Research On Link Model And Fast Packet Scheduling In TD-SCDMA HSDPA

Data services are growing and become the domaint traffic load in mobile network. Traditional 3G neworks like TD-SCDMA system, with peak data reate of 2Mbps, cannot meet the growing provision of data service, especially downlink multimedia service. In this context, High Speed Downlink Packet Access is proposed by 3GPP in Release 5 specification, which can provide high data rates up to 10Mbps for downlink packet service like WAP browsing, FTP download and online video. HSDPA enhancement feature can be used in WCDMA FDD, UTAR TDD and TD-SCDMA system, and detailed implementations are very similar in these system. This dissertion focuses on the HSDPA implementation in TD-SCDMA system.HSDPA is a set of radio enhancement technology. It introduces a new transport channel HS-DSCH and related functinonal entity to enhance the radio access nework. At lower level, it incorporates AMC and HARQ to provide high data rates. Fast packet scheduling algorithm is one of the key technologies in HSDPA. The HSDPA 3GPP protocol model is analized in this dissertation. Detaild transport layer channel encoding procedures, especially HARQ procedure,16QAM constellation rearrangement and HS-DSCH to HS-PDSCH mapping, as well as soft bit LLR calculation are discussed. Based the discussion, a Monte Carlo link level simulator is implemented.This dissertation also proposes a TD-SCDMA HSDPA link mode. The proposed link model estimates transmission block error rate using the mutual information beween the channel-encoded bit the transmitter and the post-rate-dematching soft bit at the receiver. Compared to other link model, the proposed link model use modeling methods like QPSK SNR combination and 16QAM SNR equivalence to incorpate TD-SCDMA HSDPA techniques including rate matching, HARQ, 16QAM constalletion rearrangement naturally, thus can provide better accuray while maintaing a relative low time and space complexisity given the large number of combinations of TFCs, modulation and channel encoder encoding rate. What's more, modulized structure makes the link model easily extensible for future systems. Simulation result and modeling error analysis shows the superiority of this HSDPA link model.Based on the discussion of UMTS QoS classification, a general HSDPA fast packet scheduling model is proposed, including algorithm input/output. Scheduling algorithm assessment methodology and fairness criteria are discussed, followed by introduction of some classifical scheduling algorithms for nonreal time and real time service.Two extentions of the utility-function based HSDPA fast packet scheduling algorithms are proposed: Newton-based scheduling algorithm and two-dimentional utility function scheduling algorithm. While the Newton-based scheduling algorithm is suitable for the dynamic characteristic of HSDPA system including short TTI and fast link adaption, and thus can be used in non real time traffic scenario to increase the system utility; the two-dimenstional utility function algorithm tries to take account both throughput and HOL delay in the scheduling strategy, which is necessary in mixed traffic scenario where there are multiple types of traffic with different QoS requirements. Simulation results show that the propsed Newton-based PF scheduling algorithm outperforms PF by about 8% in total system utility for background traffic; the two-dimenstional utility function method has lower packet drop rate than MAXCI, PF and DSDFQ method, and can guarantee the throughput of real time traffic in favor of background traffic in mixed traffic scenario.At the last part of this dissertation, the whole work of the dissertation is outlined and the further research topics are discussed.