Spread spectrum transmitter and communications system using multiple spreading codes
First Claim
1. A spread spectrum transmitter comprising:
- a shift register having a plurality of stages including a first stage,a plurality of taps connected to selected ones of said stages,a plurality of exclusive-OR gates connected to said taps, each exclusive-OR gate outputting a different spread spectrum code, said exclusive-OR gates thereby collectively outputting a plurality of spread spectrum codes, andmeans for selecting, in response to a data signal, one of said spread spectrum codes for transmission, said one selected spread spectrum code being fed back from said means for selecting into the first stage of said shift register.
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Abstract
A spread spectrum transmitter for generating a plurality of spread spectrum codes comprises a shift register having a plurality of stages, with a plurality of tap sets connected to selected ones of said stages. Each tap set defines a different spread spectrum code, which may be maximal or non-maximal. Outputs from the tap sets are combined using exclusive-OR gates and fed back to through a table of logic gates to the input of the shift register. A serial data register is loaded from a data stream and clocked periodically into a parallel data register. The parallel data register corresponds to a data symbol and is connected to the table, whereby one of the spread spectrum codes at a time is selected. A code portion of the spread spectrum code up to a designated length is generated for each data symbol. More than one code portion may be simultaneously sent using offset quadrature phase shift keying. A receiver may detect the code portion or code portions sent by delaying the received signal and combining it with a plurality of delayed versions thereof, the delay period for each delayed version corresponding to the tap locations in the tap set of the transmitter shift register.
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Citations
33 Claims
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1. A spread spectrum transmitter comprising:
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a shift register having a plurality of stages including a first stage, a plurality of taps connected to selected ones of said stages, a plurality of exclusive-OR gates connected to said taps, each exclusive-OR gate outputting a different spread spectrum code, said exclusive-OR gates thereby collectively outputting a plurality of spread spectrum codes, and means for selecting, in response to a data signal, one of said spread spectrum codes for transmission, said one selected spread spectrum code being fed back from said means for selecting into the first stage of said shift register. - View Dependent Claims (2, 3, 4, 5, 6, 29, 30)
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7. A spread spectrum transmitter for generating a plurality of spread spectrum codes, comprising:
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a shift register having a plurality of stages, a plurality of tap sets connected to selected ones of said stages, each tap set defining a different spread spectrum code, wherein each of said spread spectrum codes corresponds to a unique series of data bits, and whereby said shift register outputs one of said spread spectrum codes in response to selection of one of said tap sets, a data register coupled to a data stream, and a code selector connected to said data register whereby one of said tap sets is selected for transmission in response to the contents of said data register, said code selector being connected in feedback configuration to the first stage of said shift register. - View Dependent Claims (8, 9, 10, 11, 12, 31)
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13. A spread spectrum transmitter comprising:
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a shift register having a plurality of stages, a plurality of tap sets coupled to selected ones of said stages, each tap set defining a spreading code from among a plurality of spreading codes, means for periodically selecting one of said spreading codes at a time in response to a data stream, and means for generating, in response to each selected spreading code, a code portion of the selected spreading code, said code portion having a code length L, wherein L is less than or equal to the code length of the shortest of said spreading codes, wherein said code portion is fed back into said shift resister. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A spread spectrum transmitter for generating a plurality of spread spectrum codes, comprising:
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a shift register having a plurality of stages, a plurality of tap sets connected to selected ones of said stages, each tap set defining a different spread spectrum code, wherein each of said spread spectrum codes corresponds to a unique series of data bits, and whereby said shift register outputs one of said spread spectrum codes in response to selection of one of said tap sets, a first data register coupled to a data stream, said first data register serially receiving said data stream, a second data register coupled to said first data register, said second data register periodically receiving the contents of said first data register in parallel, said first data register being clocked by a first data clock, and said second data register being clocked by a second data clock, wherein the rate of said first data clock is an integral multiple of the rate of said second data clock, and a code selector connected to said second data register, whereby an output of one of said tap sets is selected for transmission, said output being coupled to the input of said shift register. - View Dependent Claims (25, 26, 27, 28, 32)
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33. A method for transmitting a spread spectrum signal, comprising the steps of:
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serially clocking a data stream into a first data register; transferring in parallel the contents of said first register into a second data register; simultaneously generating a plurality of spread spectrum codes by serially clocking a shift register and, for each spread spectrum code being simultaneously generating, modulo-two adding the contents of at least two stages of said shift register; periodically selecting for transmission one of said spread spectrum codes according to the contents of said second data register; and feeding back said selected one of said spread spectrum codes into said shift register.
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Specification