4.11 HS-DSCH procedure

25.2243GPPPhysical layer procedures (TDD)TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.11.1 Link adaptation procedure

For HS-DSCH, the modulation scheme and effective code rate shall be selected by higher layers located within the NodeB. This shall be achieved by appropriate selection of an HS-DSCH transport block size, modulation format and resources by higher layers. Selection of these parameters may be based on CQI reports from the UE.

The overall HS-DSCH link adaptation procedure consists of two parts:

Node B procedure:

1) The NodeB shall transmit HS-SCCH carrying a UE identity identifying the UE for which HS-DSCH TTI allocation has been given. In the case of HS-DSCH transmissions in consecutive TTIs to the same UE, the same HS-SCCH shall be used for associated signalling.

2) The NodeB transmits HS-DSCH to the UE using the resources indicated in the HS-SCCH.

3) Upon receiving the HS-SICH from the respective UE, the status report (ACK/NACK and CQI) shall be passed to higher layers.

UE procedure:

1) When indicated by higher layers, the UE shall start monitoring all HS-SCCHs that are in its HS-SCCH set as signalled to it by higher layers. The information carried on the HS-SCCH is described in [8].

2) In the case that a HS-SCCH is identified to be correct by its CRC, the UE shall read the HS-PDSCHs indicated by the HS-SCCH. In the case that a HS-SCCH is identified to be incorrect, the UE shall discard the data on the HS-SCCH and return to monitoring.

3) After reading the HS-PDSCHs, the UE shall generate an ACK/NACK message and transmit this to the NodeB in the associated HS-SICH, along with the most recently derived CQI.

The mapping of HS-PDSCH channelisation code set and timeslot information carried by the HS-SCCH for a given HS-DSCH TTI is described in [9].

For a given allocation of HS-PDSCH resources to a UE for a specific HS-DSCH TTI, the following shall apply:

– If timeslot information on HS-SCCH indicates two or more timeslots, none of these timeslots shall comprise a beacon channel.

– If timeslot information on HS-SCCH indicates a single timeslot and this timeslot comprises a beacon channel then:

– The Node-B shall not indicate SF=1 for any HS-PDSCH resource.

– The set of HS-PDSCH resources allocated by the Node-B to a UE shall exclusively comprise either beacon function or non-beacon function physical channels. The Node B shall therefore not allocate both beacon function and non-beacon function physical channels within the beacon timeslot to the UE. If the HS-DSCH for a specific HS-DSCH TTI is mapped to the beacon channel, this shall be signalled using k_start = 1 and k_stop = 1. For a definition of the first and last allocated channelisation code indices k_start and k_stop on HS-SCCH refer to [9].

– When SCTD antenna diversity is applied to the beacon channel, then the presence of channelisation code within the channelisation code set information on HS-SCCH shall implicitly indicate the presence of channelisation code .

4.11.2 HS-DSCH channel quality indication procedure

The channel quality indicator (CQI) provides the NodeB with an estimate of the code rate that would have maximised the single-transmission throughput of the previous HS-DSCH transmission if decoded in isolation. The CQI report requires to be referenced to a given set of HS-PDSCH resources by the NodeB, but note that the UE is not restricted to making measurements only on these reference resources when deriving a given CQI. The reference resources for a CQI report shall be a set of HS-PDSCH resources that were received by the UE in a single TTI, and contain a complete transport block. These resources will be known to the NodeB from the relative timings of the HS-SICH carrying the CQI and previous HS-DSCH transmissions to the UE.

The CQI consists of two fields; a Recommended Transport Block Size (RTBS) and a Recommended Modulation Format (RMF). The UE shall use the same mapping table for these fields as is being used for the time slot information and modulation scheme information fields respectively of the HS-SCCH [18].

The reporting procedure is as follows:

1. The UE receives a message on an HS-SCCH telling it which resources have been allocated to it for the next associated HS-DSCH transmission.

2. The UE reads the associated HS-DSCH transmission, and makes the necessary measurements to derive a CQI that it estimates would have given it the highest single-transmission throughput for the allocated resources whilst achieving a BLER of no more than 10 %.

BLER, in this context, is defined as the probability that a transport block transmitted using the RTBS and RMF is received in error if decoded in isolation. For the purposes of this calculation, it shall be assumed that the transport block that would be transmitted with these parameters would use redundancy version parameters s = 1 and r = 0. Note that, by this definition, a UE shall never report a CQI that corresponds to a code rate greater than unity.

Using this definition of BLER, single-transmission throughput shall be defined as follows :

single-transmission throughput = (1 – BLER)  RTBS

3, The CQI report derived from a given HS-DSCH transmission shall be reported to the NodeB in the next HS-SICH available to the UE following that HS-DSCH transmission, unless that HS-SICH immediately follows the last allocated HS-DSCH timeslot, in which case the subsequent available HS-SICH shall be used by the UE. This HS-SICH may not necessarily be the same HS-SICH that carries the ACK/NACK information for that HS-DSCH transmission. The UE shall always transmit the most recently derived CQI in any given HS-SICH, which may mean that some CQI reports are discarded without being transmitted to the NodeB.