Method and system for calibrating a transceiver array

• US 9,172,454 B2
• Filed: 10/03/2014
• Issued: 10/27/2015
• Est. Priority Date: 11/01/2013
• Status: Active Grant

• Current Assignee: Magnolia Broadband Incorporated
• Original Assignee: Magnolia Broadband Incorporated
• Inventors: Harel, Haim, Chen, Phil F., Kludt, Kenneth, Rivingston, Thorp
• Primary Examiner(s): Phan, Tri H
• Application Number:
  US14/505,655
• Publication Number:
  US 20150124634A1
• Time in Patent Office: 389 Days
• Field of Search: 370215-216, 370241-252, 370463-469
• US Class Current: 1/1
• CPC Class Codes: H04B 17/12 of transmit antennas, e.g. of the amplitude or phase
• CPC Class Codes: H04B 7/04 using two or more spaced independent antennas
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic

Abstract

A system and method for compensating phase differences between multiple local oscillators and group delay differences between multiple transceivers. The system may include; an antenna array; a plurality of transceivers connected to said antennas and operatively associated each with a local oscillator (LO), wherein at least some of the transceivers do not share a common LO, and wherein at least some of the LOs are using a common reference oscillator; a common digital beamformer circuit connected to the transceivers; a baseband processor configured to operate the system at a specified communication scheme; and a calibration circuit and software modules configured to eliminate or reduce mismatches and phase deviations between the different transceivers, wherein the calibration circuit and software modules are incorporated in system such that the elimination or reduction of mismatches and phase deviations is non-interrupting with a continuous operation of the system at the specified communication scheme.

Claims

1. A system comprising:

an antenna array comprising antennas;

a plurality of transceivers connected to said antennas and each transceiver operatively associated with a local oscillator (LO), wherein at least some of the transceivers are not associated with the same LO, and wherein at least some of the LOs use a common reference oscillator;

a common digital beamformer circuit connected to said transceivers;

a baseband processor configured to operate the transceivers and beamformer circuit at a specified communication scheme; and

a calibration circuit,

wherein said calibration circuit and said baseband processor executing software modules are configured to reduce mismatches and phase deviations between the transceivers in a non-interrupting manner with a continuous operation of the system at the specified communication scheme.

2. The system according to claim 1, wherein said calibration circuit and said baseband processor executing software are configured to enable the common digital beamformer to generate calibration pilot signals injected to the inputs of the transceivers, via a digital-to-analog converter and an additional RF up-converter, and wherein the calibration circuit and said baseband processor are further configured to determine phase and amplitude differences between the plurality of transceivers'"'"' receivers, based on the digital output of said receivers across the bandwidth of the transceiver.

3. The system according to claim 2, wherein the calibration pilot comprises a narrowband signal.

4. The system according to claim 1, wherein said calibration circuitry and software modules are based on auxiliary hardware and auxiliary software, enabling the common digital beamformer entity to pick up its own downlink signal from each transmitting part of the said transceivers, via a calibration RF down-converter and an analog-to-digital converter, and further configured to determine phase and amplitude differences between the plurality of transceivers'"'"' transmitters, based on the digital output of said transmitters across the bandwidth of the transceiver, where said down-converter input is sequentially switched between each said transmitting part of the transceivers.

5. The system according to claim 1, wherein the specified communication scheme is Time-Domain-Duplex (TDD) exhibiting a time gap between transmit and receive.

6. The system according to claim 5, wherein the baseband processor is configured to avoid interruption of the operation of the system for calibration purposes, by using the transmit-receive time gap for switching the receivers array away from the antenna array, and connecting them to outputs of the calibration RF up-converter, and feeding the input of said up-converter with a calibration pilot signal generated by the common digital beamformer, for a partial part of said time gap, and further measuring the digitized output of the receivers array by the said common digital beamformer.

7. The system according to claim 5, wherein the baseband processor is further configured to avoid interruption of the operation of the system for calibration purposes by sequentially feeding the transmitting part of the transceivers via an RF splitter to the input of the calibration down-converter and measure the said down-converter digitized output during the time gap between transmit and receive.

8. The system according to claim 5, wherein said time gap between transmit and receive is divided up into several fields, so that the first field is left unused for guard time purposes, then the next field is used for receivers calibration, then the next one is used for calibration processing by the common digital beamformer, then the next one is used to apply phase adjustment to RF or digital parts of the system, and then the last field is not used to allow for guard time before switching back to active mode is taking place.

9. The system according to claim 5, wherein the down-link RF output of a given transceiver is fed into the calibration RF down-converter for a plurality of μ

secs before the transmit timeslot is ending, and after transmission is turned off, the digital output of the said down-converter is being capture and processed by the common digital beamformer, and phase adjustment is subsequently applied.

10. The system according to claim 9, wherein selection of specific time period for wideband calibration is based on measurements of temperature fluctuation and current fluctuations at the power amplifiers array, and the setting of thresholds that will increase sampling rate per increased fluctuation magnitude.

11. The system according to claim 10, wherein the selection of specific time period for narrow band calibration addressing the LO phase alignment, is based on factory measurements that determine inter-transceiver phase uncertainty over time.

12. The system according to claim 1, wherein the system is implemented as a part of a base station or a subscriber unit.

13. A method comprising:

providing a plurality of transceivers connected to an antenna array and operatively associated each with a local oscillator (LO), wherein at least some of the transceivers do not share a common LO, and wherein at least some of the LOs are using a common reference oscillator;

digitally beamforming signals coming and going to the transceivers;

operating the transceivers at a specified communication scheme using a baseband processor; and

eliminating or reducing mismatches and phase deviations between the different transceivers using a calibration circuit and software modules executed on the baseband processor,

wherein said calibration circuit is incorporated in transceivers such that the elimination or reduction of mismatches and phase deviations is non-interrupting with a continuous operation of the transceivers at the specified communication scheme.

14. The method according to claim 13, wherein said calibration circuit and software modules are based on auxiliary hardware and auxiliary software, enabling the common digital beamformer to generate calibration pilot signals injected to the inputs of the receiving part of the transceivers, via a digital-to-analog converter and an additional RF up-converter, and further configured to determine phase and amplitude differences between the plurality of transceivers'"'"' receivers, based on the digital output of said receivers across the bandwidth of the transceiver.

15. The method according to claim 14, wherein the calibration pilot comprises a narrowband signal.

16. The method according to claim 13, wherein said calibration circuitry and software modules are based on auxiliary hardware and auxiliary software, enabling the common digital beamformer entity to pick up its own downlink signal from each transmitting part of the said transceivers, via a calibration RF down-converter and an analog-to-digital converter, and further configured to determine phase and amplitude differences between the plurality of transceivers'"'"' transmitters, based on the digital output of said transmitters across the bandwidth of the transceiver, where said down-converter input is sequentially switched between each said transmitting part of the transceivers.

17. The method according to claim 13, wherein the specified communication scheme is Time-Domain-Duplex (TDD) exhibiting a time gap between transmit and receive.

18. The method according to claim 17, wherein the baseband processor is further configured to avoid interruption of the operation of the system for calibration purposes, by using the transmit-receive time gap for switching the receivers array away from the antenna array, and connecting them to outputs of the calibration RF up-converter, and feeding the input of said up-converter with a calibration Pilot signal generated by the common digital beamformer, for a partial part of said time gap, and further measuring the digitized output of the receivers array by the said common digital beamformer.

19. The method according to claim 17, wherein the baseband processor is further configured to avoid interruption of the operation of the system for calibration purposes by sequentially feeding the transmitting part of the transceivers via an RF splitter to the input of the calibration down-converter and measure the said down-converter digitized output during the time gap between transmit and receive.

20. The method according to claim 17, wherein said time gap between transmit and receive is divided up into a plurality of fields, so that the first field is left unused for guard time purposes, the next field is used for receiver calibration, the next one is used for calibration processing by the common digital beamformer, the next one is used to apply phase adjustment to RF or digital parts of the system, and the last field is not used to allow for guard time before switching back to active mode takes place.

21. The method according to claim 17, wherein the down-link RF output of a given transceiver is fed into the calibration RF down-converter for a plurality of μ

secs before the transmit timeslot is ending, and after transmission is turned off, the digital output of the said down-converter is captured and processed by the common digital beamformer, and phase adjustment is subsequently applied.

22. The method according to claim 21, wherein selection of specific time period for wideband calibration is based on measurements of temperature fluctuation and current fluctuations at the power amplifiers array, and the setting of thresholds that will increase sampling rate per increased fluctuation magnitude.

23. The method according to claim 21, wherein the selection of specific time period for narrow band calibration addressing the LO phase alignment is based on factory measurements that determine inter-transceiver phase uncertainty over time.

24. The method according to claim 13, wherein the method is implemented as a part of a base station or a subscriber unit.