Hard handoff procedure for dedicated and high speed shared channels
View Patent ↗A wireless communication network ( 20 ) utilizes a hard handoff procedure for switching between cells serving a mobile station ( 40 ). In a disclosed example, the existing link between the mobile station ( 40 ) and a serving base station ( 38 ) is not released until a new link between a target base station ( 32 ) and a mobile station ( 40 ) is established. At the same time, however, the mobile station maintains only one base station or link within its active set at all times. The disclosed example is useful for dedicated channel and shared channel communications in CDMA systems, for example.
1. A method of communicating between a mobile station, a serving base station and a target base station comprising:
establishing a new link between the target base station and the mobile station before releasing an existing link between the mobile station and the serving base station while having only the existing link in an active set for the mobile station before releasing the existing link by
(A) determining if a handoff is desired between the serving base station and the target base station;
(B) initiating the new link between the mobile station and the target base station;
(C) transmitting an active set update message to the mobile station using the existing link between the serving base station and the mobile station;
(D) achieving uplink synchronization for the target base station to communicate with the mobile station;
(E) receiving at least one signal over the new link indicating that the mobile station has processed the transmitted active set update message; and
(F) releasing the existing link responsive to the at least one signal of step (E).
2. The method of claim 1 , comprising communicating between the mobile station and the target base station using the new link only after completing step (F).
3. The method of claim 1 , wherein step (A) comprises receiving a handoff request from the mobile station and comprising selecting the target base station based at least in part on the received request from the mobile station.
4. The method of claim 1 , wherein step (B) comprises providing the target base station with physical layer control information comprising at least a radio link setup request, a packet data convergence protocol and a radio link control.
5. The method of claim 4 , wherein step (D) comprises initiating the uplink synchronization responsive to the physical layer control information.
6. The method of claim 1 , comprising
providing physical layer control information for downlink synchronization between the target base station and the mobile station from the target base station to the serving base station; and
transmitting the provided physical layer control information from the serving base station to the mobile station.
7. The method of claim 6 , comprising transmitting the provided physical layer control information to the mobile station prior to completing step (D).
8. The method of claim 1 , comprising
receiving a plurality of measurement reports from the mobile station over the existing link; and
predicting the desired handoff based on the received measurement reports.
9. The method of claim 8 , comprising predicting the target base station.
10. The method of claim 1 , comprising receiving at least one signal from the mobile station over the existing link that is indicative of a desire of the mobile station for a handoff and performing step (A) responsive to the received at least one signal.
11. The method of claim 1 , comprising buffering bearer traffic between the mobile station and the serving base station while performing steps (A) through (F).
12. The method of claim 1 , comprising achieving downlink synchronization between the mobile station and the target base station prior to performing step (F).
13. The method of claim 12 , comprising receiving downlink physical layer control information over the existing link, the downlink physical layer control information originating from the target base station for downlink synchronization between the target base station and the mobile station.
14. The method of claim 1 , comprising
determining a characteristic of the existing link;
determining the characteristic of the new link;
determining a difference between the determined characteristics; and
performing step (A) if the determined difference exceeds a threshold that is selected to minimize replacement hysteresis.
15. The method of claim 1 , comprising providing at least one signal indicating a desire for the mobile station to handoff from the existing base station using the existing link.