replica of the transmitted bipolar pseudo-random code having said predetermined assigned code sequence shift; generating a second bipolar pseudo-random code that is a replica of the transmitted bipolar pseudo-random code having an unassigned code sequence shift; combining said first and second bipolar pseudo-random codes to obtain a trinary sequence; cross-correlating said transmitted binary pseudo-random codes and said trinary code sequence; and in response, generating a receiver timing signal.
Claim 24
Dependent Claim
12 words
The method of Claim 20, wherein said processing step includes a subtraction.
Claim 25
Dependent Claim
18 words
The method of Claim 20 or 21, wherein said binary code sequence is a maximal length (HL) sequence.
Claim 26
Dependent Claim
20 words
The method of Claim 20, 21 or 22, wherein said binary code sequence is a phase shift keyed (PSK) signal.
Claim 27
Dependent Claim
164 words
In a data receiver adapted to receive a data signal from one of a plurality of transmitters each transmitting a data signal spread by a common pseudo-random code which is a different assigned shift of a common pseudo-random code sequence and a signal from a timing signal source, a method of synchronizing the receiver to a predetermined one of said transmitters transmitting a data signal spread by the pseudo-random code having said predetermined assigned code sequence, characterized by the steps of: (a) sampling said data signal at a rate equal to,the frequency of the timing signal source or an integral multiple thereof; (b) combining one or more consecutive data samples together to generate a data sample point corresponding to a particular timing point of said timing signal source; (c) detecting which one of said data sample points has a maximum value; and (d) locking the receiver to the timing point of the timing signal source corresponding to said detected maximum value data sample point.
Claim 28
Dependent Claim
164 words
In a data receiver adapted to receive a data signal from one of a plurality of transmitters each transmitting a data signal spread by a common pseudo-random code which is a different assigned shift of a common pseudo-random code sequence and a signal from a timing signal source, a method of synchronizing the receiver to a predetermined one of said transmitters transmitting a data signal spread by the pseudo-random code having said predetermined assigned code sequence, characterized by the steps of: (a) sampling said data signal at a rate equal to,the frequency of the timing signal source or an integral multiple thereof; (b) combining one or more consecutive data samples together to generate a data sample point corresponding to a particular timing point of said timing signal source; (c) detecting which one of said data sample points has a maximum value; and (d) locking the receiver to the timing point of the timing signal source corresponding to said detected maximum value data sample point.
Claim 29
Dependent Claim
188 words
In a direct sequence spread spectrum code division multiplex system comprising a timing'signal source, a plurality of transmitters synchronized to the timing signal source and each transmitting a data signal spread by common pseudo-random code which is a different assigned shift of a common pseudo-random code sequence, and a receiver normally synchronized to the timing signal source for receiving said transmitted pseudo-random code having a predetermined assigned code sequence shift, a method of synchronizing the receiver to a predetermined one of said transmitters transmitting a data signal spread by the pseudo-random code having said predetermined assigned code sequence, characterized by the steps of: (a) sampling said data signal at a rate equal to the frequency of the timing signal source or an integral multiple thereof; , (b) combining one or more consecutive data samples together to generate a data sample point corresponding to a particular timing point of said timing signal source; (c) detecting which one of said data sample points has a maximum value; and (d) locking the receiver to the timing point of the timing signal source corresponding to said detected maximum value data sample point.
Claim 30
Dependent Claim
188 words
In a direct sequence spread spectrum code division multiplex system comprising a timing'signal source, a plurality of transmitters synchronized to the timing signal source and each transmitting a data signal spread by common pseudo-random code which is a different assigned shift of a common pseudo-random code sequence, and a receiver normally synchronized to the timing signal source for receiving said transmitted pseudo-random code having a predetermined assigned code sequence shift, a method of synchronizing the receiver to a predetermined one of said transmitters transmitting a data signal spread by the pseudo-random code having said predetermined assigned code sequence, characterized by the steps of: (a) sampling said data signal at a rate equal to the frequency of the timing signal source or an integral multiple thereof; , (b) combining one or more consecutive data samples together to generate a data sample point corresponding to a particular timing point of said timing signal source; (c) detecting which one of said data sample points has a maximum value; and (d) locking the receiver to the timing point of the timing signal source corresponding to said detected maximum value data sample point.
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