多天线无线数据通信系统中多用户分集的研究

研究当接收天线不少于发送天线时多输入多输出(MIMO)系统的多用户分集能力。首先从理论上分析了发送天线个数等于1和2时最大似然接收和迫零接收系统的平均吞吐量和调度增益,以及仿真分析了发送天线个数大于2时系统性能。理论分析和仿真表明：在多用户的MIMO系统中,接收的平均信噪比、用户个数、收发天线个数、接收机的结构等对于多用户分集有很大的影响。当发送天线个数为1时,接收天线较少(1,2,3)和平均信噪比为．10dB时调度增益很大,但调度增益随着天线个数和发送功率增大急剧下降。和最大似然接收相比,迫零接收具有更大的多用户分集增益,因此迫零接收机的吞吐量可以很容易超过最大似然接收机。     

非相干天线选择算法

基于广义似然比检验(GLRT)与天线选择相结合,提出了平瑞利衰落信道的非相干天线选择(NON-AS)算法,天线选择和信号检测无需信道状态信息.NON-AS算法适用于多输入多输出(MIMO)系统的接收端,接收天线选择是基于每个天线瞬时接收到信号矢量的F-2范数.与相干检测的天线选择相比,NON-AS算法不需要估计信道,大大降低了系统复杂性.成对错误概率分析和仿真结果表明:在高信噪比情况下,选择有最大范数的接收天线,系统能实现和使用全部接收天线相同的分集增益.     

几种接收机在MIMO信道下的性能比较

多入多出（MIMO）无线信道具有空间复用增益和分集增益特性,因此MIMO系统和单入单出（SISO）无线系统相比能够获得更高的频谱效率。本文在不同天线组合下分析了几种MIMO空时信号处理算法的性能,仿真结果和理论分析表明：空间复用增益和分集增益不能同时获得最大,因此在设计MIMO通信系统时可根据实际情况选择天线数,即不仅考虑系统抵抗信道衰落的分集增益,还要考虑能够提供更高的数据传输速率,通过折衷考虑空间复杂增益和分集增益,从更全面的观点评估系统的性能。     

基于复杂系统自组织MIMO无线传输分集和编码技术研究现状及其技术路线

空间分集与编码调制技术相结合的空时编码技术,可以获得分集和编码增益,具有优异的抗衰落性能。传统空时编码和多输入多输出(MIMO)技术是通过多天线来实现空间分集的,但是由于移动台的尺寸和载频的限制,使多天线技术很难实现。基于复杂系统自组织MIMO无线传输分集和编码技术成为解决这一问题的可选方案,并且无需通过信道反馈信息,动态分配资源,提高了端到端的通信服务质量(QoS)和信道容量。     

分集接收技术在海上升空通信中继系统中的应用

海上升空通信中继系统是解决海上广域无线宽带通信的重要手段,但其性能易受海面波动带来的多径衰落影响。为了有效提升中继系统接收信号质量,提出了一种多天线分集接收方法,通过现场可编程门阵列(Field Programmable Gate Array, FPGA)实现相应的接收处理。仿真分析及实验室测试表明,所提出的四天线分集接收技术能够带来近6 dB的合成增益。经海上对比试验验证,采用所提出的多天线分集接收技术的升空通信中继系统,其数据接收完整性提升了10%～20%,系统性能显著改善。     

一种基于分布式空时码的协作MIMO分集复用折衷新方案

协作MIMO通过多个单天线节点的相互协作构造多发射天线,以此形成一种虚拟MIMO多天线阵列获得空间分集增益。考虑到协作MIMO特点,天线间采用分布式空时编码进行编码协作。文章研究了协作MIMO中基于分布式空时码(DSTC)的分集复用折衷(DMT)新方案,该方案通过推导两种DSTC的中断概率与分集增益表达式,结合两类DSTC的DMT策略,根据改变复用增益阈值自适应获得最佳DMT与中断性能。数值仿真表明,所提的DMT策略可以逼近协作MIMO的DMT上限,协作节点采用该策略的中断性能仅次于上限的中断性能。在多节点构成协作MIMO网络分布式空时编码协作中,提出的DMT新方案可使系统高效地获得协作分集增益与中断性能。     

应用于MIMO系统终端的腰带式可穿戴天线

提出一种应用于MIMO无线通信系统移动终端的腰带式可穿戴外置多天线.这一MIMO多天线系统利用合理的布局,可获取各种分集增益.天线单元采用开槽的电磁耦合微带贴片天线,减小了天线尺寸,也降低了人体吸收率.通过MIMO系统试验平台的外场测试,得到了多天线系统的相关性系数矩阵以及误码率等重要的实验数据.测试结果表明:在保持总发射功率不变的情况下,相较于传统的单发单收天线,这一多天线系统可显著降低传输误码率,进而有效提高通信系统容量与质量.     

MIMO的天线系统设计

系统地描述了MIMO分集性能衡量指标,并对空间分集、方向图分集、极化分集进行了概念描述。进而根据MIMO系统天线设计的要求和特点,结合新型MIMO系统天线单元和天线阵列,分析了其设计思路,同时重点设计了一种用于MIMO系统的终端阵列天线,即单层矩形切角贴片天线,并对其S 参数和方向图进行了模拟和分析。模拟结果对合理设计MIMO系统发射和接收端天线阵列具有现实意义。     

差分空时系统的天线选择算法

一般的天线选择算法都需要信道状态信息,根据信道参数选择天线.然而,估计多输入多输出(MIMO)系统的信道参数大大增加了系统复杂性,而且,在快衰落信道中,信道估计是很困难的.基于正交空时编码和接收信号向量的范数,提出了非相干的天线选择算法(NON-AS),不需要估计信道,并将算法应用于差分空时系统.性能分析和仿真结果表明,在高信噪比情况下,NON-AS算法能实现和完全复杂性系统同样的分集增益.     

基于最大比合并的MIMO分集系统递增天线选择算法

MIMO分集系统天线选择技术可以在不增加系统射频链路的情况下,达到与全天线几乎相同的分集增益.针对发送端采用最大比发送,接收端采用最大比合并的MIMO分集系统,提出了一种递增天线选择方法,每次增加一根天线,并使得它与已选出的天线结合起来具有最大的信噪比增益.相对于对所有可用天线集进行遍历的最优算法,它减小了需要搜索的范围和每次搜索的计算量,降低了复杂度;相对于功控天线选择算法,它考虑了新增天线与已选出天线集之间的相关性,改善了性能.仿真结果表明,在误比特率、信道容量和信噪比增益方面,此算法和最优算法性能相近,且不随可用天线数和选出天线数的改变而改变.     

A review of antennas and propagation for MIMO wireless communications

Multiple-input-multiple-output (MIMO) wireless systems use multiple antenna elements at transmit and receive to offer improved capacity over single antenna topologies in multipath channels. In such systems, the antenna properties as well as the multipath channel characteristics play a key role in determining communication performance. This paper reviews recent research findings concerning antennas and propagation in MIMO systems. Issues considered include channel capacity computation, channel measurement and modeling approaches, and the impact of antenna element properties and array configuration on system performance. Throughout the discussion, outstanding research questions in these areas are highlighted.     

Adaptive antennas for space-time codes in outdoor channels

Space-time codes have been introduced to improve mobile system performance in a multipath fading environment. We consider a multiple-input multiple-output (MIMO) system with m mobile antennas and n base station antennas, in which there are L multipaths at the base station at distinct angles of arrival. We show that when the channel has no intersymbol interference (ISI), then adaptive antennas in the form of beamforming, can be combined with space-time coding, to achieve a diversity gain of mL and a large signal-to-noise ratio (SNR) gain whenever n/spl ges/L. When the channel has ISI, beamforming can be used by the MIMO systems to achieve an SNR gain over a single-input multiple-output system, although both systems have the same diversity gain.     

Polarization diversity measurements and analysis for antenna configurations at 1800 MHz

In wireless communication systems, multipath interference has a significant impact on system design and performance. Fast fading variations are caused by the coherent summation of multiple echoes from many reflection points reaching the receive antenna. Antenna diversity is one technique that can be used to overcome multipath fading. A test system used to measure the diversity performance of an antenna pair was used to experimentally determine the complex correlation coefficient between the two antenna branches. A local mean estimation algorithm based on the channel mean square error equalization was implemented. Thus, the two parameters that determine the expected diversity gain, i.e., the complex correlation coefficient and the mean level signal difference, were estimated. The test system was used to evaluate the polarization diversity performance of different antenna pairs in Rayleigh and Rician environments, both in the absence and in the presence of a human head phantom.     

Octagonal DGS based dual polarised ring-shaped antenna for MIMO communications

In this article, a dual polarised Microstrip patch antenna is proposed for 2*2 MIMO communications. The proposed antenna is suitable for GSM/DCS-1800 and LTE-1900 bands as diversity and multiple-input multiple-output (MIMO) antenna. Different from conventional MIMO antennas, the radiating aperture is shared among the radiators, which greatly reduces the overall size of the MIMO antenna system. An isolation enhancement of 30 dB between the input ports is achieved by integrating cross-connected octagonal shaped Defected Ground Structure to the ground plane. Furthermore, the Multi-antenna system performance metrics such as Envelope Correlation Co-efficient, diversity gain and Mean Effective Gain, and Total Active Reflection Co-efficient are also computed. The Proposed antenna shows a gain of 3.63 dBi at 1950 MHz. The simulated and measured results demonstrate that the proposed antenna has good impedance matching, isolation and dual polarisation characteristics. From the performance metrics, the proposed antenna performs well in multipath environment.     

Correlation and channel capacity of MIMO systems employing multimode antennas

A novel way of exploiting higher modes of antennas as diversity branches in multiple-input-multiple-output (MIMO) systems is introduced. Essentially, antennas employing multiple modes offer characteristics similar to an antenna array, through multiple modes and using only a single element. The physical mechanism that yields different received signals is the fact that each mode has a different radiation pattern. Analytical expressions for the correlation between signals received by different modes are presented for a biconical and a circular microstrip antenna that employs higher order modes. It is found that the correlation is low enough to yield a significant diversity gain. Furthermore, the channel capacity of a MIMO system using a multimode antenna, i.e., an antenna employing multiple modes, is found to be comparable to the capacity of an array. Since only one element is needed, the multimode antenna offers several advantages over traditional arrays, and is an interesting antenna solution for future high capacity MIMO systems.     

B3G空中接口技术分析--MIMO信道测量

在多径信道中,使用多天线的MIMO无线系统能够比单天线系统提供更高的信道容量,而信道测量是决定通信性能的一个重要因素。对目前国际范围内现有的MIMO信道测量进行了研究,并做了归纳和分类。此外,对MIMO信道测量方法进行了分析,并给出了一些针对MIMO信道测量系统设计的建议,为B3G空中接口技术研究提供了技术支持。     

Exploiting Multipath Diversity in Multiple Antenna OFDM Systems With Spatially Correlated Channels

Multiple antennas are useful in orthogonal frequency division multiplexing (OFDM) systems for providing transmit and receive diversity to overcome fading. Typically, these designs require considerable separation between the antennas. Spatial correlation is introduced when antennas are not well separated, and it often leads to performance degradation in a flat fading environment. However, in frequency selective fading channels with rich multipath diversity, OFDM receivers can overcome this performance degradation due to antenna correlation. This is due to transformation of a highly spatially correlated channel impulse response to a less spatially correlated channel frequency response inherently by an OFDM system in the presence of rich multipath diversity. We illustrate this for a simple receive diversity OFDM system and hence introduce the concept of space sampling at the receiver where antennas are placed relatively close to each other. The minimum separation required between the antennas under such circumstances is derived analytically, and it is shown that even with a separation of only$0.44lambda$, the required spatial correlation in the channel frequency response becomes sufficiently low. Simulated performance results with such spacing for various multiple antenna OFDM systems corroborate the analytical results.     

On the Performance of Space–Time Block-Coded MIMO Video Communications

The problem of efficient video communications over multiple-input-multiple-output (MIMO) wireless systems is of great significance due to the high capacity of the multiple antenna system. The high data rates provided by the MIMO system can be traded off with diversity gain by using different channel-coding schemes. Also, by using different video source-coding methods, high compression gain can be traded off with the error resilience gain. One should jointly consider source coding and channel coding when designing a MIMO wireless video system. However, little is known so far about what combinations of channel-coding and source-coding methods have the best overall performance in a MIMO system. In this paper, by comparing the performances of several different typical combinations through both theoretical and simulation studies, we show that no single combination is the best for the entire range of channel conditions, but rather, different combinations may be best for a subrange