Method of assigning a mobile unit to a tracking area based on a location update frequency

1. A method for implementation in a wireless communication system including first base stations that operate according to a first technology and are assigned to at least one first technology-specific tracking area and second base stations that operate according to a second technology and are assigned to at least one second technology-specific tracking area, comprising:

detecting a transition of a mobile unit between said at least one first technology-specific tracking area and said at least one second technology-specific tracking area;

determining, in response to detecting the transition, a location update frequency indicating a frequency of transitions of the mobile unit between said at least one first technology-specific tracking area and said at least one second technology-specific tracking area

assigning the mobile unit to a shared tracking area based on the location update frequency, the shared tracking area comprising at least one first base station and at least one second base station.

2. The method of claim 1 , wherein the mobile unit determines the location update frequency.

3. The method of claim 2 , wherein the mobile unit requests assignment to shared tracking area when the location update frequency exceeds a selected threshold, and wherein assigning the mobile unit to the shared tracking area comprises assigning the mobile unit to the shared tracking area in response to the request.

4. The method of claim 3 , wherein determining the location update frequency comprises initiating a timer in response to a-detecting the transition between said at least one first technology-specific tracking area and said at least one second technology-specific tracking area.

5. The method of claim 4 , wherein determining the location update frequency comprises determining a number of location updates transmitted by the mobile unit in response to transitions between said at least one first technology-specific tracking area and said at least one second technology-specific tracking area during a time period indicated by the timer.

6. The method of claim 1 , wherein assigning the mobile unit to the shared tracking area comprises assigning the mobile unit to the shared tracking area when the location update frequency exceeds a selected threshold.

7. The method of claim 1 , wherein the mobile unit selects the shared tracking area.

8. The method of claim 1 , wherein assigning the mobile unit to the shared tracking area comprises assigning the mobile unit to the shared tracking area at a node associated with at least one network serving the shared tracking area.

9. The method of claim 1 , wherein assigning the mobile unit comprises providing information indicative of the assignation of the mobile unit to the shared tracking area to the mobile unit.

10. The method of claim 1 , wherein assigning the mobile unit comprises assigning the mobile unit to the shared tracking area such that paging messages are provided to the mobile unit via said at least one first base station or said at least one second base station included in the shared tracking area.

11. The method of claim 1 , wherein assigning the mobile unit to the shared tracking area comprises assigning the mobile unit to the technology-specific tracking area based on a timer that is restarted when a technology change happens and continues counting up (or down) when no technology change happens.

12. The method of claim 11 , comprising initiating the timer in response to selecting the shared tracking area and assigning the mobile unit to either the first technology-specific tracking area or the second technology-specific tracking area after a predetermined duration indicated by the timer.

13. The method of claim 1 , comprising determining a number of transitions between technology-specific tracking areas after the mobile unit has been assigned to the shared tracking area.

14. The method of claim 13 , wherein comprising maintaining the assignment of the mobile unit to the shared tracking area in response to determining that the number of transitions between technology-specific tracking areas after the mobile unit has been assigned to the shared tracking area exceeds a predetermined threshold.

15. The method of claim 1 , wherein the mobile unit detects the transition between said at least one first technology-specific tracking area and said at least one second technology-specific tracking area.

16. The method of claim 1 , wherein a common node detects the transition between said at least one first technology-specific tracking area and said at least one second technology-specific tracking area, and wherein the common node is communicatively coupled to said at least one first base station and said at least one second base station.

17. The method of claim 16 , wherein the common node determines the location update frequency.

18. The method of claim 17 , wherein the common node determines the location update frequency using a record of previous registrations of mobile units.

19. The method of claim 17 , wherein the common node keeps track of tracking areas visited by the mobile unit and determines whether the mobile unit is ping-ponging based on the tracking areas visited by the mobile unit.