Method and apparatus for calibrating radio frequency base stations using antenna arrays

• US 6,037,898 A
• Filed: 10/10/1997
• Issued: 03/14/2000
• Est. Priority Date: 10/10/1997
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: ArrayComm LLC (Ygomi LLC)
• Inventors: Parish, David M., Farzaneh, Farhad, Barratt, Craig H.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US08/948,772
• Time in Patent Office: 886 Days
• Field of Search: 342/378, 342/174
• US Class Current: 342/174
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements

Abstract

A method operating in a communications station for calibrating the communications station, the communications station including an antenna array of antenna elements, each having associated with it and included in a transmit apparatus chain and a receiver apparatus chain. The method comprises transmitting a prescribed signal from each antenna element using the transmit apparatus chain associated with the antenna element while receiving the transmitted signal in receiver apparatus chains not associated with the antenna. Calibration factors for each antenna element are determined as dependent on the associated transmit apparatus chain and receiver apparatus chain transfer functions using the prescribed signal and each of the signals received during transmissions. A communications station also is described which includes: an antenna array of a plurality of elements, each antenna element having associated with it and included in a transmit apparatus chain and a receiver apparatus chain; transmitting means configured to transmit a prescribed signal from each antenna element while receiving the transmitted signal in at least one receiver apparatus chain not associated with the transmitting antenna element; a memory coupled to the receiver apparatus chains for storing the signals received during the transmissions of the prescribed signals; and a signal processor coupled to the memory and configured to determine calibration factors for each antenna element, the calibration factors for a particular antenna element based on the transmit apparatus chain and receiver apparatus chain transfer functions of the transmit and receiver apparatus chains, respectively, that are associated with the particular antenna element.

Claims

1. A method for calibrating a communications station without requiring any equipment in addition or external to the communication station, the communications station comprising an antenna array with a plurality of antenna elements, a receiver apparatus chain for each antenna element, and a transmit apparatus chain for each antenna element, each receiver apparatus chain including its antenna element, and each transmit apparatus chain including its antenna element, relative phase and amplitude behavior of each receiver apparatus chain essentially describable by a receiver apparatus chain transfer function for said each receiver apparatus chain, relative phase and amplitude behavior of each transmit apparatus chain essentially describable by a transmit apparatus chain transfer function for said each transmit apparatus chain, the method comprising:

(a) transmitting a first prescribed signal from a first antenna element through a first transmit apparatus chain while receiving the transmitted signal in at least one antenna element through its receiver apparatus chain, the receiving antenna element not the first antenna element, the first antenna element being part of the first transmit apparatus chain;

(b) repeating step (a) transmitting prescribed signals from other antenna elements through other transmit apparatus chains until prescribed signals have been transmitted from all antenna elements for which calibration factors are required, and any prescribed signal transmission from any particular antenna element has been received by a sufficient number of the other antenna elements to determine the required set of calibration factors; and

(c) determining calibration factors for each antenna element used in said step (a) and the repetitions of said step (b), each antenna element having one or more calibration factors for a particular antenna element based on the transmit apparatus chain and receiver apparatus chain transfer functions of the transmit and receiver apparatus chains, respectively, that include the particular antenna element, said determining using the first prescribed signal and the prescribed signals and each of the signals received in step (a) and the repetitions (b),

the method not requiring any equipment in addition or external to the communication station.

2. The method of claim 1 wherein step (a) and the repetitions (b) of step (a) further include storing the signals received, and wherein each of the received signals used in said determining step (c) are the signals stored in step (a) and the repetitions (b) of step (a).

3. The method of claim 2 wherein the same prescribed signal is used in step (a) and the repetitions (b) of step (a).

4. The method of claim 2 wherein said step (c) includes determining the transmit and receiver apparatus chain transfer functions.

5. The method of claim 3 wherein the communications station is part of a communications system which includes at least one subscriber unit, downlink communication and uplink communication between the communications station and the subscriber unit occurring in the same frequency channel, and wherein a single calibration factor is determined in said step (c) for any antenna element, the single calibration factor being in phase a function of the difference between the transmit apparatus chain transfer function phase and the receiver apparatus chain transfer function phase of the transmit and receiver apparatus chains, respectively, that share said any antenna element.

6. The method of claim 3 wherein the communications station is part of a communications system which includes at least one subscriber unit, downlink communication and uplink communication between the communications station and the subscriber unit occurring in the same frequency channel, and wherein a single calibration factor is determined in said step (c) for any antenna element, the single calibration factor being a function of the ratio of the transmit apparatus chain transfer function to the receiver apparatus chain transfer function, the receiver and transmit apparatus chain in the ratio sharing said any antenna element.

7. The method of claim 3 wherein determining step (c) determines calibration factors that are dependent on frequency.

8. The method of claim 4 wherein one receiver apparatus chain and one transmit apparatus chain sharing a common antenna element are respectively designated as a reference receive apparatus chain and a reference transmit apparatus chain, and all receiver and transmit apparatus chain transfer functions are respectively determined relative to the reference receive apparatus and reference transmit apparatus transfer functions.

9. The method of claim 5 wherein one antenna element is designated as a reference antenna element, and all calibration factors not of the reference antenna element are respectively determined relative to the calibration factor of the reference antenna element.

10. The method of claim 6 wherein one antenna element is designated as a reference antenna element, and all calibration factors not of the reference antenna element are respectively determined relative to the calibration factor of the reference antenna element.

11. The method of claim 9 wherein step (c) includes determining calibration factors that are essentially independent of frequency, the calibration factor for a particular antenna element that is not the reference antenna element being in phase a function of phase difference between the signal received at the receiver apparatus chain that includes the particular antenna element when the prescribed signal is transmitted from the transmit apparatus chain that includes the reference antenna element, and the signal received at the receiver apparatus chain that includes the reference antenna element when the prescribed signal is transmitted from the transmit apparatus chain that includes the particular antenna element.

12. The method of claim 10 wherein step (c) includes determining calibration factors that are essentially independent of frequency, the calibration factor for a particular antenna element that is not the reference antenna element being a function of the ratio of the signal received at the receiver apparatus chain that includes the particular antenna element when the prescribed signal is transmitted from the transmit apparatus chain that includes the reference antenna, to the signal received at the receiver apparatus chain that includes the reference antenna element when the prescribed signal is transmitted from the transmit apparatus chain that includes the particular antenna element.

13. A method for sending a downlink signal from a communications station to a subscriber unit, the communications station comprising an antenna array with a plurality of antenna elements, a receiver apparatus chain for each antenna element, and a transmit apparatus chain for each antenna element, each receiver apparatus chain including its antenna element, and each transmit apparatus chain including its antenna element, relative phase and amplitude behavior of each receiver apparatus chain essentially describable by a receiver apparatus chain transfer function for said each receiver apparatus chain, relative phase and amplitude behavior of each transmit apparatus chain essentially describable by a transmit apparatus chain transfer function for said each transmit apparatus chain, the method comprising:

(a) performing an experiment at the communications station to determine a set of calibration factors, the set including a single calibration factor for each particular antenna element for which calibration is required, the single calibration factor dependent on the receiver apparatus chain transfer function and the transmit apparatus chain transfer function of the particular antenna element;

(b) weighting the downlink signal according to a set of transmit weights to form a set of weighted transmit signals for each antenna element, the transmit weight for the particular antenna element determined from signals received at the antenna array during uplink communications with the subscriber unit and from the single calibration factor of the particular antenna element determined in step (b); and

(c) transmitting the weighted transmit signals through the transmit apparatus chains.

14. The method of claim 13,

wherein the communications station is able to communicate in the uplink with the subscriber unit by processing received signals, each received signal determined from a corresponding signal at one of the antenna elements, the processing including weighting the received signals according to a set of receive weights determined from the received signals, each receive weight corresponding to one of the antenna elements, and

wherein the transmit weight for the particular antenna element is determined from the receive weight corresponding to the particular antenna element and from the calibration factor of the particular antenna element.

15. The method of claim 14 wherein downlink communication and uplink communication between the communications station and the subscriber unit occur in the same frequency channel and wherein the calibration factor used in step (b) is in phase a function of the difference between the transmit apparatus chain transfer function phase and the receiver apparatus chain transfer function phase for the corresponding antenna element, and wherein each transmit weight is proportional to the corresponding receive weight and to the corresponding calibration factor.

16. The method of claims 14 wherein downlink communication and uplink communication between the communications station and the subscriber unit occur in the same frequency channel and wherein the calibration factor used in step (b) is a function of the ratio of the receiver apparatus chain transfer function to the transmit apparatus chain transfer function for the corresponding antenna element, and wherein each transmit weight is proportional to the corresponding receive weight and to the corresponding calibration factor.

17. The method of claim 15 wherein determining step (a) determines calibration factors that are dependent on frequency.

18. The method of claim 15 wherein said step (a) includes:

(i) transmitting a prescribed signal through a first transmit apparatus chain while receiving the transmitted signal through at least one receiver apparatus chain that does not include the same antenna element as the first transmit apparatus chain;

(ii) repeating step (i) using other transmit apparatus chains and receive apparatus chains until all transmit apparatus chains have been transmitted through and a transmission from any particular antenna element has been received through a sufficient number of the receive apparatus chains of the other antenna elements to determine the required calibration factors, and

(iii) determining the calibration factors from each of the signals received in step (i) and from the prescribed signals used in the transmissions of step (i).

19. The method of claim 18 wherein said step (a) further includes:

(iv) storing the signals received in step (i),

wherein said step (iii) of determining determines the calibration factors from signals stored in step (iv) and the repetitions in repeating step (a)(ii).

20. The method of claim 18 wherein the same prescribed signal is used in the repetitions in repeating step (a)(ii).

21. The method of claim 19 wherein the same prescribed signal is used in the repetitions in repeating step (a)(ii).

22. The method of claim 20 wherein one antenna element is designated as a reference antenna element, and all calibration factors not of the reference antenna element are respectively determined relative to the calibration factor of the reference antenna element.

23. The method of claim 13, wherein the experiment of step (a) requires no equipment in addition or external to the communications station.

24. A self-calibrating communications station not requiring additional or external equipment for calibration, the communication station comprising

(a) an antenna array with a plurality of antenna elements;

(b) a receiver apparatus chain for each antenna element, each receiver apparatus chain including its antenna element;

relative phase and amplitude behavior of each receiver apparatus chain essentially describable by a receiver apparatus chain transfer function for said each receiver apparatus chain; and

(c) a transmit apparatus chain for each antenna element, each transmit apparatus chain including its antenna element, relative phase and amplitude behavior of each transmit apparatus chain essentially describable by a transmit apparatus chain transfer function for said each transmit apparatus chain;

(d) transmitting means configured to transmit a prescribed signal from each antenna element using the antenna element'"'"'s transmit apparatus chain while receiving the transmitted signal in at least one receiver apparatus chain not of the transmitting antenna element;

(e) a memory coupled to the receiver apparatus chains for storing the signals received during the transmissions of the prescribed signals; and

(f) a signal processor coupled to the memory and configured to determine calibration factors for each antenna element, the calibration factors for a particular antenna element based on the transmit apparatus chain and receiver apparatus chain transfer functions of the transmit and receiver apparatus chains, respectively, that include the particular antenna element, said determining using the prescribed signal and each of the received signals stored in the memory and not requiring any equipment external or in addition to the communication station.

25. The communications station of claim 24 wherein said step (c) includes determining the transmit and receiver apparatus chain transfer functions.

26. The communications station of claim 24 wherein the communications station is part of a communications system which includes at least one subscriber unit, downlink communication and uplink communication between the communications station and the subscriber unit occurring in the same frequency channel, and wherein the signal processor determines a single calibration factor for any antenna element, the single calibration factor being in phase a function of the difference between the transmit apparatus chain transfer function phase and the receiver apparatus chain transfer function phase of the transmit and receiver apparatus chains, respectively, that share said any antenna element.

27. The communications station of claim 24 wherein the communications station is part of a communications system which includes at least one subscriber unit, downlink communication and uplink communication between the communications station and the subscriber unit occurring in the same frequency channel, and wherein the signal processor determines a single calibration factor for any antenna element, the single calibration factor being a function of the ratio of the transmit apparatus chain transfer function to the receiver apparatus chain transfer function, the receiver and transmit apparatus chain in the ratio sharing said any antenna element.

28. The communications station of claim 24 wherein the signal processor determines calibration factors that are dependent on frequency.

29. The communications station of claim 28 wherein one receiver apparatus chain and one transmit apparatus chain sharing a common antenna element are respectively designated as a reference receive apparatus chain and a reference transmit apparatus chain, and all receiver and transmit apparatus chain transfer functions are respectively determined relative to the reference receive apparatus and reference transmit apparatus transfer functions.

30. The communications station of claim 26 wherein one antenna element is designated as a reference antenna element, and all calibration factors not of the reference antenna element are respectively determined relative to the calibration factor of the reference antenna element.

31. The communications station of claim 27 wherein one antenna element is designated as a reference antenna element, and all calibration factors not of the reference antenna element are respectively determined relative to the calibration factor of the reference antenna element.

32. The communications station of claim 30 wherein the signal processor determines calibration factors that are essentially independent of frequency, the calibration factor for a particular antenna element that is not the reference antenna element being in phase a function of phase difference between the signal received through the receiver apparatus chain that includes the particular antenna element when the prescribed signal is transmitted through the transmit apparatus chain that includes the reference antenna, and the signal received through the receiver apparatus chain that includes the reference antenna element when the prescribed signal is transmitted through the transmit apparatus chain that includes the particular antenna element.

33. The communications station of claim 30 wherein the signal processor determines calibration factors that are essentially independent of frequency, the calibration factor for a particular antenna element that is not the reference antenna element being a function of the ratio of the signal received through the receiver apparatus chain that includes the particular antenna element when the prescribed signal is transmitted through the transmit apparatus chain that includes the reference antenna, to the signal received through the receiver apparatus chain that includes the reference antenna element when the prescribed signal is transmitted through the transmit apparatus chain that includes the particular antenna element.