Method and apparatus for implementing measurement based dynamic frequency hopping in wireless communication systems

• US 6,549,784 B1
• Filed: 05/14/1999
• Issued: 04/15/2003
• Est. Priority Date: 12/28/1998
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Kostic, Zoran, Sollenberger, Nelson Ray
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Milord, Marceau
• Application Number:
  US09/312,279
• Time in Patent Office: 1,432 Days
• Field of Search: 455/501, 455/502, 455/504, 455/513, 455/525, 455/67.1, 455/67.4, 455/62, 455/63, 375/132, 375/130, 370/203, 370/260, 370/285
• US Class Current: 455/501
• CPC Class Codes: H04B 1/715 Interference-related aspects
• CPC Class Codes: H04B 2001/7154 with means for preventing interference
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

Proposed is a method and apparatus for reducing interference in a frequency hopping wireless communications system. In one embodiment of the present invention, a base station and a terminal station each using an orthogonal frequency division multiplexing (OFDM) technique to simultaneously measure an interference level for each system frequency and to enable high speed frequency hop pattern changes which can follow changes in desired and interfering signal levels due to changes in co-channel interference or shadow fading. The terminal station interference level measurement values are then transmitted to the base station. Next, the base station identifies each frequency hop pattern currently in use by each terminal station communicating with that base station. The base station then uses both the base station interference level measurements and the terminal station interference level measurements to identify each frequency hop pattern in which at least one of the current system frequencies should be replaced with a system frequency having a lower interference level. Next, the base station replaces no more than a predetermined number of the current system frequencies within the identified frequency hop pattern(s). The above steps are executed at each base station within the system while ensuring that nearby interfering base stations do not replace frequencies at the same time.

Claims

1. A method for reducing interference in a frequency hopping wireless communication system comprising a plurality of base stations each adapted to communicate with one or more of a plurality of terminal stations by transmitting one or more of a plurality of system frequencies through a propagation medium, the method comprising the steps of:

measuring, simultaneously, an interference level for each system frequency;

determining a frequency hop pattern for each base station/terminal station link, said frequency hop pattern comprising at least two system frequencies;

analyzing each determined frequency hop pattern, using said measured interference levels, to identify each frequency hop pattern in which at least one system frequency should be replaced with a second system frequency having a lower interference level than said at least one system frequency;

replacing no more than a predetermined number of said at least one system frequencies within each identified frequency hop pattern with a corresponding number of system frequencies having lower measured interference levels; and

executing said measuring, determining, analyzing and replacing steps at each of said plurality of base stations.

2. The method of claim 1, further comprising the step of:

precluding more than one nearby interfering base station from simultaneously executing said replacing step.

3. The method of claim 1, wherein said measuring step is accomplished using orthogonal frequency division multiplexing (OFDM).

4. The method of claim 1, wherein said measuring step is accomplished using one of said plurality of base stations and at least one of said plurality of terminal stations communicating with said one base station.

5. The method of claim 1, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each system frequency in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

assigning a cumulative score to each of said identified frequency hop patterns using said ranking information, said cumulative score obtained by summing said rank numbers associated with each of said system frequencies within each of said identified frequency hop patterns; and

ranking each of said identified frequency hop patterns according to said assigned cumulative score information.

6. The method of claim 5, wherein said replacing step comprises:

replacing system frequencies within a ranked frequency hop pattern having a worst cumulative score with system frequencies from a group comprising system frequencies having a lowest associated interference level;

replacing system frequencies within a ranked frequency hop pattern having a next worst cumulative score with available system frequencies from a group comprising system frequencies having a next lowest associated interference level; and

repeating said next worst cumulative score replacing step until frequencies within each of said identified frequency hop patterns have been replaced.

7. The method of claim 1, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each system frequency in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

assigning a cumulative score to each of said identified frequency hop patterns using said ranking information, said cumulative score obtained by summing said rank numbers associated with each of said system frequencies within each of said identified frequency hop patterns;

ranking each of said identified frequency hop patterns according to said assigned cumulative score information;

identifying each ranked frequency hop pattern with a cumulative score below a predetermined threshold value; and

marking, as unavailable, each system frequency within each of said ranked frequency hop patterns identified as below said predetermined threshold value.

8. The method of claim 7, wherein said replacing step comprises:

replacing, among a group of ranked frequency hop patterns having a cumulative score above said predetermined threshold value, system frequencies within a frequency hop pattern having a worst cumulative score with available system frequencies from a group comprising system frequencies having a lowest associated interference level;

replacing, among said group of ranked frequency hop patterns having a cumulative score above said predetermined threshold value, system frequencies within a frequency hop pattern having a next worst cumulative score with available system frequencies from a group comprising system frequencies having a next lowest associated interference level; and

repeating said next worst cumulative score replacing step until frequencies within each of said identified frequency hop patterns have been replaced.

9. The method of claim 1, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each of said system frequencies in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level; and

analyzing each frequency used in each frequency dwell of each ranked frequency hop pattern to identify frequencies having a rank number in a higher end of a range of rank numbers.

10. The method of claim 9, wherein said replacing step comprises:

replacing each of said identified higher rank number frequencies with a frequency having a lower rank number; and

ensuring a same frequency is not used in a same frequency dwell within more than one frequency hop pattern.

11. The method of claim 1, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each of said system frequencies in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

identifying each system frequency within each frequency dwell of each ranked frequency hop pattern to identify frequencies having a rank number above a predetermined threshold value; and

marking, as unavailable, each system frequency having a rank number below said predetermined threshold value.

12. The method of claim 11, wherein said replacing step comprises:

replacing, within each identified frequency hop pattern, each system frequency having a rank number above said predetermined threshold value with an available frequency having a rank number below said predetermined threshold value; and

ensuring a same system frequency is not used in a same frequency dwell within more than one frequency hop pattern.

13. A computer-readable medium whose contents cause a computer system to reduce interference in a wireless communications system comprising a plurality of base stations each adapted to communicate with one or more of a plurality of terminal stations by transmitting one or more of a plurality of system frequencies through a propagation medium, the computer-readable medium performing the steps of:

measuring, simultaneously, an interference level for each system frequency;

determining a frequency hop pattern for each base station/terminal station link, said frequency hop pattern comprising at least two system frequencies;

analyzing each determined frequency hop pattern, using said measured interference levels, to identify each frequency hop pattern in which at least one system frequency should be replaced with a second system frequency having a lower interference level than said at least one system frequency;

replacing no more than a predetermined number of said at least one system frequencies within each identified frequency hop pattern with a corresponding number of system frequencies having lower measured interference levels; and

executing said measuring, determining, analyzing and replacing steps at each of said plurality of base stations.

14. The computer-readable medium of claim 13, further performing the step of:

precluding more than one nearby interfering base station from simultaneously executing said replacing step.

15. The computer-readable medium of claim 14, wherein said measuring step is accomplished using orthogonal frequency division multiplexing (OFDM).

16. The computer-readable medium of claim 14, wherein said measuring step is accomplished using one of said plurality of base stations and at least one of said plurality of terminal stations communicating with said one base station.

17. The computer-readable medium of claim 13, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each system frequency in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

assigning a cumulative score to each of said identified frequency hop patterns using said ranking information, said cumulative score obtained by summing said rank numbers associated with each of said system frequencies within each of said identified frequency hop patterns; and

ranking each of said identified frequency hop patterns according to said assigned cumulative score information.

18. The computer-readable medium of claim 17, wherein said replacing step comprises:

replacing system frequencies within a ranked frequency hop pattern having a worst cumulative score with system frequencies from a group comprising system frequencies having a lowest associated interference level;

replacing system frequencies within a ranked frequency hop pattern having a next worst cumulative score with available system frequencies from a group comprising system frequencies having a next lowest associated interference level; and

repeating said next worst cumulative score replacing step until frequencies within each of said identified frequency hop patterns have been replaced.

19. The computer-readable medium of claim 13, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each system frequency in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

assigning a cumulative score to each of said identified frequency hop patterns using said ranking information, said cumulative score obtained by summing said rank numbers associated with each of said system frequencies within each of said identified frequency hop patterns;

ranking each of said identified frequency hop patterns according to said assigned cumulative score information;

identifying each ranked frequency hop pattern with a cumulative score below a predetermined threshold value; and

marking, as unavailable, each system frequency within each of said ranked frequency hop patterns identified as below said predetermined threshold value.

20. The computer-readable medium of claim 19, wherein said replacing step comprises:

replacing, among a group of ranked frequency hop patterns having a cumulative score above said predetermined threshold value, system frequencies within a frequency hop pattern having a worst cumulative score with available system frequencies from a group comprising system frequencies having a lowest associated interference level;

replacing, among said group of ranked frequency hop patterns having a cumulative score above said predetermined threshold value, system frequencies within a frequency hop pattern having a next worst cumulative score with available system frequencies from a group comprising system frequencies having a next lowest associated interference level; and

repeating said next worst cumulative score replacing step until frequencies within each of said identified frequency hop patterns have been replaced.

21. The computer-readable medium of claim 13, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each of said system frequencies in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level; and

analyzing each frequency used in each frequency dwell of each ranked frequency hop pattern to identify frequencies having a rank number in a higher end of a range of rank numbers.

22. The computer-readable medium of claim 21, wherein said replacing step comprises:

replacing each of said identified higher rank number frequencies with a frequency having a lower rank number; and

ensuring a same frequency is not used in a same frequency dwell within more than one frequency hop pattern.

23. The computer-readable medium of claim 13, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each of said system frequencies in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

identifying each system frequency within each frequency dwell of each ranked frequency hop pattern to identify frequencies having a rank number above a predetermined threshold value; and

marking, as unavailable, each system frequency having a rank number below said predetermined threshold value.

24. The computer-readable medium of claim 23, wherein said replacing step comprises:

replacing, within each identified frequency hop pattern, each system frequency having a rank number above said predetermined threshold value with an available frequency having a rank number below said predetermined threshold value; and

ensuring a same system frequency is not used in a same frequency dwell within more than one frequency hop pattern.

25. A method for reducing interference in a frequency hopping wireless communication system comprising a plurality of base stations each adapted to communicate with one or more of a plurality of terminal stations by transmitting one or more of a plurality of system frequencies through a propagation medium, the method comprising the steps of:

measuring an interference level for each system frequency;

determining a frequency hop pattern for each base station/terminal station link, said frequency hop pattern comprising at least two system frequencies;

analyzing each determined frequency hop pattern, using said measured interference levels, to identify each frequency hop pattern in which at least one system frequency should be replaced with a second system frequency having a lower interference level than said at least one system frequency;

replacing no more than a predetermined number of said at least one system frequencies within each identified frequency hop pattern with a corresponding number of system frequencies having lower measured interference levels;

executing said measuring, determining, analyzing and replacing steps at each of said plurality of base stations; and

precluding more than one nearby interfering base station from simultaneously executing said replacing step.

26. The method of claim 25, wherein each system frequency is measured simultaneously using orthogonal frequency division multiplexing (OFDM).

27. The method of claim 26, wherein said measuring step is accomplished using one of said plurality of base stations and at least one of said plurality of terminal stations communicating with said one base station.

28. The method of claim 25, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each system frequency in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

assigning a cumulative score to each of said identified frequency hop patterns using said ranking information, said cumulative score obtained by summing said rank numbers associated with each of said system frequencies within each of said identified frequency hop patterns; and

ranking each of said identified frequency hop patterns according to said assigned cumulative score information.

29. The method of claim 28, wherein said replacing step comprises:

replacing system frequencies within a ranked frequency hop pattern having a worst cumulative score with system frequencies from a group comprising system frequencies having a lowest associated interference level;

replacing system frequencies within a ranked frequency hop pattern having a next worst cumulative score with available system frequencies from a group comprising system frequencies having a next lowest associated interference level; and

repeating said next worst cumulative score replacing step until frequencies within each of said identified frequency hop patterns have been replaced.

30. The method of claim 29, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each system frequency in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

assigning a cumulative score to each of said identified frequency hop patterns using said ranking information, said cumulative score obtained by summing said rank numbers associated with each of said system frequencies within each of said identified frequency hop patterns;

ranking each of said identified frequency hop patterns according to said assigned cumulative score information;

identifying each ranked frequency hop pattern with a cumulative score below a predetermined threshold value; and

marking, as unavailable, each system frequency within each of said ranked frequency hop patterns identified as below said predetermined threshold value.

31. The method of claim 30, wherein said replacing step comprises:

replacing, among a group of ranked frequency hop patterns having a cumulative score above said predetermined threshold value, system frequencies within a frequency hop pattern having a worst cumulative score with available system frequencies from a group comprising system frequencies having a lowest associated interference level;

replacing, among said group of ranked frequency hop patterns having a cumulative score above said predetermined threshold value, system frequencies within a frequency hop pattern having a next worst cumulative score with available system frequencies from a group comprising system frequencies having a next lowest associated interference level; and

repeating said next worst cumulative score replacing step until frequencies within each of said identified frequency hop patterns have been replaced.

32. The method of claim 25, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each of said system frequencies in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level; and

analyzing each frequency used in each frequency dwell of each ranked frequency hop pattern to identify frequencies having a rank number in a higher end of a range of rank numbers.

33. The method of claim 32, wherein said replacing step comprises:

replacing each of said identified higher rank number frequencies with a frequency having a lower rank number; and

ensuring a same frequency is not used in a same frequency dwell within more than one frequency hop pattern.

34. The method of claims 25, wherein said analyzing step comprises:

associating each system frequency with a corresponding measured interference level;

ranking each of said system frequencies in an increasing order according to said associated interference levels, wherein a lowest rank number is assigned to a system frequency having a lowest associated interference level and a highest rank number is assigned to a system frequency having a highest interference level;

identifying each system frequency within each frequency dwell of each ranked frequency hop pattern to identify frequencies having a rank number above a predetermined threshold value; and

marking, as unavailable, each system frequency having a rank number below said predetermined threshold value.

35. The method of claim 34, wherein said replacing step comprises:

replacing, within each identified frequency hop pattern, each system frequency having a rank number above said predetermined threshold value with an available frequency having a rank number below said predetermined threshold value; and

ensuring a same system frequency is not used in a same frequency dwell within more than one frequency hop pattern.

36. A computer-readable medium whose contents cause a computer system to reduce interference in a wireless communications system comprising a plurality of base stations each adapted to communicate with one or more of a plurality of terminal stations by transmitting one or more of a plurality of system frequencies through a propagation medium, the computer-readable medium performing the steps of:

measuring an interference level for each system frequency;

determining a frequency hop pattern for each base station/terminal station link, said frequency hop pattern comprising at least two system frequencies;

analyzing each determined frequency hop pattern, using said measured interference levels, to identify each frequency hop pattern in which at least one system frequency should be replaced with a second system frequency having a lower interference level than said at least one system frequency;

replacing no more than a predetermined number of said at least one system frequencies within each identified frequency hop pattern with a corresponding number of system frequencies having lower measured interference levels;

executing said measuring, determining, analyzing and replacing steps at each of said plurality of base stations; and

precluding more than one nearby interfering base station from simultaneously executing said replacing step.

37. The computer-readable medium of claim 36, wherein said measuring step is accomplished using orthogonal frequency division multiplexing (OFDM).

38. The computer-readable medium of claim 37, wherein said measuring step is accomplished using one of said plurality of base stations and at least one of said plurality of terminal stations communicating with said one base station.

39. An apparatus for reducing interference in a frequency hopping wireless communications system, comprising:

a processor;

a wideband transceiver adapted to be connected to said processor;

an antenna adapted to be connected to said wideband transceiver;

a computer-readable memory adapted to be connected to said processor; and

a quality measurement module within said computer-readable memory, said quality measurement module including computer program code segments executed by said processor to implement the steps of;

measuring, simultaneously, an interference level for each system frequency; and

transmitting values representing said measured interference levels to a second apparatus.

40. The apparatus of claim 39, wherein said measuring step is accomplished using orthogonal frequency division multiplexing (OFDM).

41. An apparatus for reducing interference in a frequency hopping wireless communications system, comprising:

a processor;

a wideband transceiver adapted to be connected to said processor;

an antenna adapted to be connected to said wideband transceiver;

a computer-readable memory adapted to be connected to said processor;

a quality measurement module within said computer-readable memory; and

a frequency hop pattern adaptation module within said computer-readable memory;

wherein said quality measurement module and said frequency hop pattern adaptation module including computer program code segments executed by said processor to implement the steps of;

measuring, simultaneously, an interference level for each system frequency;

determining a frequency hop pattern for each base station/terminal station link, said frequency hop pattern comprising at least two system frequencies;

analyzing each determined frequency hop pattern, using said measured interference levels, to identify each frequency hop pattern in which at least one system frequency should be replaced with a second system frequency having a lower interference level than said at least one system frequency; and

replacing no more than a predetermined number of said at least one system frequencies within each identified frequency hop pattern with a corresponding number of system frequencies having lower measured interference levels.

42. The apparatus of claim 41, wherein said measuring step is accomplished using orthogonal frequency division multiplexing (OFDM).