Spread-spectrum multiplexed transmission system
First Claim
1. A multi-channel spread-spectrum transmission system, wherein a plurality of spread-spectrum signals are frequency division multiplexed to provide multiple transmission channels, comprising:
- a plurality of transmitters each for transmitting a signal having a plurality of spaced spectral lines or bands produced by modulating a carrier with a pseudo-noise code, such that the transmitted signal of each channel has an information bandwidth which is significantly less than its spectral line or band spacing and the spread-spectrum signals each have centre frequencies which are spaced, respectively, by frequency increments selected to cause the spectral lines or bands of the respective transmitted signals to be interleaved, the selected frequency increments being less than the transmitter bandwidth of each signal.
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Accused Products
Abstract
A spread-spectrum transmission system wherein a plurality of spread-spectrum signals are frequency division multiplexed by offsetting the center or carrier frequencies of the spread-spectrum signals by a fraction of the spectral-line spacing of the signals. The signals are generated by modulating a carrier with a pseudo-noise (PN) code signal. At a receiver, demultiplexing is carried out by mixing (42) the received multiplexed signal with a plurality of local oscillator frequencies (43) which are offset from each other in the same manner as the centre or carrier frequencies of the multiplexed spread-spectrum signals. The mixed signals are then further mixed (45) with generated PN code signals (47) corresponding to those used to generate the multiplexed spread-spectrum signals. The epoch of each generated PN code signal is then advanced or retarded in response to a respective epoch control signal (48) generated by a respective controller (46). After mixing (45) the signals are passed through respective narrowband filters (49) to select the baseband signals which are then fed to the respective controllers (46) to enable the generation of the epoch control signals (48 ). When applied to a vehicle tracking system a number of spaced receivers are utilized.
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Citations
46 Claims
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1. A multi-channel spread-spectrum transmission system, wherein a plurality of spread-spectrum signals are frequency division multiplexed to provide multiple transmission channels, comprising:
a plurality of transmitters each for transmitting a signal having a plurality of spaced spectral lines or bands produced by modulating a carrier with a pseudo-noise code, such that the transmitted signal of each channel has an information bandwidth which is significantly less than its spectral line or band spacing and the spread-spectrum signals each have centre frequencies which are spaced, respectively, by frequency increments selected to cause the spectral lines or bands of the respective transmitted signals to be interleaved, the selected frequency increments being less than the transmitter bandwidth of each signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A receiver for receiving a plurality of transmitted spread-spectrum signals which are frequency division multiplexed to provide a plurality of transmission channels, wherein the channels are distinguished by respective signal centre frequencies, each signal comprising a plurality of spaced spectral lines or bands produced by modulating a carrier with a pseudo-noise code, the carrier consisting of a band of frequencies due to the statistical uncertainty of its frequency, the transmitted signal of each channel having an information bandwidth which is significantly less than its spectral line or band spacing, and where the centre frequencies of the spread-spectrum signals are spaced by frequency increments selected to cause spectral lines or bands of the respective transmitted signals to be interleaved, the selected frequency increments being less than the transmitted bandwidth of each signal, said receiver comprising:
receiver means including a plurality of receiver channels, correlation means being provided for each receiver channel to cause the spread-spectrum signal received on a respective channel to be collapsed to a narrow bandwidth corresponding to the transmission channel signal bandwidth which comprises the sum of the carrier frequency uncertainty bandwidth and the channel information bandwidth such that it is selected by being passed through a narrowband filter having a bandwidth corresponding to said transmission channel signal bandwidth, eliminating essentially all interference from other channels as well as wideband noise lying outside the filter bandwidth. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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19. A multi-vehicle vehicle location and tracking system capable of tracking a plurality of vehicles at the same time, comprising:
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a) a plurality of mobile radio-frequency transmitters each mounted on a vehicle to transmit a spread-spectrum signal comprising a plurality of spaced spectral lines or bands and having an information bandwidth which is significantly less than its spectral line or band spacing, the spread-spectrum signal being produced by modulating a carrier with a pseudo-noise code and the spread-spectrum signals from respective individual transmitters having centre frequencies which are spaced from each other by frequency increments selected to cause spectral lines or bands of the respective transmitted signals to be interleaved, the selected frequency increments being less than the transmitted bandwidth of each signal; b) at least three multi-channel receivers positioned at known spaced locations each being arranged to receive the spread-spectrum signals transmitted by each of the transmitters, correlation means being included in each channel receiver to cause the spread-spectrum signal received from an individual transmitter associated with the respective channel to be collapsed to a narrow bandwidth corresponding to the transmitted channel signal bandwidth which comprises the sum of the carrier frequency uncertainty bandwidth and the channel information bandwidth such that it is selected by being passed through a narrowband filter, thereby eliminating essentially all interference from the transmitted signals of other channels as well as wideband noise lying outside the filter bandwidth; and
control means communicating with each of the from a receivers and including signal processing means to measure differences in the propagation time from a respective transmitter to each receiver for each one of said transmitted signals and to thereby calculate the position of the respective transmitter relative to the receivers. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 28)
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27. The method of providing multi-channel communication within a spectrum comprising:
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transmitting a plurality of spread-spectrum signals frequency multiplexed within said spectrum, each signal comprising a plurality of frequency-spaced spectral lines or bands produced by modulating an information-bearing carrier with a pseudo-noise code such that each channel has an information bandwidth significantly less than the frequency spacing of its spectral lines or bands, wherein each spread-spectrum signal carrier frequency is selected to be spaced from adjacent carrier frequencies by a frequency increment such as to cause the spectral lines or bands of respective transmitted signals to be interleaved, said frequency increment being less than the transmitted bandwidth of each signal; and processing each received signal of said transmitted signal by correlating a composite signal of all the received spread-spectrum signals with a locally-generated pseudo-noise code to cause the spread-spectrum signal on a respective channel to be collapsed to a narrow bandwidth substantially corresponding to the transmitted signal information bandwidth, and passing said collapsed signal through a narrowband filter corresponding to the respective channel centre frequency so as to pass only transmitted signal information and eliminate interference from other received spread-spectrum signals as well as widened noise lying outside the filter bandwidth.
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29. A method of transmitting in a multi-channel communications system, a plurality of spread-spectrum signals being frequency division multiplexed within said spectrum, comprising:
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for each signal, modulating an information-bearing carrier with a pseudo-noise code to provide a plurality of frequency-spaced spectral lines or bands, such that each channel has an information bandwidth significantly less than the frequency spacing of its spectral lines or bands; and selecting each spread-spectrum signal carrier frequency to be spaced from adjacent carrier frequencies by a frequency increment such as to cause the spectral lines or bands of respective transmitted signals to be interleaved, said frequency increment being less than the transmitted bandwidth of each signal. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37)
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38. The method of processing, in a multi-channel communication system, each of a plurality of spread-spectrum signals being multiplexed within said spectrum, wherein the channels are distinguished by respective signal centre frequencies, each signal comprising a plurality of spaced spectral lines or bands, and the respective signal centre frequencies being such that the spectral lines or bands of the individual channel signals are interleaved to form a composite signal, comprising:
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correlating a composite signal of all the received spread-spectrum signals with a locally generated pseudo-noise code to cause the spread-spectrum signal on a respective channel to be collapsed to a narrow bandwidth substantially corresponding to the transmitted signal information bandwidth; and passing said collapsed signal through a narrowband filter corresponding to the respective channel centre frequency so as to pass only transmitted signal information and eliminate interference from other received spread-spectrum signals as well as wideband noise lying outside the filter bandwidth. - View Dependent Claims (39, 40, 41, 42, 43, 44, 45, 46)
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Specification