Method and system for avoiding bad frequency subsets in a frequency hopping cordless telephone system

• US 6,480,721 B1
• Filed: 07/10/1998
• Issued: 11/12/2002
• Est. Priority Date: 07/10/1998
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Siemens Information And Communication Mobile LLC (Siemens AG)
• Inventors: Sydon, Uwe, Sastrodjojo, Paulus, Dicker, Olaf, Kockmann, Juergen
• Primary Examiner(s): Hunter, Daniel
• Assistant Examiner(s): CHOW, CHARLES CHIANG
• Application Number:
  US09/113,396
• Time in Patent Office: 1,586 Days
• Field of Search: 455/464, 455/450, 455/452, 455/67.3, 455/74.1, 455/575, 455/62, 455/63, 455/67.1, 370/329, 370/330, 370/341, 370/95.1, 370/333, 370/252, 370/465, 370/468, 379/59, 375/132, 714/704-706
• US Class Current: 455/464
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04B 1/715 Interference-related aspects
• CPC Class Codes: H04B 2001/7154 with means for preventing interference

Abstract

A method and system are disclosed for avoiding bad frequency subsets in a frequency hopping cordless telephone system. A base station communicates with the handsets using frequencies selected from active frequency subsets. Bad frequency subsets are avoided by monitoring the air interface between the base station and handsets for errors in active frequency subsets. Errors in each active frequency subset are counted during a short-term interval using an associated short-term error counter and during a long-term interval using an associated long-term error counter. After each short-term interval, it is evaluated whether any of the short-term error counters has a value that is greater than a defined threshold. After each long-term interval, it is evaluated whether any of the long-term error counters has a value greater than an error count for a blocked frequency subset. A blocked frequency subset is then substituted for an active frequency subset if an associated short-term error counter is greater than the defined threshold or if a long-term error counter is greater than the error count for a blocked frequency subset.

Claims

1. A system for avoiding bad frequency subsets in a frequency hopping cordless telephone system, the system comprising:

a plurality of handsets; and

a base station communicating with the handsets using frequencies selected from active frequency subsets, the base station avoiding bad frequency subsets by;

monitoring an air interface between the base station and the handsets for errors in active frequency subsets;

counting errors in each active frequency subset during a short-term interval using an associated short-term error counter and during a long-term interval using an associated long-term error counter;

evaluating, after each short-term interval, whether any of the short-term error counters has a value that is greater than a defined threshold;

evaluating, after each long-term interval, whether any of the long-term error counters has a value greater than an error count for a blocked frequency subset; and

substituting a blocked frequency subset for an active frequency subset if an associated short-term error counter is greater than the defined threshold or if a long-term error counter is greater than the error count for a blocked frequency subset.

2. The system of claim 1, wherein the base station can initialize the short-term error counters, the long-term error counters and data relating to blocked frequency subsets and associated error counts.

3. The system of claim 1, wherein counting errors comprises incrementing the short-term error counters and the long-term error counters based upon bad packet data, indicated by a bad synchronization word, and based upon bad cyclic redundancy checks.

4. The system of claim 1, wherein the short-term interval is one second, and the long-term interval is five seconds.

5. The system of claim 4, wherein each short-term counter is an eight bit counter that is cleared every second, while each long-term counter is a sixteen bit counter that is cleared every five seconds.

6. The system of claim 5, wherein substituting is accomplished by updating the data storing information about the blocked frequency subsets to reflect a substitution.

7. The system of claim 1, wherein evaluating whether any of the long-term error counters has a value greater than the error count for a blocked frequency subset comprises reducing the error count for a blocked frequency subset after each long-term interval for a defined number of long-term intervals.

8. The system of claim 1, wherein there are twelve frequency subsets of which ten are active and two are blocked.

9. The system of claim 8, wherein the twelve frequency subsets each comprise eight frequencies from a frequency band divided into ninety-six frequencies.

10. The system of claim 9, wherein the frequency band is an ISM band from 2.4 GHz to 2.4835 GHz.

21. The system of claim 1, wherein a blocked frequency subset has previously been an active frequency subset.

22. The system of claim 1, wherein substituting a blocked frequency subset for an active frequency subset comprises using both the blocked frequency subset and the active frequency subset for frequency hopping for a defined period before completing the substitution.

11. A method for avoiding bad frequency subsets in a frequency hopping cordless telephone system, the method comprising:

monitoring an air interface between a base station and handsets for errors in active frequency subsets;

counting errors in each active frequency subset during a short-term interval using an associated short-term error counter and during a long-term interval using an associated long-term error counter;

evaluating, after each short-term interval, whether any of the short-term error counters has a value that is greater than a defined threshold;

evaluating, after each long-term interval, whether any of the long-term error counters has a value greater than an error count for a blocked frequency subset; and

substituting a blocked frequency subset for an active frequency subset if an associated short-term error counter is greater than the defined threshold or if a long-term error counter is greater than the error count for a blocked frequency subset.

12. The method of claim 11, further comprising initializing the short-term error counters, the long-term error counters and data relating to blocked frequency subsets and associated error counts.

13. The method of claim 11, wherein counting errors comprises incrementing the short-term error counters and the long-term error counters based upon bad packet data, indicated by a bad synchronization word, and based upon bad cyclic redundancy checks.

14. The method of claim 11, wherein the short-term interval is one second, and the long-term interval is five seconds.

15. The method of claim 14, wherein each short-term counter is an eight bit counter that is cleared every second, while each long-term counter is a sixteen bit counter that is cleared every five seconds.

16. The method of claim 11, wherein substituting is accomplished by updating the data storing information about the blocked frequency subsets to reflect a substitution.

17. The method of claim 11, wherein evaluating whether any of the long-term error counters has a value greater than the error count for a blocked frequency subset comprises reducing the error count for a blocked frequency subset after each long-term interval for a defined number of long-term intervals.

18. The method of claim 11, wherein there are twelve frequency subsets of which ten are active and two are blocked.

19. The method of claim 18, wherein the twelve frequency subsets each comprise eight frequencies from a frequency band divided into ninety-six frequencies.

20. The method of claim 19, wherein the frequency band is an ISM band from 2.4 GHz to 2.4835 GHz.

23. The method of claim 11, wherein a blocked frequency subset has previously been an active frequency subset.

24. The method of claim 11, wherein substituting a blocked frequency subset for an active frequency subset comprises using both the blocked frequency subset and the active frequency subset for frequency hopping for a defined period before completing the substitution.