HSDPA Concepts

The Configuration of HSDPA is as follows:


For the configuration of HSDPA, following logical and physical resources needs to be allocated to UE by UTRAN in any of the reconfiguration message:

1. AM / UM Mode RBs mapped on to HS-DSCH
2. HS-DSCH TrCH - with DCH or without DCH
3. HS-SCCH set
4. DL Info per RL containing F-DPCH or DPCH configuration 
5. HS-PDSCH configuration is given in HS-SCCH 

High Speed - Physical Downlink Shared Channel (HS-PDSCH):

• HS - PDSCH is a DL shared physical channel
• SF = 16, so at max only 16 HS-PDSCH physical channels can be allocated, but by doing so all physical resources (codes) of the cell get exhausted
• Number of HS-PDSCH channels has to be planned in such a way that a cells physical resources are utilized efficiently among dedicated and other common resources.
• Shared between all the UEs in a Cell

MAC-d flows:

• MAC-d flow is the flow of PDUs which are MAC-d multiplexed
• It is almost similar to DCH TrCH
• MAC-d flow signifies a specific QoS on which, logical channels of same QoS are mapped
• MAC-d flows are between MAC-d and MAC-hs or MAC-ehs

HARQ:

• Hybrid Automatic Repeat Request

HARQ Entiry:

• There is only one HARQ Entity per UE in UTRAN.
• The HARQ entity adds Queue ID, Transmit Sequence Number (TSN) and HARQ Process Identifier to the transmitted MAC- hs / MAC - ehs PDU
• There is one HARQ Entity in the UE, which process HARQ Process Identifier received on HS-SCCH associated with MAC - hs PDU received on HS-DSCH.
• Each received MAC - hs PDU is allocated to the HARQ Process, identified by HARQ Process Identifier of the MAC - hs PDU.

HARQ process:

• HARQ Process handles one MAC - hs / MAC - ehs PDU
• MaxHProcesses = Maximum number of H-ARQ processes = 8
• Each HARQ Process has SoftBuffer to store MAC- hs / ehs PDUs

TX / UTRAN side:

• The HARQ process sets the New data indicator in transmitted MAC-hs PDUs. UTRAN should:
• set the New Data Indicator to the value "0" for the first MAC-hs PDU transmitted by a HARQ process;
• not increment the New Data Indicator for retransmissions of a MAC-hs PDU;
• increment the New Data Indicator with one for each transmitted MAC-hs PDU containing new data.
• The HARQ process processes received status messages. UTRAN should:
• deliver received status messages to the scheduler.

RX / UE side:

• HARQ Process, process the New Data Indicator associated with each MAC - hs PDU, indicated by Lower layers

If the MAC-hs PDU is received within 5 sub-frames from the reception of the previous MAC-hs PDU intended for this HARQ process; 

• discard the MAC-hs PDU.

When operating in CELL_DCH state, or in CELL_FACH state with a dedicated H-RNTI, if the MAC-ehs PDU is received within 5 sub-frames from the reception of the previous MAC-ehs PDU intended for this HARQ process:

• discard the MAC-ehs PDU.

=> This means each HARQ Process can be scheduled only once in 5 Sub-frame


1 Radio Frame = 10 ms
1 Radio Frame = 15 slots
1 Sub - Frame = 3 Slots = 2ms
1 Slot = 2560 chips