Method and apparatus for spread spectrum code pulse position modulation
First Claim
1. An apparatus for transmitting information across a communication channel, said apparatus comprising:
- a first spread spectrum code generator for generating a first or second spread spectrum codeword to convey at least one bit of information, said codewords consisting of a plurality of chips transmitted during a symbol duration, said codewords having a main lobe in one of said chip positions upon matched filtering in a receiver;
said first spread spectrum code generator further comprising a means for modulating the position of said codeword generated by said first spread spectrum code generator relative to the center of said symbol duration to modulate the position of said main lobe in said receiver output to convey one or more additional bits of information;
a first carrier signal source;
a modulator connected to said first spread spectrum code generator and said first carrier signal source, said modulator generating a first carrier signal modulated by said generated codeword having its position modulated relative to the center of said symbol duration; and
means for applying said modulated carrier signal to an input of said communication channel.
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Abstract
A spread spectrum code pulse position modulated communication system is disclosed. The frequency spectrum of a transmitted signal is spread by encoding bits with a predefined spectrum-spreading codeword which is in accordance with regulatory requirements or other standardization decisions. When the predefined spread spectrum codeword is passed through a filter matched to the characteristics of the codeword, a peak is detected in the main lobe. A positive main lobe can indicate a binary value of "0" and a negative main lobe, associated with the inverse of the predefined codeword, can represent a binary value of "1". Additional information is conveyed by modulating the position of the center of the codeword within the symbol duration. In one embodiment, the position of the center of the codeword is varied among eight positions. Thus, eight signal states are available, and three additional bits may thereby be conveyed. Two differently and independently time-shifted spread spectrum codewords may be modulated, each with one of two orthogonal carrier signals, such as a sine and a cosine wave, thereby conveying a total of eight bits per symbol duration. Here, a symbol duration is the duration of a codeword.
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Citations
20 Claims
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1. An apparatus for transmitting information across a communication channel, said apparatus comprising:
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a first spread spectrum code generator for generating a first or second spread spectrum codeword to convey at least one bit of information, said codewords consisting of a plurality of chips transmitted during a symbol duration, said codewords having a main lobe in one of said chip positions upon matched filtering in a receiver; said first spread spectrum code generator further comprising a means for modulating the position of said codeword generated by said first spread spectrum code generator relative to the center of said symbol duration to modulate the position of said main lobe in said receiver output to convey one or more additional bits of information; a first carrier signal source; a modulator connected to said first spread spectrum code generator and said first carrier signal source, said modulator generating a first carrier signal modulated by said generated codeword having its position modulated relative to the center of said symbol duration; and means for applying said modulated carrier signal to an input of said communication channel. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for receiving a plurality of bits of information transmitted across a communication channel, one or more of said received bits being encoded using a first or second spread spectrum codeword transmitted during a symbol duration to convey at least one bit of information, said generated codeword having a main lobe upon matched filtering, one or more additional received bits being encoded by shifting the position of said generated codeword relative to the center of said symbol duration to modulate the position of said main lobe upon said matched filtering, said receiver apparatus comprising:
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a filter matched to said first and second spread spectrum codewords; means for analyzing said filter output to detect the polarity and position of said main lobe relative to the center of said symbol duration; and means for analyzing said polarity and position information of said main lobe to decode said transmitted data. - View Dependent Claims (8, 9, 10)
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11. A communication system comprising:
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a transmitter for encoding data using a spread spectrum codeword to convey at least one bit of information, said codeword consisting of a plurality of chips transmitted during a symbol duration, said codeword having a main lobe in one of said chip positions upon matched filtering, said transmitter further including means for shifting the position of said generated codeword relative to the center of said symbol duration to modulate the position of said main lobe upon said matched filtering to convey one or more additional bits of information; a receiver including a filter matched to said codeword, said receiver further including means for analyzing said filter output to detect the polarity and position of said main lobe to decode said transmitted data; and a communication channel for connecting said transmitter and receiver. - View Dependent Claims (12)
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13. A method for transmitting data across a communication channel, said transmission method comprising the steps of:
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generating a first or second spread spectrum codeword to convey at least one bit of information, said codewords consisting of a plurality of chips transmitted during a symbol duration, said codeword having a main lobe in one of said chip positions upon matched filtering in a receiver; modulating the position of said generated codeword relative to the center of said symbol duration to produce a modulated codeword in which the position of said main lobe in said receiver output is employed to convey one or more additional bits of information; generating a first carrier signal; modulating said first carrier signal using said modulated codeword; and applying said modulated carrier signal to an input of said communication channel. - View Dependent Claims (14, 15, 16, 17)
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18. A method for receiving a plurality of bits of information transmitted across a communication channel, one or more of said received bits being encoded using a first or second spread spectrum codeword transmitted during a symbol duration to convey at least one bit of information, said codeword having a main lobe upon matched filtering, one or more additional received bits being encoded by shifting the position of said generated codeword relative to the center of said symbol duration to modulate the position of said main lobe upon said matched filtering, said method for receiving comprising the steps of:
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filtering said received signal using a filter matched to said spread spectrum codewords; analyzing said filter output to detect the polarity and position of said main lobe relative to the center of said symbol duration; and analyzing the polarity and position of said main lobe to decode said transmitted data. - View Dependent Claims (19, 20)
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Specification