DOWNLINK PACKET DATA CONVERGENCE PROTOCOL BEHAVIOR DURING HANDOVER

• US 20080310368A1
• Filed: 06/17/2008
• Published: 12/18/2008
• Est. Priority Date: 06/18/2007
• Status: Active Grant

• Current Assignee: LG Electronics, Inc. (LG Corporation)
• Original Assignee: LG Electronics, Inc. (LG Corporation)
• Inventors: Fischer, Patrick
• Granted Patent: US 8,054,836 B2
• Time in Patent Office: Days
• US Class Current: 370/331
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04W 36/0007 for multicast or broadcast services, e.g. MBMS multicast or broadcast application services H04W4/06; resource management for broadcast services H04W72/30; connection management for selective distribution or broadcast H04W76/40
• CPC Class Codes: H04W 36/02 Buffering or recovering information during reselection ; Modification of the traffic flow during hand-off

Abstract

The present invention relates to maintaining an order of received data units during a handover procedure in a wireless communication system. The present invention includes receiving a plurality of data units from a source station according to a sequence prior to handover to a target base station, wherein each data unit includes a sequence number, receiving at least one data unit having a sequence number after handover from a target base station, and delivering to a higher layer all data units received from the source base station prior to handover and having sequence numbers smaller than a sequence number of the at least one data unit received from the target base station after handover.

Claims

1. A method for maintaining an order of received data units during a handover procedure in a wireless communication system, the method comprising:

receiving a plurality of data units from a source base station according to a sequence prior to handover to a target base station, wherein each data unit includes a sequence number;

receiving at least one data unit having a sequence number after handover from a target base station; and

delivering to a higher layer all data units received from the source base station prior to handover and having sequence numbers smaller than a sequence number of the at least one data unit received from the target base station after handover.

2. The method of claim 1, further comprising:

delivering all data units received before starting handover which are available sequentially to a higher layer, wherein a sequentially available data unit has a sequence number immediately sequential to a sequence number of a next available data unit or the sequence number of the at least one data unit received from the target base station after starting handover.

3. The method of claim 1, further comprising:

starting a timer at the start of handover; and

delivering the data units to the higher layer when the timer expires.

4. The method of claim 2, further comprising:

starting a timer at the start of handover; and

delivering the data units to the higher layer when the timer expires.

5. The method of claim 2, wherein the data units are delivered to the higher layer upon receiving an indication from at least one of the source base station and the target base station to deliver the data units.

6. A method for maintaining an order of received data units during a handover procedure in a wireless communication system, the method comprising:

receiving a plurality of data units according to a sequence prior to starting handover, wherein each data unit includes a sequence number;

receiving at least one data unit having a sequence number after starting handover; and

delivering to a higher layer all data units received prior to starting handover and having sequence numbers smaller than a sequence number of the at least one data unit received after starting handover.

7. The method of claim 6, further comprising:

delivering all data units received before starting handover which are available sequentially to a higher layer, wherein a sequentially available data unit has a sequence number immediately sequential to a sequence number of a next available data unit or the sequence number of the at least one data unit received after starting handover

8. The method of claim 6, further comprising:

starting a timer at the start of handover; and

delivering the data units to the higher layer when the timer expires.

9. The method of claim 7, further comprising:

starting a timer at the start of handover; and

delivering the data units to the higher layer when the timer expires.

10. The method of claim 7, wherein the data units are delivered to the higher layer upon receiving an indication to deliver the data units.

11. A method for maintaining an order of received data units during a handover procedure in a wireless communication system, the method comprising:

receiving a plurality of data units according to a sequence prior to starting handover, wherein each data unit includes a sequence number;

receiving at least one data unit having a sequence number after starting handover;

starting a timer at the start of handover;

delivering to a higher layer all data units received prior to starting handover and having sequence numbers smaller than a sequence number of the at least one data unit received after starting handover when the timer expires; and

delivering all data units received before starting handover which are available sequentially to a higher layer when the timer expires, wherein a sequentially available data unit has a sequence number immediately sequential to a sequence number of a next available data unit or the sequence number of the at least one data unit received after starting handover.

12. A method for maintaining an order of data units during a handover procedure in a wireless communication system, the method comprising:

transmitting a plurality of data units from a source base station to a mobile terminal according to a sequence prior to handover to a target base station, wherein each data unit includes a sequence number;

informing the target base station of a highest sequence number of a data unit previously transmitted by the source base station; and

transmitting at least one data unit having a sequence number from the target base station to the mobile terminal after handover,

wherein the at least one data unit is transmitted from the target base station with regard to the highest sequence number of the data unit previously transmitted by the source base station.

13. The method of claim 12, wherein the target base station receives information regarding the highest sequence number after handover from at least one of:

the mobile terminal; and

the source base station.

14. The method of claim 12, further comprising:

transmitting the at least one data unit from the target base station with a sequence number higher than the highest sequence number of the data unit previously transmitted by the source base station,

wherein the at least one data unit has not been previously transmitted,

wherein the source base station and the target base station discard all data units that have been previously transmitted.

15. The method of claim 12, further comprising:

forwarding from the source base station to the target base station all unacknowledged data units previously transmitted by the source base station to the mobile terminal;

transmitting the forwarded data units from the target base station to the mobile terminal; and

transmitting the at least one data unit from the target base station with a sequence number higher that the highest sequence number of the data unit previously transmitted by the source base station, wherein the at least one data unit has not been previously transmitted.

16. The method of claim 15, wherein the data units forwarded from the source base station are received by the target base station in sequential order according to their respective sequence numbers.

17. The method of claim 16, wherein the target base station discards a data unit having a sequence number that is out-of-sequence with the sequential order of the data units forwarded from the source base station.

18. The method of claim 15, wherein the target base station transmits to the mobile terminal the forwarded data units previously transmitted by the source base station before transmitting the at least one data unit not previously transmitted.

19. The method of claim 15, wherein the target base station transmits data units to the mobile terminal in a sequentially increasing order according to their respective sequence numbers.

20. The method of claim 15, further comprising informing the target base station of a latest sequence number of a data unit previously received by the mobile terminal.

21. The method of claim 20, further comprising:

determining in the target base station that a sequence number of a forwarded data unit for transmission to the mobile terminal does not sequentially correspond with the latest sequence number of the data unit previously received by the mobile terminal; and

removing the sequence number of the forwarded data unit and transmitting the forwarded data unit out-of-sequence from the target base station to the mobile terminal if a data unit sequentially corresponding with the latest sequence number of the data unit previously received by the mobile terminal is not received by the target base station before a predetermined time elapses.

22. The method of claim 20, further comprising:

determining in the target base station that a sequence number of a forwarded data unit for transmission to the mobile terminal does not sequentially correspond with the latest sequence number of the data unit previously received by the mobile terminal; and

discarding the forwarded data unit.

23. A method for maintaining an order of received data units during a handover procedure in a wireless communication system, the method comprising:

receiving a plurality of data units according to a sequence prior to starting handover, wherein each data unit includes a sequence number;

starting a timer at the start of handover; and

delivering all data units received before starting handover that are not in sequence to a higher layer when the timer expires.

24. A method for detecting an error in the order of received data units in a wireless communication system, the method comprising:

receiving a plurality of data units according to a sequence, wherein each data unit includes a sequence number,

wherein no error occurs if a currently received data unit has a sequence number within an interval from a last received data unit sequence number to a predetermined sequence number after the last received data unit sequence number, and

wherein an error occurs if the currently received data unit has a sequence number beyond the interval from the last received data unit sequence number to the predetermined sequence number after the last received data unit sequence number.

25. A method for maintaining an order of data units during a handover procedure in a wireless communication system, the method comprising:

transmitting a plurality of data units according to a sequence from a source base station to a mobile terminal, wherein each data unit includes a sequence number;

transmitting a handover request from a source base station to a target base station; and

transmitting from the source base station to the target base station information related to an appropriate sequence number to be used by the target base station for transmission,

wherein the target base station determines the appropriate sequence number for transmission using the information from the source base station.

26. The method of claim 25, wherein the information comprises one of:

a next sequence number to be used by the target base station for transmission;

a highest sequence number of a data unit previously transmitted by the source base station; and

a timestamp and an expected data rate/sequence number rate.

27. The method of claim 25, wherein the appropriate sequence number is greater than a highest sequence number of a data unit previously transmitted by the source base station.