【作者】 陈禹；

【导师】 温向明；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2010， 博士

【摘要】 LTE是在超3G的技术基础上研发出的“准4G技术”,其目的是为了迎接WiMax等移动宽带无线接入技术的市场挑战、进一步改进和增强现有3G技术,以提高3G在新兴宽带无线接入市场的竞争力。尤其是在移动通信技术的迅猛发展和近几年来基于HSPA的商用网络启动,LTE已引起了越来越多的关注。目前LTE第一个版本的标准已经完成,各个主要厂商已经纷纷推出了样机设备,使得移动通信系统在很好的保证用户QoS的情况下通信速率达到了一个前所未有的高度。TD-LTE作为TD-SCDMA的后续演进标准,其采用OFDM、MIMO等先进的无线传输技术、全IP系统架构和扁平网络结构的标准势必会成为我国移动通信产业关注的焦点和热点。我国的LTE标准也就是TD-LTE,做为一个刚刚制定完成的标准,还存在版本完善、增强和下一步演进的过程。在TD-LTE的改进中,物理层技术是提高系统性能的关键,其以达到降低时延、提高用户的数据速率、增大系统容量和覆盖范围以及降低成本的目的。其中同步过程、功率控制过程、随机接入过程、物理下行共享信道相关过程、物理上行共享信道相关过程和物理共享控制信道过程是LTE系统物理层过程的主要过程。移动终端通过随机接入过程与基站建立上行初始同步,利用同步跟踪来完成对上行用户信道的跟踪,完成用户上行信号发射时间的调整,有效的控制方法能够较好地跟踪用户信道响应的变化,使得主峰位置较好地收敛于循环前缀中合理的位置。通过小区搜索过程,用户终端(UE)可以搜索到一个可用的小区,并获得符号同步和帧同步,设计合理的检测方案,UE才能获取本小区更详细的信息以及邻近小区的信息,才可以监听寻呼或发起寻呼。随机接入(Random Access)是UE在开始和网络通信之前的接入过程,接收机中检测方法对虚警和漏警概率的正确检测才能满足LTE系统的性能要求。对于高码率、高阶调制的数据传输,符号定时偏差对系统性能影响较大,符号定时偏差越大,系统性能下降也越明显,在小区搜索完成后,需要设计一种精确的符号定时算法,使符号定时偏差的范围降到最低。针对上述问题,本文从LTE数字蜂窝移动通信网Uu接口物理层领域的研究热点出发,分别对LTETDD物理层过程中的上行同步控制、小区搜索、随机接入和下行符号定时进行了深入、系统地研究,并取得了一定数量的创新科研成果,主要内容包括：1、在理论分析上行同步过程的基础上,利用信道冲激响应原理提出了一种定时发送预值的测算方法,设计为移动台提供发送的定时提前量,并重新设计阈值检测方法。2、对3GPP LTE TDD系统的下行链路小区搜索及初始化载波同步标准化工作进行跟踪研究,理论推导给出下行链路符号定时、扇区ID检测、粗频偏估计和小区组ID检测的算法。仿真的同时对小区搜索各个步骤的复杂度做了分析和统计比较,提出一种使用FFT快速算法的简化措施来有效降低运算复杂度的算法。3、在理论研究LTE-TDD系统随机接入过程的同时,分析了随机接入信道的帧结构以及码序列和相应的资源映射等相关内容。提出了一种PRACH的接收机算法,并设计了接收机中的检测门限,最后对接收机算法进行了性能仿真,验证该算法的可行性。4、深入研究了LTE TDD系统链路与系统的接口模型和下行符号定时同步的问题,在此基础上推出了一种下行链路符号定时同步的算法,并对该算法进行了计算机仿真。结论表明该算法比已有算法定时跟踪准确,受信噪比影响小,算法复杂度低,在不同信道环境下均可正常工作等优点。通过以上四个方面的研究,为TD-LTE网络的业务可用性提供了较为完整的应用方案,较好的解决了LTE网络的综合性能,为TD-SCDMA系统的相关技术和LTE系统的实际情况相结合提供了保障机制。更多还原

【Abstract】 To encounter the challenge of the wimax, the Long Term Evolution system is the fourth generation for the wireless cellular network, especially after the HSPA (High Speed Packet Access) network. Currently, the first version for the LTE is achieved; moreover, the prototype is released by many manufacturing company, furthermore, to providing the QoS for the user has gained more attention. As an evaluation technology of the TD-SCDMA technology, the LTE is viewed as the focus for the mechanism of OFDM, MIMO adopted to enhance the capability of the wireless transmission.Considering about the state of our country, the TD-LTE system is determined to be an important technology in the future. As the evaluation procedure for the LTE, Physical layer technology is the key to improving system performance, to achieve lower latency and improve the user’s data rate, increasing the system capacity and coverage and reduce costs. The uplink synchronization process、power control process、random access procedure、physical downlink shared channel related processes and physical process of shared control channel is main course of the LTE system physical layer process. By through random access procedure UE establish the initial uplink synchronization with base stations, through using the synchronization tracking it can track the uplink user channel and adjust the uplink signal transmission time. Effective control can track the change of users channel response better and make better convergence of the main peak position of the cyclic prefix in the appropriate position. Through the cell search UE can search for an available cell, a well-designed test program can get more information in this district and the neighboring cell information accurately. Random Access is the beginning of the process before UE and network communications. The detection method of receiver must meet the performance requirements of LTE systems when corrected probability false alarm and false detection. For high bit rate and higher order modulation data transmission, the symbol timing offset affects greater impact on system performance. The more offset the more affect on system performance, so it need a algorithm of downlink symbol timing to minimize the scope of the symbol timing offset.Considering about the problems above, the interface of Uu is studied in detail, and upstream synchro control, cellular searching, random access and downstream symbol timing mechanism is proposed.1. In according with the analysis on the procedure of upstream synchronous, a novel data transmitting method is proposed. To adjusting the offset of the packet sending, the threshold detecting method is designed reasonable.2. Base on the reach of the cellular downstream link and the initial synchronous of the carriers, the predicting on the timing, sector ID and frequency offset is introduced; moreover, the simplified method based on the FFT theory is proposed to reduce the complexity of the algorithms.3. With the analysis on the random access for the LTE-TDD system, the frame structure and corresponding resources mapping is studied. A novel algorithm for the receiver based on the PRACH is proposed; moreover, the detecting threshold is designed; finally, the simulation results show that the proposed algorithm is actually enough.4. The timing problem in the LTE TDD system is researched deeply, and based on the downstream symbols; the function of timing synchronous is achieved effectively. Results show that the accuracy of following can be guaranteed; furthermore, the complexity and the influence on the SNR can be reduced dramatically.From the researches on the above directions, the available of TD-LTE system can be enhanced; moreover, the evaluation from TD-SCDMA to the LTE system is smoother.更多还原