The main idea in HSDPA is to use the radio resources, mainly power and code, in an optimal way, that is possible by adapting rapidly to the instantaneous radio conditions.
3 main functionalities which makes this possible are Fast Link Adaptation, Fast Hybrid ARQ (Automatic Repeat Request) and Fast Channel-dependent Scheduling.
What are the new features that enables the high data rates and better system throughput? We shall shortly introduce them in this slide and go into details in the coming slides.
We have Short Transmission Time Interval, shorter than R99. It is only 2 milliseconds and therefore reduces the round trip time.
The main benefit from shorter TTI is the reduced delays and therefore improved end-user performance. It also makes RRM functionalities much faster.
Then we have Shared Channel Transmission. One HS dedicated channel shared dynamically by all HSDPA users , mainly in the time domain.
That results in system capacity gain.
Fast Scheduling gives priority to the users with favorable radio conditions. This is also something which contributes to system capacity.
Fast link adaptation gives maximum channel utilization because data rate is adapted to radio conditions. Higher order modulation gives higher data rates.
And finally, Fast retransmissions together with soft combining leads to better end-user performance and capacity increase.
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