Multi - carrier modulation ( mcm ) is a preferable physical layer technology for bws , since it can efficiently mitigate the frequency - dependent distortion across a wide frequency band and simplify the equalization in a multipath fading environment 多载波调制( mcm )技术是适合bws的物理层调制技术,可以很好的解决宽带无线情况下出现的频率选择性衰落现象及简化多径衰落信道环境的均衡问题。
Aiming at the lower performance and floor effect of the traditional orthogonal frequency division multiplexing channel estimation , the ofdm channel estimation algorithm based on wavelet recursive least square support vector machine ( wrls - svm ) is proposed 摘要针对传统多径衰落下的ofdm导频信道估计性能低下，地板效应的缺陷，提出了基于导频的小波递归最小二乘支持向量机( wrls - svm )时变信道频率估计算法。
The algorithm takes advantages of the anti - fading capabilities in both ofdm and star - qam modulation and demodulation , and provide valuable information and for further studying the potential capability in higher - order modulation - demodulation anti - fading technologies and theories 我们的算法将ofdm和星型qam调制解调技术的抗多径衰落能力融合在一起，为进一步挖掘高阶调制解调抗衰落的潜力提供了理论依据。
Based on detailed theoretical analysis and research of the mobile channel , firstly it introduces the basis principle of ofdm and concisely present some measures to overcome multipath fading , and then discusses several key techniques of ofdm concretely : 1 在对移动信道进行详细的理论分析和研究的基础上，首先给出了ofdm的基本原理，并简要介绍了克服多径衰落的一些措施。然后具体讨论了ofdm的几种关键技术： 1
Simulation results show that abf - csma / ca protocol can realize space - division - multiple - access ( sdma ) and provide very high channel utilization . chapter 3 considers employing smart antennas in the central access point ( cap ) of wireless internet access networks 第三章研究了智能天线在internet无线接入网络中的应用，主要考虑使用智能天线对抗同信道干扰与多径衰落，增加覆盖范围，并在mac层实现智能天线与网络的有机结合。
Then , analytical expressions of the bit error rates are derived under rayleigh fading model and multi - path rayleigh fading channel model . analytical and simulation results are compared . the multi - path performance of the non - coherent dcsk system is also compared with that of the coherent csk system 接着对非相干dcsk系统在瑞利衰落及多径瑞利衰落信道下进行性能分析,通过仿真实验来验证理论分析结果,并与相干csk系统的抗多径衰落性能比较。
At last , the basic theory of fractal and its application in modeling multi - path fading channel are introduced . by studying its fractal parameters , the channel is reconstructed based on wavelet theory . finally , we preset the possibility of applying this model to power and rate control in cdma 论文介绍了分形的基本理论，分形理论在建模无线传输信道上的应用，及用小波的方法重构了多径衰落信道，探讨了采用基于分形预测的功率速率控制技术的可行性。
On the other hand , cdma ( code - division multiple access ) communication system has been widely considered as the mainstream of 3g communication system , because it has the good qualities such as high utilization ratio of frequency band , low transmission power , powerful anti - multiple path falling and flexible capacity 另一方面， cdma通信系统以其高频谱利用率、低发射功率、强抗多径衰落特性、软容量等优点，已被广泛认为是第三代移动通信系统的主流。
These limit its application in ever - increasing communication demand . this thesis focuses on some technical difficulties encountered in the long distance wireless communication and tackles the task by applying ofdm ( orthogonal frequency - division multiplexing ) techniques in the communication system . this hence improves the overall communication system ' s performance by overcoming the effects such like multi - path fading and doppler spread in the frequency domain 本文主要从调制技术方面入手，针对无线远距离通信信道的一些问题，将正交频分复用( ofdm )技术应用于超短波无线远距离移动通信系统，克服了超短波无线远距离移动通信中所面临的多径衰落和多普勒频移等因素的影响。
The method was correlate search and fft carrier detection , which could solve the problem of the capture of the spread spectrum code under the condition of low snr and big frequency offset . we also put forward a method , shift receiving window and correlate with local sequence , which not only could solve the problem of symbol synchronization but also could acquire the statistics of the multipath . then we utilized the results of the channel estimation and the technology of rake receiver to decode the received spread spectrum sequence and acquire rude information 方案中提出了：相关搜索、 fft检测信号载波的方法，解决了低信噪比、大频差条件下扩频码的同步捕获难题；滑动相关完成位同步的方法，解决了低信噪比下的同步问题；在时域利用相关进行信道估计，然后利用rake接收技术完成相关解扩的方法，一定程度上解决了多径衰落影响解扩性能的问题。
