B3G/4G TDD试验系统与业务演示

作为国家十五“863”Future计划的重大项目，B3G TDD OFDM系统技术研究与集成的子课题于2006年6月正式通过验收。该系统采用宽带TDD OFDM MIMO技术，兼容TD—SCDMA，峰值速率可达122Mbit／s，频谱利用率为7．1bit／s／Hz。支持高清晰视频点播、FTP高速下栽、Internet、语音等业务。重点介绍了B3G—TDD试验系统的结构性能、系统参数、关键技术以及业务演示等方面的内容。     

TDD的关键技术及其应用前景

本文从时分双工(TDD)方式的相关关键技术、优缺点以及在未来移动通信系统中的地位等方面,对采用TDD方式的移动通信系统的特点与发展趋势进行了深入分析,并给出了一些发展建议.     

HSDPA＆LTE护航TD-SCDMA可持续发展

众所周知，2005年年中结束的TD—SCDMA产业化专项测试证明了TD—SCDMA系统完全可以大规模独立组网，同时基于时分双工（TDD）模式特性所采用的一些先进的关键技术也得到了有力验证。在TD—SCDMA产业已经取得全面突破，并在不久的将来实现规模商用已成必然的情况下，我国提出的这一3G标准技术的可持续发展将成为运营商（尤其是新运营商）在3G建网时进行制式选择的一个重要考虑因素。     

时分双工码分多址通信技术

第三代移动通信按工作的双工方式可分为TDD和FDD两种模式下的CDMA系统,由于TDD模式的技术优势,它正日益受到重视.本文比较了两种TDDCDMA的无线传输技术,分析了TDD模式的技术特点,包括优势和缺点,最后展望了它在3G中的应用.     

基于特征建模的TDD系统大气波导干扰控制体系研究

大气波导干扰是特定气象条件下发生的时分双工（time-division duplex，TDD）系统内干扰，是TDD移动通信系统大规模组网面临的顽疾。在总结分析大气波导干扰成因和分类等的基础上，对大气波导干扰进行建模和表征，验证了海量干扰源在时域和频域的功率集总特征，并结合大量4G/5G现网实测数据给出了典型条件下内陆波导和海面波导的量化干扰信号传播模型，对于干扰的预测和预防具有重要意义。基于干扰特征，给出了TDD系统预防大气波导干扰的帧结构与组网的4项设计原则，5G现网数据表明干扰控制方案有效，上行干扰下降10 dB以上，相关原则对于6G系统的设计也具有指导意义。     

基于TDD的第四代移动通信技术

4G网络具有极大的吸引力，它将提供更高的数据速率及频谱利用率，本文介绍了基于TDD模式的4G通信的特点及其关键技术。     

5G双工演进技术研究

5G新型双工演进技术将在TDD频谱上引入基站侧子带不重叠全双工制式,以迎合万物智联和工业互联网对低时延和大上行吞吐量同时提出的更高要求,同时还需要进一步研究并解决基站间交叉时隙干扰问题,使能公网和专网采用不同的TDD上下行时隙配比的组网方式。为满足5G新型双工演进技术的未来部署需求,对TDD宏微异时隙组网和子带不重叠全双工制式的潜在部署场景和相关干扰特征进行了分析和研究,提出潜在可行的干扰抑制方案,并通过链路预算、仿真评估和样机验证等形式论证了技术可行性。     

WCDMA与WiMAX系统共存干扰分析

国际电联ITU—R第8F工作组第14次会议为3G的FDD（频分双工模式）和TDD（时分双工模式）系统划分了2．5～2．69GHz频段。美国FCC（联邦通信委员会）在2004年允许固定微波业务使用2．495～2．69GHz频段。这极大促进了WiMAX系统在此频段的设备研制和开发。     

固定无线接入点到多点系统中时分双工与频分双工之对比

利用点到多点架构的宽带固定无线系统采用微波和毫米波频段，本文介绍了TDD与FDD应用在该系统中的差异，讨论了选择TDD而非FDD的动机，也论述了FDD赞同者所持的观点。     

基于3G技术的自组织网络研究新进展

移动自组织网络是目前个人移动通信技术的研究热点。针对基于3G技术的移动自组织网络进行了研究，论述了自组织网络关键技术的发展现状，分析了其技术特点和应用范围，重点介绍了基于3G时分双工（TDD）无线传输信道技术的FLEETNET网络，以及旨在扩展TD-SCDMA覆盖范围的自组织网络技术及应用特点，并进一步阐述了该技术今后的研究和发展方向。     

TD-LTE干扰优化中对大气波导的监测与规避

本文主要阐述大气波导产生的基础,以及TD-LTE系统如何监测到大气波导干扰,在此基础上提出大气波导干扰规避的集中方案,重点对通过参数优化调整规避及减轻大气波导干扰的优化措施进行分析。     

Spectral Efficiency of Dynamic Time Division Duplex Fixed Wireless Cellular System for Asymmetric and Dynamic Multimedia Traffic

We analyze spectral efficiency of dynamic time division duplex in a fixed wireless cellular network. Conventionally, spectral efficiency has been analyzed for static and fully loaded systems. In this paper, we investigate how asymmetric and dynamic traffic affect the spectral efficiency of Time-Division-Duplex (TDD) systems. Recently, dynamic TDD (D-TDD) has gained much attention as an efficient duplex scheme for high-speed data communications, because adaptive switching ability enables the system to obtain statistical multiplexing gain by exploiting dynamic and asymmetric data traffic. However, it has been noted that a rather strong co-channel interference can be present due to adaptive switching in a cellular network that uses frequency reuse. Thus, benefits of dynamic TDD may not be justifiable unless a proper countermeasure is employed. To suppress the effect of strong co-channel interference, we employ time slot allocation (TSA) strategy along with sector antenna layouts, as proposed in our previous work Jeong and Kavehrad (IEEE and Transactions on communication, Vol. 50, no.10 pp. 1627–1636, 2002). We note that higher spectral efficiency is obtained in D-TDD systems by employing TSA strategy. We also evaluated spectral efficiency of D-TDD system employing adaptive modulation, assuming that traffic is delay tolerant. It is observed that five times higher spectral efficiency can be obtained by employing adaptive modulation. The effect of variance of ratio of offered load on uplink and downlink is also evaluated. Our computer simulation results show that spectral efficiency of D-TDD system with time slot allocation algorithm is more than that of static TDD (S-TDD) over a large range of traffic variation. In conclusion, D-TDD system can take advantage of statistical multiplexing gain of dynamic traffic by adaptively positioning the boundary to the varying traffic bandwidth in its two-way transmissions when TSA strategy is employed for suppression of strong co-channel interference.     

An improved cooperative spectrum sensing of femtocells with hybrid TDD access scheme in massive MIMO system

To improve the sensing performance and achieve higher throughput of the femtocells (FCs) while alleviating the influence to the macrocell in the cognitive massive multiple‐input and multiple‐output system (MIMO), we propose in this paper a hybrid time‐division duplex (TDD) access scheme of the FCs with confidence factor–based weighted cooperative spectrum sensing (CSS). A first, we present an efficient hybrid TDD access scheme for better spectrum reuse of the FCs based on the typical TDD and reversed TDD schemes. Furthermore, confidence factor–based weighted CSS has been used for better spectrum sensing and interference alleviation. In the cognitive massive MIMO system, FC base stations will form dynamical clustering based on the channel conditions, sense the spectrum through cooperative scheme, and decide whether to access the spectrum or not. After information exchange within each FC cluster, the FC base stations can obtain and update their confidence factors and weight factors based on the sensing results and reliability. Numerical results and theoretical analysis show that the proposed scheme can get more accurate sensing results, increase the throughput and the spectrum access opportunity of the FCs, and efficiently alleviate the interference to the macrocell tier.     

An Overlaid Hybrid‐Division Duplex OFDMA System with Multihop Transmission

In this letter, we propose an overlaid hybrid division duplex (HDD) concept for cellular systems which divides a cell into inner and outer regions and utilizes the merits of both time division duplex (TDD) and frequency division duplex (FDD). The proposed system can take advantage of both TDD and FDD without handover between two duplex schemes. Moreover, it is shown that the proposed HDD system outperforms the conventional TDD or FDD system with mobile relay stations when the synchronization issue is considered in orthogonal frequency division multiple access systems. Thus, the proposed overlaid HDD can be considered as a new framework for future cellular systems.     

Improving coarse flame synchronization by UE-UE interference for OFDMA-TDD systems

This article studies the coarse flame synchronization of orthogonal frequency division multiplexing access-time division duplex （OFDMA-TDD） systems and proposes a new method to improve coarse frame synchronization performance. The new method utilizes the user equipment to user equipment （UE-UE） interference, which is usually considered as a specific challenge for time division duplex （TDD） and also as implicit frame boundary information to enhance coarse frame synchronization performance. Numerical results show the synchronization performance is imoroved bv the new method.     

Improving coarse frame synchronization by UE-UE interferencefor OFDMA-TDD systems

This article studies the coarse frame synchronization of orthogonal frequency division multiplexing access-time division duplex (OFDMA-TDD) systems and proposes a new method to improve coarse frame synchronization performance. The new method utilizes the user equipment to user equipment (UE-UE) interference, which is usually considered as a specific challenge for time division duplex (TDD) and also as implicit frame boundary information to enhance coarse frame synchronization performance. Numerical results show the synchronization performance is improved by the new method.     

The evolution path of 4G networks: FDD or TDD?

Frequency-division duplexing and time-division duplexing are two common duplexing methods used in various wireless systems. However, there are advantages and technical issues associated with them. In this article we discuss in detail the features, and the design and implementation challenges of FDD and TDD systems for 4G wireless systems. In particular, we present a number of advantages and flexibilities an TDD system can bring to 4G systems that an FDD system cannot offer, and identify the major challenges, including cross-slot interference, in applying TDD in practice. Due to the fact that cross-slot interference is one of the critical challenges to employing TDD in cellular networks, we also provide a quantitative analysis on its impact on co-channel and adjacent channel interfering cells     

TD-SCDMA移动通信系统无线干扰分析

在简要介绍无线干扰产生的根源的基础上,首先分析了TDD系统中的典型干扰：小区内的干扰、小区间的干扰、TDD系统与FDD系统的干扰等,然后特别研究和总结了建设基于TD-SCDMA标准的3G移动通信系统存在的无线干扰基本情形,主要有：TD-SCDMA技术内的干扰、WCDMA与TD-SCDMA的干扰、cdma2000与TD-SCDMA的干扰、TD-SCDMA与GSM/GPRS的干扰、TD-SCDMA与PHS的干扰等,并从系统工程设计和技术方案设计以及政府频率规划等角度简要指出了降低和消除干扰的方法.