SYNCHRONIZING SYSTEMS IN THE PRESENCE OF NOISE

• US 3,706,933 A
• Filed: 09/17/1963
• Issued: 12/19/1972
• Est. Priority Date: 09/17/1963
• Status: Expired due to Term

• Current Assignee: Carl D. Herold Jr, Frederick W. Bidell, James H. Lindholm
• Original Assignee: Carl D. Herold Jr, Frederick W. Bidell, James H. Lindholm
• Inventors: Bidell, Frederick W., Herold, Carl D. Jr., Lindholm, James H.
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): Birmiel, H. A.
• Application Number:
  US04/310,969
• Time in Patent Office: 3,381 Days
• Field of Search: 325/474,477,479,32,42,323
• US Class Current: 375/149
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04K 3/228 Elimination in the received signal of jamming or of data corrupted by jamming interference suppression in receivers H04B1/10
• CPC Class Codes: H04L 7/043 Pseudo-noise [PN] codes variable during transmission synchronisation of spread spectrum receivers H04B1/69

Abstract

11. In the receiver of a pseudo-random communication system in which a locally generated coded signal is to be correlated with a received similarly coded signal, means for recognizing the synchronization of said local and received signals in the presence of undesired received energy, such as noise, interference, jamming or combinations thereof, which comprises: a signal channel having input and output terminals and including in series connection between said input and output terminals a first mixer circuit, a first intermediate frequency amplifier having a bandwidth much narrower than the bandwidth of said received signal, and a first detector and filter circuit; a reference channel having an input terminal in common with said signal channel, and an output terminal, said reference channel including in series connection between its input and output terminals a second mixer circuit, a second intermediate frequency amplifier having substantially the same bandwidth as said first intermediate frequency amplifier, and a second detector and filter; means for applying said received coded signal plus undesired energy to said common input terminal; means for applying said locally generated coded signal to said first mixer; means for applying an orthogonally related version of said locally generated coded signal to said second mixer; said signal channel having a gain factor to produce a signal level at the output terminal of said signal channel lower than the signal level at the output terminal of said reference channel when said received and locally generated coded signals are not synchronized and to produce a larger signal level at the output terminal of said signal channel than the signal level at the output terminal of said reference channel when said received and locally generated coded signals are synchronized; and, means connected to the output terminals of said signal and reference channels for comparing the levels of signals appearing thereat and operative to provide an output signal indicative of which level is higher.

Claims

1. In a receiver for a pseudo-random communication system in which a locally generated coded signal is to be correlated with a received similarly coded signal, means for recognizing the synchronization of said local and received signals in the presence of undesired receiveD energy, such as noise, interference, jamming, or combinations thereof, which comprise:

a signal channel, a reference channel, means for applying said received coded signal plus undesired signal energy in parallel to said signal and reference channels, means for applying said locally generated coded signal to said signal and reference channels, means included in said reference channel to continually derive an output signal exclusively representative of uncorrelated received energy, means included in said signal channel to derive an output signal representative of correlated signal energy upon synchronization of said local and received signals, said reference channel being gain prejudiced to provide a larger output signal level than said signal channel when said local and received signals are not synchronized and to provide a smaller output signal level than said signal channel when said local and received coded signals are synchronized, and means for comparing the output signal levels from said signal and reference channels and operative to provide an output signal indicating from which of said channels the output signal level is greater.

2. A receiver in accordance with claim 1 including means for phase-locking said locally generated coded signal with said received coded signal in said signal channel in advance of correlation in said reference channel, and wherein said signal comparison means is operative to indicate whether said received energy included said coded signal.

3. A receiver in accordance with claim 1 including means for varying the timing rate of said locally generated code signal to search for a condition of synchronization, and means for applying the output signal from said signal comparison means to said timing rate varying means, said last-mentioned means being operative in response to synchronization of said local and received signals to disable said timing rate varying means.

4. In a receiver for a pseudo-random communication system in which a locally generated coded signal is to be correlated with a received similarly coded signal, means for recognizing the synchronization of said local and received signals in the presence of undesired received energy such as noise, interference, jamming, or combinations thereof, which comprises:

a signal channel having input and output terminals and including in series connection between said input and output terminals a mixer circuit, a first intermediate-frequency amplifier having a bandwidth substantially equal to the effective bandwidth of said received signal, a second intermediate-frequency amplifier having a bandwidth much narrower than the bandwidth of said first intermediate frequency amplifier, and a first detector and filter circuit;

a reference channel having an input terminal, a mixer and a first intermediate frequency amplifier in common with said signal channel, and an output terminal, said reference channel further including, between said first intermediate frequency amplifier and said output terminal, a second detector and filter circuit;

means for applying said received coded signal plus undesired energy to said common input terminal;

means for applying said locally generated coded signal to said mixer;

said second intermediate frequency amplifier having a gain factor to produce a signal level at the output terminal of said signal channel lower than the signal level at the output terminal of said reference channel when said local and received coded signals are not synchronized and to produce a larger signal level at the output terminal of said signal channel than the signal level at the output terminal of said reference channel when said local and received coded signals are synchronized; and

, means connected to the output terminals of said signal and reference channels for comparing the levels of the signals appearing thereat and operative to provide an output signal indicative of which level is higher.

5. A receiver in accordance with claim 4 including means for phase-locking said locally generated coded signal with said received coded signal in said signal channel in advance of synchronization in said reference channel, and wherein said signal comparison means is operative to indicate whether said received energy includes said coded signal.

6. A receiver in accordance with claim 4 further including an automatic gain control amplifier connected between the output terminal of said signal channel and said first intermediate frequency amplifier for applying an automatic gain control signal to said first intermediate frequency amplifier, means for varying the timing rate of said locally generated code signal to search for synchronization, and wherein said signal comparison means comprises a differential amplifier having a pair of input terminals respectively connected to the output terminals of said signal and reference channels and an output terminal, and means operative in response to the signal appearing at the output terminal of said differential amplifier upon synchronization of said local and received coded signals to disable said timing rate varying means.

7. A receiver in accordance with claim 4 including, in said reference channel, a third amplifier connected between said first intermediate frequency amplifier and said second detector and filter circuit, said third amplifier having substantially the same bandwidth as said second intermediate frequency amplifier and being offset in center frequency from the center frequency of said second amplifier by at least two multiples of the bandwidth of said second amplifier.

8. A receiver in accordance with claim 4 further including an automatic gain control circuit connected between the output terminal of said signal channel and said first intermediate frequency amplifier, a third amplifier in said reference channel connected between said first intermediate frequency amplifier and said second detector and filter circuit, said third amplifier having substantially the same bandwidth as said second intermediate frequency amplifier and having a center frequency offset from the center frequency of said second amplifier by at least two multiples of the bandwidth of said second amplifier, means for varying the timing rate of said locally generated code signal to search for synchronization, and wherein said signal comparison means comprises a differential amplifier having a pair of input terminals respectively connected to the output terminals of said signal and reference channels and an output terminal, and means operative in response to the signal appearing at the output terminal of said differential amplifier upon synchronization of said local and received coded signals to disable said timing rate varying means.

9. A receiver in accordance with claim 4 including, in said reference channel, a third intermediate frequency amplifier connected between said first intermediate frequency amplifier and said second detector and filter circuit, said third intermediate frequency amplifier having a bandwidth at least as wide as the bandwidth of said first intermediate frequency amplifier and a notch characteristic which has substantially the same bandwidth as said second intermediate frequency amplifier centered about the common intermediate frequency of said first and second intermediate frequency amplifiers.

10. A receiver in accordance with claim 4 further including an automatic gain control circuit connected between the output terminal of said signal channel and said first intermediate frequency amplifier, a third amplifier in said reference channel connected between said first intermediate frequency amplifier and said second detector and filter circuit, said third amplifier having a bandwidth at least as wide as the bandwidth of said first intermediate frequency amplifier and a notch characteristic which has substantially the same bandwidth as said second intermediate frequency amplifier centered about the common intermediate frequency of said first and second intermediate frequency amplifiers, means for varyIng the timing rate of said locally generated coded signal to search for synchronization, and wherein said signal comparison means comprises a differential amplifier having a pair of input terminals respectively connected to the output terminals of said signal and reference channels, and an output terminal, and means operative in response to the signal appearing at the output terminal of said differential amplifier upon synchronization of said local and received coded signals to disable said timing rate varying means.

12. A receiver in accordance with claim 11 further including an automatic gain control circuit connected between the output terminal of said reference channel and said first and second intermediate frequency amplifier and operative to apply an automatic gain control signal to both said first and second amplifiers, means for varying the timing rate of said locally generated coded signal to search for synchronization in said signal channel, and wherein said signal comparison means comprises a differential amplifier having a pair of input terminals respectively connected to the output terminals of said signal and reference channels, and an output terminal, and means operative in response to the signal appearing at the output terminal of said differential amplifier upon synchronization of said received and locally generated coded signals to disable said timing rate varying means.

13. A receiver in accordance with claim 11 wherein said first and second intermediate frequency amplifiers have substantially the same gain and further including an attenuator connected between said first mixer circuit and said first intermediate amplifier having an attenuation factor to provide the aforesaid gain factor in said signal channel.

14. In a receiver for a correlation communication system in which a locally generated signal is to be correlated with a received signal, means for recognizing the synchronization of said local and received signals, comprisIng:

a signal channel, a reference channel, means for applying said received signal plus undesired signal energy in parallel to said signal and reference channels, means for applying said locally generated signal to said signal and reference channels, means included in said reference channel to continually derive an output signal exclusively representative of uncorrelated received energy, means included in said signal channel to derive an output signal representative of correlated signal energy upon synchronization of said local and received signals, and means for comparing the output signal levels from said signal and reference channels and operative to provide an output signal indicating the state of synchronization of said local and received signals.