基于OFDM星载交换的星地下行链路跨层设计

该文基于一种全新的基于OFDM的星载交换方案,给出了此星载交换方案的星地下行链路跨层设计工作流程和相关实现方法,此方法根据星地下行链路信号发射功率上限、关于每个地面设备的当前点波束星地下行链路信道状态、每个星地下行链路传输业务目的地、业务类型、业务传输速率要求等参数,实现在属于不同地面设备的各个星地下行链路传输业务之间自适应分配子载波并自适应配置每个子载波的调制制式,生成每个传输业务与子载波的对应关系,充分利用链路资源并满足传输业务的QoS要求。     

OFDM/OQAM系统自适应波形设计及多址接入系统

基于传统正交频分复用技术的OFDMA多址接入技术仍然存在循环前缀-正交频分复用(CP-OFDM)技术的固有缺陷,即循环前缀的添加降低了系统频谱利用率,多普勒频移对传统OFDMA系统产生较强的子载波间干扰,且对相邻频带的其他无线传输系统引入较强的相邻信道干扰。该文主要讨论基于扩展高斯函数的正交频分复用系统自适应波形设计,通过信道散射函数选择合适的扩展因子参数,获取更高的频谱利用率和抑制符号间干扰和子载波间干扰。最后该文将自适应波形设计的思想扩展至基于扩展高斯函数的多址接入系统,使每个用户能够根据信道条件选择合适的成形滤波器函数,进而使多址接入系统达到全局最优化。仿真结果验证了该文方法的有效性。     

OFDM系统中卷积码纠错性能分析

OFDM因能有效对抗频率选择性衰落和窄带干扰,成为802．11无线通信的物理层标准。论文使用不同的编码效率的卷积码,对OFDM系统的抗干扰能力进行仿真,得到对应的信噪比与误码率的关系,并数值分析了编码效率与编码增益之间的折中关系。结果表明,编码效率的损失,则能带来误码率的改善。在语音通信误码率的一般要求下,损失1／3的编码效率可以增加的编码增益,约为3dB．     

RoF非线性链路对OFDM信号的影响

正交频分复用OFDM（Orthogonal Frequency Division Multiplexing）与光载无线电ROF（Radio OverFiber）技术结合为实现低成本、高速数据传输的无线网络提供了可能。但RoF链路的非线性降低了系统性能。丈中在分析Machzehnder调制器的静态模型基础上,提出用Volterra级数与冲击响应分析模型相结合模型化RoF非线性系统。在此模型基础上分析Mach-Zehnder调制器以及射频放大器非线性对OFDM信号的影响。仿真分析显示非线性会使OFDM信号频谱展宽,降低信号幅度,并且随着光调制指数的增加误差矢量,带外干扰增加。为OFDM-RoF系统的线性化处理以及系统光调制器调制指教的选择提供了理论依据。     

基于OFDM系统的随机信道接入方案

双忙音多址信道接入(DBTMA)协议是一种信道利用率较高的无线局域网信道随机接入控制方案。但是, 该协议的硬件实现复杂度较高。该文在对DBTMA协议进行简单修改的基础上,结合节能意识多址接入(PAMAS) 协议提出了一种基于OFDM系统的DBTMA信道接入系统,并对此系统做了简要分析。分析结果显示,该文提出的随机信道接入系统的性能良好且实现方式简单。     

OFDM及其链路级单台的Simulink实现

第四代移动通信的核心技术——正交频分复用(OFDM)，正越来越受到人们的关注。本详细讨论了如何利用Simulink进行OFDM系统链路级的仿真，并构建了分别采用理想信道估计、LS信道估计和MMSE信道估计等三种方法的OFDM系统链路级平台模型，最后对每一种OFDM系统的平台进行了仿真比较。     

一种适用于宽带无线移动通信系统下行链路的TDS-OFDM发送方法

本文将主要介绍宽带无线城域网系统(BRadio)中下行链路的TDS-OFDM(时域同步正交频分复用)发送方法.TDS-OFDM是针对宽带无线传输信道设计的一种多载波调制方式,既适用于具有多径干扰和多普勒频移的地面数字电视广播传输信道,也适用于其他宽带数字传输系统.TDS-OFDM技术已经在地面数字多媒体/电视广播(DMB-T)传输系统中得到了应用,在此基础上,本文结合对已有的宽带无线移动通信系统的研究,对宽带无线移动通信系统的帧结构、OFDM符号组成、子载波分配方案进行了改进,使TDS-OFDM能够适用于宽带无线移动通信系统,满足其需求.     

OFDM系统仿真与性能分析

正交频分复用（OFDM）是一种特殊的多载波方案,它既是一种调制技术,也是一种复用技术。由于其具有良好的抗频率选择性衰落或窄带干扰、频谱利用率高和成本低的优点,应用越来越广泛。采用Simulink搭建的OFDM仿真系统,既能有效测试OFDM的性能指标,也能研究和理解OFDM特点和具体应用。     

OFDM系统仿真与分析

正交频分复用(OFDM)是一种多载波数字调制技术,它能有效地克服传输中的多径干扰和消除码间串扰,所以在高速数据传输中得到了广泛的应用.这里将OFDM系统引入高斯白噪声信道中,实现高速数据的传输,并对误码率进行分析.     

Performance of an OFDM Based Downlink Multiple Access System for Indoor Wireless Communications

We have analyzed the downlink performance of a multiuser Orthogonal Frequency Division Multiplexing based multiple access system for indoor wireless communications. The optimization problem for minimizing the total transmit power from a base station while satisfying the bit-rate and bit-error rate criterion of the various portable users in the system has been outlined. The analytical solution obtained cannot be realized in a simple manner and we present a realizable method for the combined allocation of subcarriers, modulation mode, and power to the signals transmitted to the different users. Simulation results are used to compare the performance of the analytical solution with that using the new method under various channel conditions. Performance comparisons between the new method and an OFDM-TDMA system clearly indicate the advantages of the new algorithm under most conditions. The correlation of the frequency-domain channel strengths among the various users is shown to have an influence on the performance of the new algorithm.     

一种多用户MIMO/OFDM下行链路保障QoS的自适应传输机制

在用户QoS参数限制下,该文提出一种在多用户MIMO/OFDM下行链路使系统总速率最大的资源分配机制。基站应用空分多址接入,使得每个子载波可支持多个用户,应用线性预编码方法抵消用户间的干扰,提出保障QoS的自适应功率、比特分配方案。该文并提出两种可应用到实际系统的低复杂度的比特加载和比特去除算法,仿真结果表明,该两种方法性能可非常接近最优遍历算法。     

Adaptive Modulation and Multiple Access for the OFDM Transmission Technique

For the transmission of flexible andhigh data rates in future mobile communicationsystems, the multicarrier transmission technique(Orthogonal Frequency Division Multiplexing, OFDM) canbe regarded as a possible alternative tosingle-carrier transmission that is used in today'ssystems. One of the advantages of OFDM is theflexibility concerning modulation and multiple accesstechniques. Since in OFDM the total bandwidth isdivided into a large number of subcarriers, it can beflexibly shared among all the users. In addition, themodulation scheme can be individually chosen for eachsubcarrier, thus granting the possibility of anadaptation to the radio channel characteristics. Inthis paper, the combination of two different multipleaccess schemes, OFDM-FDMA and OFDM-TDMA, and anappropriate adaptive modulation technique isconsidered for the downlink of a communication system.Different degrees of adaptivity are analysed andcompared to show the benefit of an ``intelligent'multiple access and modulation strategy. For thegiven parameters and assumptions, OFDM-TDMA withadaptive modulation yields an improvement of 6 dB insignal-to-noise ratio (SNR) at a bit error rate (BER)of 10^-2. When OFDM-FDMA with adaptive subcarrierallocation is applied, the SNR gain amounts to 12.5 dB(BER of 10^-2).     

OFDM技术在无线接入中的应用

文章首先介绍了OFDM的关键实现技术，然后结合不同无线通信环境的特点，对OFDM在无线局域网和固定无线接入中的应用进行了分析。     

Near Optimum Power Control Scheme for Downlink in the W-CDMA Cellular System

The downlink power control problem in W-CDMA is studied using a new near optimum power control scheme (model). The downlink cell capacity is given for both the old given by Gejji and our new model. A capacity increase of 7.5% for the special case = 0 (no orthogonality between users) and a generalization of the old model are obtained using the new model.     

OFDM技术及其性能分析

随着越来越多的无线设备走进人们的生活，大量的多媒体业务也随之出现了，由于传送多媒体业务需要一定的带宽的保证，传统的无线网络的带宽在扩展多媒体业务方面也显出了一定的不足。OFDM调制技术的出现，从一定程度上解决了用户对带宽的要求。而且OFDM调制技术也是针对无线网络设计的，能够更加充分地利用现有的带宽，而且能够很好地对抗频率选择性衰落或窄带干扰。在4G的标准中将会被作为底层的调制技术以提供更高的传输质量。     

A Simplified Downlink Transmission and Receiving Scheme for IDMA

In this paper, we propose a downlink transmission and receiving scheme for interleave-division multiple access （IDMA） system based on time-division duplexing （TDD） mode and time-reversal （TR） technique. The proposed scheme uses the time-reversed version of the channel impulse responses （CIR） obtained from the transmitted signal at base uplink to pre-process the station. By exploiting the weak correlations of fading channels for different user ends （UE）, it is helpful to alleviate the multi-user interference （MUI） and co-channel interference （CCI）. Moreover, the application of the TR technique in a multiple input-single output （MISO） configuration can reduce the delay spread of the channel impulse response, and mitigate inter-symbol interference （ISI）. The UE can be simplified by canceling the iteration operation. Thus the data detection of the proposed scheme is rather simple as compared with the traditional IDMA, the complexity and computational load of UE is decreased substantially, and the proposed scheme provides a great deal of privacy and security to mobile users.     

Subcarrier and Power Allocation for the Downlink of Multiuser OFDM Transmission

In this paper, a new algorithm for subcarrier and power allocation for the downlink of multiuser OFDM transmission is presented. The proposed algorithm is more stable and it offers a lower complexity and better performance than previous existing algorithms. Khalid El Baamrani was born in Ouarzazate, Morocco in 1976. He received the License degree (equiv. B.A.) in electronic engineering from the University of Cadi Ayyad, Marrakech, Morocco, in 1998, the D.E.S.A. (equiv. M.A) in electrical engineering from the University of CadiAyyad, Marrakech, Morocco, in 2000, the certificate in engineering of the data-processing networks and telecommunications from the national institute of posts and telecommunications, Rabat, Morocco in 2002 and the Ph.D. degree at University of Cadi Ayyad, Marrakech, Morocco in 2005. His research interests include multicarrier modulation, communication theory, multiuser information theory, OFDM and DSL systems. Victor P. Gil Jiménez received the B. Eng. in Telecommunications with honors from University of Alcalá in 1998 and the M. Eng. in Telecommunications and the PhD. degree both from the University Carlos III de Madrid in 2001 and 2005, respectively. He is with the Department of Signal Theory and Communications at the University Carlos III de Madrid as an Assistant Professor. He worked at the Spanish Antarctica Base in 1999 as Communications Staff. He visited University of Leeds and Chalmers Technical University in 2003 and 2004 respectively. His research interests include multicarrier communications and signal processing for wireless systems. Ana Garcia Armada received the Telecommunication Engineer degree and the Ph.D in Electrical Engineering both from the Polytechnic University of Madrid (Spain) in 1994 and 1998, respectively. She is currently working as an Associate Professor at the University Carlos III de Madrid, where she has occupied several management positions. She has participated in several national and international research projects, most of them related to OFDM. She is coauthor of four books on wireless communications and signal processing. She has published 13 papers in international journals and more than 40 papers in conferences. She has contributed to international organizations such as ITU and ETSI. She has performed research stays in ESA-ESTEC, Kansas University, Stanford University and Bell Labs. Her research interests are simulation of communication systems, multicarrier and MIMO techniques.