UMTS HSDPA (document en anglais)

1. SUMMARY

Today’s mobile communication systems have been enhanced recently to more efficiently support packet

switched services. In UMTS HSDPA and E-DCH have been specified in downlink and uplink respec

tively.

By now UMTS is a well-established technology with manifold networks running globally and competitive

terminals on the market. A significant shift from traditional circuit-switched, often constant bit-rate ser

vices to IP packet switched services is expected in the near future. UMTS Release 99, based on dedicated

resource allocation per user, is not well suited for IP packet data traffic. Therefore High Speed Packet

Downlink Access (HSDPA) and Enhanced Dedicated Channel (E-DCH) have been introduced as new

features of UMTS for Downlink and Uplink in UMTS Release 5 and Release 6, respectively. This technol

ogy called High Speed Packet Access (HSPA) claims significant enhancements in end-to-end service pro

visioning for IP based services. This introduces these future technology enhancements and assesses the

potential gains for future applications and in term user perception.

In addition to the paradigm change from using dedicated resources to making use of shared radio re

sources, the main technology changes introduced are:

• Fast Node B scheduling with adaptive coding and modulation (only downlink) to exploit the vary

ing radio channel and interference variations and accommodate bursty IP traffic,

• Node B based Hybrid ARQ to reduce retransmission round trip times and add robustness to the

system by allowing soft combining of retransmissions,

• Reduced transmission time interval (TTI) for latency reduction and to support fast scheduler de

cisions and quick HARQ retransmissions.

These added functionalities have been specified in several new MAC sub-layers and modifications of the

physical layer as is depicted in Figure 1.

...