4. hsdpa new transport & physical channels

8/6/2019 4. HSDPA New Transport & Physical Channels

1/12

HSDPA, Version 1.1e T.O.P. BusinessInteractive GmbH Page 1 of 12

4 New Transport & Physical Channels


2/12


4.1 Overview .......................................................................................34.2 The new HS-DSCH........................................................................44.3 The new HS-SCCH........................................................................54.4 The new HS-PDSCH .....................................................................64.5 The new HS-DPCCH .....................................................................74.6 Physical Layer Operation (1/5) ....................................................84.6 Physical Layer Operation (2/5) ....................................................94.6 Physical Layer Operation (3/5) ..................................................104.6 Physical Layer Operation (4/5) ..................................................114.6 Physical Layer Operation (5/5) ..................................................12


3/12


4.1 Overview

For user data and signaling information transport, HSDPA uses one new transport channel

and three new physical channels as an enhancement of the physical layer specifications.The new transport channel is named High-Speed Downlink Shared Channel (HS-DSCH).The new physical channels are:

The High-Speed Physical Downlink Shared Channel (HS-PDSCH) that carries actualHSDPA data of HS-DSCH transport channel.

The High-Speed Shared Control Channel (HS-SCCH) that informs the UE how toreceive HS-PDSCH in the same Transmission Time Interval.

The High-Speed Dedicated Physical Control Channel (HS-DPCCH) for MAC-hsAck/Nack information and general Channel Quality Information.

Let us have a closer look at each of the new channels.


4/12


4.2 The new HS-DSCH

The transport channel carrying the user data with HSDPA operation is described as the High-

speed Downlink Shared Channel. We will identify its properties by comparing them withthose of the Rel. 99 Downlink Shared Channel (DSCH). Both transport channels supportMulti-Code operation as described earlier.HS-DSCH use Adaptive Modulation and Coding for a robust bit encoding and a Fast Layer 1Hybrid Automatic Repeat Request for a reliable data packet transfer. In contrast, Rel 99DSCH uses Fast Power Control and a variable Spreading Factor to cope with interference onthe air interface.


5/12


4.3 The new HS-SCCH

The high-speed shared control channel (HS-SCCH) is the downlink signaling channel thatcarries key physical layer control information to enable decoding of the data on HS-DSCHand to perform the possible physical layer combining of the data in the case ofretransmission of an erroneous packet.HS-SCCH information includes:

The channelization code set modulation scheme, transport block size, transmission time interval, H-ARQ process information and redundancy version.


6/12


4.4 The new HS-PDSCH

The high-speed physical downlink shared channel (HS-PDSCH) is the physical channel that

carries the user-specific packet data in the DL from the transport channel HS-DSCH. It has afixed spreading factor of 16 and multi-code transmission using 1 to 15 codes with QPSK or16QAM modulation. The peak data rate is 10Mbit/s if 16 quadrature amplitude modulation(16QAM) is applied. It always starts 2 Timeslots or 5,120 chips after the transmission of theHS-SCCH.An associated Rel. 99 DPCH, Dedicated Physical Channel, is needed for each HSDPA UserEquipment for signaling and uplink data.


7/12


4.5 The new HS-DPCCH

The high-speed dedicated physical control channel (HS-DPCCH) is the uplink signaling

channel that carries necessary control data. These are ARQ acknowledgements anddownlink quality feedback information to be used in the basestation scheduler. It carries anACK/NACK indication, to reflect the results of the cyclic redundancy checking after thepacket decoding and combining.It also carries the downlink channel quality indicator (CQI) to indicate which estimatedtransport block size, modulation type and number of parallel codes could be receivedcorrectly with reasonable block error rate in the DL.


8/12


4.6 Physical Layer Operation (1/5)

The HSDPA physical layer operation goes through the following steps. The scheduler in the

Node B evaluates the channel conditions for different users, e.g. how much data is pendingin the buffer for each user, how much time has elapsed since a certain user was last served,for which users retransmissions are pending and so on.Deciding the exact criteria that are taken into account in the scheduler is a vendor-specificimplementation issue.


9/12



Once it is been determined that a terminal will be served in a particular Time Transmission

Interval, the Node B identifies the necessary HS-DSCH parameters. E.g. how many codesare available or can be filled, can 16 QAM be used and what are the limits of the terminalcapabilities? The terminal soft memory capability also defines which kind of HARQ can beused.


10/12



The Node B starts to transmit the HS-SCCH two slots before the corresponding HS-DSCH

TTI to inform the terminal of the necessary parameters. The mobile decodes this data andstores it for further use. Now the terminal can determine to which HARQ process the databelongs and if it has to be combined with data already in the buffer.


11/12



Upon decoding the potentially combined data, the terminal sends an ACK/NACK indicator inthe uplink direction using a High-Speed Dedicated Physical Control Channel. This indicator isbased on the outcome of the CRC check conducted with the received HS-DSCH data. lf thenetwork continues to transmit data for this particular mobile in consecutive TTIs, the terminalwill use the same HS-SCCH that was decoded during the previous TTI.


12/12



HSDPA terminal operation has to obey strict timing values between HS-SCCH reception,

HS-DSCH decoding and uplink ACK/NACK messages in HS-PDCCH. The key timing valuefrom the terminal point of view is a 7.5 time slot spacing from the end of the HS-DSCH TTI tothe start of the HS-PDCCH in the uplink.

4. hsdpa new transport & physical channels

Documents