Multi-rate spread system
First Claim
1. A transmitter for a direct sequence, spread spectrum communication system, the transmitter comprising:
- (a) means for receiving an information-bearing input signal at a variable data rate;
(b) means for producing a code signal comprising a pseudorandom sequence of chips at a chip rate;
(c) DS modulation means for modulating the information-bearing signal with the code signal to produce a DS modulated signal such that each bit of the information-bearing signal is modulated with N chips of the code signal, N being an integer greater than 1; and
(d) timing means for causing the value of N to vary as the variable data rate varies, such that the chip rate of the DS modulated signal is substantially constant as the data rate varies.
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Accused Products
Abstract
Apparatus and a method for transmitting a direct sequence, spread spectrum communication system signal. A transmitter (10) that receives a variable data rate information bearing input signal from a digital data source (12) includes a forward error correction encoder (80) that provides redundancy and an interleaver (82) that rearranges the input data. The forward error correction encoder and interleaver minimize the effect of errors that arise in the propagation of the transmitted signal. The output of the interleaver is applied to the input of a Hadamard encoder (84), which converts data words from the interleaver into one of N orthogonal codes, producing a Hadamard signal that varies at a bit rate that changes as the data rate of the information bearing signal varies. A pseudorandom number code generator (16) produces a code signal comprising a pseudorandom sequence of chips supplied at a constant chip rate. The Hadamard signal is input to a direct sequence (DS) modulator that modulates the information bearing signal with the code signal, using an integer number (greater than one) of chips to modulate each bit of the Hadamard signal. As the data rate of the information bearing signal varies, the number of chips per bit of the Hadamard signal is varied so as to minimize variations in the chip rate of the DS modulated signal. The transmitter is preferably combined with a receiver (29) in a transceiver. The receiver demodulates a received signal, and correlates it with a code signal from a pseudorandom number code generator (40) corresponding to the pseudorandom number code generator in the transmitter. The receiver also includes a Hadamard decoder (94), deinterleaver (96), and forward error correction decoder (98). A frequency hopping capability is optionally provided.
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Citations
20 Claims
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1. A transmitter for a direct sequence, spread spectrum communication system, the transmitter comprising:
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(a) means for receiving an information-bearing input signal at a variable data rate; (b) means for producing a code signal comprising a pseudorandom sequence of chips at a chip rate; (c) DS modulation means for modulating the information-bearing signal with the code signal to produce a DS modulated signal such that each bit of the information-bearing signal is modulated with N chips of the code signal, N being an integer greater than 1; and (d) timing means for causing the value of N to vary as the variable data rate varies, such that the chip rate of the DS modulated signal is substantially constant as the data rate varies. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A direct sequence, spread spectrum communication system, comprising:
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(a) a transmitter having; (i) a transmit pseudorandom number code generator that produces a code signal comprising a pseudorandom sequence of chips at a chip rate; (ii) a DS modulator for modulating a variable rate information bearing input signal comprising a plurality of bits with the code signal to produce a DS modulated signal, such that each of the plurality of bits of the information-bearing signal is modulated with N chips of the code signal, N being an integer greater than 1; and (iii) timing means for causing the value of N to vary as a rate of the information bearing input signal varies; and (b) a receiver having; (i) a receive pseudorandom number code generator that produces a code signal corresponding to the code signal of the transmit pseudorandom number code generator; and (ii) correlator means, coupled to the receive pseudorandom number code generator, for correlating a demodulated signal received from the transmitter to recover the information bearing input signal. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A method for producing a direct sequence, spread spectrum communication system signal, the method comprising the steps of:
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(a) receiving an information-bearing input signal at a variable data rate; (b) producing a code signal comprising a pseudorandom sequence of chips at a chip rate; (c) modulating the information-bearing signal with the code signal to produce a DS modulated signal such that each bit of the information-bearing signal is modulated with N chips of the code signal, N being an integer greater than 1; and (d) causing the value of N to vary as the variable data rate varies. - View Dependent Claims (18, 19, 20)
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Specification