Intermediate relay station of a digital microwave communication system using service channel for monitoring and controlling space and/or time diversity, heterodyne relay, phase control, frequency control, with phase shift keying modulation

• US 5,592,507 A
• Filed: 09/18/1995
• Issued: 01/07/1997
• Est. Priority Date: 07/07/1992
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Kobayashi, Kenzo
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): LUTHER, WILLIAM A
• Application Number:
  US08/529,416
• Time in Patent Office: 477 Days
• Field of Search: 375/211, 375/214, 375/216, 375/220, 375/260, 375/261, 375/267, 375/268, 375/269, 375/272, 375/273, 375/283, 375/299, 375/323, 375/324, 375/327, 375/340, 375/347, 375/349 , 375/362, 375/356, 375/376, 375/259, 375/344, 375/339, 324/76.41, 331/22, 331/30, 331/31, 359/191, 370/39, 370/110.4, 370/74, 370/75, 370/76, 370/122, 370/121, 340/425.1, 379/338, 455/7, 455/13.1
• US Class Current: 375/211
• CPC Class Codes: H04B 7/084 Equal gain combining, only phase adjustments antenna beam scanning or forming by phase or amplitude control H01Q3/26, e.g. phased arrays

Abstract

A microwave digital communication system PSK-modulates a microwave carrier by using a main signal and, further, frequency-modulates it by using a service channel (SC) signal for monitoring and controlling the system. An intermediate relay station employing a space diversity reception system converts a received microwave into an intermediate frequency (IF) to extract the SC signal, and converts the IF signal into a microwave to transmit, thus performing heterodyne relay. The intermediate relay station generates a phase error signal corresponding to the frequency deviation of the IF received signal, by using the IF received signal and an IF reference signal having a fixed frequency equal to the carrier frequency of the IF received signal, and extracts the phase error signal as an SC signal. The SC signal is inputted as a control signal to a VCO for generating a receiving-side local oscillation signal so that the frequency of that follows the variation of the frequency deviation of the received microwave. Thereby, the IF received signal is phase-locked by the IF reference signal, thus suppressing the frequency modulation component of the IF received signal caused by the SC signal. Because the intermediate relay station causes no increase in the frequency modulation factor while adding an SC signal, this relay station facilitates easily regeneration of the carrier performed by the receiving terminal station.

Claims

1. An intermediate relay station of a microwave communication system, which uses a microwave carrier that is modulated by a main signal being transmitted and frequency-modulated by a service channel signal for monitoring and controlling said microwave communication system, and which comprises a plurality of intermediate relay stations for receiving the main signal by using a space diversity system and relaying the main signal by heterodyne relay, said intermediate relay station comprising:

a pair of receiving mixer means for frequency-converting first and second received microwave signals received by two antennas apart from each other, each of said first and second received microwave signals containing a frequency modulation component, into first and second intermediate frequency received signals by using a receiving-side local oscillation signal produced by a receiving-side local oscillator;

phase shifter means for shifting the phase of said first intermediate frequency received signal so that a phase difference between carriers of said first and second intermediate frequency received signals exists, the phase difference arising from the difference of propagation paths of the microwave carriers, is compensated;

adding means for adding the first intermediate frequency received signal whose phase has been shifted and the second intermediate frequency received signal whose phase has not been shifted, in order to generate a third intermediate frequency received signal;

fixed-frequency oscillating means for generating an intermediate frequency reference signal having a fixed frequency equal to a frequency of a carrier of said third intermediate frequency received signal;

phase difference detecting means for inputting said intermediate frequency reference signal and said third intermediate frequency received signal, and for generating a control signal corresponding only to a frequency deviation in said third intermediate frequency received signal, the frequency deviation arising from the frequency modulation with said service channel signal;

a VCO device used as said receiving-side local oscillator, responsive to said control signal, generating said receiving-side local oscillation signal whose frequency varies so that each of the first and second intermediate frequency received signals is frequency-locked to the frequency of said intermediate frequency reference signal from said fixed-frequency oscillating means;

service channel signal extracting means for outputting said control signal as said service channel signal; and

transmitting mixer means for converting the third intermediate frequency received signal, having a reduced frequency modulation component, into a transmitting microwave.

2. An intermediate relay station according to claim 1, wherein said microwave carrier is modulated with said main signal by multi-phased shift keying modulation.

3. An intermediate relay station according to claim 2, wherein said phase difference detecting means comprises:

a quadrature demodulator device, multiplying said third intermediate frequency received signal by said intermediate frequency reference signal and by another intermediate frequency reference signal having a phase shifted by π

/2 from the phase of said intermediate frequency reference signal so as to generate phase difference signals, and outputting said phase difference signals to two channels including Channel I and Channel Q; and

a multiplying device, multiplying a frequency of an output from said quadrature demodulator device so as to eliminate a phase shift keying modulation component, and outputting said control signal corresponding only to a frequency deviation in said third intermediate frequency received signal, the frequency deviation arising from the frequency modulation with said service channel signal.

4. An intermediate relay station according to claim 1, wherein said phase shifter means includes an endless phase shifter provided between said receiving-side local oscillator outputting said receiving-side local oscillation signal and one of said pair of receiving mixer means.

5. An intermediate relay station of a microwave communication system, which uses a microwave carrier that is modulated by a main signal being transmitted and frequency-modulated by a service channel signal for monitoring and controlling said microwave communication system, and which comprises a plurality of intermediate relay stations for receiving the main signal by using a space diversity system and relaying the main signal by heterodyne relay, said intermediate relay station comprising:

a pair of first receiving mixer means for frequency-converting first and second received microwave signals received by two antennas apart from each other, each of said first and second received microwave signals containing a frequency modulation component, into first and second intermediate frequency received signals by using a first receiving-side local oscillation signal produced by a first receiving-side local oscillator;

phase shifter means for shifting the phase of said first intermediate frequency received signal so that a phase difference between carriers of said first and second intermediate frequency received signals, the phase difference arising from the difference of propagation paths of the microwave carriers, is compensated;

adding means for adding the first intermediate frequency received signal whose phase has been shifted and the second intermediate frequency received signal whose phase has not been shifted, in order to generate a third intermediate frequency received signal;

second receiving mixer means for frequency-converting said third intermediate frequency received signal from said adding means into a fourth intermediate received signal by using a second receiving-side local oscillation signal produced by a second receiving-side local oscillator;

fixed-frequency oscillating means for generating a first intermediate frequency reference signal having a fixed frequency equal to a frequency of a carrier of said fourth intermediate frequency received signal;

phase difference detecting means for inputting said first intermediate frequency reference signal and said fourth intermediate frequency received signal, and for generating a control signal corresponding only to a frequency deviation in said fourth intermediate frequency received signal, the frequency deviation arising from the frequency modulation with said service channel signal;

a VCO device used as said receiving-side local oscillator, responsive to said control signal, generating said receiving-side local oscillation signal whose frequency varies so that the fourth intermediate frequency received signal is frequency-locked to the frequency of said first intermediate frequency reference signal from said fixed-frequency oscillating means;

service channel signal extracting means for outputting said control signal as said service channel signal; and

transmitting mixer means for converting the fourth intermediate frequency received signal, in which a frequency modulation component has been reduced into a transmitting microwave.

6. An intermediate relay station according to claim 5, wherein said microwave carrier is modulated with said main signal by multi-phased shift keying modulation.

7. An intermediate relay station according to claim 6, wherein said phase difference detecting means comprises:

a quadrature demodulator device, multiplying said fourth intermediate frequency received signal by said first intermediate frequency reference signal and by a second intermediate frequency reference signal having a phase shifted by π

/2 from the phase of said first intermediate frequency reference signal so as to generate phase difference signals, and outputting said phase difference signals to two channels including Channel I and Channel Q; and

a multiplying device, multiplying a frequency of an output from said quadrature demodulator device so as to eliminate a phase shift keying modulation component, and outputting said control signal corresponding only to a frequency deviation in said fourth intermediate frequency received signal, the frequency deviation arising from the frequency modulation with said service channel signal.

8. An intermediate relay station of a microwave communication system, comprising:

first and second receiving mixer means for frequency-converting first and second received microwave signals into first and second intermediate frequency received signals;

phase shifter means for shifting the phase of said first intermediate frequency received signal so that a phase difference between carriers of said first and second intermediate frequency received signals, the phase difference arising from the difference of propagation paths of the microwave carriers, is compensated;

adding means for adding the first intermediate frequency received signal whose phase has been shifted and the second intermediate frequency received signal whose phase has not been shifted, in order to generate a third intermediate frequency received signal;

fixed-frequency oscillating means for generating an intermediate frequency reference signal having a fixed frequency equal to a frequency of a carrier of said third intermediate frequency received signal;

phase difference detecting means for inputting said intermediate frequency reference signal and said third intermediate frequency received signal, and for generating a control signal corresponding only to a frequency deviation in said third intermediate frequency received signal, the frequency deviation arising from a frequency modulation with a service channel signal;

a VCO device, responsive to said control signal, generating a receiving-side local oscillation signal whose frequency varies so that each of the first and second intermediate frequency received signals is frequency-locked to the frequency of said intermediate frequency reference signal from said fixed-frequency oscillating means; and

transmitting mixer means for converting the third intermediate frequency received signal, in which a frequency modulation component has been reduced into a transmitting microwave.

9. An intermediate relay station of a microwave communication system, comprising:

a pair of first receiving mixer means for frequency-converting first and second received microwave signals received by two antennas apart from each other into first and second intermediate frequency received signals;

phase shifter means for shifting the phase of said first intermediate frequency received signal so that a phase difference between carriers of said first and second intermediate frequency received signals, the phase difference arising from the difference of propagation paths of the microwave carriers, is compensated;

adding means for adding the first intermediate frequency received signal whose phase has been shifted and the second intermediate frequency received signal whose phase has not been shifted, in order to generate a third intermediate frequency received signal;

second receiving mixer means for frequency-converting said third intermediate frequency received signal from said adding means into a fourth intermediate frequency received signal;

fixed-frequency oscillating means for generating a first intermediate frequency reference signal having a fixed-frequency equal to a frequency of a carrier of said fourth intermediate frequency received signal;

phase difference detecting means for inputting said intermediate frequency reference signal and said fourth intermediate frequency received signal, and for generating a control signal corresponding only to a frequency deviation in said fourth intermediate frequency received signal, the frequency deviation arising from a frequency modulation with a service channel signal;

a VCO device, responsive to said control signal, generating a receiving-side local oscillation signal whose frequency varies so that the fourth intermediate frequency received signal is frequency-locked to said first intermediate frequency reference signal from said fixed-frequency oscillating means; and

transmitting mixer means for converting the fourth intermediate frequency received signal, having a reduced frequency modulation component, into a transmitting microwave.

10. An intermediate relay station of a microwave communication system, which uses a microwave carrier that is modulated by a main signal being transmitted and frequency-modulated by a service channel signal for monitoring and controlling said microwave communication system, and which comprises a plurality of intermediate relay stations for receiving the main signal by using a space diversity system and relaying the main signal by heterodyne relay, said intermediate relay station comprising:

a pair of first receiving mixer means for frequency-converting first and second received microwave signals received by two antennas apart from each other, each of said first and second microwave signals containing a frequency modulation component, into first and second intermediate frequency received signals by using a first receiving-side local oscillation signal produced by a first receiving-side local oscillator;

phase shifter means for shifting the phase of said first intermediate frequency received signal so that a phase difference between carriers of said first and second intermediate frequency received signals, the phase difference arising from the difference of propagation paths of the microwave carriers, is compensated;

adding means for adding the first intermediate frequency received signal whose phase has been shifted and the second intermediate frequency received signal whose phase has not been shifted, in order to generate a third intermediate frequency received signal;

second receiving mixer means for frequency-converting said third intermediate frequency received signal from said adding means into a fourth intermediate frequency received signal by using a second receiving-side local oscillation signal produced by a second receiving-side local oscillator;

third receiving mixer means for frequency-converting the fourth intermediate frequency received signal into the first intermediate frequency received signal;

fixed-frequency oscillating means for generating a first intermediate frequency reference signal having a frequency equal to a frequency of a carrier of said first intermediate frequency signal from said third receiving mixer means;

phase difference detecting means for inputting said first intermediate frequency reference signal and said first intermediate frequency signal, and for generating a control signal corresponding only to a frequency deviation in said first intermediate frequency signal, the frequency deviation arising from the frequency modulation with said service channel signal;

a VCO device used as said second receiving-side local oscillator, responsive to said control signal, generating said second receiving-side local oscillation signal whose frequency varies so that the first intermediate frequency signal is frequency-locked to the frequency of said first intermediate frequency reference signal from said fixed-frequency oscillating means;

service channel signal extracting means for outputting said control signal as said service channel signal; and

transmitting mixer means for converting said first intermediate frequency signal, in which a frequency modulation component has been reduced into a transmitting microwave.

11. An intermediate relay station of a microwave communication system, which uses a microwave carrier that is modulated by a main signal being transmitted and frequency-modulated by a service channel signal for monitoring and controlling said microwave communication system, and which comprises a plurality of intermediate relay stations for receiving the main signal by using a space diversity system and relaying the main signal by heterodyne relay, said intermediate relay station comprising:

a pair of first receiving mixer means for frequency-converting first and second received microwave signals received by two antennas apart from each other, each of said first and second microwave signals containing a frequency modulation component, into first and second intermediate frequency received signals by using a first receiving-side local oscillation signal produced by a first receiving-side local oscillator;

phase shifter means for shifting the phase of said first intermediate frequency received signal so that a phase difference between carriers of said first and second intermediate frequency received signals, the phase difference arising from the difference of propagation paths of the microwave carriers, is compensated;

adding means for adding the first intermediate frequency received signal whose phase has been shifted and the second intermediate frequency received signal whose phase has not been shifted, in order to generate a third intermediate frequency received signal;

second receiving mixer means for frequency-converting said third intermediate frequency received signal from said adding means into a fourth intermediate frequency received signal;

third receiving mixer means for frequency-converting the fourth intermediate frequency received signal into a first intermediate frequency signal by using a third receiving-side local oscillation signal produced by a third receiving-side local oscillator;

fixed-frequency oscillating means for generating a first intermediate frequency reference signal having a frequency equal to a frequency of a carrier of said first intermediate frequency signal from said third receiving mixer means;

phase difference detecting means for inputting said first intermediate frequency reference signal and said first intermediate frequency signal, and for generating a control signal corresponding only to a frequency deviation in said first intermediate frequency signal, the frequency deviation arising from the frequency modulation with said service channel signal;

a VCO device used as said third receiving-side local oscillator, responsive to said control signal, generating said third receiving-side local oscillation signal whose frequency varies so that the first intermediate frequency signal is frequency-locked to the frequency of said first intermediate frequency reference signal from said fixed-frequency oscillating means;

service channel signal extracting means for outputting said control signal as said service channel signal; and

transmitting mixer means for converting said first intermediate frequency signal, in which a frequency modulation component has been reduced into a transmitting microwave.