《《HSDPA Basic》.ppt

HSDPA Basics Filiz Gulkan Outline HSDPA Principles HSDPA Channel Structure HSDPA Power Allocation Architectural Impact Planning and dimensioning aspects Abbreviations and references HSDPA Basics What is High Speed Downlink Packet Access (HSDPA)? Key Idea in HSDPA Basic Features  Short 2 ms TTI Reduced air-interface delay Improved end-user performance Required by TCP at high data rates Necessary to benefit from other HS-DSCH features Fast Link Adaptation Fast hybrid ARQ Fast Channel-dependent Scheduling Shared Channel Transmission A set of radio resources dynamically shared among multiple users, primarily in the time domain Efficient code utilization Efficient power utilization Fast Channel-dependent Scheduling Scheduling = which UE to transmit to at a given time instant and at what rate Formally part of MAC-hs (a new MAC sub-layer in RBS) Basic idea: transmit at fading peaks May lead to large variations in data rate between users Tradeoff: fairness vs cell throughput Fast Channel-dependent Scheduling Examples of scheduling algorithms Round Robin (RR) Cyclically assign the channel to users without taking channel conditions into account Simple but poor performance Proportional Fair (PF) Assign the channel to the user with the best relative channel quality High throughput, fair Max C/I Ratio Assign the channel to the user with the best channel quality High system throughput but not fair Fast Link Adaptation and higher modulation Adjust transmission parameters to match instantaneous channel conditions HS DL Shared Channel: Rate control (no Fast Power control) Adaptive coding Adaptive modulation (QPSK or 16QAM) Adapt on 2 ms TTI basis ? fast R99: Power control (no Rate control ? constant data rate possible) Higher Modulation HS-DSCH supports both QPSK and 16QAM 16QAM is optional in RBS 16QAM is mandatory in the UE, except for the 2 lowest UE categories 16QAM gives approximately double data rates 16QAM is mainly useful at good radio conditions 16QAM typ