HSDPA技术简介和分析课件

1、ContentOverviewTechnical Details（Including Characteristic， Performance and Complexity）AMC，H-ARQ，FCS Impacts on R99（Including radio protocols， UE，NodeB，RNC， MAC，Interfate Iub & Iur）Conclusions第1页，共54页。What is HSDPA?HSDPA is abbreviation of High Speed downlink packet access.It can apply to UTRA in ord

2、er to provide very high speed downlink packet access. HSDPA is extending UTRA with a new transport channel HS-DSCH (High Speed Downlink Shared Channel). 第2页，共54页。Why Introduced HSDPA?Use of HS-DSCH will enhance the UTRA support for interactive, background, and, to some extent, streaming services, in

3、 terms of Higher peak data rates Improved overall cell throughput kbps/MHz/cell Reduced delay 第3页，共54页。HS-DSCH L1 Structure in Code Domain 第4页，共54页。Sharing第5页，共54页。Technologies to support HSDPAAdaptive Modulation and CodingHybrid ARQFast Cell SelectionMultiple Input Multiple Output Antenna technique

4、sStand alone DSCH第6页，共54页。AMC（Adaptive Modulation and Coding）Why introduce AMC? 无线链路的信道质量是时变的，任何对链路变化进行的适应都有易于接收信号的质量。Link adapation FunctionPower controlAMC 第7页，共54页。AMC Basic PrinciplePrinciple of changing MCSusers in favorable positions e.g. users close to the cell site are typically assigned hig

5、her order modulation with higher code rates (e.g. 64 QAM with R=3/4 Turbo Codes) users in unfavorable positions e.g. users close to the cell boundary, are assigned lower order modulation with lower code rates (e.g. QPSK with R=1/2 Turbo Codes) 第8页，共54页。MCS（Modulation and Coding Scheme）MCS LevelInfo

6、Rate（Mbps）Code RateModulation710.83/464QAM67.23/416QAM54.81/216QAM45.43/48PSK33.63/4QPSK22.41/2QPSK11.21/4QPSK第9页，共54页。AMC Physical Layer Structure第10页，共54页。AMC benefitsMain benefits处于有利位置的用户可以得到更高的数据速率，提高小区平均吞吐量； 链路自适应基于改变调制编码方案代替改变发射功率减小干扰， AMC在不使用快速下行功率控制的条件下允许达到较高的频谱利用率和高的数据速率。第11页，共54页。选择MCS的方法

7、 MCS的选择基于下行信道的质量。根据UE的反馈信息 UE对下行信道质量进行测量，有两种可能：UE估计/预测下行信道质量并计算合适的传输格式报告给Node-B； UE估计/预测下行信道质量并报告给Node-B； 不根据UE的反馈信息Node-B不通过来自UE的反馈决定传输格式，而通过其他信息估计下行信道质量。 第12页，共54页。下行信道质量估计基于C/I方法：使用CPICH RSCP/ISCP测量下行信道质量。缺点：公共导频问题 ，不知道如何和自适应天线和波束成形很好的一起工作 。基于TPC方法：使用下行DPCH的TPC估计下行信道质量。优点：不增加UE的复杂度，DPCH和HS-DSCH采用

8、同一个波束 。不存在公共导频问题。缺点：不适于在软切换情况下的工作。第13页，共54页。Some challenge & noticerequire more advanced receiver techniques and more advanced receiver structures sensitive to measurement error Errors in the channel estimate will cause the scheduler to select the wrong data rate and either transmit at too high a po

9、wer, wasting system capacity, or too low a power, raising the block error rate sensitive to measurement delay Delay in reporting channel measurements also reduces the reliability of the channel quality estimate.第14页，共54页。Discuss FocusIs 8PSK needed?Is 64QAM needed?7 level MCS or 5 level MCS?第15页，共54

10、页。 Hybrid ARQ第16页，共54页。HARQ的分类按选择机制selective repeat (SR)stop-and-wait (SAW)按实现方法 HARQ Type HARQ Type (Incremental Redundancy scheme)HARQ Type (Incremental Redundancy scheme)multiple redundancy versionsmultiple redundancy versions第17页，共54页。HARQ的分类TypeH-ARQ The ARQ method used in current 3GPP specific

11、ations is referred to as HARQ type I;the CRC is added and the data is encoded with a forward error correction (FEC) code;Type II H-ARQ additional redundant information is incrementally transmitted if the decoding fails on the first attempt; Neednt to repeat information bits if transmission is unsecc

12、essful;（type need）第18页，共54页。HARQ的分类Type H-ARQLike type II hybrid ARQ, type III hybrid ARQ also belongs to the incremental redundancy ARQ schemes ;each retransmission is self-decodable which is not the case with H-ARQ-type II ;Chase combining (also called H-ARQ-type-III with one redundancy version) t

13、he same FEC coding is used for each retransmission, similar to the operation of HARQ type I ;the erroneous packets are stored in the receiver and combined with retransmissions of the packet ;Diversity (time) gain is thus obtained; 第19页，共54页。Hybrid ARQ Type 第20页，共54页。Hybrid ARQ Type - 第21页，共54页。SR (1

14、/2) characteristicA common type of ARQ protocol employed by many systems including RLC R99 insensitive to delayOnly erroneous blocks are re-transmitted A sequence number is required to identify the block The greater the feedback delay the larger the maximum sequence number must be. 第22页，共54页。SR (2/2

15、) Two difficultiesUE memory requirements are high the mobile needs to store soft samples for each partially received block. Requires the receiver to reliably determine the sequence number of each transmission. 第23页，共54页。SAW HARQ (1/4)CharacteristicStop-and-wait is one of the simplest forms of ARQ .

16、In stop-and-wait, the transmitter operates on the current block until the block has been received successfully. stop-and-wait protocol & Hybrid ARQ protocol 第24页，共54页。SAW HARQ (2/4)Advantagerequire very little overhead ;control overhead is minimal ;Acknowledgement overhead is minimal ;memory require

17、ments at the UE are minimized ;第25页，共54页。SAW HARQ (3/4)major drawback - acknowledgements are not instantaneous and therefore after every transmission, the transmitter must wait to receive the acknowledgement prior to transmitting the next block. - the channel remains idle and system capacity goes wa

18、sted. 第26页，共54页。SAW HARQ (4/4) Robustess第27页，共54页。N channel SAW HARQ no system capacity goes wasted the receiver has to store N blocks 第28页，共54页。Timing relations for 2-channel HARQ process 第29页，共54页。Chase CombiningThe simplest form of Hybrid ARQ scheme was proposed by Chase, also called H-ARQ-type-I

19、II with one redundancy version.The basic idea in Chases combining scheme is to send a number of repeats of each coded data packet and allowing the decoder to combine multiple received copies of the coded packet weighted by the SNR prior to decoding. 第30页，共54页。Combining Schemes第31页，共54页。Combining Sch

20、emesThe second is the best.第32页，共54页。RCPT codes in HARQ 第33页，共54页。Complexity Evaluation (1/2)Processing timeThe time required for processing the tasks depends on the number of timeslots in the HSDPA TTI (number of bits to be processed). The shorter the HSDPA TTI the less time there is available for

21、processing. 第34页，共54页。Complexity Evaluation(2/2)Required memory of UE receiver windows.The longer the HSDPA TTI the more memory is required of UE.The UE buffer size is likely to be a UE capability.第35页，共54页。Tasks to be introduced (1/2)Node B processing tasksDecode the ACK/NACK transmitted in uplink

22、Make a scheduling decision on which UE is due to receive data among the UEs having data in the transmission buffer Set TFCI and other information fields on downlink control channels 第36页，共54页。Tasks to be introduced (2/2)UE processing tasks Decode TFCI, HSDPA TTI sequence info etc Despreading and dem

23、odulation Soft combine retransmitted HSDPA TTI in the receiver buffer for the correct subchannel Decode HSDPA TTI for the subchannelCheck CRC to decide whether the HSDPA TTI was received correctly Generate ACK/NACK signaling for uplink 第37页，共54页。Discuss FocusHARQ Scheme - IR or Chase Combining?More

24、proposals are Chase combining for its simplicity. Synchronous vs Asynchronous SAW HARQ Number of SAW Subchannels?N=4 or N=5 is proposedHow to porform with AMC?Not to change MCS between retransmissions is proposed.第38页，共54页。FCS（Fast Cell Selection）Fast Cell Selection implies that the UE should decide

25、 on the “best” cell for HSDPA transmission and signal this to the network. The physical layer requirements of Fast Cell Selection is conceptually similar to physical layer aspect of Site Selection Diversity Transmission (SSDT) included in Release 99. 第39页，共54页。FCS分类Intra-Node B FCSInter-Node B FCSTw

26、o schedulersRound Robin MAX C/IMain benefit improves throughput and residual FER for UEs in multi-coverage regions 第40页，共54页。FCSCompare with SSDT in R99In case of SSDT, the “best” cell (the so-called “primary cell”) is selected based on measurements of CPICH RSCP for the cells in the active set. The

27、 same measurements can be used as a basis for fast cell selection. In case of SSDT, the best cell is reported to the network using physical-layer (DPCCH) signalling with a maximum rate of 500 Hz. Basically identical signalling could be used for fast cell selection. 第41页，共54页。FCSImpact on InterfacesI

28、ubIurDiscuss Focuspotential performance increaseIntra-Node B FCS vs Inter-Node B FCS第42页，共54页。MIMODiversity techniques based on the use of multiple downlink transmit antennas are well known. Multiple input multiple output (MIMO) processing employs multiple antennas at both the base station transmitt

29、er and terminal receiver, providing several advantages over transmit diversity techniques with multiple antennas only at the transmitter and over conventional single antenna systems. 第43页，共54页。MIMO BenefitIf multiple antennas are available at both the transmitter and receiver, the peak throughput ca

30、n be increased using a technique known as code re-use. With code re-use, each channelization/scrambling code pair allocated for HS-DSCH transmission can modulate up to M distinct data streams, where M is the number of transmit antennas. 第44页，共54页。Stand alone DSCHDefinitionA standalone DSCH is a DSCH

31、 on a downlink carrier that is different from the WCDMA carrier that carries its companion DPCH BenefitBy assigning up to whole carrier for the HS-DSCH, the maximum power and code space available for HS-DSCH transmission would be increased as no resource has to be set aside for DCH or common channel

32、s. 第45页，共54页。Stand alone DSCHPerform schemeBase W-CDMABase OFDM第46页，共54页。Stand alone DSCH ImpactThe introduction of the Stand-alone DSCH would lead to some modifications of the physical layer structure as far as physical channel characteristics are concerned. Impact is mostly on the UE, as a double receiver would be needed du