Base station controlled handoff method and apparatus

• US 5,794,149 A
• Filed: 12/29/1995
• Issued: 08/11/1998
• Est. Priority Date: 12/29/1995
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Hoo, John
• Primary Examiner(s): Bost, Dwayne D.
• Assistant Examiner(s): GELIN, JEAN ALLAND
• Application Number:
  US08/580,681
• Time in Patent Office: 956 Days
• Field of Search: 455/438, 455/436, 455/437, 455/411, 370/331
• US Class Current: 455/438
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: H04W 36/38 by fixed network equipment

Abstract

A handoff method and apparatus are disclosed for use in a wireless communication network in which a base station servicing a call selects a handoff candidate base station based in part on subscriber-specific information. For example, in some wireless networks, certain subscribers can only access a limited number of base stations and the subscriber-specific information identifies such access limitations. A central control processor provides the subscriber-specific information to the base station servicing the call during the course of the call. The base station is then operable to select a handoff candidate from the one or more neighbor base stations based on one or more neighbor base station signal quality measurements and subscriber-specific information.

Claims

1. A base station for use in a wireless communication network including a switching center and one or more neighbor base stations, said switching center having access to subscriber-specific parameters and operable to generate subscriber-specific information therefrom, said base station comprising:

a) a radio for communicating with a wireless terminal using radio signals;

b) a circuit connected to the radio for converting radio signals to digital signals, said circuit operable to provide the digital signals to the switching center;

c) a base station controller operable to select a handoff candidate from the one or more neighbor base stations based on one or more neighbor base station signal quality measurements and subscriber-specific information received from the switching center; and

transmit a request signal to the handoff candidate requesting a handoff.

2. The base station of claim 1 wherein the base station controller is further operable to:

transmit an information signal to the switching center after the handoff has occurred, the information signal containing information identifying the handoff candidate; and

receive an update signal from the switching center containing updated subscriber-specific information.

3. The base station of claim 1 wherein the base station controller is further operable to select the handoff candidate based on subscriber-specific information, wherein the subscriber-specific information comprises a neighbor blocking list, said neighbor blocking list identifying those of the one or more neighbor base stations for which handoff is prohibited.

4. Base station of claim 3 wherein the base station controller is further operable to select from neighbor base stations the candidate handoff base station by:

receiving from the wireless terminal a signal containing information representative of one or more signal quality measurements, the signal quality measurements corresponding to each of one or more neighbor base stations;

determining whether there is an eligible handoff candidate, the eligible handoff candidate comprising one of the one or more neighbor base stations, said determination based in part on the signal quality measurements; and

determining whether handoff is permitted to the eligible handoff candidate based on the neighbor blocking list.

5. The base station of claim 1 wherein the base station comprises a first face of a multiple-face base station and the handoff candidate comprises a second face of the multiple-face base station.

6. The base station of claim 3 wherein the radio is operable to communicate with the wireless terminal over a first radio channel, said first radio channel defined in part by a frequency band, and wherein the base station controller is operable to:

receive a handoff acknowledgement signal from the handoff candidate indicating that the handoff candidate can communicate on a second radio channel, said second radio channel defmed in part by the frequency band; and

transmit a handoff signal to the wireless terminal causing the wireless terminal to begin radio communications with the handoff candidate.

7. The base station of claim 1 wherein the radio is operable to communicate with the wireless terminal over a first radio channel, said first radio channel defmed in part by a frequency band, and wherein the base station controller is operable to:

receive a handoff acknowledgement signal from the handoff candidate indicating that the handoff candidate has resources available to communicate on a second radio channel, said second radio channel defined in part by the frequency band; and

transmit a handoff signal to the wireless terminal causing the wireless terminal to begin radio communications with the handoff candidate.

8. The base station of claim 1 wherein the base station controller is further operable to release control of the call after the handoff candidate begins communicating with the wireless terminal.

9. The base station of claim 1 wherein said radio communicates with the wireless terminal using code division multiple access ("CDMA") signals.

10. A switching center coupled to a plurality of base stations, each base station associated with one or more neighbor base stations, said switching center comprising:

a) a digital control switch for receiving call signals from one or more base stations, the digital control switch operable to provide the call signals to a communications network;

b) a central control processor that is operable to, upon notification of a base station status change for a call,

generate a first list comprising neighbor base stations associated with one or more base stations servicing the call,

generate from the first list a second list of subscriber ineligible neighbors based on subscriber-specific parameters, and

provide an update signal containing data representative of the second list to a primary base station.

11. The switching center of claim 10 wherein the central control processor is further operable to provide said update signal to the primary base station within a handoff acknowledgement signal.

12. The switching center of claim 10 wherein the central control processor is operable to generate said first list and second list upon notification of a base station status change comprising an origination of the call.

13. The switching center of claim 12 wherein the central control processor is further operable to provide the update signal to the primary base station within a call attribute signal.

14. The switching center of claim 10 wherein the central control processor is operable to generate said first list and second list upon notification of a base station status change comprising a soft handoff, wherein said soft handoff includes an addition of a secondary base station to service the call.

15. The switching center of claim 14 the central control processor is further operable to provide the update signal to the primary base station within a handoff acknowledgement signal.

16. The switching center of claim 10 wherein said primary base station comprises a first face of a multi-face base station, and the central control processor is operable to generate said first list and second list upon notification of a base station status change comprising a softer handoff, wherein said softer handoff includes an addition of a second face of the multi-face base station to service the call.

17. The switching center of claim 16 the central control processor is further operable to provide the update signal to the first face of the multi-face base station within a handoff acknowledgement signal.

18. The switching center of claim 10 wherein the central control processor is operable to generate said first list and second list upon notification of a base station status change comprising a handoff wherein at least one base station is added to service the call and at least one base station is dropped from servicing the call.

19. The switching center of claim 10 wherein the central control processor is further operable to provide an update signal containing data representative of the first list to the primary base station.

20. The switching center of claim 10 wherein the central control processor is further operable to generate the second list of subscriber-ineligible neighbors from the first list of neighbor base stations by

i) obtaining subscriber-specific parameters representative of one or more subscriber-specific features;

ii) determining whether a first parameter of the one or more subscriber-specific parameters render a selected base station from the first list ineligible as a handoff candidate; and

iii) repeating step ii) for a plurality of the base stations identified on the first list of neighbor base stations.

21. The switching center of claim 10 wherein said digital control switch is operable to receive call signals in the form of digital data packets.

22. The switching center of claim 10 wherein the digital control switch further comprises a speech handler, said speech handler operable to receive call signals associated with the call and convert the call signals into a format convertible with an external network.

23. A method of performing a handoff during a call in a wireless communication system, the wireless communication system comprising a switching center, a first base station servicing the call prior to handoff, and a second base station, said method comprising:

a) executing the handoff between the first base station and the second base station, wherein the second base station is added to service the call;

b) notifying the switching center that the handoff has occurred;

c) employing the central control processor to determine a list of neighbor base stations which are ineligible for a subsequent handoff; and

d) forwarding the list to at least one base station servicing the call after execution of the handoff.

24. The method of claim 23 wherein step c) further includes employing the central control processor to determine the list of neighbor base stations which are ineligible for a subsequent handoff using subscriber-specific parameters.

25. The method of claim 23 wherein step a) further includes executing a soft handoff between the first base station and the second base station and step d) further includes forwarding the list to first base station.

26. The method of claim 23 further including a step e) selecting a handoff candidate for a subsequent handoff based on the list.

27. The method of claim 23 wherein step c) further comprises first employing the central control processor to determine a first list of neighbor base stations associated with the call and then determining the list of neighbor base stations which are ineligible for a subsequent handoff based on the first list.

28. The method of claim 23 wherein step a) further includes executing a semisoft handoff between the first base station and second base station and step d) further includes forwarding the list to the second base station.

29. The method of claim 27 wherein step b) further comprises providing an information signal to the switching center after the handoff has occurred, the information signal containing information identifying the second base station;

and wherein step c) further comprises determining the first list of neighbor base stations based in part on the information signal.

30. The method of claim 26 wherein step e) further comprises

receiving from a wireless terminal associated with the call a signal containing information representative of one or more signal quality measurements, the signal quality measurements corresponding to each of one or more neighbor base stations;

determining whether there is an eligible handoff candidate, the eligible handoff candidate comprising one of the one or more neighbor base stations, said determination based in part on the signal quality measurements; and

determining whether handoff is permitted to the eligible handoff candidate based on the list.