Method and apparatus for receiving and despreading a continuous phase-modulated spread spectrum signal using self-synchronizing correlators

• US 5,627,856 A
• Filed: 06/07/1995
• Issued: 05/06/1997
• 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:
  US08/480,442
• Time in Patent Office: 699 Days
• Field of Search: 375/206, 375/207, 375/208, 375/209, 375/210, 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

Apparatus and method for despreading a received continuous phase modulated spread spectrum signal includes a power divider for dividing a received spread spectrum signal into a real signal and an imaginary signal. A real CPM correlator demodulates the real signal into I and Q components and separately correlates the real I component and the real Q component without generating a correlation sequence, thereby performing self-synchronizing correlation. Likewise, an imaginary CPM correlator demodulates the imaginary signal into I and Q components and separately correlates the imaginary I component and the imaginary Q component without generating a correlation sequence, thereby performing self-synchronizing correlation. The real I and imaginary I correlation signals are combined into a final I correlation signal, and the real Q and imaginary Q correlation signals are combined into a final Q 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 real CPM correlator for correlating said real signal and generating a real I correlation signal and a real Q correlation signal without generating a correlation sequence, said real CPM correlator comprising a self-synchronizing real I digital correlator and a self-synchronizing real Q digital correlator,

an imaginary CPM correlator for correlating said imaginary signal and generating an imaginary I correlation signal and an imaginary Q correlation signal without generating a correlation sequence, said imaginary CPM correlator comprising a self-synchronizing imaginary I digital correlator and a self-synchronizing imaginary Q digital correlator,

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

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

2. The apparatus of claim 1 wherein said means for combining said real I correlation signal and said imaginary I correlation signal into a final I correlation signal comprises a means for computing a square root of a sum of a square of said real correlation signal and a square of said imaginary correlation signal, and wherein said means for combining said real Q correlation signal and said imaginary Q correlation signal into a final Q correlation signal comprises a means for computing a square root of a sum of a square of said real Q correlation signal and a square of said imaginary Q correlation signal.

3. 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,

generating a real I signal and a real Q signal from said real signal,

correlating said real I signal and said real Q signal and generating a real I correlation signal and a real Q correlation signal without generating a correlation sequence,

generating an imaginary I and an imaginary Q signal from said imaginary signal,

correlating said imaginary I signal and said imaginary Q signal and generating an imaginary I correlation signal and an imaginary Q correlation signal without generating a correlation sequence,

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

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

4. The method of claim 3 wherein said step of combining said real I correlation signal and said imaginary I correlation signal into a final I correlation signal comprises the step of computing a square root of a sum of a square of said real I correlation signal and a square of said imaginary I, correlation signal, and wherein said step of combining said real Q correlation signal and said imaginary Q correlation signal into a final Q correlation signal comprises the step of computing a square root of a sum of a square of said real Q correlation signal and a square of said imaginary Q correlation signal.

5. An apparatus comprising:

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

a real CPM correlator connected to said real signal, said real CPM correlator generating a real I correlation signal and a real Q correlation signal without comparing said real signal against a correlation sequence;

an imaginary CPM correlator connected to said imaginary signal, said imaginary CPM correlator generating an imaginary I correlation signal and an imaginary Q correlation signal without comparing said imaginary signal against a correlation sequence;

an I combining circuit connected to said real I correlation signal and to said imaginary I correlation signal, said I combining circuit outputting a final I correlation signal; and

a Q combining circuit connected to said real Q correlation signal and to said imaginary Q correlation signal, said Q combining circuit outputting a final Q correlation signal.

6. The apparatus of claim 5 wherein said final I correlation Signal comprises a sum one a square of said real I correlation signal and a square of said imaginary I correlation signal, and wherein said final Q correlation signal comprises a sum of a square of said real Q correlation signal and a square of said imaginary Q correlation signal.

7. The apparatus of claim 5 wherein said real CPM correlator comprises

a real I demodulator connected to said real signal,

a real Q demodulator connected to said real signal,

a real I self-synchronizing correlator connected to said real I demodulator, and

a real Q self-synchronizing correlator connected to said real Q demodulator;

and wherein said imaginary CPM correlator comprises

an imaginary I demodulator connected to said imaginary signal,

an imaginary Q demodulator connected to said imaginary signal,

an imaginary I self-synchronizing correlator connected to said imaginary I demodulator, and

an imaginary Q self-synchronizing correlator connected to said imaginary Q demodulator.

8. The apparatus of claim 7 wherein said real I demodulator, said real Q demodulator, said imaginary I demodulator, and said imaginary Q demodulator each output a baseband signal.

9. A method comprising the steps of:

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

generating a real I correlation signal from said real signal without comparing said real signal against a correlation sequence;

generating a real Q correlation signal from said real signal without comparing said real signal against a correlation sequence;

generating an imaginary I correlation signal from said imaginary signal without comparing said imaginary signal against a correlation sequence;

generating an imaginary Q correlation signal from said imaginary signal without comparing said imaginary signal against a correlation sequence;

combining said real I correlation signal and said imaginary I correlation signal into final I correlation signal; and

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

10. The method of claim 9 wherein said step of combining said real I correlation signal and said imaginary I correlation signal into final I correlation signal comprises the step of generating a sum of a square of said real I correlation signal and a square of said imaginary I correlation signal, and wherein said step of combining said real Q correlation signal and said imaginary Q correlation signal into a final Q correlation signal comprises the step of generating a sum of a square of said real Q correlation signal and a square of said imaginary Q correlation signal.

11. The method of claim 9 wherein said step of generating said real I correlation signal from said real signal without comparing said real signal against a correlation sequence comprises the steps of

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

generating a plurality of phase-offset real I signals from said real I signal, and

multiplying said plurality of phase-offset real I signals to generate said real I correlation signal;

wherein the step of generating said real Q correlation signal from said real signal without comparing said real signal against a correlation sequence comprises the steps of

demodulating said real signal with a second non-coherent reference signal orthogonal to said first non-coherent reference signal to generate a real Q signal,

generating a plurality of phase-offset real Q signals from said real Q signal, and

multiplying said plurality of phase-offset real Q signals to generate said real Q correlation signal;

wherein said step of generating said imaginary I correlation signal from said imaginary signal without comparing said imaginary signal against a correlation sequence comprises the steps of

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

generating a plurality of phase-offset imaginary I signals from said imaginary I signal, and

multiplying said plurality of phase-offset imaginary I signals to generate said imaginary I correlation signal;

and wherein the step of generating an imaginary Q correlation signal from said imaginary signal without comparing said real signal against a correlation sequence comprises the steps of

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

generating a plurality of phase-offset imaginary Q signals from said imaginary Q signal, and

multiplying said plurality of phase-offset imaginary Q signals to generate said imaginary Q correlation signal.

12. The apparatus of claim 9 wherein said real I signal, said real Q signal, said imaginary I signal, and said imaginary Q signal are baseband signals.

13. An apparatus comprising:

a power divider having as an input a received spread spectrum signal as outputs a real signal and an imaginary signal;

a real demodulator connected to said real signal and to a non-coherent local reference signal, said real demodulator outputting a demodulated real signal;

a real correlator connected to said demodulated real signal, said real correlator outputting a real correlation signal without comparing said demodulated real signal with a correlation sequence;

an imaginary demodulator connected to said imaginary signal and to said non-coherent local reference signal, said imaginary demodulator outputting a demodulated imaginary signal;

an imaginary correlator connected to said demodulated imaginary signal, said imaginary correlator outputting an imaginary correlation signal without comparing said demodulated imaginary signal with a correlation sequence; and

a combining circuit connected to said real correlation signal and to said imaginary correlation signal.

14. The apparatus of claim 13 wherein said combining circuit generates a sum of a square off said real correlation signal and a square of said imaginary correlation signal.

15. The apparatus of claim 13 further comprising

a second real demodulator connected to said real signal and to a second non-coherent local reference signal orthogonal to said first non-coherent local reference signal, said second real demodulator outputting a second demodulated real signal;

a second real correlator connected to said second demodulated real signal, said second real correlator outputting a second real correlation signal without comparing said second demodulated real signal with a correlation sequence;

a second imaginary demodulator connected to said imaginary signal and to said second non-coherent local reference signal, said second imaginary demodulator outputting a second demodulated imaginary signal;

a second imaginary correlator connected to said second demodulated imaginary signal, said second imaginary correlator outputting a second imaginary correlation signal without comparing said second demodulated imaginary signal with a correlation sequence; and

a second combining circuit connected to said second real correlation signal and to said second imaginary correlation signal.

16. The apparatus of claim 15 wherein said second combining circuit generates a sum of a square of said second real correlation signal and a square of said second imaginary correlation signal.

17. A method comprising the steps of:

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

demodulating said real signal using a first non-coherent local reference signal, and generating a demodulated real signal thereby;

generating a real correlation signal from said demodulated real signal without comparing said demodulated real signal against a correlation sequence;

demodulating said imaginary signal using said first non-coherent local reference signal, and generating a demodulated imaginary signal thereby;

generating an imaginary correlation signal from said demodulated imaginary signal without comparing said demodulated imaginary signal against a correlation sequence; and

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

18. The method of claim 17 wherein said step of combining said real correlation signal and said imaginary correlation signal into a final correlation signal comprises the step of generating a sum of a square of said real correlation signal and a square of said imaginary correlation signal.

19. An apparatus comprising:

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

a real CPM correlator connected to said real signal, said real CPM correlator generating a real I correlation signal and a real Q correlation signal without comparing said real signal against a correlation sequence;

an imaginary CPM correlator connected to said imaginary signal, said imaginary CPM correlator generating an imaginary I correlation signal and an imaginary Q signal without comparing said imaginary signal against a correlation sequence;

wherein said real CPM correlator and said imaginary CPM correlator each comprise an I demodulator connected to an I correlator and a Q demodulator connected to a Q-correlator;

an I combining circuit connected to said real I correlation signal and to said imaginary I correlation signal, said I combining circuit outputting a final I correlation signal; and

a Q combining circuit connected to said real Q correlation signal and to said imaginary Q correlation signal, said Q combining circuit outputting a final Q correlation signal.

20. 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 real CPM correlator for correlating said real signal and generating a real I correlation signal and a real Q correlation signal without generating a correlation sequence, said real CPM correlator comprising

a real I correlation shift register,

a real I correlation multiplier connected to a plurality of taps from different chip locations of said real I correlation shift register,

a real Q correlation shift register, and

a real Q correlation multiplier connected to a plurality of taps from different chip locations of said real Q correlation shift register,

an imaginary CPM correlator for correlating said imaginary signal and generating an imaginary I correlation signal and an imaginary Q correlation signal without generating a correlation sequence, said imaginary CPM correlator comprising

an imaginary I correlation shift register,

an imaginary I correlation multiplier connected to a plurality of taps from different chip locations of said imaginary I correlation shift register,

an imaginary Q correlation shift register, and

an imaginary Q correlation multiplier connected to a plurality of taps from different chip locations of said imaginary Q correlation shift register, and

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

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

21. The apparatus of claim 20 wherein said means for combining said real I correlation signal and said imaginary I correlation signal into a final I correlation signal comprises a means for computing a square root of a sum of a square of said real I correlation signal and a square of said imaginary I correlation signal, and wherein said means for combining said real Q correlation signal and said imaginary Q correlation signal into a final Q correlation signal comprises a means for computing a square root of a sum of a square of said real Q correlation signal and a square of said imaginary Q correlation signal.