Spread spectrum code tracking loop

• US 4,285,060 A
• Filed: 02/28/1978
• Issued: 08/18/1981
• Est. Priority Date: 02/28/1978
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Cobb, Raymond F., Pelchat, M. Guy
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/882,069
• Time in Patent Office: 1,267 Days
• Field of Search: 325/30, 325/32, 325/65, 325/474, 325/475, 325/476, 325/44, 325/58, 325/419, 325/442, 325/324, 325/346, 329/120, 329/124, 375/1, 375/58, 375/83, 375/120, 455/304
• US Class Current: 375/376
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop

Abstract

A code tracking loop for a spread spectrum receiver includes a pair of mixer circuits to which phase offset or relatively delayed pseudo noise code signals are applied and combined with an incoming IF spread spectrum signal. The output of the mixers are coupled to a sum and difference hybrid. The hybrid produces a sum signal corresponding to the sum of the mixer outputs and a difference signal corresponding to the difference between the mixer outputs. These sum and difference signals are separately filtered, amplified and then coupled to a further mixer or phase detector. Appropriate AGC circuitry is controlled by the envelope of the sum signal to adjust the gains of the respective amplifiers. The output of the phase detector is proportional to the difference between the squares of the outputs of the hybrid and represents the phase of the sum signal relative to the difference signal. This phase-representative signal is coupled through a tracking loop filter to control the voltage controlled clock for the local PN code generator. A significant advantage of the inventive system is that even if the gains of the separate channels are not equal, this gain difference does not erroneously affect the output of the phase detector.

Claims

1. A code timing recovery system for a spreadspectrum receiver comprising:

first means for combining a received spreadspectrum signal containing a transmitted random sequence of pulses with first and second locally generated random sequences of pulses having a prescribed phase difference therebetween, to thereby produce first and second output signals representative of correlations of the random sequence of pulses contained in said received spread-spectrum signal with said first and second locally generated random sequences of pulses, respectively, and

second means, coupled to said first means, for controlling the timing of said first and second locally generated random sequence of pulses in accordance with the difference between the squares of said first and second output signals.

2. In a code timing recovery system for a spread-spectrum receiver wherein a pair of phase displaced, locally generated random signal sequences are correlated with a random signal sequence contained in a transmitted spread-spectrum signal, to obtain first and second correlation signals, and said first and second correlation signals are coupled through first and second amplifier channels to a signal combining circuit for deriving a control signal by which the timing of said pair of locally generated random signal sequences relative to the random signal sequence contained in the transmitted spread-spectrum signal is controlled,

the improvement wherein the timing control imparted by said derived control signal is independent of the gains of said first and second amplifier channels.

3. In a code timing recovery system for a spread-spectrum receiver wherein a pair of phase displaced, locally generated random signal sequences are correlated with a random signal sequence contained in a transmitted spread-spectrum signal to obtain first and second correlation signals, and said first and second correlation signals are coupled through first and second amplifier channels and combined to provide a control signal by which the timing of said pair of locally generated random signal sequences relative to the random signal sequence contained in the transmitted spread-spectrum signal is adjusted, the improvement comprising the step of generating said control signal to adjust said timing independent of the gains of said first and second amplifier channels.

4. A code timing recovery system for a spreadspectrum receiver comprising:

first means for combining a received spreadspectrum signal containing a transmitted random signal sequence with first and second locally generated random signal sequences having a prescribed phase difference therebetween to thereby produce first and second output signals representative of correlations of the random signal sequence contained in said received spread-spectrum signal with said first and second locally generated random signal sequences, respectively,

second means, coupled to said first means, for generating a pair of third and fourth output signals respectively representative of the sum of and difference between said first and second output signals, respectively,

third means, coupled to said second means, for combining said third and fourth output signals to produce a fifth output signal; and

fourth means, coupled to said third means, for controlling the timing of said first and second locally generated random signal sequences in accordance with said fifth output signal.

5. A code timing recovery system according to claim 4, wherein said third means comprises means for producing said fifth output signal in accordance with the product of said third and fourth output signals.

6. A code timing recovery system according to claim 4, further including fifth means, coupled between said second and third means, for respectively amplifying said third and fourth output signals.

7. A code timing recovery system according to claim 5, further including fifth means, coupled between said second and third means, for respectively amplifying said third and fourth output signals.

8. A code timing recovery system according to claim 6, further including sixth means for controlling the amplification of said third and fourth output signals in accordance with said third output signal.

9. A code timing recovery system according to claim 7, further including sixth means for controlling the amplification of said third and fourth output signals in accordance with said third output signal.

10. A method for controlling the timing of a locally generated code in a spread-spectrum receiver comprising the steps of:

combining a received spread-spectrum signal containing a transmitted random signal sequence with first and second locally generated random signal sequences having a prescribed phase difference therebetween to thereby produce first and second signals representative of correlations of the random signal sequence contained in said received spread-spectrum signal with said first and second locally generated random signal sequences, respectively,

generating a pair of third and fourth signals respectively representative of the sum of and difference between said first and second signals, respectively,

combining said third and fourth signals to produce a fifth signal; and

controlling the timing of said first and second locally generated random signal sequences in accordance with said fifth signal.

11. A method according to claim 10, wherein said combining step comprises producing said fifth signal in accordance with the product of said third and fourth signals.

12. A method according to claim 10, further including the step of respectively amplifying said third and fourth signals.

13. A method according to claim 11, further including the step of respectively amplifying said third and fourth signals.

14. A method according to claim 12, further including the step of controlling the amplification of said third and fourth signals in accordance with said third signal.

15. A method according to claim 13, further including the step of controlling the amplification of said third and fourth signals in accordance with said third signal.