Calibration of signal strength measurements in a cellular communications system

• US 6,859,642 B2
• Filed: 11/29/2002
• Issued: 02/22/2005
• Est. Priority Date: 04/29/2002
• Status: Active Grant

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Korpela, Sari, Schwarz, Uwe
• Primary Examiner(s): APPIAH, CHARLES NANA
• Application Number:
  US10/306,839
• Publication Number:
  US 20040102158A1
• Time in Patent Office: 816 Days
• Field of Search: 455/67.11, 455/62, 455/446, 455/63.1, 455/435.1, 455/511, 455/525, 455/513, 455/67.13, 455/226.2, 455/423, 455/67.16, 455/450, 455/452.2, 375/227
• US Class Current: 455/67.11
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 17/26 using historical data, averaging values or statistics
• CPC Class Codes: H04B 17/309 Measuring or estimating channel quality parameters
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 17/327 Received signal code power [RSCP]
• CPC Class Codes: H04W 36/00837 Determination of triggering parameters for hand-off
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 52/0245 according to signal strength
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Signal strength measurements for different frequencies in different cells are calibrated in a cellular communications system. The signal strength of first and second frequencies in at least one cell of a plurality of cells is repeatedly measured. A measurement history is created for said first and second frequencies in at least the one cell. Each measurement history is based on the signal strength measurements of one of the first and second frequencies in the respective one cell. The measurement histories are stored. A respective correction factor is determined for each possible pair of first and second frequencies in at least the one cell. Each correction factor is based on the stored measurement history of the first and second frequencies in the pair. The respective correction factor for a pair of first and second frequencies cell is applied when comparing the signal strength measurements of the first and second frequencies in said pair.

Claims

1. A method of calibrating signal strength measurements in cellular communications, comprising:

repeatedly making signal strength measurements of first and second frequencies in at least one cell of a plurality of cells;

creating a plurality of measurement histories for said first and second frequencies in said at least one cell of said plurality of cells, each one of said plurality of measurement histories based on the signal strength measurements of one of said first and second frequencies in said at least one cell of said plurality of cells;

storing said plurality of measurement histories;

determining a respective correction factor for each possible pair of first and second frequencies in said at least one of said plurality of cells by comparing the signal strength measurements of said first and second frequencies in said pair, each correction factor based on the stored measurement history of the respective first and second frequencies in the pair; and

applying the respective correction factor of said pair of first and second frequencies.

2. A method in accordance with claim 1, wherein the first and second frequencies are downlink frequencies, and the first frequency is in a different band than the second frequency.

3. A method in accordance with claim 2, wherein said different band is an additional extension band including frequencies of at least 2.5 GHz.

4. A method in accordance with claim 2, wherein the first downlink frequencies and the second downlink frequencies have the same cell coverage.

5. A method in accordance with claim 1, in which the signal strength measurements are RSSI measurements.

6. A method in accordance with claim 1, in which a correction factor is separately determined for each call made by a mobile terminal.

7. A method in accordance with claim 1, wherein the measurement histories are stored in a base station or base station controller.

8. A method in accordance with claim 6, wherein the signal strength measurements of the first and second frequencies are made in a User Equipment and reported to the base station or base station controller.

9. A method in accordance with claim 6, wherein the base station or base station controller also has knowledge of the loading of the cells corresponding to the measurement histories.

10. A method in accordance with claim 6, wherein said base station or base station controller automatically determines the respective correction factors for the plurality of cells and triggers verification of interference detection.

11. A method in accordance with claim 10, wherein verification is triggered in accordance with the equation:

RSSI_{2.1 GHz}=RSSI_{2.5 GHz}+(DL TxPwr_{2.1 GHz}−

DL TxPwr_2.5GHz)+attenuation_{2.5 GHz}+cell

specific correction factor where the term “

(DL TxPwr_{2.1 GHz}−

DL TxPwr_{2.5 GHz})”

reflects the signal strength variation due to changing load, the term “

attenuation_{2.5 GHz}”

is a fixed offset attributable to the attenuation at 2.5 GHz, and the term “

cell specific correction factor”

is automatically determined based on the measurement history for said first and second frequency of the cell.

12. A method in accordance with claim 11, wherein the attenuation offset is fixed at substantially 2.57 dB.

13. A method in accordance with claim 11, wherein interference detection verification is triggered if RSSI_{2.1 GHz} exceeds the right hand term in the equation.

14. A method in accordance with claim 6, wherein the UE compares the signal strength measurements of the first and second frequencies, and reports only the difference between the measurements to the base station or base station controller.

15. A network element in accordance with claim 14, in which the signal strength measurements are RSSI measurements.

16. A network element in accordance with claim 14, wherein the signal strength measurements of the first and second frequencies are made in a User Equipment.

17. A network element in accordance with claim 14, wherein the network element is a base station controller, base station or other network element capable of performing the method.

18. A network element in accordance with claim 14, wherein said network element automatically determines the respective correction factors for the plurality of cells and triggers verification of interference detection.

19. A network element in accordance with claim 18, wherein verification is triggered in accordance with the equation:

RSSI_{2.1 GHz}=RSSI_{2.5 GHz}+(DL TxPwr_{2.1 GHz}−

DL TxPwr_{2.5 GHz})+attenuation_{2.5 GHz}+cell

specific correction factor where the term “

(DL TxPwr_{2.1 GHz}−

DL TxPwr_{2.5 GHz})”

reflects the signal strength variation due to changing load, the term “

attenuation_{2.5 GHz}”

is a fixed offset attributable to the attenuation at 2.5 GHz, and the term “

cell specific correction factor”

is automatically determined based on the measurement history of the cell.

20. A network element in accordance with claim 19, wherein the attenuation offset is fixed at substantially 2.57 dB.

21. A network element in accordance with claim 19, wherein interference detection verification is triggered if RSSI_{2.1 GHz} exceeds the right hand term in the equation.

22. A network element in accordance with claim 14, wherein the network element receives only the difference between the signal strength measurements.

23. A mobile terminal in accordance with claim 22, wherein the first and second frequencies are downlink frequencies, and the first frequencies are in a different band than the second frequencies.

24. A mobile terminal in accordance with claim 22, wherein the first downlink frequencies and the second downlink frequencies have the same cell coverage.

25. A mobile terminal in accordance with claim 22, in which the signal strength measurements are RSSI measurements.

26. A mobile terminal in accordance with claim 22, wherein the calibration method is automatically performed.

27. A mobile terminal in accordance with claim 22, wherein the calibration method is semi-automatically performed.

28. A mobile terminal in accordance with claim 22, wherein the mobile terminal provides only the signal strength measurements to a base station.

29. A mobile terminal in accordance with claim 22, wherein the information relating to the signal strength measurements comprises the difference between the signal strength measurements to a base station.

30. A mobile terminal in accordance with claim 29, wherein the information relating to signal strength measurement histories comprises an average value of the signal strength measurements in each signal strength measurement history.

31. A mobile terminal in accordance with claim 22, wherein the information relating to the signal strength measurements comprises information relating to signal strength measurement histories.

32. A network element for use in a cellular communications system, said network element performing a method of calibrating signal strength measurements from a plurality of cells, said method comprising:

receiving signal strength measurements of first and second frequencies in at least one cell of a plurality of cells;

creating a plurality of measurement histories for said first and second frequencies in said at least one cell of said plurality of cells, each one of said plurality of measurement histories based on the signal strength measurements of one of said first and second frequencies in said at least one cell of said plurality of cells;

storing said plurality of measurement histories;

determining a respective correction factor for each possible pair of first and second frequencies in said at least one of said plurality of cells by comparing the signal strength measurements of said first and second frequencies in said pair, each correction factor based on the stored measurement history of the respective first and second frequencics in the pair; and

applying the respective correction factor of a pair of first and second frequencies.

33. A network element in accordance with claim 32, wherein the first and second frequencies are downlink frequencies, and the first frequency is in a different band than the second frequency.

34. A network element in accordance with claim 32, wherein said different band is an additional extension band including frequencies of at least 2.5 GHz.

35. A network element in accordance with claim 32, wherein the first downlink frequencies and the second downlink frequencies have the same cell coverage.

36. A mobile terminal for use in a cellular communications system, said mobile terminal calibrating signal strength measurements, said calibration method comprising:

making repeated signal strength measurements of a plurality of first frequencies and a plurality of second frequencies;

providing information relating to said signal strength measurements to a base station;

receiving respective correction factors from a base station for each possible pair of first and second frequencies by comparing the signal strength measurements of said first and second frequencies, each respective correction factor based on said information relating to said signal strength measurements provided to said best station; and

applying the respective correction factor received for a pair of first and second frequencies.

37. A mobile terminal in accordance with claim 36, wherein said different band is an additional extension band including frequencies of at least 2.5 GHz.

38. A cellular communications network, said network performing a method of calibrating signal strength measurements from at least one cell of a plurality of cells, said network comprising:

at least one mobile terminal, said at least one mobile terminal making repeated signal strength measurements of a plurality of first frequencies and a plurality of second frequencies; and

a base station in said at least one cell, said base station receiving information relating to said signal strength measurements from said at least one mobile terminal,

wherein said network performs a calibration method comprising;

creating a plurality of measurement histories for said first and second frequencies in said at least one cell of said plurality of cells by comparing the signal strength measurements of said first and second frequencies, each one of said plurality of measurement histories based on the signal strength measurements of one of said first and second frequencies in said at least one cell of said plurality of cells;

storing said plurality of measurement histories;

determining a respective correction factor for each possible pair of first and second frequencies in said at least one of said plurality of cells, each correction factor based on the stored measurement history of the respective first and second frequencies in the pair; and

applying the respective correction factor of a pair of first and second frequencies.

39. A network in accordance with claim 38, wherein the first and second frequencies are downlink frequencies, and the first frequencies are in a different band than the second frequencies.

40. A network in accordance with claim 38, wherein said different band is an additional extension band including frequencies of at least 2.5 GHz.

41. A network in accordance with claim 38, wherein the first downlink frequencies and the second downlink frequencies have the same cell coverage.

42. A network in accordance with claim 38, in which the signal strength measurements are RSSI measurements.

43. A network in accordance with claim 38, wherein the calibration method is automatically performed.

44. A network in accordance with claim 38, wherein the calibration method is semi-automatically performed.

45. A network in accordance with claim 38, wherein the mobile terminal provides only the signal strength measurements to a base station.

46. A network in accordance with claim 38, wherein the information relating to the signal strength measurements comprises the difference between the signal strength measurements to a base station.

47. A mobile terminal in accordance with claim 38, wherein the information relating to the signal strength measurements comprises information relating to signal strength measurement histories.

48. A mobile terminal in accordance with claim 47, wherein the information relating to signal strength measurement histories comprises an average value of the signal strength measurements in each signal strength measurement history.