Cellular system hand-off protocol

• US 6,088,591 A
• Filed: 06/28/1996
• Issued: 07/11/2000
• Est. Priority Date: 06/28/1996
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Aironet Wireless Communications, Inc. (Cisco Systems, Inc.)
• Inventors: Spry, Andrew J., Smith, Douglas A., Belanger, Philip H., Trompower, Michael L., Shah, Nainesh P.
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): TRAN, CONGVAN
• Application Number:
  US08/672,751
• Time in Patent Office: 1,474 Days
• Field of Search: 455/436, 455/438, 455/439, 455/432, 455/434, 455/515, 455/450, 455/452, 455/453, 455/435, 370/330, 370/331, 375/202
• US Class Current: 455/438
• CPC Class Codes: H04B 1/7143 Arrangements for generation of hop patterns
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/067 Details of the timestamp structure
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

A cellular communication system hand-off protocol which helps minimize down time associated with a mobile device roaming among different cells in which different cells employ different communication channels (e.g., different frequency hopping sequences). In a preferred embodiment, each base station is configured to communicate its own particular hopping sequence to all other base stations via the system backbone. Each base station then provides to mobile devices which are registered thereto information regarding the particular hopping sequences employed by other base stations servicing cells into which the mobile device may roam. Such information includes the particular hopping sequences together with an indication of what location in the sequence the base stations are currently at in any given time. In addition, such information may include an indication of the intervals at which a base station is configured to transmit a beacon packet (for passive scanning operation), or at what intervals test pattern packets are transmitted to allow for signal quality evaluation.

Claims

1. In a cellular communication system comprising a backbone, and a first base station and a plurality of associated base stations each coupled to said backbone, each of said plurality of base stations respectively communicating on a selected one of a plurality of communication channels, a method comprising the steps of:

each of said plurality of associated base stations conveying information to said first base station related to said respective communication thereof;

said first base station receiving said information in a memory and transmitting selected information to an associated mobile device registered with said first base station, wherein the selected information is associated only with a reduced set of the plurality of associated base stations which are predetermined to have a cell area selected from one of adjacent to and overlapping with the cell area of the first base station;

said mobile device registering with one of the reduced set of the plurality of associated base stations based on the selected information.

2. The method of claim 1, wherein each of said plurality of communication channels is represented by at least one of a unique hop sequence, a unique modulation type, and a unique PN code.

3. The method of claim 1, wherein said information is conveyed to said first base station in a packet format.

4. The method of claim 1, wherein said first base station selects its own communication channel based at least in part on the information received from said plurality of associated base stations.

5. The method of claim 4, wherein said first base station selects its own communication channel such that it is different than the communication channel upon which any of said plurality of associated base stations are operating.

6. The method of claim 1, wherein said information received by said first base station includes hop sequence information and timing information.

7. The method of claim 6, wherein said information received by said first base station further includes test pattern interval information.

8. The method of claim 6, wherein said information received by said first base station further includes beacon interval information.

9. In a cellular communication system comprising a backbone, and a plurality of base stations each coupled to said backbone, each of said base stations communicating on a selected one of a plurality of communication channels, a method of informing a mobile device registered to a first of said plurality of base stations of respective communication channel information related to a plurality of associated base stations, comprising the steps of:

each of said plurality of associated base stations conveying information to said first base station related to said respective communication channel thereof;

said first base station receiving said information; and

said first base station transmitting a selected portion of said information to said mobile device wherein the selected portion of said information is associated only with a reduced set of the plurality of associated base stations which are predetermined to have a cell area selected from one of adjacent to and overlapping with the cell area of the first base station.

10. The method of claim 9, wherein said step of transmitting at least a portion of said information occurs prior to said mobile device registering with one of said plurality of associated base stations.

11. The method of claim 9, wherein each of said plurality of communication channels is represented by at least one of a unique hop sequence, a unique modulation type, and a unique PN code.

12. The method of claim 11, wherein said mobile device is a mobile terminal.

13. The method of claim 9, wherein said information is conveyed to said first base station in a packet format.

14. The method of claim 9, wherein said selected portion of said information transmitted to the mobile device includes hop sequence information and timing information.

15. The method of claim 14, wherein said mobile device jumps directly to the communication channel which one of said plurality of associated base stations is expected to be at based at least in part on the hop sequence information and the timing information transmitted.

16. A cellular communication system, comprising:

a backbone;

a plurality of base stations each coupled to said backbone, each of said base stations communicating on one of a plurality of different communication channels;

at least one mobile device, each of said mobile devices communicating with said backbone via registration with a selected one of said plurality of base stations, each of said base stations including;

wireless communication means for communicating information between said backbone and any of said at least one mobile devices which are registered to said base station;

means for conveying communication channel information to other of said plurality of base stations in said cellular communication system;

means for receiving communication channel information from said other base stations; and

means for wirelessly transmitting a selected portion of said communication channel information received to mobile devices currently registered to said base station, wherein said selected portion of said communication channel information is associated only with a reduced set of the plurality of base stations which are predetermined to have a cell area selected from one of adjacent to and overlapping with the cell area of said currently registered base station.

17. The system of claim 16, wherein each of said plurality of communication channels is represented by at least one of a unique hop sequence, a unique modulation type, and a unique PN code.

18. The system of claim 16, wherein said information received from said other base stations includes hop sequence information and timing information related to said other base stations communication channel.

19. The system of claim 18, wherein said information received from said other base stations further includes test pattern interval information.

20. The system of claim 18, wherein said information received from said other base stations further includes beacon interval information.

21. The system of claim 16, wherein each of said base stations further includes:

means of wirelessly transmitting a roaming counter to said mobile devices currently registered to said base station, said information wirelessly transmitted to mobile devices currrntly registered to said base station includes a roaming counter including a value representing a number of times a respective mobile terminal previously registered to said base station roamed to another of said plurality of base stations over a predetermined period of time.

22. A base station for use in a cellular communication system, comprising said base station along with a plurality of similar associated base stations each of which are coupled to a backbone, with each of said plurality of similar associated base stations each of which arc coupled to a backbone, with each of said plurality of similar associated base stations potentially serving as a respective wireless communication link between said backbone and at least one mobile device registered thereto, said base station comprising:

wireless communication means for communicating information between said backbone and any of said at least one mobile devices which are registered to said base station;

means for conveying communication channel information to other of said plurality of similar associated base stations in said cellular communication system;

means for receiving communication channel information from said other plurality of similar associated base stations; and

means for wirelessly transmitting a selected portion of said communication channel information received from said other plurality of similar associated base stations to said at least one mobile device currently registered to said base station wherein said selected portion of said communication channel information is associated only with a reduced set of the plurality of base stations which are predetermined to have a cell area selected from one adjacent to and overlapping with the cell area of said currently registered base station.

23. The base station of claim 22, further comprising:

means for wirelessly transmitting a roamed to counter to said mobile devices currently registered to said base station, wherein said roamed to counter includes a value representing a number of times a respective mobile terminal previously registered to said base station roamed to another of said plurality of similar associated base stations over a predetermined period of time.

24. The base station of claim 22, further comprising:

means for wirelessly transmitting updated information to said mobile devices currently registered to said base station, wherein said updated information includes updated communication channel information related to at least a portion of said at least one plurality of similar associated base stations.

25. The base station of claim 22, wherein said communication channel information includes hop sequence information and timing information.

26. The base station of claim 22, wherein communication channel information is conveyed in packet format.

27. In a cellular communication system comprising a backbone, and a plurality of base stations each coupled to said backbone, each of said base stations communicating on a selected one of a plurality of communication channels, a method of transferring communication channel information, comprising the steps of:

transmitting to a first of said plurality of base stations communications channel information related to of at least one of said plurality of base stations by a mobile device

receiving said communication channel information by said first base station; and

transmitting selected portions of said communication channel information to an associated mobile device registered with said first base station, wherein the selected information is associated only with a reduced set of the plurality of base stations which are predetermined to have a cell area selected from one of adjacent to and overlapping with the cell area of the first base station.

28. The method of claim 27, wherein said mobile device was previously registered with another of said plurality of base stations.

29. The method of claim 28, further comprising the step of:

determining at said first base station a roam to indicator indicative of which of said plurality of associated base stations said mobile terminal registered therewith was previously registered.

30. The method of claim 27, wherein said communication channel information includes hop sequence information and timing information.

31. A method of facilitating a mobile terminal'"'"'s ability to lock on to a base station communication channel upon said mobile terminal passively scanning for said communication channel by listening for beacons transmitted by said base station, said method comprising the step of decreasing an interval between which beacons are transmitted by said base station if current traffic load on said base station is below a predetermined threshold.

32. A mobile device for use in a cellular communication system, said cellular communication system comprising a backbone and a plurality of base stations coupled thereto, said mobile device capable of communicating with said backbone via one of said plurality of base stations to which the mobile device is currently registered;

said mobile device comprising;

wireless communication means for communicating information between said mobile device and said backbone;

means for receiving roaming information from said one base station, said roaming information including communication channel information related to other of said base stations wherein said roaming information includes only communication channel information related to base stations which are predetermined to have a cell area selected from one of adjacent to and overlapping with the cell area of the one base station; and

means for jumping directly to a communication channel at which one of said other base stations is expected to be based in part on received roaming information.

33. The mobile device of claim 32, further comprising:

means for moving quickly through at least one other communication channel at which said one base station is expected to be in the event said mobile device is not able to lock on to said one base station upon jumping directly to said communication channel.

34. The mobile device of claim 32, further comprising:

means for prioritizing an order in which to attempt to lock on to said other base stations based in part on said roaming information.

35. The mobile device of claim 34, wherein said order selected is based in part on a roam counter information included in said roaming information, said roam counter information having values representing the number of times mobile terminals previously registered to said one base station roamed to each of said other base stations over a predetermined period of time.

36. The mobile device of claim 32, wherein said communication channel information includes hop sequence information and timing information.

37. The mobile device of claim 32, wherein said mobile device is a mobile terminal having a bar code scanner.

38. The mobile device of claim 32, wherein said roaming information is received in packet format.

39. A mobile device for use in a cellular communication system, said cellular communication system comprising a backbone and a plurality of base stations having respective cell areas coupled thereto, said mobile device capable of communicating with said backbone via one of said plurality of base stations to which the mobile device is currently registered, said mobile device comprising:

wireless communication means for communicating information between said mobile device and said backbone;

means for receiving communication information, including hop sequence information related to other of said base stations from said one base station;

means for storing said hop sequence information;

means for computing a communication channel at which at least one of said other base stations is expected to be based on said hop sequence information, wherein said communication information includes a roam counter valve indicative of which of said plurality of base stations have cell areas selected from one of adjacent to and overlapping with the cell area of said one base station; and

means for jumping directly to the communication channel.

40. The mobile device of claim 39, wherein said mobile device is a mobile terminal having a bar code reader.

41. The mobile device of claim 39, wherein said mobile device further comprises:

means for determining whether said at least one other base station is communicating on said communication channel by listening for beacons on said communication channel.

42. The mobile device of claim 41, further comprising:

means for moving quickly through at least one other communication channel at which said one other base station is expected to be in the event said mobile device does not receive a beacon.

43. The mobile device of claim 39, wherein said mobile device further comprises:

means for determining whether said at least one other base station is communicating on said communication channel by transmitting a probe packet on said communication channel and waiting a predetermined period of time to receive a response.

44. The mobile device of claim 43, further comprising:

means for moving quickly through at least one other communication channel at which said one other base station is expected to be in the event said mobile device does not receive a response.

45. In a cellular communication system comprising a backbone, and first and second base stations each coupled to said backbone, each of said first and second base stations communicating on a selected one of a plurality of communication channels, a method comprising the steps of:

conveying from said second base station to said first base station information related to said second base station'"'"'s hopping sequence;

receiving said information by said first base station;

storing said information in memory associated with said first base station;

computing within said first base station a communication channel upon which said second base station is expected to be, based on said information stored in said first base station;

transmitting from said first base station to a registered mobile device said communication channel computed; and

receiving said communication channel computed by said mobile device.

46. The method of claim 45, wherein said mobile device jumps directly to a current communication channel upon which said second base station is expected to be based on said received communication channel and listens for beacons on said current communication channel to determine whether said second base station is currently communicating on said current communication channel.