Method and apparatus for reception and noncoherent serial correlation of a continuous phase modulated signal

• US 5,629,956 A
• Filed: 06/07/1995
• Issued: 05/13/1997
• Est. Priority Date: 09/09/1994
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Omnipoint Corp. (Deutsche Telekom AG)
• Inventors: Durrant, Randolph L., Burbach, Mark
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): GLUCK, JEFFREY WILLIAM
• Application Number:
  US08/480,167
• Time in Patent Office: 706 Days
• Field of Search: 375/206-210, 375/336, 375/343, 375/200
• US Class Current: 375/150
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04J 14/005 Optical Code Multiplex
• CPC Class Codes: H04L 27/2014 in which the phase changes in a piecewise linear manner during each symbol period, e.g. minimum shift keying, fast frequency shift keying H04L27/201 takes precedence
• CPC Class Codes: H04L 27/2278 using correlation techniques, e.g. for spread spectrum signals
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

A technique for modulating and demodulating continuous phase modulation (CPM) spread spectrum signals and variations thereof. A transmitter encodes M data bits using a selected spread spectrum code, divides the spread spectrum code into a plurality of chip codes (such as even chips and odd chips), independently modulates the even and odd chips with orthogonal carrier signals using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and divides it into a real signal and an imaginary signal. The real signal is connected to a first correlator which divides its input into a real I signal and a real Q signal, serially correlates the real I signal with the odd chips of a chip code and the real Q signal with the even chips of the chip code, and combines the correlation signals into a real correlation signal. The imaginary signal is connected to a second correlator which divides its input into an imaginary I signal and an imaginary Q signal, serially correlates the imaginary I signal with the odd chips of the chip code and the imaginary Q signal with the inverse of the even chips of the chip code, and combines the correlation signals into an imaginary correlation signal. The real and imaginary correlation signals are combined into a unified correlation signal.

Claims

1. An apparatus for despreading a received continuous phase modulated spread spectrum signal comprising:

a power divider for dividing a received spread spectrum signal into a real signal and an imaginary signal,

a first serial correlator for correlating said real signal and generating a real correlation signal,

a second serial correlator for correlating said imaginary signal and generating an imaginary correlation signal,

wherein at least one of said first serial correlator and said second serial correlator comprises an I demodulator and a Q demodulator, and

means for combining said real correlation signal and said imaginary correlation signal.

2. The apparatus of claim 1 wherein said first serial correlator and said second serial correlator each comprises:

a power divider for dividing an input signal into a first signal and a second signal, said first signal and said second signal being duplicates of one another,

means for demodulating said first signal with a first non-coherent local reference signal to generate an I signal,

means for demodulating said second signal with a second non-coherent local reference signal to generate a Q signal, said second non-coherent local reference signal phase offset from said first non-coherent local reference signal by 90 degrees,

an I multiplier for multiplying said I signal with an odd chip signal representing the odd chips of a chip sequence and for generating an I product signal,

a Q multiplier for multiplying said Q signal either with an even chip signal representing the even chips of said chip sequence for said first serial correlator or with an inverse of said even chips for said second serial correlator, and for generating a Q product signal,

an I integrator for integrating said I product signal and generating an I correlation signal,

a Q integrator for integrating said Q product signal and generating a Q correlation signal, and

a summer for combining said I correlation signal and said Q correlation signal into an output correlation signal.

3. The apparatus of claim 2 wherein said odd chip signal and said even chip signal each comprises a tri-valued return-to-zero waveform.

4. The apparatus of claim 1 wherein said means for combining comprises a means for computing a root of a sum of a square of the real correlation signal and a square of the imaginary correlation signal.

5. A non-coherent serial CPM correlator for despreading a received continuous phase modulated spread spectrum signal comprising:

a power divider connected to a received spread spectrum signal, and having as outputs a real signal and an imaginary signal;

a real serial correlator connected to said real signal and having as an output a real correlation signal, said real serial correlator comprising;

a real power divider connected to said real signal, and having as outputs a first signal and a second signal, said first signal and said second signal being duplicates of one another,

a real I demodulator connected to said first signal and to a first non-coherent local reference signal, and having as an output a real I signal,

a real Q demodulator connected to said second signal and to a second non-coherent local reference signal, and having as an output a real Q signal, said second non-coherent local reference signal phase offset from said first non-coherent local reference signal by 90 degrees,

a real I multiplier connected to said real I signal and to an odd chip signal representing the odd chips of a chip sequence and having as an output a real I product signal,

a real Q multiplier connected to said real Q signal and to an even chip signal representing the even chips of said chip sequence and having as an output a real Q product signal,

a real I integrator connected to said real I product signal and having as an output a real I correlation signal,

a real Q integrator connected to said real Q product signal and having as an output a real Q correlation signal, and

a real summer connected to said real I correlation signal and to said real Q correlation signal, and having as an output said real correlation signal;

an imaginary serial correlator connected to said imaginary signal and having as an output an imaginary correlation signal, said imaginary serial correlator comprising;

an imaginary power divider connected to said imaginary signal, and having as outputs a third signal and a fourth signal, said third signal and said fourth signal being duplicates of one another,

an imaginary I demodulator connected to said third signal and to said first non-coherent local reference signal, and having as an output an imaginary I signal,

an imaginary Q demodulator connected to said fourth signal and to said second non-coherent local reference signal, and having as an output an imaginary Q signal,

an imaginary I multiplier connected to said imaginary I signal and to said odd chip signal, and having as an output an imaginary I product signal,

an imaginary Q multiplier connected to said imaginary Q signal and to an inverse of said even chip signal, and having as an output an imaginary Q product signal,

an imaginary I integrator connected to said imaginary I product signal and having as an output an imaginary I correlation signal,

an imaginary Q integrator connected to said imaginary Q product signal and having as an output an imaginary Q correlation signal, and

an imaginary summer connected to said imaginary I correlation signal and to said imaginary Q correlation signal, and having as an output said imaginary correlation signal; and

means for combining said real correlation signal and said imaginary correlation signal into a final correlation signal.

6. The non-coherent serial CPM correlator of claim 5 wherein said odd chip signal and said even chip signal each comprises a tri-valued return-to-zero waveform.

7. The non-coherent serial CPM correlator of claim 5 wherein said means for combining comprises a means for computing a root of a sum of a square of the real correlation signal and a square of the imaginary correlation signal.

8. A method for despreading a received continuous phase modulated spread spectrum signal comprising the steps of:

dividing a received spread spectrum signal into a real signal and an imaginary signal;

correlating said real signal to generate a real correlation signal, said step of correlating said real signal further comprising the steps of

dividing said real signal into a first signal and a second signal, said first signal and said second signal being duplicates of one another,

demodulating said first signal with a first non-coherent local reference signal to generate a real I signal,

demodulating said second signal with a second non-coherent local reference signal to generate a real Q signal, said second non-coherent local reference signal phase offset from said first non-coherent local reference signal by 90 degrees,

multiplying said real I signal with an odd chip signal representing the odd chips of a chip sequence to generate a real I product signal,

multiplying said real Q signal with an even chip signal representing the even chips of said chip sequence to generate a real Q product signal,

integrating said real I product signal to generate a real I correlation signal,

integrating said real Q product signal to generate a real Q correlation signal, and

summing said real I correlation signal and said real Q correlation signal into said real correlation signal,

correlating said imaginary signal to generate an imaginary correlation signal, said step of correlating said imaginary serial further comprising the steps of

dividing said imaginary signal into a third signal and a fourth signal, said third signal and said fourth signal being duplicates of one another,

demodulating said third signal with said first non-coherent local reference signal to generate an imaginary I signal,

demodulating said fourth signal with said second non-coherent local reference signal to generate an imaginary Q signal,

multiplying said imaginary I signal with said odd chip signal to generate an imaginary I product signal,

multiplying said imaginary Q signal with an inverse of said even chip signal to generate an imaginary Q product signal,

integrating said imaginary I product signal to generate an imaginary I correlation signal,

integrating said imaginary Q product signal to generate an imaginary Q correlation signal, and

summing said imaginary I correlation signal and said imaginary Q correlation signal into said imaginary correlation signal; and

combining said real correlation signal and said imaginary correlation signal into a final correlation signal.

9. The method of claim 8 wherein said odd chip signal and said even chip signal each comprises a tri-valued return-to-zero waveform.

10. The method of claim 9 wherein said means for combining comprises a means for computing a root of a sum of a square of the real correlation signal and a square of the imaginary correlation signal.

11. An apparatus for despreading a received continuous phase modulated spread spectrum signal comprising:

a power divider connected to a received spread spectrum signal, having as outputs a real signal and an imaginary signal,

a first serial correlator connected to said real signal and having as an output a real correlation signal,

a second serial correlator connected to said imaginary signal and having as an output an imaginary signal, and

a calculation circuit connected to said first serial correlator and said second serial correlator, said calculation circuit outputting a unified correlation signal corresponding to a combination of said real correlation signal and said imaginary correlation signal.

12. The apparatus of claim 11 wherein said first serial correlator and said second serial correlator each comprises:

a power divider having as outputs a first signal and a second signal, said first signal and said second signal being duplicates of one another,

an I demodulator connected to said first signal and to a first non-coherent local reference signal, and having as an output an I signal,

a Q demodulator connected to said second signal and to a second non-coherent local reference signal, and having as an output a Q signal, said second non-coherent local reference signal phase offset from said first non-coherent local reference signal by 90 degrees,

an I multiplier connected to said I signal and to an odd chip signal representing the odd chips of a chip sequence, and having as an output an I product signal,

a Q multiplier connected to said Q signal and to either an even chip signal representing the even chips of said chip sequence for said first serial correlator or to an inverse of said even chips for said second serial correlator, and having as an output a Q product signal,

an I integrator connected to said I product signal and having as an output an I correlation signal,

a Q integrator connected to said Q product signal and having as an output a Q correlation signal, and

a summer connected to said I correlation signal and to said Q correlation signal, and outputting a correlation signal.

13. The apparatus of claim 12 wherein said odd chip signal and said even chip signal each comprises a tri-valued return-to-zero waveform.

14. The apparatus of claim 11 wherein said unified correlation signal represents a root of a sum of a square of said real correlation signal and a square of said imaginary correlation signal.