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

• US 5,610,940 A
• Filed: 06/07/1995
• Issued: 03/11/1997
• 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:
  US08/480,668
• Time in Patent Office: 643 Days
• Field of Search: 375/200, 375/206, 375/208, 375/209, 375/210, 375/343, 375/274
• 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 real CPM correlator which demodulates its input into a real I signal and a real Q signal, separately 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 an imaginary CPM correlator which demodulates its input into an imaginary I signal and an imaginary Q signal, separately 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. 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,

demodulating said real signal into a real I signal and a real Q signal,

demodulating said imaginary signal into an imaginary I signal and an imaginary Q signal,

correlating said real I signal with the odd chips of a chip sequence to generate a real I correlation signal,

correlating said real Q signal with the even chips of said chip sequence to generate a real Q correlation signal,

correlating said imaginary I signal with said odd chips to generate an imaginary I correlation signal,

correlating said imaginary Q signal with said even chips to generate an imaginary Q signal,

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

2. The method of claim 1 wherein said step of combining further comprises the steps of:

summing said real I correlation signal and said real Q correlation signal to generate a real correlation signal,

summing said imaginary I correlation signal and said imaginary Q correlation signal to generate an imaginary correlation signal, and

computing a square root of a sum of a square of said real correlation signal and a square of said imaginary correlation signal to generate said final correlation signal.

3. 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 correlation signal,

an imaginary CPM correlator for correlating said imaginary signal and generating an imaginary correlation signal,

wherein at least one of said real CPM correlator and said imaginary CPM correlator comprises an I demodulator and a Q demodulator, and

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

4. The apparatus of claim 3 wherein said real CPM correlator and said imaginary CPM correlator each comprises:

means for dividing an input signal into a first signal and a second signal,

an I demodulator for demodulating said first signal into an I signal, said I demodulator further comprising a first local reference signal not phase matched with a carrier of said spread spectrum signal,

a Q demodulator for demodulating said second signal into a Q signal, said Q demodulator further comprising a second local reference signal having the same frequency as said first local reference signal and phase offset by 90 degrees from said first local reference signal,

an I correlator for correlating said I signal with the odd chips of a chip sequence and generating an I correlation signal,

a Q correlator for correlating said Q signal with the even chips of said chip sequence for said real CPM correlator or with the inverse of said even chips for said imaginary CPM correlator, and for generating a Q correlation signal, and

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

5. The apparatus of claim 4 wherein said I correlator comprises an I register having a plurality of chip locations for receiving an input signal, a plurality of I multipliers for comparing alternating ones of said chip locations with said odd chips and generating a plurality of I comparison signals, and an I summer for combining said I comparison signals into an I correlation signal, and wherein said Q correlator comprises a Q register having a plurality of chip locations for receiving an input signal, a plurality of Q multipliers for comparing alternating ones of said chip locations with said even chips for said real CPM correlator or with the inverse of said even chips for said imaginary CPM correlator and generating a plurality of Q comparison signals, and a Q summer for combining said Q comparison signals into a Q correlation signal.

6. The apparatus of claim 3 wherein said means for combining comprises means for generating a square root of a sum of a square of said real correlation signal and a square of said imaginary correlation signal.

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

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

a real CPM correlator connected to said real signal and having as an output a real correlation signal, said real CPM correlator comprising a real I demodulator connected to said real signal and having as an output a real I signal, and a real Q demodulator connected to said real signal and having as an output a real Q signal;

an imaginary CPM correlator connected to said imaginary signal and having as an output an imaginary correlation signal, said imaginary CPM correlator comprising an imaginary I demodulator connected to said imaginary signal and having as an output an imaginary I signal, and an imaginary Q demodulator connected to said imaginary signal and having as an output an imaginary Q signal; and

a calculation circuit connected to said real correlation signal and said imaginary correlation signal, and having as an output a unified correlation signal.

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

a real power divider connected to said real signal, and having as outputs a first real signal and a second real signal, said real I demodulator and said real Q

demodulator each connected to different ones of said first real signal and said second real signal,

a first local reference signal not phase matched with a carrier of said spread spectrum signal, said first local reference signal connected to said real I demodulator,

a second local reference signal having the same frequency as said first local reference signal and phase offset by 90 degrees from said first local reference signal, said second local reference signal connected to said real Q demodulator,

a real I correlator connected to said real I signal and to the odd chips of a chip sequence, and having as an output a real I correlation signal,

a real Q correlator connected to said real Q signal and to the even chips of said chip sequence, 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 a real correlation signal;

and

wherein said imaginary CPM correlator comprises

an imaginary power divider connected to said imaginary signal, and having as outputs a first imaginary signal and a second imaginary signal, said imaginary I demodulator and said imaginary Q demodulator each being connected to different ones of said first imaginary signal and said second imaginary signal,

a first connection between said first local reference signal and said imaginary I demodulator,

a second connection between said second local reference signal and said imaginary Q demodulator,

an imaginary I correlator connected to said imaginary I signal and to said odd chips, and having as an output an imaginary I correlation signal,

an imaginary Q correlator connected to said imaginary Q signal and to the inverse of said even chips, 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 an imaginary correlation signal.

9. The apparatus of claim 8 wherein said real I correlator and said imaginary I correlator each comprises:

an I register having a plurality of chip locations for receiving an I signal,

a plurality of I multipliers connected to alternating ones of said chip locations and to said odd chips, said I multipliers outputting a plurality of I comparison signals, and

an I summer connected to said I comparison signals and having as an output an I correlation signal, and wherein said real Q correlator and said imaginary Q correlator each comprises;

a Q register having a plurality of chip locations for receiving a Q signal,

a plurality of Q multipliers connected to alternating ones of said chip locations and to said even chips for said real Q correlator or to the inverse of said even chips for said imaginary Q correlator, said Q multipliers outputting a plurality of Q comparison signals, and

a Q summer connected to said Q comparison signals and having as an output a Q correlation signal.

10. The apparatus of claim 7 wherein said unified correlation signal comprises a square root of a sum of a square of said real correlation signal and a square of said imaginary correlation signal.

11. A non-coherent CPM receiver comprising

a signal divider connected to a received continuous phase modulated (CPM) signal, and having as outputs a real signal and an imaginary signal;

a real CPM correlator connected to said real signal, said real CPM correlator comprising

a real I demodulator and correlator connected to said real signal and to a first chip signal generated using a non-coherent clock, and having as an output a real I correlation signal,

a real Q demodulator and correlator connected to said real signal and to a second chip signal generated using said non-coherent clock, and having as an output a real Q correlation signal, and

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

an imaginary CPM correlator connected to said imaginary signal, said imaginary CPM correlator comprising

an imaginary I demodulator and correlator connected to said imaginary signal and to said first chip signal, and having as an output an imaginary I correlation signal,

an imaginary Q demodulator and correlator connected to said imaginary signal and to an inverse of said second chip signal, and having as an output an imaginary Q correlation signal, and

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

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

12. The non-coherent CPM receiver of claim 11 wherein

said real combining circuit comprises a real summer connected to said real I correlation signal and to said real Q correlation signal, and a real squaring circuit connected to said real summer,

said imaginary combining circuit comprises an imaginary summer connected to said imaginary I correlation signal and to said imaginary Q correlation signal, and an imaginary squaring circuit connected to said imaginary summer, and

said combining circuit comprises a summer connected to said real correlation signal and said imaginary correlation signal, and a square root circuit connected to said summer.

13. The non-coherent CPM receiver of claim 11 wherein said first chip signal comprises every other chip of a pseudo-random chip sequence, and wherein said second chip signal comprises the remaining chips of said pseudo-random chip sequence.

14. The non-coherent CPM receiver of claim 13 wherein said first chip signal comprises the odd chips of said pseudo-random chip sequence, and said second chip signal comprises the even chips of said pseudo-random chip sequence.