Spread spectrum communications system

• US 5,216,693 A
• Filed: 11/13/1991
• Issued: 06/01/1993
• Est. Priority Date: 11/13/1990
• Status: Expired due to Term

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Nakamura, Masaru
• Primary Examiner(s): SWANN, TOD R
• Application Number:
  US07/791,250
• Time in Patent Office: 566 Days
• Field of Search: 380/34, 375/1
• US Class Current: 375/142
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04J 13/0022 PN, e.g. Kronecker
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04J 2013/0037 Multilevel codes

Abstract

A spread spectrum communications system in which one of a transmitter or a receiver uses a PN code sequence while another side uses a code sequence to which is used constant pattern signals comprising an arbitrary combination of three values of positive, negative and zero for each code of a same PN code sequence. A correlator performs cross correlation process of a code sequence to which the PN code sequence and the pattern signal have been used.

Claims

1. A spread spectrum communications system comprising:

a transmitter having first generating means for generating a first code signal which periodically varies, modulation means for modulating said first code signal in accordance with input information supplied to said transmitter, and output means for outputting a transmit signal which is modulated by said modulation means; and

a receiver which receives the transmit signal from said transmitter, said receiver having second generating means for generating a second code signal which periodically varies, said second code signal having a predetermined relationship with respect to said first code signal, synchronizing means for synchronizing said second code signal with said transmit signal based on an auto correlation relationship between said second code signal and said transmit signal, and a demodulation means for demodulating said transmit signal synchronized with said second code signal in a state where said synchronizing means synchronizes said second code signal with said transmit signal so that reproducing data corresponding to said input information supplied to said transmitter is obtained,

wherein one of said first and second code signals varies in accordance with a first code sequence which is a pseudo noise code sequence formed of a plurality of chips, and another one of said first and second signals varies in accordance with a second code sequence divided into a plurality of chips each of which corresponds to one of the chips of said pseudo noise code sequence, each of the chips of said second code sequence being formed of a first period having a positive value, a second period having a zero value and third period having a negative value.

2. A spread spectrum communications system as claimed in claim 1, wherein one of said first and second generating means has a signal generator for generating a three state code which varies between positive, zero and negative values in accordance with a predetermined pattern, and multiplication means for multiplying the pseudo noise code sequence by the three state code so that said second code sequence is obtained.

3. A spread spectrum communications system as claimed in claim 2, wherein said three state code has a pattern in which a first section having a positive value, a second section having a zero and a third section having a negative value are arranged in this order.

4. A spread spectrum communications system as claimed in claim 3, wherein said first period has a length of xT, the second period has a length of (1-2x)T, and the third period has a length of xT, where by 0<

x<

0.5, and T is a total length of the PN code of the three state code.

5. A spread spectrum communications system as claimed in claim 1, wherein said synchronizing means has a correlator for correlating said second code signal with said transmit signal and for outputting a correlate value corresponding to an auto correlation relationship between a control signal and said transmit signal, and has a voltage control oscillator to which said auto correlation value is supplied, said voltage control oscillator to which said auto correlation value is supplied controlling said second code signal so as to synchronize said second code signal with an input data signal.

6. A spread spectrum communications system as claimed in claim 1, wherein said second code signal generated by said second generating means of said receiver varies in accordance with the pseudo noise sequence.

7. A spread spectrum communications system as claimed in claim 4, wherein said demodulation means has a wave-form shaping circuit which generates said correlate value and demodulates said transmit signal in accordance with said auto correlation value.

8. A spread spectrum communication system comprising:

a transmitter having reference signal generating means for generating a reference signal which periodically varies in accordance with a pseudo noise code sequence formed of a plurality of chips, signal generating means for generating a plurality of code signals based on said reference signal, each of said code signals periodically varying in accordance with the pseudo noise code sequence, and phases of said code signals differing from each other, modulation means for modulating each of said code signals in accordance with a corresponding one of input data sequences supplied to said transmitter, multiplexing means for multiplexing the code signals which are modulated by said modulation means so that a multiplex signal is obtained, said multiplex signal varying in accordance with a code sequence formed of a plurality of chips each of which corresponds to one of the chips of said code sequence and each having a first section, a second section and a third section which are arranged in this order, the first section having a first predetermined value, the third section having a second predetermined value, and each of the first and second predetermined values in the code signals which are modulated by said modulation means are arranged in the second section, and outputting means for outputting a transmit signal which is obtained based on the multiplex signal;

a receiver which receives the transmit signal from said transmitter, said receiver having a code signal generating means for generating a second code signal which periodically varies in accordance with the pseudo noise code sequence, synchronizing means for synchronizing the second code signal with one of a plurality of components corresponding to the code signals multiplexed in said transmit signal based on an auto correlation relationship between said second code signal and said transmit signal, and demodulation means for demodulating the transmit signal in synchronization with the second code signal in a state where said synchronizing means synchronizes said second code signal with said one of the plurality of components corresponding to the code signals multiplexed in said transmit signal so that reproducing data corresponding to one of a plurality of data sequences supplied to said transmitter is obtained.

9. A spread spectrum communications system as claimed in claim 8, wherein said first predetermined value is a positive value, and said second predetermined value is a negative value.

10. A spread spectrum communications system as claimed in claim 8, wherein said first predetermined value is a negative value, and said second predetermined value is a positive value.

11. The spread spectrum communication system as claimed in claim 8,

wherein said modulation means has a shift register which shifts a phase of said first code signal, and generates a delay pseudo noise code which is inputted to said output means.

12. The spread spectrum communication system as claimed in claim 8,

wherein said multiplexing means has a multiplexer which selects an output signal corresponding to a predetermined signal.

13. The spread spectrum communications system as claimed in claim 8,

wherein said modulation means has an exclusive-OR circuit for said data signal and said first code signal.

14. The spread spectrum communications system as claimed in claim 8,

wherein said second code generating means includes a shift register which generates a phase of said pseudo noise code corresponding to each data channel of said transmit signal.

15. The spread spectrum communications system as claimed in claim 8,

wherein demodulation means includes a plural number of said correlator for demodulating several data in said one chip of said pseudo noise.

16. A spread spectrum communications system comprising;

a transmitter having reference signal generating means for generating a reference signal which periodically varies in accordance with a pseudo noise code sequence formed of a plurality of chips, signal generating mean for generating a plurality of code signals based on said reference signal, each of said code signals periodically varying in accordance with the pseudo noise code sequence, and phases of said code signals differing from each other, modulation means for modulating each of said code signals in accordance with a corresponding one of input data sequences supplied to said transmitter, multiplexing means for multiplexing the code signals which are modulated by said modulation means so that a multiplex signal is obtained, said multiplex signal corresponding to the pseudo noise code for a first section with respect to a single chip time of the pseudo noise code, to the same pseudo noise code differing only by a phase and transfer data for each section where a single chip time is divided over a plural number of sections for a second section, and to a code opposite the pseudo noise code for a third section;

a receiver which receives the transmit signal from said transmitter, said receiver having a code signal generating means for generating a second code signal which periodically varies in accordance with the pseudo noise code sequence, synchronizing means for synchronizing the second code signal with one of a plurality of components corresponding to the code signals multiplexed in said transmit signal based on an auto correlation relationship between said second code signal and said transmit signal, and demodulation means for demodulation the transmit signal in synchronization with the second code signal in a state where said synchronizing means synchronizing said second code signal with said one of the plurality of components corresponding to the code signals multiplexed in said transmit signal so that reproducing data corresponding to one of a plurality of data sequences supplied to said transmitter is obtained.

17. A spread spectrum communications system as claimed in claim 16, wherein said first section has a first predetermined value which is a positive value, and said third section has a second predetermined value which is a negative value.

18. A spread spectrum communications system as claimed in claim 16, wherein said first section has a first predetermined value which is a negative value, and said third section has a second predetermined value which is a positive value.

19. The spread spectrum communication system as claimed in claim 16, wherein said modulation means has a shift register which shifts a phase of said first code signal, and generates a delay pseudo noise code which is inputted to said output means.

20. The spread spectrum communication system as claimed in claim 16, wherein said multiplexing means has a multiplexer which selects an output signal corresponding to a predetermined signal.

21. The spread spectrum communication system as claimed in claim 16, wherein said modulation means has an exclusive-OR circuit for said data signal and said first code signal.

22. The spread spectrum communications system as claimed in claim 16, wherein said second code generating means includes a shift register which generates a phase of said pseudo noise code corresponding to each data channel of said transmit signal.

23. The spread spectrum communications system as claimed in claim 16, wherein said demodulation means includes a plural number of correlators for demodulating several data in said one chip of said pseudo noise.