Method and apparatus for selecting a radio link control protocol data unit size
A method and apparatus are used to create RLC PDUs in advance of the E-TFC selection for the MAC PDU that will include this or these RLC PDU(s). The apparatus may be configured to pre-generate RLC PDUs for transmission in a later TTI. This approach avoids the large peak processing requirement due to the tight delay constraint if any RLC PDU to be included into a MAC PDU had to be created after the determination of the size of this MAC PDU, i.e. after E-TFC selection. The method and apparatus maintain an approximate match between the size of an RLC PDU and the size of the MAC PDU it is included into. Maintaining this approximate match ensures that the RLC PDU error rate due to HARQ residual errors remains low. This approach may be designed as “semi-radio aware” or “radio-aware with delay”.
1. A method for use in a wireless transmit/receive unit (WTRU) for generating a radio link control (RLC) protocol data unit (PDU), the method comprising:
determining whether there is data available for transmission;
on a condition that a total amount of data in outstanding RLC PDUs that are pre-generated for transmission in a later transmission time interval (TTI) is within a predetermined limit, pre-generating an RLC PDU for transmission in the later TTI, wherein the predetermined limit corresponds to a factor multiplied by a maximum amount of data for transmission allowed by a current grant for a current TTI; and
setting a size of a data field in the RLC PDU, wherein the size of the data field is determined such that an RLC PDU size matches an amount of data allowed for transmission by the current grant for the current TTI.
2. The method of claim 1 , wherein the amount of data allowed for transmission is based on a number of bits of a currently selected enhanced dedicated channel (E-DCH) transport format combination (E-TFC).
3. The method of claim 1 further comprising accounting for a selected power offset for determining the maximum amount of data allowed for transmission.
4. The method of claim 3 , wherein the selected power offset corresponds to a power offset of a hybrid automatic repeat request (HARM) profile of a highest priority MAC-d flow selected in the current TTI.
5. The method of claim 4 , wherein the highest priority MAC-d flow selected in the current TTI is determined by an enhanced dedicated channel (E-DCH) transport format combination (E-TFC) procedure.
6. The method of claim 3 , wherein the selected power offset corresponds to a power offset of a hybrid automatic repeat request (HARD) profile of a MAC-d flow of a logical channel to which the data belongs.
7. The method of claim 1 , wherein the current grant is a scheduled grant on a condition that the data belongs to a logical channel mapped to a scheduled MAC-d flow.
8. The method of claim 1 , wherein the current grant is a non-scheduled grant on a condition that the data belongs to a logical channel mapped to a non-scheduled MAC-d flow.
9. The method of claim 1 , wherein the RLC PDU size is set to a maximum RLC PDU size on a condition that the amount of data for transmission allowed by the current grant for the current TTI exceeds the maximum RLC PDU size.
10. The method of claim 1 , wherein the RLC PDU size is set to a minimum RLC PDU size on a condition that the amount of data for transmission allowed by the current grant for the current TTI is below the minimum RLC PDU size.
11. The method of claim 1 , wherein an RLC PDU of a smaller size than the RLC PDU size is pre-generated on a condition that there is insufficient available data.
12. The method of claim 1 , further comprising storing the RLC PDU in memory for inclusion into a MAC PDU for transmission in the later TTI.
13. The method of claim 1 , wherein the amount of data allowed for transmission is a smaller value between the maximum amount of data allowed for transmission by the current grant for the current TTI and a maximum amount of data allowed for transmission based on a maximum transmission power of the WTRU.
14. The method of claim 1 , wherein the size of the data field of the RLC PDU is selected on a periodic basis, wherein the periodic basis includes at least one of a transmission time interval (TTI) basis, a predetermined TTI basis, at an E-TFC selection, when a new RLC PDU is generated from a segmentation or concatenation of RLC service data units (SDUs), when the RLC receives new data, when a serving grant is updated, upon an active set update procedure, when a serving cell changes, upon setup, configuration, or reconfiguration of a radio bearer, a transport channel, or a physical channel, and upon reception of minimum or maximum values from RRC signaling.
15. The method of claim 1 , wherein the size of the data field of the RLC PDU is selected upon a triggering event, the triggering event including at least one of a change in an available number of bits in a transport block, a change in an enhanced dedicated channel (E-DCH) transport format combination index (E-TFCI), a change in a WTRU power headroom, or a change in the serving grant.
16. The method of claim 1 wherein the RLC PDU size is determined at an E-TFC selection in which data from a logical channel is included in an enhanced MAC PDU.
17. The method of claim 1 wherein the RLC PDU size is determined at an E-TFC selection in which one or more HARQ processes are configured to transmit at least one of scheduled data or non-scheduled data.
18. The method of claim 1 wherein the RLC PDU size is determined at an E-TFC selection in which data from a MAC-d flow of a logical channel is included in an enhanced MAC PDU or in which the MAC-d flow of the logical channel is allowed to be multiplexed.
19. A wireless transmit/receive unit (WTRU), the WTRU comprising:
a processor configured to:
determine whether there is data available for transmission;
on a condition that a total amount of data in outstanding RLC PDUs that are pre-generated for transmission in a later transmission time interval (TTI) is within a predetermined limit, pre-generate an RLC PDU for transmission in the later TTI, wherein the predetermined limit corresponds to a factor multiplied by a maximum amount of data for transmission allowed by a current grant for a current TTI; and
set a size of a data field in the RLC PDU, wherein the size of the data field is selected such that an RLC PDU size matches an amount of data allowed for transmission by the current grant for the current TTI.
20. The WTRU of claim 19 , wherein the amount of data allowed for transmission is based on a number of bits of a currently selected enhanced dedicated channel (E-DCH) transport format combination (E-TFC).
21. The WTRU of claim 19 , wherein the processor is further configured to determine the RLC PDU size at a transmission time interval (TTI).
22. The WTRU of claim 19 , wherein the processor is further configured to:
determine the RLC PDU size at an enhanced dedicated channel (E-DCH) transport format combination (E-TFC) selection in which data from a logical channel is included in an enhanced MAC PDU.
23. The WTRU of claim 19 , wherein the processor is further configured to:
determine the RLC PDU size at an enhanced dedicated channel (E-DCH) transport format combination (E-TFC) selection in which one or more HARQ processes are configured to transmit at least one of scheduled data or non-scheduled data.
24. The WTRU of claim 19 , wherein the processor is further configured to:
determine the RLC PDU size at an enhanced dedicated channel (E-DCH) transport format combination (E-TFC) selection in which data from a MAC-d flow of a logical channel is included in an enhanced MAC PDU or in which the MAC-d flow of the logical channel is allowed to be multiplexed.
25. The WTRU of claim 19 , wherein the amount of data allowed for transmission is the maximum amount of data allowed for transmission by the current grant for the current TTI.