Piecewise coherent, combined frequency and phase-shift-keyed signal demodulator

• US 4,247,943 A
• Filed: 05/21/1979
• Issued: 01/27/1981
• Est. Priority Date: 05/21/1979
• Status: Expired due to Term

• Current Assignee: Northrop Corporation
• Original Assignee: Northrop Corporation
• Inventors: Malm, Robert
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/041,053
• Time in Patent Office: 617 Days
• Field of Search: 179/15 BC, 178/66 R, 178/88, 325/320, 329/110, 329/112, 329/124, 329/122, 329/153, 329/154, 329/50, 340/171 R, 340/207 R, 340/207 P, 340/170, 364/484, 364/701, 364/702, 364/703, 364/117, 364/480, 375/53, 375/54, 375/80, 375/81, 375/82, 375/83, 375/86, 375/90, 375/97, 375/79, 375/46, 375/91, 455/255, 455/258, 455/260, 331/1 A, 331/1 R, 331/25, 370/19, 370/20
• US Class Current: 375/323
• CPC Class Codes: H04L 27/32 Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26

Abstract

A system for demodulating piecewise coherent, combined frequency and phase-shift-keyed signals that are modulateed by orthogonal or biorthogonal code words. Rather than maintain local reference signals in phase-lock with the received signal, the system mixes the received signal with both sine and cosine signals at both the mark and the space frequencies to obtain multiple outputs which are correlated with each of the code words utilized by the system to determine the particular code words that have been received.

Claims

1. A system for obtaining a demodulated signal from a piecewise coherent, combined frequency and phase-shift-keyed signal modulated by code words selected from a predetermined set of such code words comprising:

a. mark-frequency synthesizer means for synthesizing a sine and a cosine signal at the mark frequency of the signal to be demodulated,

b. space-frequency synthesizer means for generating a sine and a cosine signal at the space frequency of the signal to be demodulated,

c. a first mixer which mixes the signal to be demodulated with the sine wave from the mark-frequency synthesizer means,

d. a second mixer which mixes the signal to be demodulated with the cosine signal from the mark-frequency synthesizer means,

e. a third mixer which mixes the signal to be demodulated with the cosine signal from the space frequency synthesizer means,

f. a fourth mixer which mixes the signal to be demodulated with the sine signal from the space-frequency synthesizer means,

g. a first integrator and dumper which integrates and dumps the output of the first mixer,

h. a second integrator and dumper which integrates and dumps the output of the second mixer,

i. a third integrator and dumper which integrates and dumps the output of the third mixer,

j. a fourth integrator and dumper which integrates and dumps the output of the fourth mixer,

k. a first analog to digital converter which converts the analog output of the first integrator and dumper into digital data,

l. a second analog to digital converter which converts the analog output of the second integrator and dumper into digital data,

m. a third analog to digital converter which converts the analog output of the third integrator and dumper into digital data,

n. a fourth analog to digital converter which converts the analog output of the fourth integrator and dumper into digital data, and

o. an arithmetic processor for correlating each of the code words within the set of code words with combinations of the outputs of the first, second, third and fourth analog to digital converters and selecting the largest of the correlations, said processor having as its output the demodulated signal representing the code words which produced the largest correlation.

2. The system of claim 1 wherein the set of code words is a set of orthogonal code words.

3. The system of claim 1 wherein the set of code words is a set of biorthogonal code words.

4. The system of claim 2 wherein the correlation by the arithmetic processor of each of the possible code words with combinations of the outputs of the first, second, third and fourth analog to digital converters comprises:

a. for periods of time during which the demodulated signal, which was demodulated δ

periods previously, is likely to have been demodulated correctly, the correlation of each of the code words with the sum of the product of the output of the first analog to digital converter with the code word received δ

periods previously, and the correlation of each of the code words with the sum of the product of the output of the second analog to digital converter with the code word received δ

periods previously and the product of the output of the third analog to digital converter with the complement of the code word received δ

periods previously, and

b. for periods of time during which the demodulated signal, which was demodulated δ

periods previously, is not likely to have been demodulated correctly, the correlation of each of the code words with the sum of the outputs of the first and fourth analog to digital converters and the correlation of each of the code words with the sum of the outputs of the second and third analog to digital converters.