In-order data delivery during handover in a wireless communication system

1. A method for a target base station of a wireless communication system during handover of user equipment (UE) from a source base station to the target base station, comprising:

determining a value for a timer based on at least one of load on a first interface between the source base station and the target base station, load on a second interface between the source base station and a gateway, load on a third interface between the target base station and the gateway, information for last forwarded packets for prior handovers of other UEs, and quality-of-service (QoS) profile of data being sent to the UE;

starting the timer in the target base station after a data path from the gateway to the UE has been switched from the source base station to the target base station;

receiving forwarded packets for the UE from the source base station;

receiving new packets for the UE from the gateway;

sending forwarded packets received prior to expiration of the timer to the UE before any new packets; and

terminating the timer upon receiving an end marker packet from the source base station.

2. The method of claim 1 , wherein the starting the timer comprises starting the timer upon receiving a first new packet for the UE from the gateway.

3. The method of claim 1 , further comprising:

sending a first message to initiate switching of the data path from the source base station to the target base station; and

receiving a second message indicating completion of the switching of the data path.

4. The method of claim 3 , wherein the starting the timer comprises

starting the timer upon receiving a first new packet for the UE from the gateway when it precedes receipt of the second message.

5. The method of claim 3 , wherein the first message comprise a Handover Complete message and the second message comprises a Handover Complete Acknowledgement (Ack) message.

6. The method of claim 3 , wherein the first message comprise a Path Switch Request message and the second message comprises a Path Switch Request Acknowledgement (Ack) message.

7. The method of claim 1 , further comprising:

sending the forwarded packets to the UE without waiting for expiration of the timer; and

sending the new packets to the UE after expiration of the timer.

8. The method of claim 1 , further comprising:

discarding forwarded packets received after expiration of the timer.

9. The method of claim 1 , further comprising:

sending forwarded packets received after expiration of the timer to the UE if no new packets have been sent to the UE.

10. The method of claim 1 , further comprising:

receiving from the source base station the end marker packet indicating no more packets to forward to the target base station; and

sending the new packets to the UE after terminating the timer.

11. The method of claim 1 , wherein the forwarded packets from the source base station and the new packets from the gateway comprise Packet Data Convergence Protocol (PDCP) service data units (SDUs) or Internet Protocol (IP) packets.

12. The method of claim 2 , wherein the forwarded packets and the new packets are for delivery to the UE.

13. The method of claim 1 , further comprising:

dynamically updating a value for the timer as follows:

T

⁡

(

k

)

{

=

T

⁡

(

k

-

1

)

+

Δ

UP

if

⁢

⁢

D

⁡

(

k

)

>

T

⁡

(

k

-

1

)

{

=

T

⁡

(

k

-

1

)

-

Δ

DN

if

⁢

⁢

D

⁡

(

k

)

≤

T

⁡

(

k

-

1

)

Where:

D(k) is a delay of a last packet forwarded by the source base station for a k-th handover to the target base station,

T(k) is the timer value after the k-th handover, and

Δ UP is an up step and Δ DN is a down step for adjusting the timer value.

14. The method of claim 13 , wherein:

Δ DN =Δ UP ((100 −Q )/ Q )

Where:

Q is a percentage of handovers in which last forwarded packets are received before expiration of the timer.

15. An apparatus for wireless communication, comprising:

at least one processor configured to participate in handover of a user equipment (UE) from a source base station to a target base station, to determine a value for a timer based on at least one of load on a first interface between the source base station and the target base station, load on a second interface between the source base station and a gateway, load on a third interface between the target base station and the gateway, information for last forwarded packets for prior handovers of other UEs, and quality-of-service (QoS) profile of data being sent to the UE, to start the timer after a data path from the gateway to the UE has been switched from the source base station to the target base station, to receive forwarded packets for the UE from the source base station, to receive new packets for the UE from the gateway, to send forwarded packets received prior to expiration of the timer to the UE before any new packets, and to terminate the timer upon receiving an end marker packet from the source base station.

16. The apparatus of claim 15 , wherein the at least one processor is configured to send a first message to initiate switching of the data path from the source base station to the target base station, to receive a second message indicating completion of the switching of the data path, and to start the timer upon receiving a first new packet for the UE from the gateway when it precedes the second message.

17. The apparatus of claim 15 , wherein the at least one processor is configured to send the forwarded packets to the UE without waiting for expiration of the timer, and to send the new packets to the UE after expiration of the timer.

18. The apparatus of claim 15 , wherein the at least one processor is configured to receive from the source base station the end marker packet indicating no more packets to forward to the target base station, and to send the new packets to the UE after terminating the timer.

19. An apparatus for a target base station of a wireless communication system, comprising:

means for determining a value for a timer based on at least one of load on a first interface between a source base station and the target base station, load on a second interface between the source base station and a gateway, load on a third interface between the target base station and the gateway, information for last forwarded packets for prior handovers of other UEs, and quality-of-service (QoS) profile of data being sent to a UE;

means for starting the timer after a data path from the gateway to the UE of the wireless communication system has been switched from the source base station to the target base station during a handover of the UE;

means for receiving forwarded packets for the UE from the source base station;

means for receiving new packets for the UE from the gateway;

means for sending forwarded packets received prior to expiration of the timer to the UE before any new packets; and

means for terminating the timer upon receiving an end marker packet from the source base station.

20. The apparatus of claim 19 , further comprising:

means for sending a first message to initiate switching of the data path from the source base station to the target base station;

means for receiving a second message indicating completion of the switching of the data path; and

means for starting the timer upon receiving a first new packet for the UE from the gateway when it precedes receipt of the second message.

21. The apparatus of claim 19 , further comprising:

means for sending the forwarded packets to the UE without waiting for expiration of the timer; and

means for sending the new packets to the UE after expiration of the timer.

22. The apparatus of claim 19 , further comprising:

means for receiving from the source base station the end marker packet indicating no more packets to forward to the target base station; and

means for sending the new packets to the UE after terminating the timer.

23. A computer program product, comprising:

a non-transitory computer-readable medium comprising:

code for causing at least one computer to participate in handover of a user equipment (UE) from a source base station to a target base station,

code for causing the at least one computer to determine a value for a timer based on at least one of load on a first interface between the source base station and the target base station, load on a second interface between the source base station and a gateway, load on a third interface between the target base station and the gateway, information for last forwarded packets for prior handovers of other UEs, and quality-of-service (QoS) profile of data being sent to the UE;

code for causing the at least one computer to start the timer after a data path from the gateway to the UE has been switched from the source base station to the target base station,

code for causing the at least one computer to receive forwarded packets for the UE from the source base station,

code for causing the at least one computer to receive new packets for the UE from the gateway,

code for causing the at least one computer to send forwarded packets received prior to expiration of the timer to the UE before any new packets; and

code for causing the at least one computer to terminate the timer upon receiving an end marker packet from the source base station.

24. The computer program product of claim 23 , the computer-readable medium further comprising:

code for causing the at least one computer to send a first message to initiate switching of the data path from the source base station to the target base station,

code for causing the at least one computer to receive a second message indicating completion of the switching of the data path, and

code for causing the at least one computer to start the timer upon receiving a first new packet for the UE from the gateway when it precedes receipt of the second message.

25. The computer program product of claim 23 , the computer-readable medium further comprising:

code for causing the at least one computer to send the forwarded packets to the UE without waiting for expiration of the timer, and

code for causing the at least one computer to send the new packets to the UE after expiration of the timer.

26. The computer program product of claim 23 , the computer-readable medium further comprising:

code for causing the at least one computer to receive from the source base station the end marker packet indicating no more packets to forward to the target base station, and

code for causing the at least one computer to send the new packets to the UE after terminating the timer.