11a Downlink Control Channel Discontinuous Reception in CELL_DCH state (1.28Mcps TDD only)
25.3083GPPHigh Speed Downlink Packet Access (HSDPA)Overall descriptionRelease 17Stage 2TS
In 1.28Mcps TDD, the downlink control channel discontinuous reception is a configuration of CELL_DCH state. The Node B has a fast mechanism to revert to the continuous DL transmission autonomously and instantaneously based on standardised rules if more data arrives to the transmission buffer.
When the downlink control channel discontinuous reception is enabled, the UE is not required to receive physical downlink control channels, except if any of the following conditions apply:
1. The UE has received DRX de-activation.
2. The UE shall receive E-HICH subframes corresponding to an E-DCH transmission.
3. The UE shall receive an HS-SCCH subframe due to the HS-SCCH reception pattern.
4. The UE shall monitor the HS-SCCH subframes when the timer Inactivity Threshold for HS-SCCH DRX cycle (described in [10])has not expired.
5. The UE shall monitor the full E-AGCH transmissions from the serving E-DCH cell:
– when TEBS is larger than zero,
– or due to the E-AGCH reception pattern,
– or when UE should receive an E-HICH transmission,
– or the timer E_AGCH_Inactivity_Monitor_Threshold has not expired.
The HS-SCCH reception pattern is defined in such a way that the UE must receive one HS-SCCH sub-frame every HS-SCCH DRX cycle sub-frames. The HS-SCCH reception pattern can be offset using HS-SCCH DRX offset so that different UEs have the HS-SCCH reception phase at different times.
The HS-SCCH reception pattern is illustrated by Figure 11a-1. The grey subframes correspond to the HS-SCCH reception pattern HS-SCCH DRX cycle =4.
Figure 11a-1: Example for HS-SCCH reception pattern for LCR TDD
The E-AGCH reception pattern is defined as a same way as the HS-SCCH reception pattern.
12 HS-SCCH-less HS-DSCH transmission in FDD
The HS-SCCH-less HS-DSCH transmission is a mechanism whereby the first HS-DSCH transmission of small transport blocks on predefined HS-DSCH is performed without the accompanying HS-SCCH and HARQ retransmissions of the first HS-DSCH transmission are accompanied by the HS-SCCH.
HS-SCCH-less HS-DSCH transmission mechanism is configuration of CELL_DCH state, when F-DPCH is configured without DCH configured in Downlink or Uplink. The HS-SCCH-less HS-DSCH transmission mechanism can be configured with or without a configuration of discontinous transmission and reception as defined in subclause 11. However, if Downlink DRX is configured the times at which the UE is mandated to be receiving HS-PDSCH and/or HS-SCCH should be taken into account by the Node B scheduler.
Furthermore, an HS-SCCH-less HS-DSCH transmission has the following characteristics:
– The modulation used is restricted to QPSK.
– 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.
– The HS-PDSCH CRC is 24-bits long and is UE specific.
– Its generation follows the same procedure as the CRC currently on the HS-SCCH, and therefore is covered by the 16-bit UE specific H-RNTI.
– At most two pre-defined HS-PDSCH OVSF codes are assigned per UE
– The pre-defined HS-PDSCH OVSF codes are semi-statically assigned per UE.
– At anytime, the UE may receive an HS-SCCH-less HS-DSCH transmission on one or two of the configured codes and must perform blind decoding on all 4 configured formats.
– In order to perform blind decoding on the pre-defined HS-PDSCH OVSF codes, UE must maintain a cyclic soft buffer storing 13 contiguous TTIs.
– The UE does not transmit negative acknowledgements (NACK) in the first transmission when decoding the chosen formats. It transmits ACK or NACKs for the retransmissions.
– HARQ is limited to:
– 2 retransmissions.
– The redundancy version is pre-defined and not configurable.
– The HARQ retransmissions of an HS-SCCH-less HS-DSCH transmission are accompanied by an HS-SCCH, which is sent with the same channel coding and decoding as the Release 5/6 HS-SCCH. Some of the bits of the HS-SCCH are reinterpreted in order to signal the UE the following information.
– That the HS-SCCH is intended for HS-SCCH-less operation
– Whether the retransmission is the first retransmission or the second retransmission
– The channelization code and the transport block size used by the HARQ process
– The HARQ combining information – in the form of an offset from the current TTI indicating where the previous transmission was sent
In addition, the UE continues to attempt reception of the legacy HS-SCCH in the configured HS-SCCH set.
For a UE configured for HS-SCCH-less operation, the serving HS-DSCH cell can deactivate and reactivate HS-SCCH-less operation by transmitting an HS-SCCH order to the UE.
12.1 HS-SCCH-less timing and operation
The timing of the HS-SCCH-less operation is similar to the timing in legacy HSDPA operation. It is depicted in Figure 12.1-1.
Figure 12.1-1: Illustration of the HS-SCCH-less operation
The first and second 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; namely the HS-SCCH starts and ends one slot before the HS-PDSCH transmission boundaries.
If the UE is able to decode the first transmission successfully, it sends an ACK to the Node B over the HS-DPCCH. If it is not able to decode the first transmission, it buffers the data sent on the TTI. The retransmissions do not require any blind combining or decoding operation as the HS-SCCH accompanying the retransmissions carry the information needed.
In order to combine the initial HS-SCCH-less HS-DSCH transmission with the subsequent retransmissions, the new HS-SCCH format contains a pointer to the TTI where the previous transmission has been performed. In addition, the redundancy version is pre-defined for the initial transmission as well as the potential subsequent retransmissions.