HS-DSCH

For HSDPA, a new transport layer channel, High-Speed Downlink Shared Channel (HS-DSCH), has been

added to UMTS release 5 and further specification. It is implemented by introducing three new physical

layer channels: HS-SCCH, HS-DPCCH and HS-PDSCH. The High Speed-Shared Control Channel (HS-

SCCH) informs the user that data will be sent on the HS-DSCH, 2 slots ahead. The Uplink High Speed-

Dedicated Physical Control Channel (HS-DPCCH) carries acknowledgment information and current

channel quality indicator (CQI) of the user. This value is then used by the base station to calculate how

much data to send to the user devices on the next transmission. The High Speed-Physical Downlink

Shared Channel (HS-PDSCH) is the channel mapped to the above HS-DSCH transport channel that

carries actual user data.

[edit]Hybrid automatic repeat-request (HARQ)

Data is transmitted together with error correction bits. Minor errors can thus be corrected without

retransmission; see forward error correction.

If retransmission is needed, the user device saves the packet and later combines it with retransmitted

packet to recover the error-free packet as efficiently as possible. Even if the retransmitted packets are

corrupted, their combination can yield an error-free packet. Retransmitted packet may be either identical

(chase combining) or different from the first transmission (incremental redundancy).

Since HARQ retransmissions are processed at the physical layer, their 12 ms round-trip time is much

lower compared to higher layer retransmissions.

Above is feature comparison of HSDPA and R99.For my opinion the big change are

Modulation Scheme, TTI and Soft Handover Type.

Let talk about Handover, for HSDPA only one active set can be clamp in one time.

Modulation scheme very due to air condition time by time (Ec/Io) and Transmission Block

reduced to 2 ms.