2. 2
HSDPA new channels
• HSDPA introduces specific channels, 1transport and 3 physical channels:
– The transport channel High Speed Downlink Shared Channel (HS-DSCH) is a
resource existing only in downlink and carries user data in HSDPA.
– The High Speed Physical Downlink Shared Channel (HS-PDSCH) is a downlink
physical channel, to which the HS-DSCH channels are mapped.
– The High-Speed Shared Control Channels (HS-SCCH) is used for downlink
control signaling and carries indication about UE scheduling.
– One Associated Dedicated Channel (A-DCH) pair (UL & DL) per HSDPA user in
connected state, used for control signaling and uplink data transmission. The
uplink control information is carried by the Uplink High Speed Dedicated Physical
Control Channel (HS-DPCCH).
A-DCH
4. 4
An overview of HS-DSCH and its associated channels
CN RNC RBS UE
-
DPCCH
DPDCH
HS DPCCH
HS-SCCH
HS-PDSCH
HS -DSCH
DCCH
DCCH
DTCH
Interactive PS RAB
DTCH
Interactive PS RAB
DTCH
Interactive PS RAB
DCCH
NAS
DCCH
NAS
RRC
User 1
User 2
User n
For each
user
Radio Access Bearers:
- Interactive
- Background
Logical Channels:
-Dedicated Control Channel, DCCH
-Dedicated Traffic Channel, DTCH
Transport Channels:
-Dedicated Channel, DCH
-High-Speed Downlink Shared Channel, HS-DSCH
Physical Channels:
-Dedicated Physical Channel, DPCH
-DPCCH, Dedicated Physical Control Channel
-DPDCH, Dedicated Physical Data Channel
-HS-DPCCH, HS-DSCH Dedicated Physical Control Channel
-HS-DSCH Shared Control Channel, HS-SCCH
-High Speed Physical Downlink Shared Channel, HS-PDSCH
DPCH
DCH
DCH
Iu Iub Uu
5. 5
HS-DSCH : High-Speed Dedicated Shared Channel
• HS-DSCH is the transport channel used for data transmission on the
downlink and is shared by all users in the cell. In the HSDPA first phase
product release:
– the sharing of code resource is done in the time domain on a 2 ms time basis
(TTI).
– The shared code resource consists of 5 channelization codes with fixed
spreading factor SFHS-DSCH = 16, in this time frame.
• The HS-DSCH cannot be in soft/softer handover and no fast power
control is used.
• The HS-DSCH uses all the excess power from the available transmission
power at the base station left from the common and dedicated channels
6. 6
HS-SCCH: High-Speed Shared Control Channel
• HS-SCCH is a downlink physical channel used to carry HS-DSCH related
control signaling (Physical Layer signaling).
• It is shared among the HSDPA users on time division basis (TTI), with the
same scheduling as for HS-DSCH.
• All UEs listen to the same HS-SCCH channel and after decoding, decide
whether the information to start listening the HS-PDSCH was intended to
that UE.
• Informs the UE about:
– HS-DSCH code set
– Modulation scheme (QPSK/16QAM)
– HS-DSCH transport format (number of transport blocks per TTI and number of
bits per transport block)
– Hybrid ARQ information
• Never in soft handover
• The HS-SCCH has a spreading factor SFHS-DSCH = 128
7. 7
A-DCH: Associated Dedicated Channel
• One A-DCH pair is set up for every HSDPA user in connected state.
• It is used for control signaling (RRC and NAS) in UL and DL.
• It is a new Radio Bearer corresponding to a 3.4 kbps SRB in the DL (Sf
256).
• In the uplink A-DCH is also used as the channel for data transmission,
where the rate can be either 384 kbps or 64 kbps.
– The uplink data rate 384 kbps is selected as first priority and 64 kbps is used as a
fall back rate if the path loss is judged to be too large or 384 kbps radio bearer
setup fails for any reason (e.g. lack of radio or hardware resources).
• The uplink A-DCH channel also contains the High-Speed Dedicated
Physical Control Channel (HS-DPCCH), the new physical channel that
carries the L1 related signaling in UL.
8. 8
HS-DPCCH: High-Speed Dedicated Physical Control
Channel
• It is used for transmitting the following information from UE to RBS:
– HARQ acknowledgement (1 bit coded in 10)
– Channel quality indicator (5 bits coded to 20 bits in 2 slots)
– channel quality measurements based on CPICH
– reporting rate is configurable through RRC/NBAP signaling
– information reflecting the instantaneous downlink radio channel conditions to assist the RBS
in the transport format selection (fast link adaptation) and the scheduling
– The HS-DPCCH has a spreading factor SFHS-DSCH = 256
• The A-DCH both UL and DL can be in soft/softer handover whilst the HS-
DPCCH can never be in soft handover (softer is possible).
• HS-DPCCH (UL) is transmitted within a dedicated channel. The main idea
is that it is power controlled from the other part of the A-DCH.
9. 9
HSDPA Channel Operation
HS-DPCCH: CQI
HS-SCCH: DL Transfer Information
HS-DSCH: Data Transfer
HS-DPCCH: ACK/NACK
Physical Channels:
-Dedicated Physical Channel, DPCH
-DPCCH, Dedicated Physical Control Channel
-DPDCH, Dedicated Physical Data Channel
-HS-DPCCH, HS-DSCH Dedicated Physical Control Channel
-HS-DSCH Shared Control Channel, HS-SCCH
-High Speed Physical Downlink Shared Channel, HS-PDSCH
10. 10
UserPlane: Overview
• There are 8 steps to transmit on the HS-DSCH:
– In the RNC, the Interactive RAB is mapped to a radio bearer to be transmitted on
the HS-DSCH.
– The radio bearer is then processed by the RLC and MAC-d layer 2 protocols in
the RNC.
– The resulting MAC-d PDUs are transmitted over Iub to the RBS using the HS-
DSCH frame protocol.
– The MAC–hs receive the Channel Quality Indicator “adjusted” by the Node B
– The MAC-hs scheduling function selects in each TTI the user to which the HS-
DSCH is transmitted.
– Following the selection of a user, the user data to transmit on the HS-DSCH is put
into one of several HARQ processes in the MAC-hs HARQ protocol.
– The amount of data to transmit is determined by the TFRC selection algorithm.
– Hence the data is transmitted to the UE over the air interface.
