【作者】 林雁；

【导师】 乐光新；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2011， 博士

【摘要】 随着多媒体业务的日新月异和互联网技术的迅猛发展,通信技术经历了令人不可思议的高速发展阶段。移动通信系统从第一代模拟通信、第二代数字通信迅速地发展到第三代以及后三代/第四代(B3G/4G, Beyond Three Generation/Four Generation)高速无线宽带网络,在技术实现上逐步演进。长期演进计划(LTE, Long Term Evolution)是3GPP(3rd Generation Partnership Project)在“移动通信宽带化”和“宽带接入移动化”的趋势下,基于几十年B3G/4G研究的技术储备研发的4G技术。LTE通信系统采用正交频分复用(OFDM, Orthogonal Frequency Division Multiplexing)和多输入多输出(MIMO, Multi-input Multi-output)相结合的MIMO-OFDM作为核心技术以提高数据速率、系统容量和业务性能。本论文致力于研究LTE通信系统中的小区搜索、信号检测接收和资源跨层调度等问题,主要工作如下：1、研究了LTE通信系统小区搜索问题。LTE系统定义了两种循环前缀(CP,Cyclic Prefix)类型,即常规CP和扩展CP。本论文对LTE小区搜索中的CP类型判决和辅同步信号(SSS, Secondary Synchronization Signal)检测算法提出了改进：基于滑动窗相关方法并利用门限值直接判断CP类型,然后移除CP,经快速傅立叶变换(FFT, Fast Fourier Transformation)到频域后,利用SSS的偶数序列的相关运算判断小区组标识号并用奇数序列的相关运算加以验证。通过算法分析和仿真证明所提的算法提高了小区搜索的有效性,在保证检测性能的同时大大降低计算复杂度,非常适合实际系统应用。2、研究了MIMO系统在无线衰落信道下的检测接收技术。为对抗OFDM系统中的频率选择性衰落和时间选择性衰落引起的干扰,提出了结合内环串行判决反馈线性最小均方误差(SDF-LMMSE, Sequential Decision Feedback Linear Minimum Mean Squared Error)检测和外环并行干扰消除(PIC, Parallel Interference Cancellation)的迭代检测接收算法。SDF-LMMSE检测能够有效地对抗信道频率选择性衰落导致的空频编码内的多用户干扰,而PIC能够有效地消除载波间干扰(ICI, Inter-carrier Interference)。仿真和分析表明,所提算法的检测性能优于经典最大似然(ML, Maximum Likelihood)线性检测和PIC方法,与球译码(SD, Sphere Decoding)检测算法的效果接近,且计算复杂度被大大降低。3、研究了LTE无线通信系统的链路自适应跨层调度问题,提出一种联合物理(PHY, Physical)层和媒体接入控制(MAC, Medium Access Control)层的信道自适应与缓存可知(CABA, Channel-adapted and Buffer-aware)的调度算法。该调度策略根据上行链路反馈的信道质量指示(CQI, Channel Quality Indicator),预编码矩阵指示(PMI, Precoding Matrix Indicator)和秩指示(RI, Rank Indication),考虑缓存队列的状态信息和等待时长,区分实时和非实时业务的优先级,保证用户间的公平性,联合PHY层与MAC层统筹分配系统资源。通过仿真证明所提算法与典型的轮循(RR, Round Robin)调度、纯机会主义(PO, Pure Opportunistic)调度、比例公平(PF, Proportional Fair)调度算法相比,能够在较低丢包率的前提下获得较高的系统吞吐量,同时兼顾用户公平性的原则。更多还原

【Abstract】 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.更多还原