HSDPA

This page shows how a test network sets up an HSDPA radio bearer on a 1.28 Mcps TDD cell, the TDD option that TD-SCDMA networks use. Both views come from one tester decode of a RadioBearerSetup message in its r5 form. The first view is the MAC and transport channel part, which configures the MAC-hs entity of the UE. The second view is the physical channel part, which places the HS-SCCH, the HS-SICH and the DPCH pair into timeslots and codes. A last section shows how the UE finds its HS-PDSCH, which the message does not configure at all. The values are checked against 25.331 v19.0.1, 25.221 v19.0.0 and 25.222 v19.0.0.

The topics on this page are listed below.

MAC/Transport Layer

Let's start with the part of the message that configures MAC-hs. HSDPA moves retransmission and reordering from the RNC down to the Node B. So the UE needs a matching HARQ entity and a reordering queue before the first HS-DSCH block arrives. The tree below carries exactly that configuration, together with the H-RNTI that addresses the UE.

Each line of the tree is one IE with its ASN.1 type. The bracket holds the decoded value, or the presence bits of a SEQUENCE. OPTIONAL:Exist marks an optional IE that is present, and OPTIONAL:Omit marks one that is absent.

Decoded RadioBearerSetup-r5 from a tester log, captured. Field values are from a live capture, not from the specification.

+-radioBearerSetup-r5 ::= SEQUENCE [001000100001001010101011111]
| +-new-H-RNTI ::= BIT STRING SIZE(16) [1010101010101010] OPTIONAL:Exist
| | +-DL-AddReconfTransChInformation-r5 ::= SEQUENCE [0]
| |   +-dl-TransportChannelType ::= CHOICE [hsdsch]
| |   | +-hsdsch ::= NULL
| |   +-tfs-SignallingMode ::= CHOICE [hsdsch]
| |   | +-hsdsch ::= SEQUENCE [11]
| |   |   +-harqInfo ::= SEQUENCE OPTIONAL:Exist
| |   |   | +-numberOfProcesses ::= INTEGER (1..8) [8]
| |   |   | +-memoryPartitioning ::= CHOICE [explicit]
| |   |   |   +-explicit ::= SEQUENCE OF SIZE(1..maxHProcesses[8]) [8]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   |     +-HARQMemorySize ::= ENUMERATED [hms20800]
| |   |   +-addOrReconfMAC-dFlow ::= SEQUENCE [10] OPTIONAL:Exist
| |   |     +-mac-hs-AddReconfQueue-List ::= SEQUENCE OF SIZE(1..maxQueueIDs[8]) [1] OPTIONAL:Exist
| |   |     | +-MAC-hs-AddReconfQueue ::= SEQUENCE [1]
| |   |     |   +-mac-hsQueueId ::= INTEGER (0..7) [0]
| |   |     |   +-mac-dFlowId ::= INTEGER (0..7) [0]
| |   |     |   +-reorderingReleaseTimer ::= ENUMERATED [rt120]
| |   |     |   +-mac-hsWindowSize ::= ENUMERATED [mws16]
| |   |     |   +-mac-d-PDU-SizeInfo-List ::= SEQUENCE OF SIZE(1..maxMAC-d-PDUsizes[8]) [1]
| |   |     |     +-MAC-d-PDUsizeInfo ::= SEQUENCE
| |   |     |       +-mac-d-PDU-Size ::= INTEGER (1..5000) [336]
| |   |     |       +-mac-d-PDU-Index ::= INTEGER (0..7) [0]

The transport channel type is hsdsch, and tfs-SignallingMode is hsdsch as well. So the message defines no transport format set for this channel. The Node B picks the transport format in each TTI and signals it on the HS-SCCH instead. What RRC does fix is the HARQ entity and the reordering queue, as the bullets below explain.

new-H-RNTI is the identity of the UE on the HS-SCCH : the value 1010101010101010 is 0xAAAA. The Node B masks the CRC of each HS-SCCH with this 16-bit identity. The UE therefore decodes only the HS-SCCH blocks that are meant for it.
Eight HARQ processes share the soft buffer explicitly : numberOfProcesses is 8, and memoryPartitioning is explicit. Each of the eight processes gets hms20800, which is 20800 soft channel bits. The total is 8 x 20800 = 166400 bits, and it must fit within the soft buffer capability of the UE.
One queue carries all the data : mac-hsQueueId is 0 and mac-dFlowId is 0. So one MAC-d flow feeds one reordering queue.
The reordering window is 16 and T1 is 120 ms : mac-hsWindowSize mws16 sets the receiver window. The IE reorderingReleaseTimer rt120 sets the timer T1 to 120 ms. When T1 expires, the UE stops waiting for a missing PDU and delivers the PDUs after it.
The MAC-d PDU size is 336 bits : mac-d-PDU-Size is 336 with index 0. The index is the SID value that the MAC-hs header carries for this size.

The listing below holds the 25.331 definitions behind these lines. You can compare each value of the tree with its value range here.

Following is based on 25.331 v19.0.1 (Release 19)

HARQ-Info ::=						SEQUENCE {
	numberOfProcesses					INTEGER (1..8),
	memoryPartitioning					CHOICE {
		implicit							NULL,
		explicit							SEQUENCE (SIZE (1..maxHProcesses)) OF
												HARQMemorySize
	}
}

MAC-hs-AddReconfQueue ::=			SEQUENCE {
	mac-hsQueueId						INTEGER(0..7),
	mac-dFlowId							MAC-d-FlowIdentity,
	reorderingReleaseTimer				T1-ReleaseTimer,
	mac-hsWindowSize					MAC-hs-WindowSize,
	mac-d-PDU-SizeInfo-List				MAC-d-PDU-SizeInfo-List				OPTIONAL
}

MAC-hs-WindowSize ::=				ENUMERATED {
										mws4, mws6, mws8, mws12, mws16, mws24, mws32 }

T1-ReleaseTimer ::=					ENUMERATED {
										rt10, rt20, rt30, rt40, rt50,
										rt60, rt70, rt80, rt90, rt100,
										rt120, rt140, rt160, rt200, rt300,
										rt400 }

MAC-d-PDUsizeInfo ::=				SEQUENCE{
	mac-d-PDU-Size						INTEGER (1..5000),
	mac-d-PDU-Index						INTEGER(0..7)
}

Physical Layer - Slot Allocation

Now let's move from MAC to the physical channels. A 1.28 Mcps TDD sub-frame is 5 ms long and has seven normal timeslots. Each timeslot holds up to 16 codes at SF16. The message must tell the UE which timeslot and which code carries each of its channels. Figure 1 draws the result, and the two captures after it show the IEs that produce it.

Figure 1 draws two sub-frames side by side. Each column is a timeslot, from Slot 0 to Slot 6, with the DwPTS, the guard period and the UpPTS drawn in grey between Slot 0 and Slot 1. Each row is one SF16 code position, from 1 to 16. The orange cells mark the channels that RRC configures for this UE. The light orange area in Slot 2 to Slot 6 marks the HS-PDSCH area, and a note at the top explains it.

TD-SCDMA HSDPA slot allocation of DPCH, HS-SCCH, HS-SICH and HS-PDSCH

Figure 1. Slot allocation of the HSDPA radio bearer. RRC fixes the DPCH pair, the HS-SCCH and the HS-SICH. The HS-PDSCH in Slot 2 to Slot 6 is assigned in each TTI on the HS-SCCH.

Slot 0, code 1 is the dlDPCH : the DL CCTrCH uses timeslotNumber 0 with one SF16 code.
Slot 0, codes 7 and 8 are the HS-SCCH : firstChannelisationCode is cc16-7 and secondChannelisationCode is cc16-8. In 1.28 Mcps TDD, one HS-SCCH is two physical channels, HS-SCCH1 and HS-SCCH2, each at SF16. That is why the IE carries two codes.
Slot 1, codes 1 to 8 are the ulDPCH : the UL CCTrCH uses one SF2 code, cc2-1. An SF2 code takes the code tree space of eight SF16 codes, so the diagram fills eight rows.
Slot 1, code 11 is the HS-SICH : hs-sich-configuration sets timeslotNumber 1 and channelisationCode cc16-11. The HS-SICH is an uplink channel, so it sits in the uplink timeslot.
Slot 2 to Slot 6 is only a candidate area : RRC gives no HS-PDSCH code here. The note in the diagram says that the xtbs field of the HS-SCCH sets the slot. In 25.222 v19.0.0, the timeslots come from the time slot information bits xts. The xtbs bits carry the transport block size index. The last section of this page covers these fields.

The capture below is the downlink part. The red lines are the containers of the HS-SCCH, the HS-SICH and the DL timeslot. The blue lines are the timeslot and code values drawn in Figure 1.

Decoded RadioBearerSetup-r5 from a tester log, downlink part, captured. Field values are from a live capture, not from the specification.

| +-dl-HSPDSCH-Information ::= SEQUENCE [10] OPTIONAL:Exist
| | +-hs-scch-Info ::= SEQUENCE OPTIONAL:Exist
| | | +-modeSpecificInfo ::= CHOICE [tdd]
| | |   +-tdd ::= CHOICE [tdd128]
| | |     +-tdd128 ::= SEQUENCE OF SIZE(1..maxHSSCCHs[4]) [1]
| | |       +-HS-SCCH-TDD128 ::= SEQUENCE
| | |         +-timeslotNumber ::= INTEGER (0..6) [0]
| | |         +-firstChannelisationCode ::= ENUMERATED [cc16-7]
| | |         +-secondChannelisationCode ::= ENUMERATED [cc16-8]
| | |         +-midambleAllocationMode ::= CHOICE [defaultMidamble]
| | |         | +-defaultMidamble ::= NULL
| | |         +-midambleConfiguration ::= INTEGER (1..8) [4]
| | |         +-bler-target ::= INTEGER (-63..0) [0]
| | |         +-hs-sich-configuration ::= SEQUENCE
| | |           +-timeslotNumber ::= INTEGER (0..6) [1]
| | |           +-channelisationCode ::= ENUMERATED [cc16-11]
| | |           +-midambleAllocationMode ::= CHOICE [defaultMidamble]
| | |           | +-defaultMidamble ::= NULL
| | |           +-midambleConfiguration ::= INTEGER (1..8) [8]
| | |           +-nack-ack-power-offset ::= INTEGER (-7..8) [0]
| | |           +-power-level-HSSICH ::= INTEGER (-120..-58) [-60]
| | |           +-tpc-step-size ::= ENUMERATED [s1]
| | +-measurement-feedback-Info ::= SEQUENCE OPTIONAL:Omit
| | +-modeSpecificInfo ::= CHOICE [tdd]
| |   +-tdd ::= CHOICE [tdd128]
| |     +-tdd128 ::= SEQUENCE [1]
| |       +-hs-PDSCH-Midamble-Configuration-tdd128 ::= SEQUENCE OPTIONAL:Exist
| |         +-midambleAllocationMode ::= CHOICE [defaultMidamble]
| |         | +-defaultMidamble ::= NULL
| |         +-midambleConfiguration ::= INTEGER (1..8) [4]
| +-dl-InformationPerRL-List ::= SEQUENCE OF SIZE(1..maxRL[8]) [1] OPTIONAL:Exist
|   +-DL-InformationPerRL-r5 ::= SEQUENCE [100]
|     +-dl-DPCH-InfoPerRL ::= CHOICE [tdd] OPTIONAL:Exist
|     | +-tdd ::= SEQUENCE [10]
|     |   +-dl-CCTrChListToEstablish ::= SEQUENCE OF SIZE(1..maxCCTrCH[8]) [1] OPTIONAL:Exist
|     |   | +-DL-CCTrCh-r4 ::= SEQUENCE [110]
|     |   |   +-tfcs-ID ::= INTEGER (1..8) [1] OPTIONAL:Exist
|     |   |   +-timeInfo ::= SEQUENCE [10]
|     |   |   | +-activationTime ::= INTEGER (0..255) [0] OPTIONAL:Exist
|     |   |   | +-durationTimeInfo ::= INTEGER OPTIONAL:Omit
|     |   |   +-commonTimeslotInfo ::= SEQUENCE [10] OPTIONAL:Exist
|     |   |   | +-secondInterleavingMode ::= ENUMERATED [frameRelated]
|     |   |   | +-tfci-Coding ::= ENUMERATED [tfci-bits-8] OPTIONAL:Exist
|     |   |   | +-puncturingLimit ::= ENUMERATED [pl1]
|     |   |   | +-repetitionPeriodAndLength ::= CHOICE OPTIONAL:Omit
|     |   |   +-tddOption ::= CHOICE [tdd128]
|     |   |   | +-tdd128 ::= SEQUENCE [1]
|     |   |   |   +-dl-CCTrCH-TimeslotsCodes ::= SEQUENCE OPTIONAL:Exist
|     |   |   |     +-firstIndividualTimeslotInfo ::= SEQUENCE [0]
|     |   |   |     | +-timeslotNumber ::= INTEGER (0..6) [0]
|     |   |   |     | +-tfci-Existence ::= BOOLEAN [TRUE]
|     |   |   |     | +-midambleShiftAndBurstType ::= SEQUENCE
|     |   |   |     | | +-midambleAllocationMode ::= CHOICE [defaultMidamble]
|     |   |   |     | | | +-defaultMidamble ::= NULL
|     |   |   |     | | +-midambleConfiguration ::= INTEGER (1..8) [4]
|     |   |   |     | +-modulation ::= ENUMERATED [mod-QPSK]
|     |   |   |     | +-ss-TPC-Symbols ::= ENUMERATED [one]
|     |   |   |     | +-additionalSS-TPC-Symbols ::= INTEGER OPTIONAL:Omit
|     |   |   |     +-dl-TS-ChannelisationCodesShort ::= SEQUENCE
|     |   |   |     | +-codesRepresentation ::= CHOICE [bitmap]
|     |   |   |     |   +-bitmap ::= BIT STRING [1000000000000000]
|     |   |   |     +-moreTimeslots ::= CHOICE [noMore]
|     |   |   |       +-noMore ::= NULL

A few values in this capture need the scaling rule of 25.331 before you can read them. The comment in the ASN.1 says "Actual value midambleConfiguration = IE value * 2". So midambleConfiguration 4 on the HS-SCCH and on the HS-PDSCH means 8 midambles. The value 8 on the HS-SICH means 16 midambles.

The HS-SICH part also carries the power settings of this uplink channel. The IE power-level-HSSICH is PRX_HS-SICH, the desired receive power at the Node B, here -60 dBm. The UE starts the HS-SICH at P_HS-SICH = PRX_HS-SICH + L_PCCPCH, where L_PCCPCH is the path loss. After that, the TPC commands on the HS-SCCH move the power in steps of 1 dB, which tpc-step-size s1 selects. The value 0 of nack-ack-power-offset means that a NACK and an ACK use the same target power.

The IE bler-target is the log₁₀ of the HS-SCCH BLER quality target, in steps of 0.05. The value 0 gives log₁₀ = 0, which is the top of the range from -3.15 to 0. So this test setup asks for no real HS-SCCH quality target. 25.331 also notes that this IE is not present in Rel-6 and beyond, where HS-SCCH-TDD128-r6 has no bler-target.

One more line needs care. The DL timeslot shows the bitmap 1000000000000000. In the named-bit list of DL-TS-ChannelisationCodesShort, bit 0 is chCode16-SF16 and bit 15 is chCode1-SF16. Read in that order, the leading 1 would select code 16. Figure 1 draws the dlDPCH on code 1, however. The capture alone does not show whether the tester prints the bit string in the opposite order. So check the bit order of your decoder before you read a code number from a bitmap.

The capture below is the uplink part. It sets the power control and the synchronisation of the UL DPCH, and then places the UL CCTrCH into Slot 1.

Decoded RadioBearerSetup-r5 from a tester log, uplink part, captured. Field values are from a live capture, not from the specification.

| | +-ul-DPCH-Info ::= SEQUENCE [1]
| |   +-ul-DPCH-PowerControlInfo ::= CHOICE [tdd] OPTIONAL:Exist
| |   | +-tdd ::= SEQUENCE [1]
| |   |   +-ul-TargetSIR ::= INTEGER (0..62) [48] OPTIONAL:Exist
| |   |   +-ul-OL-PC-Signalling ::= CHOICE [individuallySignalled]
| |   |     +-individuallySignalled ::= SEQUENCE
| |   |       +-tddOption ::= CHOICE [tdd128]
| |   |       | +-tdd128 ::= SEQUENCE
| |   |       |   +-tpc-StepSize ::= INTEGER (1..3) [1]
| |   |       +-primaryCCPCH-TX-Power ::= INTEGER (6..43) [12]
| |   +-modeSpecificInfo ::= CHOICE [tdd]
| |     +-tdd ::= SEQUENCE [110]
| |       +-ul-TimingAdvance ::= CHOICE [enabled] OPTIONAL:Exist
| |       | +-enabled ::= SEQUENCE
| |       |   +-tddOption ::= CHOICE [tdd128]
| |       |     +-tdd128 ::= SEQUENCE [10]
| |       |       +-ul-SynchronisationParameters ::= SEQUENCE OPTIONAL:Exist
| |       |       | +-stepSize ::= INTEGER (1..8) [1]
| |       |       | +-frequency ::= INTEGER (1..8) [1]
| |       |       +-synchronisationParameters ::= SEQUENCE OPTIONAL:Omit
| |       +-ul-CCTrCHList ::= SEQUENCE OF SIZE(1..maxCCTrCH[8]) [1] OPTIONAL:Exist
| |       | +-UL-CCTrCH-r4 ::= SEQUENCE [11]
| |       |   +-tfcs-ID ::= INTEGER (1..8) [1] OPTIONAL:Exist
| |       |   +-ul-TargetSIR ::= INTEGER (0..62) [48]
| |       |   +-timeInfo ::= SEQUENCE [10]
| |       |   | +-activationTime ::= INTEGER (0..255) [0] OPTIONAL:Exist
| |       |   | +-durationTimeInfo ::= INTEGER OPTIONAL:Omit
| |       |   +-commonTimeslotInfo ::= SEQUENCE [11] OPTIONAL:Exist
| |       |   | +-secondInterleavingMode ::= ENUMERATED [frameRelated]
| |       |   | +-tfci-Coding ::= ENUMERATED [tfci-bits-16] OPTIONAL:Exist
| |       |   | +-puncturingLimit ::= ENUMERATED [pl0-56]
| |       |   | +-repetitionPeriodAndLength ::= CHOICE [repetitionPeriod1] OPTIONAL:Exist
| |       |   |   +-repetitionPeriod1 ::= NULL
| |       |   +-tddOption ::= CHOICE [tdd128]
| |       |     +-tdd128 ::= SEQUENCE [1]
| |       |       +-ul-CCTrCH-TimeslotsCodes ::= SEQUENCE OPTIONAL:Exist
| |       |         +-dynamicSFusage ::= BOOLEAN [FALSE]
| |       |         +-firstIndividualTimeslotInfo ::= SEQUENCE [0]
| |       |         | +-timeslotNumber ::= INTEGER (0..6) [1]
| |       |         | +-tfci-Existence ::= BOOLEAN [TRUE]
| |       |         | +-midambleShiftAndBurstType ::= SEQUENCE
| |       |         | | +-midambleAllocationMode ::= CHOICE [defaultMidamble]
| |       |         | | | +-defaultMidamble ::= NULL
| |       |         | | +-midambleConfiguration ::= INTEGER (1..8) [8]
| |       |         | +-modulation ::= ENUMERATED [mod-QPSK]
| |       |         | +-ss-TPC-Symbols ::= ENUMERATED [one]
| |       |         | +-additionalSS-TPC-Symbols ::= INTEGER OPTIONAL:Omit
| |       |         +-ul-TS-ChannelisationCodeList ::= SEQUENCE OF SIZE(1..2) [1]
| |       |         | +-UL-TS-ChannelisationCode ::= ENUMERATED [cc2-1]
| |       |         +-moreTimeslots ::= CHOICE [noMore]
| |       |           +-noMore ::= NULL
| |       +-ul-CCTrCHListToRemove ::= SEQUENCE OF OPTIONAL:Omit

In 1.28 Mcps TDD, ul-TargetSIR is not a SIR at all. The ASN.1 comment says that it corresponds to PRX_DPCHdes, with PRX_DPCHdes = IE value - 120. The value 48 therefore means a desired receive power of -72 dBm. The IE primaryCCPCH-TX-Power 12 gives the P-CCPCH transmit power of 12 dBm, and the UE uses it to calculate the path loss L_PCCPCH. The initial UL DPCH power is then PRX_DPCHdes + L_PCCPCH, and the closed loop continues with tpc-StepSize 1, which is 1 dB.

The IE ul-SynchronisationParameters carries stepSize 1 and frequency 1. These are the step size and the frequency of the uplink timing adjustment, and 1 and 1 are also the default values. The UL CCTrCH uses 16 TFCI bits, while the DL CCTrCH uses 8.

The listing below holds the 25.331 definitions of the HS-SCCH and HS-SICH containers, which the red lines of the downlink capture show.

Following is based on 25.331 v19.0.1 (Release 19)

HS-SCCH-TDD128 ::=				SEQUENCE {
	timeslotNumber						TimeslotNumber-LCR-r4,
	firstChannelisationCode				HS-ChannelisationCode-LCR,
	secondChannelisationCode			HS-ChannelisationCode-LCR,
	midambleAllocationMode				CHOICE {
		defaultMidamble						NULL,
		commonMidamble						NULL,
		ueSpecificMidamble					INTEGER(0..15)
	},
	-- Actual value midambleConfiguration = IE value * 2
	midambleConfiguration				INTEGER (1..8),
	bler-target							Bler-Target,
	hs-sich-configuration				HS-SICH-Configuration-TDD128
}

HS-SICH-Configuration-TDD128 ::=	SEQUENCE {
	timeslotNumber						TimeslotNumber-LCR-r4,
	channelisationCode					HS-ChannelisationCode-LCR,
	midambleAllocationMode				CHOICE {
		defaultMidamble						NULL,
		ueSpecificMidamble					SEQUENCE {
			midambleShift						MidambleShiftLong
		}
	},
	-- Actual value midambleConfiguration = IE value * 2
	midambleConfiguration				INTEGER (1..8),
	nack-ack-power-offset				INTEGER (-7..8),
	power-level-HSSICH					INTEGER (-120..-58),
	tpc-step-size						ENUMERATED { s1, s2, s3 , spare1}
}

RRC places the control channels, not the data channel : the message fixes the DPCH pair, the HS-SCCH and the HS-SICH. The HS-PDSCH has no fixed code.
The HS-SCCH and the HS-SICH come as a pair : each HS-SCCH-TDD128 entry carries its own hs-sich-configuration. The UE answers on the HS-SICH that belongs to the HS-SCCH it decoded.
Some IE values are scaled : midambleConfiguration is doubled, and ul-TargetSIR is offset by -120 dBm in 1.28 Mcps TDD. Read the ASN.1 comments before you quote a value from a log.
An SF2 uplink code fills half of the code tree : cc2-1 covers the space of SF16 codes 1 to 8 in Slot 1.

How does the UE find its HS-PDSCH in each TTI ?

Figure 1 leaves a question open. If RRC gives no HS-PDSCH code, how does the UE know where its data is ? The answer is the HS-SCCH. In every 5 ms TTI the Node B decides which UE to serve, and it sends that decision on the HS-SCCH of the chosen UE.

For 1.28 Mcps TDD, 25.222 lists the fields of one HS-SCCH as follows.

Channelisation code set information, 8 bits : xccs. The first 4 bits give the start code and the last 4 bits give the stop code. The HS-PDSCH codes run contiguously from the start code to the stop code.
Time slot information, 5 bits : xts. Bit xts,n stands for timeslot n+1, so the five bits cover Slot 2 to Slot 6. Slot 1 cannot carry HS-DSCH. Slot 0 can be used only when higher layers allow it, and then xts,1 stands for Slot 0.
Modulation scheme information, 1 bit : xms, the modulation scheme of the HS-PDSCH.
Transport block size information, 6 bits : xtbs, the transport block size index.
HARQ and retransmission fields : the HARQ process, 3 bits, the redundancy version, 3 bits, and the new data indicator, 1 bit.
HS-SCCH cyclic sequence number, 3 bits : xhcsn.
UE identity, 16 bits : xue, the H-RNTI. It is not sent as bits of its own but masks the CRC.

Now the two parts of the message come together. The H-RNTI from the MAC part lets the UE find its HS-SCCH, and the HS-SCCH codes from the physical part tell the UE where to look. The HS-SCCH then gives the codes, the timeslots and the transport block size of the HS-PDSCH for this TTI. After decoding the HS-PDSCH, the UE sends ACK or NACK on the associated HS-SICH. The same HS-SICH also carries the recommended modulation format RMF and the recommended transport block size RTBS, which play the role of a CQI.

The HARQ process number on the HS-SCCH points to one of the eight processes of the MAC part. That process owns 20800 soft channel bits, and the UE soft-combines a retransmission there. The reordering queue then puts the MAC-hs PDUs back in order, within the window of 16 and the T1 of 120 ms.

The HS-PDSCH is scheduled per TTI : its codes and timeslots arrive on the HS-SCCH in every TTI, never in the RRC message.
Timeslots come from xts, not from xtbs : xts selects the timeslots and xtbs gives the transport block size index. The note in Figure 1 names the wrong field.
The H-RNTI is the key to the HS-SCCH : without the right H-RNTI, the CRC check fails and the UE ignores the block.
The HS-SICH closes the loop : it returns ACK or NACK together with RMF and RTBS, and the Node B uses them for the next scheduling decision.

Reference

25.331 Radio Resource Control RRC protocol specification - v19.0.1, subclauses 8.5.7 Open loop power control and 10.3.6.17 Downlink channelisation codes, and the ASN.1 of HARQ-Info, MAC-hs-AddReconfQueue, HS-SCCH-TDD128, HS-SICH-Configuration-TDD128 and UL-DPCH-PowerControlInfo-r4
25.221 Physical channels and mapping of transport channels onto physical channels TDD - v19.0.0, subclauses 5A.3.10 HS-SCCH and 5A.3.11 HS-SICH
25.222 Multiplexing and channel coding TDD - v19.0.0, subclauses 4.6 Coding/Multiplexing for HS-SCCH and 4.7 Coding for HS-SICH