| With multi-media services rapid expansion and internet technology quick advancing, mobile telecommunication experiences incredible high-speed development stage, which evolves in technology implementation from one generation (1G) based on analog signals and two generation (2G) ground on digital signals to three generation (3G), beyond three generation and four generation (B3G/4G) wireless broadband network with the character of high speed digital multi-media services. Drawn by "mobility of the broad band" and "broadband of the mobile telecommunication", long term evolution (LTE) is proposed by the third generation partnership project (3GPP) as four generation technology based on the last decades technical storage of B3G/4G research. LTE adopts MIMO-OFDM integrated by orthogonal frequency division multiplexing (OFDM) and multi-input multi-output (MIMO) as the core technology, which is dedicated to improve data rate, system capacity and business performance. This dissertation studies LTE system's cell search, signals detection receiving and resource cross-layer scheduling etc. themes. The major achievements are outlined as follows.1. Cell search is the basic premise for synchronization of LTE wireless system. The LTE system defines two types of CP (Cyclic Prefix), normal CP and extended CP. In this dissertation an improved CP type decision and SSS (Secondary Synchronization Signal) detection algorithm in cell search is presented. Avoiding CP type blind detection, sliding window correlation detection toward receiving signals is adopted to decide CP type based on a pre-defined threshold. Instead of blind detection toward even-numbered signals and odd-numbered signals of SSS, the even-numbered signals are utilized to correlation detection firstly, and then the odd-numbered signals are used to further verify the result detected by even-numbered signals. The simulation results show the proposed algorithm effectively reduces computation complexity without the detection performance degradation and is very suitable for application.2. We investigate MIMO receiver structure under wireless fading channels. An iterative algorithm of inner loop sequential decision feedback linear minimum mean squared error (SDF-LMMSE) detection and outer loop parallel interference cancellation (PIC) is proposed against the time and frequency selective fading in OFDM system. The SDF-LMMSE detection can eliminate multi-user interference within space frequency (SF) coding introduced by channels frequency selectivity fading, and the PIC can also cancel the inter-carrier interference (ICI) greatly. Through analysis and simulation, the inner loop SDF-LMMSE detection and outer loop PIC shows superior detection capability than the classic maximum likelihood (ML) linear detection and PIC method. In addition, the proposed algorithm reduces computation complexity and its detection performance is close to that of sphere decoding (SD) algorithm.3. Through cross-layer scheduling research of link adaptation in LTE system, a channel-adapted and buffer-aware (CABA) scheduling algorithm is proposed. The scheme allocates system resource jointly physical (PHY) layer and medium access control (MAC) layer according to channel quality indicator (CQI), precoding matrix indicator (PMI) and rank indication (RI) feed back with the uplinks, considers buffer status and queueing time, distinguishes different priority of real time (RT) services and non-real time (NRT) services, guarantees certain fairness among users. Compared with conventional scheduling algorithms, for example round robin (RR), pure opportunistic (PO) and proportional fair (PF), the simulation results show the proposed mechanism can achieve higher system throughput and lower packet loss probability without ignoring user fairness principle. |
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