19 HS-SCCH-less HS-DSCH transmission in 1.28Mcps TDD

25.3083GPPHigh Speed Downlink Packet Access (HSDPA)Overall descriptionRelease 17Stage 2TS

The HS-DSCH semi-persistent scheduling transmission is a mechanism whereby the first HS-DSCH transmission of transport blocks on the semi-persistent HS-DSCH resources is performed without the accompanying HS-SCCH and HARQ retransmissions of the first HS-DSCH transmission on the semi-persistent HS-DSCH resources are accompanied by a new format HS-SCCH.

HS-DSCH semi-persistent scheduling transmission mechanism is a configuration of CELL_DCH state, when the semi-persistent HS-DSCH resources are configured for a UE. And the semi-persistent HS-DSCH resources can be configured and reconfigured by a new format HS-SCCH.

Furthermore, an HS-DSCH semi-persistent scheduling transmission has the following characteristics:

– Only 4 pre-defined TB formats for MAC-hs or MAC-ehs PDUs are allowed.

– These 4 formats are chosen semi-statically, and maybe independently configured per UE.

– HARQ is limited to:

– The redundancy version is pre-defined.

– The HARQ retransmissions of an HS-DSCH semi-persistent scheduling are accompanied by an HS-SCCH.

In addition, the UE continues to attempt reception of the legacy HS-SCCH in the configured HS-SCCH set. The Node B shall transmit at most one HS-SCCH to a UE in one TTI.

19.1 HS-DSCH semi-persistent scheduling timing and operation

For the retransmission of the HS-DSCH semi-persistent scheduling transmission, the timing for HS-SCCH and HS-DSCH and the timing for HS-DSCH and HS-SICH is similar to the timing in legacy HSDPA operation.

The retransmissions can be asynchronous with respect to the first transmission, and with respect to each other. The accompanying HS-SCCH follows the same timing relationship with the HS-PDSCH transmission as legacy transmissions do.

If the UE is able to decode the first transmission successfully, it sends an ACK to the Node B over the HS-SICH. If it is not able to decode the first transmission, it sends an NACK to the Node B over the HS-SICH and buffers the data sent on the TTI. The retransmissions do not require any blind combining or decoding operation as the new format HS-SCCH accompanying the retransmissions carry the information needed.

In order to combine the initial HS-DSCH semi-persistent scheduling transmission with the subsequent retransmissions, the new HS-SCCH format contains a pointer to the TTI where the previous transmission has been performed.

If the UE has both semi-persistent HS-PDSCH resources and legacy scheduling resources in the same TTI, UE shall only receive data on legacy scheduling HS-PDSCH resources.

19.2 Assignment/reassignment of semi-persistent HS-PDSCH resources for HS-DSCH semi-persistent scheduling transmission

For the HS-DSCH semi-persistent scheduling transmission, Node B sends the control commands on HS-SCCH to assign/reassign the semi-persistent HS-PDSCH resources.

If the UE receives these commands correctly, the UE shall feedback the RTBS with the value of zero and ACK on the HS-SCCH associated HS-SICH. UE should stop receiving data on the previous HS-PDSCH and stop sending feedback on the corresponding HS-SICH and begin to receive data on the reassigned HS-PDSCH and send feedback on its associated HS-SICH.

Node B checks the feedback on HS-SICH to judge whether the HS-SCCH commands have been received by the UE correctly.

If the Node B determines the UE has received the HS-SCCH commands correctly, it can schedule the previous semi-persistent HS-PDSCH resources to other users. Otherwise, it shall send the assignment/reassignment commands again.