Scanning and handover operation in multi-carrier wireless communications systems
A comprehensive solution is provided for multi-carrier scanning and handover operations in OFDM wireless systems. A multi-carrier scanning is any scanning operation that involves multi-carrier radio frequency carriers. In one embodiment, a mobile station communicates with a serving base station over a primary carrier, and performs scanning over one or more determined carriers. A multi-carrier handover is any handover operation that involves multiple radio frequency carriers. In a first embodiment, a break-before-entry (BBE) handover procedure with fast synchronization is provided. In a second embodiment, an entry-before-break (EBB) handover procedure through unavailable intervals is provided. In a third embodiment, EBB handover procedures for both inter-FA and intra-FA using multiple carriers are provided. Finally, in a fourth embodiment, intra-BS handover procedures are provided. The multi-carrier handover procedures may be applied to 2-to-2 or N-to-N carriers handover situation. The overall scanning time and handover interruption time may be reduced through the provided procedures.
1. A method of operating a mobile station to scan neighboring base stations in a multi-carrier OFDMA wireless communications system, the method comprising:
(a) determining one or more radio frequency carriers to be used for scanning, wherein the mobile station is communicating to a serving base station over a primary radio frequency carrier, and wherein the mobile station exchanges control messages with the serving base station over the primary radio frequency carrier; and
(b) performing scanning over the determined one or more radio frequency carriers; wherein the scanning involves measuring the determined radio frequency carriers of a neighbor base station or the serving base station.
2. The method of claim 1 , wherein the one or more determined radio frequency carriers comprises the primary radio frequency carrier, and wherein the mobile station maintains data communication with the serving base station on a secondary radio frequency carrier.
3. The method of claim 1 , wherein the one or more determined radio frequency carriers comprises a secondary radio frequency carrier, and wherein the mobile station maintains data communication with the serving base station on the primary radio frequency carrier.
4. The method of claim 1 , wherein the one or more determined radio frequency carriers comprises both the primary radio frequency carrier and one or more secondary radio frequency carriers.
5. The method of claim 1 , wherein scanning involves measuring another radio frequency carrier of either a neighbor base station or the serving base station.
6. The method of claim 5 , wherein the measuring comprises measurement of at least one of a radio signal strength, a carrier-to-interference noise ratio, and a round-trip delay.
7. A method of operating a mobile station to handover from a serving base station to a target base station in a multi-carrier OFDMA wireless communications system, the method comprising:
(a) receiving a handover command from the serving base station via an original primary carrier;
(b) performing synchronization procedure with the target base station using a secondary carrier without exchanging handover signaling messages with the serving base station over the secondary carrier;
(c) disconnecting all connections on all carriers from the serving base station after the synchronization procedure; and
(d) performing network reentry and thereby establishing data path with the target base station through a new primary carrier, wherein the network reentry is performed using the original primary carrier, wherein an uplink adjustment of the secondary carrier are reused by the original primary carrier for the network reentry, and wherein the original primary carrier becomes the new primary carrier.
8. The method of claim 7 , wherein the network reentry in (d) is performed using the secondary carrier, and wherein the secondary carrier becomes the new primary carrier.
9. The method of claim 7 , wherein the synchronization procedure comprises:
performing downlink physical layer synchronization;
acquiring network reentry related parameters; and
performing ranging for uplink power/timing/frequency adjustments.
10. A method of operating a mobile station to handover from a serving base station to a target base station in a multi-carrier OFDMA wireless communications system, the method comprising:
(a) receiving a handover command from the serving base station via a primary carrier, wherein the handover command comprises the target base station carrier assignment and configuration information;
(b) performing ranging and network reentry with the target base station using a secondary carrier while maintaining communications with the serving base station on the primary carrier, wherein the network reentry is performed on a target primary carrier;
(c) establishing a new primary carrier data path with the target base station, wherein the secondary carrier becomes the new primary carrier, wherein the new primary carrier data path is established to the target primary carrier, and wherein a second data path is established to a target secondary carrier; and
(d) disconnecting all connections on all carriers from the serving base station after network reentry is completed.
11. The method of claim 10 further comprising:
performing ranging with the target base station on the target secondary carrier.
12. A method of operating a mobile station to handover from a serving base station to a target base station in a multi-carrier OFDMA wireless communications system, the method comprising:
(a) receiving a handover command from the serving base station via a primary carrier, wherein the handover command comprises the target base station carrier assignment and configuration information;
(b) switching the primary carrier to another carrier;
(c) performing ranging and network reentry with the target base station using the primary carrier while maintaining communications with the serving base station on a secondary carrier, wherein the network reentry is performed on a target primary carrier;
(d) establishing a new primary carrier data path with the target base station, wherein the primary carrier remains as the new primary carrier, wherein the new primary carrier data path is established to the target primary carrier, and wherein a second data path is established to a target secondary carrier; and
(e) disconnecting all connections on all carriers from the serving base station after network reentry is completed.
13. The method of claim 12 further comprising:
performing ranging with the target base station on the target secondary carrier.
14. A method of operating a mobile station to handover from a serving base station to a target base station in a wireless communications system, the method comprising:
(a) transmitting a handover request for requesting a plurality of unavailable intervals to the serving base station via a primary carrier, wherein the length of each unavailable interval and the duration of the unavailable intervals is negotiated between the mobile station and the serving base station during handover preparation phase;
(b) performing ranging and network reentry with the target base station within the requested unavailable intervals such that communication is maintained with the serving base station;
(c) establishing a new primary carrier data path with the target base station; and
(d) maintaining communication with the serving base station until the new data path with the target base station is established.
15. The method of claim 14 , wherein the network entry is performed using a secondary carrier, and wherein the secondary carrier becomes the new primary carrier.
16. The method of claim 14 , wherein the network entry is performed using the primary carrier, and wherein the primary carrier remains as the new primary carrier.
17. A method of operating a mobile station to handover from one carrier to another carrier within a serving base station in a multi-carrier OFDMA wireless communications system, the method comprising:
(a) establishing data connections with the serving base station over an original primary carrier and a secondary carrier;
(b) receiving an intra-BS handover command from the serving base station; and
(c) establishing a new primary carrier data path with the same serving base station over the secondary carrier, wherein the original primary carrier is either disconnected or reconfigured into a new secondary carrier after the new primary carrier is established.
18. The method of claim 17 , wherein the new primary carrier is established after performing ranging using the secondary carrier.
19. The method of claim 17 , wherein the secondary carrier exists before the handover procedure, and wherein the new primary carrier is established using the secondary carrier without performing ranging.