【作者】 李长春；

【导师】 袁东风；

【作者基本信息】 山东大学 ， 通信与信息系统， 2011， 博士

【摘要】 随着人们对未来无线通信系统性能要求的不断提高,为了提高数据传输的速率和可靠性,并在有限的频带资源下提供更高的频谱效率,链路自适应传输技术已逐步成为现代乃至未来无线通信研究的关键技术之一,并受到业界广泛关注。链路自适应技术旨在根据无线信道在时间、空间和频率等维上的变化,动态地调整发射机和接收机的参数,在维持不同业务的传输质量的前提下,进一步提高无线通信系统的平均频带利用率,使无线信道资源得到最大限度的利用。自适应编码调制技术是链路自适应技术中的典型实例之一,它根据信道环境的变化自适应地调节调制编码方式,在信道环境较差时采用低阶调制和低码率的编码,而在信道条件较好时采用高阶调制和高码率的编码。本文围绕链路自适应传输技术,基于跨层联合优化方法以及AMC、HARQ、LTE-Turbo码和多天线等先进技术,从理论研究和实际应用两方面对无线通信系统的自适应传输技术进行了深入研究与分析,提出了基于HARQ和AMC的联合跨层自适应传输方案,将单天线信道环境下基于LTE-Turbo码的AMC-ARQ系统的应用扩展到多天线环境中,研究并探讨了链路自适应技术在图像传输和视频通信中的应用。本文的主要工作和创新点如下：第一,提出了基于HARQ的跨层自适应传输模式。基于自适应调制编码技术和混合自动请求重传技术的基本原理和特点,将Turbo码与上述技术相结合。研究分析了HARQ性能,在满足数据链路层的误包率和延时的前提下,将Type-II型HARQ和Type-Ⅲ型HARQ应用在物理层和数据链路层的跨层设计中；进一步研究了HARQ联合AMC技术的跨层设计,推导出了系统平均误包率和系统平均传输次数的数学表达式。仿真结果表明,采用这种跨层设计的自适应传输技术,大大降低了系统的误包率,提高了系统频谱利用率。第二,结合LTE-Turbo编码技术,提出了基于LTE-Turbo码的链路自适应传输系统模型。系统研究了链路自适应技术及其在单天线系统中的应用。由于实际的无线信道通常受各种外界干扰及多径衰落等因素影响,接收的信号会产生大幅度的变化,鉴于此,本文采用了基于LTE-Turbo码的跨层设计,在物理层采用自适应编码调制技术,同时在链路层采用选择重传ARQ机制,并对比了不同机制的性能,研究结果表明,采用AMC联合ARQ技术时的系统频带利用率会比只采用AMC技术或只采用ARQ技术时的系统频带利用率要高。第三,将AMC联合ARQ的跨层设计由单天线系统扩展到MIMO多天线信道环境下,利用Turbo码的优异编码增益及STBC可获得的分集增益,将Turbo码与STBC级联,推导出系统在Nakagami-m及Rayleigh信道下的数学模型和在不同信道状态下系统的频谱利用率特性。文中给出了采用不同信道模型和不同的发射接收方案的仿真结果,通过对比不同方案的仿真结果,可以看出采用AMC-ARQ方案在MIMO信道下系统的频谱利用率比在单天线信道下得到了很大提高。第四,从面向实际应用的角度出发,针对静态图像传输和动态视频传输,分别研究了上述自适应传输技术的实际应用。对比分析了自适应传输技术相对于其他传输技术所带来的性能优势,并对实际应用中可能涉及到的问题进行了分析总结。更多还原

【Abstract】 As the growing demands of future Wireless Communication Systems, in order to improve the rate and reliability of data transmission and improve as high as frequency spectrum utilization under the condition of limited band resources, the technology of Link Adaptive Transmission has become one of the most critical technologies for future network communication systems and largely concerned by industries.The technology of Link Adaptive Transmission is to ajust the parameters of tramsmitter and receiver dynamically on the basis of variations of time, space and fenquence in wireless channels. This technology can improve the average frequency spectrum utilization; make use of wireless channel resources as much as possible under different requirments of different kinds of services and applications. The technology of Adaptive Modulation and Coding (AMC) is one of typical technologies in Link Adaptive Transmission, which ajust the models and functions of coding according to different channel environments and variations. AMC could choose low order modulation and lower code rate on the conditions of worse channel environments, and choose high order modulations and higher code rates on the conditions of better channel environments.The thesis focus on technologies of Link Adaptive Transmission, based on joint optimization and some advanced technologies such as AMC, HARQ and LTE-Turbo. This research work research and analyse the Adaptive Transmission of wireless communication systems deeply in two categories:theoretical research and practical application. We provide the cross-layer adaptive transmission schemes based on HARQ and AMC, expand the applications of LTE-Turbo and AMC-ARQ from single antenna channel evnironments to multi antenna channel environments, and discuss the applications about picture transmissions and video transmissions using link adaptive transmission.The mainly work and innovations are listed as follow:First, the research work provides the cross-layer adaptive transmission modes. This work based on the basic principles and features of AMC and HARQ and conbines the technology of Turbo code with them. We analyse the performances of HARQ, and apply the technologies of Type-Ⅱand Type-ⅢHARQ in the corss-layer design of physical and link layer under the link layer requirements of PER and delay. For fruther research, we study the cross-layer designs which combine the HARQ and AMC, drive the mathematical expression of average frequency spectrum utilization and average transmission numbers. The simulation results show that the PER of the system can be greatly reduced and the system frequency spectrum utilization can be dramatically increased by using the proposed corss-layer adaptative transmission scheme.Second, combined with the technology of LTE-Turbo, we propose the multi antenna link adaptive transmission system model. This system researches the applications of link adaptive transmission in the environments of single and multi antenna. Because in practical conditions, the wireless channel can be influenced by outer interferences and multipath fading so the received signal could be affected greatly. According to this feature, our researches apply the cross-layer design based on LTE-Turbo, the adaptive modulation and coding in physical layer and the scheme of ARQ in link layer. By comparing the performances of different schemes and modes, we draw the conclusion that combing the technologies of AMC and ARQ would increase the frequency spectrum utilization of the communication systems compared with the only using of ARQ or AMC.Third, the research expands the cross-layer design of AMC and ARQ from single-antenna systems to MIMO systems. Using the excellent coding gain and the technology of STBC, we could get the diversity gain; combing Turbo and STBC, we derive the mathemetical models and frequency spectrum utilizations under the channels of Nakagami-m and Rayleigh. The simulation results of different channel models and transmission and receiving schemes are shown, through comparing results of different schemes, we can see that under MIMO systems, using the scheme of AMC-ARQ could extremely imporve the character of frequency spectrum utilizations.Fourth, for applications, focusing on transmissions of static pictures and videos, the thesis researches the practical applications of these technologies of adaptive transmission. Through comparing the performance advantages of adaptive transmission upon other schemes, we analyse and conclude the potential practical problems in practical applications.更多还原