选择性衰落

• Space - time block codes ( stbc ) based on orthogonal design has attracts enough attentions in its applications in mimo - ofdm systems for its full diversity exploiting and low coding / decoding complexity . these applications include not only system performance improvement , but also reduction of the peak to average power ratio in mimo - ofdm systems . under these backgrounds , this paper first studies space - time block codes under the single carrier , flat fading situation , discusses the encoding / decoding principle and its performance under different channels . then , the author focused on the performance of space - time codes under time selective and frequency selective channels , uncovered the fundamental cause of how maximum doppler shift and power delay profile influences the performance of space - time codes through deduction and simulation
  在上述背景下,本文以单载波,平坦衰落信道下的空时分组码为切入点,深入分析了其编译码原理和在不同信道情况下的性能;以此为基础,后文展开了对空时分组码在多载波,时间选择性和频率选择性衰落信道下的性能研究,通过理论推导和充分的仿真,揭示了空时/频分组码在时频选择性衰落信道中的性能变化的根本原因;在以上对多载波系统中空时分组码的研究的过程中,作者发现了空时分组码在降低系统峰平比方面应用的可行性,提出了一种降低峰平比的新方法。
• The following algorithms have been proposed and tested in the thesis : 1 frequency selective fading : combine the isomorphism between the input space and the output space and propose a new approach to blind equalization of the channel . compared with conventional methods , the new approach offers lower computational complexity , better performance , and more robust against the over - determination of the system order ; 2 time selective fading : a new approach to the equalization of time selective channel based on the zero - forced equalizer is proposed which is more simple in its structure of algorithm ; 3 time - varying channel : using the instantaneous mean value changes of the output signal to extract the information of channel variations and model it using ar model , kalman filter is then employed to track channel variations , it bears faster ability in tracking the variation of tv channels ; based on the isomorphism between the inputs and the outputs and some of the approaches using in mimo system , a new algorithm of equalization of simo time - varying channel is proposed , which also share the merits of being robust against the over - determination of the system order ; model the time - varying channel using the multi - resolution decomposition wavelets , and then a blind identification method based " on the model is proposed ; at last , a new model for equalization and identification of mimo system is proposed
  主要工作在以下几个方面： 1 、针对频率选择性衰落信道：结合输入输出空间同构关系提出一种新的频率选择性信道均衡方法，与传统方法相比，该方法计算量更小，收敛速度更快，性能更优，且对系统阶次的过确定表现稳健，具有实际均衡应用价值； 2 、针对时间选择性衰落信道：提出一种基于迫零均衡的时间选择性信道均衡方法，算法结构简单； 3 、针对时变色散信道：利用瞬态均值曲线提取信道时变信息，对之ar建模，利用卡尔曼滤波器跟踪时变信道抽头变化，可以快速跟踪信道变化；基于输入输出空间之间的同构关系以及多输入多输出系统的处理方法，提出了新的单输入多输出色散时变信道均衡与识别算法，同样具有对信道阶次过确定保持稳健的优点；结合小波多分辨率分析提出一种基于小波模型的信道盲识别算法；研究时变的多输入多输出系统的盲均衡与盲反卷积问题，给出一种时变系统处理模型。
• This article proposes the adaptive algorithm based on equal snr signal noise ratio , and applies it in adaptive ofdm system . in frequency selective fading channel , compared with the traditional ofdm system based on equal power allocation , the system outperforms in ber bit error ratio performance
  提出了一种基于最小平均误码率的自适应预处理算法，并将该算法应用于自适应ofdm系统，在频率选择性衰落信道条件下，与等功率分配的ofdm系统相比，误比特性能有了很大程度的提高。
• In adaptive multi - carrier modulation , the principle of blind detection assisted adaptive ofdm ( aofdm ) is given and a blind modulation detection algorithm is proposed for aofdm in frequency selective fading channel . the performance of the algorithm is compared with the available algorithms and the effectiveness and robustness of the blind detection algorithm are proved through simulation . 3
  对于自适应多载波调制，我们研究了ofdm调制和基于盲检测辅助的自适应ofdm的原理，提出一种在频率选择性衰落信道中aofdm信号子信道调制方式盲检测算法，并与已有的文献进行了比较，证明了算法的有效性和稳健性。
• Rtce is based on forecasting the inherent vulnerabilities to propagation of hf time - varying channel , including multipath delay , doppler spread , selective fading , interference , so this paper also introduces characteristics of hf channel in the beginning . familiar rtce systems all adopt envelope method that bello brought forward
  实时选频技术是基于对短波电离层时变信道固有的不利于电波传播的各种因素，包括信道的多径展宽、多普勒展宽、选择性衰落、噪声干扰等的预测的基础上实现的，所以在开篇对短波信道的特点进行了详细的介绍。
• Be based upon the studies of sea optical scatter channel by use of monte carlo simulation , the channel is described as a multipath routeway in this paper . the effect on the communications performance , created by the frequency selectivity decline caused by the multipath routeway , is worked over . the correlation bandwith of sea optical scatter channel is analyzed and quantified through the simulation on the computer
  基于对海水信道的蒙特卡罗模拟，本文对海水信道进行了多径化描述，研究了由于信道的多径化所产生的频率选择性衰落对通信质量的影响，分析并通过计算机模拟确定了海水信道的相关带宽。
• Meanwhile , the synchronization algorithm in the ds - ss system can be used in 2d - ss system , and good synchronization performance can be obtained , with its algorithm simplified . the third part analyzed the ber performance of mc - ss - cldd in the presence of multi - user interference in time - varying multipath fading channels
  在论文的第三部分中,研究了多用户多载波频域扩频码片级差分检测方案:从理论上分析了频率选择性衰落信道下该算法的误码率性能,同时进行了仿真验证。
• In mimo systems , the signal can be sent and received through multiple antennas or antenna arrays . the combination of ofdm and mimo can effectively alleviate the problem of multi - path propagation , increase system capacity , and obtain more robust system capability , so they are considered as the main stream techniques of the future wireless communication system
  Ofdm技术固有的抗信道多径和频率选择性衰落特性以及mimo在提高系统频谱利用率,改善无线通信系统性能等方面的巨大作用,使得这两种技术的融合成为了下一代移动通信系统的必然选择。
• The problem of signal processing for direct - sequence code - division - multiple - access ( ds - cdma ) signal over multipath frequency - selective mobile channels is considered . a new blind receiver is proposed . without the knowledge of the multiple - access interference users spreading code and the channel characteristics , the receiver achieves blind detection with prior knowledge of only the desired users spreading code and approximate timing . by using reduced rank adaptive decorrelating filter and adaptive multipath combiner which is based on decision - directed algorithm , the receiver gets the ability to combat both fading and the near - far effect at low cost . simulation results demonstrate that the proposed receiver offers high performance
  本文研究多径频率选择性衰落信道下直接序列扩频码分多址（ ds - cdma ）信号的处理问题，提出了一种新型的盲接收机.该接收机不需预知多址干扰用户的扩频码，不需预知信道参数，只需已知期望用户的扩频码和粗略的定时，就可以完成用户的盲检测.同时，该接收机通过降维自适应去相关滤波和基于判决指导的自适应多径合并，来获得低成本和良好的抗衰落、抗远近效应性能.仿真结果验证了本文提出的接收机的优良性能