基于虚拟MIMO子信道的多用户分集资源调度算法

根据多天线(MIMO)信道空间相关特性,提出一种虚拟子信道的分析方法,从子信道角度探讨信道容量在发射端已知信道响应时预期的性能改善;在此基础上,提出一种逼近信道容量上限的波束形成方法,发掘MIMO信道矩阵最大奇异值与波束形成矢量潜在的联系,并从理论角度详细分析了单用户与多用户最大奇异值联合分布特性,实现阵列增益、空间分集和多用户分集充分融合;仿真与分析表明,利用用户间潜在的随机分布特性能有效提高用户的空间分集增益,提高系统资源利用率,对系统性能改善显著.     

有限反馈下协作波束形成系统的性能仿真研究

针对实际通信系统中发射机难以获得准确的信道状态信息(CSI)的情况,基于放大前馈中继模式和两种不同的拓扑结构,提出了有限反馈的协作波束形成技术,研究了反馈信道的信道状态信息量化对系统性能的影响.仿真结果表明,协作系统的性能与中继终端的位置密切相关,当中继位于信源和目的终端的中间时,协作系统能获得最大的分集增益.信道量化对协作分集系统性能的不利影响是有限的,即使1比特的量化反馈,也能产生相当大的性能增益.     

多天线系统分集复用模式快速选择算法

对空间复用多天线系统线性接收机进行了深入分析,针对其虽应用简便却未能很好地利用分集增益的问题,提出了一种基于误码率准则的分集复用模式快速选择算法．所提算法通过低复杂度的判决准则对多天线系统分集复用模式进行选择,并将少量的信息反馈回发送端,达到充分利用多天线系统分集与复用增益的目的．与以往算法相比,所提算法可以更好地利用系统的瞬时分集增益,而且具有较低的计算复杂度,很好地满足了多天线通信系统对实时性和快速性的要求．仿真结果验证了算法的有效性和可行性．     

闭环多用户多天线Beamforming系统的性能分析

0 引言 无线通信系统需要能提高频谱效率的更加智能的技术,以满足无线频谱资源的日益匮乏.波束成型Beamforming和多输入多输出技术(MIMO,Multi Input Multi Output)都可以在基站使用多根天线,利用多天线阵列提供波束增益和发射分集,从而提高系统的性能 [1,2].     

基于信道统计相关信息反馈的POST-IDFT多波束技术

提出了适用于平稳随机的频率选择性衰落信道下的空时分组码-正交频分复用（Space—time block coding-Orthogonal frequency division moltiplexing,STBC-OFDM）系统的后-逆离散傅立叶变换（POST-IDFT）多波束形成技术。通过对空频信道统计相关矩阵进行特征分解获得多个特征模式,利用空时分组码（STBC）各发射分支信号的正交性对OFDM系统形成多个POST-IDFT波束,由STBC传输矩阵的正交性进行多波束解码。系统在获得阵列增益的基础上,其空间分集度由POST-IDFT多波束的维数决定;与OFDM子载波相比,降低了复杂度,易于实现。     

基于MUD/SD的认知无线电系统遍历容量研究

提出了基于多天线选择分集接收的多用户分集认知无线电系统模型。该系统模型由于在认知接收端采用了多天线选择分集接收,相比传统多用户分集认知无线电系统采用的单天线接收,能够进一步提高认知用户系统信道遍历容量。推导并给出了认知接收端信噪比的概率密度函数与累积分布函数,分析了多天线数目与认知用户数对系统信道遍历容量的影响,同时给出了不考虑认知用户发送功率约束条件下的认知用户系统信道遍历容量的解析表达式。     

MIMO 系统分集复用折中及自适应链路实现

多输入多输出技术可以增加分集阶数或系统自由度,以往研究多侧重于最大化其中一种增益,不能充 分利用多天线系统的性能．针对上述问题,本文提出了一种新的基于链路自适应技术的分集复用折中方法．该方法 以误比特率为判决准则,依据实时信道状态信息进行自适应码率、功率分配,并通过少量比特信息反馈到发送端来 确定系统的工作方式．同时,为降低计算量,通过对不同工作方式下接收端信噪比边界值的近似,给出了低复杂度 的次优判决准则．本文所提算法可充分利用分集、复用增益,提高系统可靠性的同时保证了较高的传输速率,具有 较小的计算量,抗扰动性强．仿真结果表明,与传统方法相比本文提出的折中方法具有较好的性能,满足了无线通 信系统实时性、快速性的要求．     

一种低复杂度非满秩正交随机波束成型传输方法

与现有研究点对点的无线通信手段不同,基于网络整体架构,分析SINR、波束矢量、用户数、吞吐量内在关联,发掘网络内部多用户空间分布不一致性带来的用户间的分集增益,提升系统的吞吐量.将随机波束成型与迫零算法有机结合,研究一种新型非满秩正交波束成型算法,克服了满秩波束间的相互干扰,提升系统容量;最后对性能作了详细分析与验证,得出几个极有意义的结论.     

基于随机波束成形MIMO系统的信道反馈算法

MIMO系统是未来移动通信发展的趋势.随机波束成形利用包含信道质量的反馈信息,可以开发多用户分集增益,进一步提高MIMO系统的容量.然而繁重的反馈信息会占据大量的无线资源,降低系统的实际效率.主要研究降低随机波束成形MIMO系统反馈开销的方法,提出了两种部分信道反馈算法:门限反馈和最优反馈.理论推导表明了系统平均容量与反馈率之间的权衡关系,仿真结果证明了只要恰当地选取反馈参数,这两种反馈算法可以在几乎不牺牲系统容量的前提下,极大节省反馈开销.其中,门限反馈在系统容量方面表现要好于最优反馈,而最优反馈在实现简便性方面要强于门限反馈,因此实际设计时要折中考虑.     

非理想CSI下MIMO MRC系统多用户分集性能分析*

针对在无线多输入—多输出（MIMO）通信系统的发射端采用波束成形、接收端采用最大比合并的MIMO MRC系统,考虑收发端仅能获得存在信道估计误差的非理想信道信息（CSI）且系统受到共信道干扰这一条件,分析系统的多用户分集性能。导出封闭形式的信号干扰噪声比的概率分布函数表达式和以平均容量的形式给出的系统多用户分集性能表达式。数值仿真证实了理论分析的结果。研究表明,信道估计误差和共信道干扰均会降低系统的多用户分集性能,而信道估计的精度是影响系统多用户分集性能的关键因素。     

Repetition-based cooperative broadcasting for vehicular ad-hoc networks

In vehicular ad hoc networks, most of critical applications involved with safety rely on reliable broadcast communications with low latency. Recently, repetition-based protocols have been proposed to meet the requirements of timeliness and reliability for broadcasting. In these protocols, a sender repeatedly retransmits the broadcast message during the lifetime of the message. However, existing protocols face serious problems such as deterioration of the signal quality caused by wireless fading. In particular, since excessive repetitions might cause network congestion and waste channel resources, reliability of broadcasting should be achieved with as small a number of repetitions as possible. In this paper, we therefore propose a novel repetition-based broadcast protocol which exploits a cooperative diversity technique (called RB-CD) making a small number of repetitions robust for wireless fading. To support this cooperative diversity, neighboring nodes transmit the same message almost simultaneously (that is, using the same repetition pattern for each other) in order to form a virtual antenna array. The virtual antenna array achieves a diversity gain at the receivers. In the RB-CD protocol, the virtual antenna array consists of the source and some of its neighbors (called relays) which participate in repeating the transmission of a broadcast message. In addition, a new distributed relay selection algorithm is introduced in the RB-CD protocol. From the ns-2 simulation results, we verified that RB-CD provides a more reliable broadcasting service due to its capability of exploiting cooperative diversity.     

Active measurements of antenna diversity performances using a specific test‐bed,in several environments

The diversity performances of the wireless devices operating in a multipath propagation environment are usually presented in terms of correlation coefficient, diversity gain and effective diversity gain. These parameters can be measured in reverberation chamber. This paper presents some active measurements of antenna diversity performances on a small wireless terminal in several realistic environments. The measurements were performed in the WiMax band, i.e. at 3.5 GHz, in a reverberation chamber where the channel is statistically uniform, in a real indoor propagation channel, and in an outdoor‐to‐indoor environment. The diversity performances are evaluated by using a specific test‐bed constituted by an arbitrary signal generator and two radio‐frequency digitizers. The effectiveness of diversity is presented in terms of effective diversity gain, signal to noise ratio, bit error rate and frame error rate. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Asymptotic SEP of MIMO beamforming in two-hop AF relaying systems

This paper derives an asymptotic average symbol error probability(SEP)expression for multiple-input multiple-output(MIMO)two-hop amplify-and-forward(AF)relay systems with optimal beamforming.The analysis at high signal-to-noise ratio(SNR)quantifies the diversity order and array gain,which are valid for any antenna numbers of the terminals and arbitrary channel fading models.It is also proved that the system performance is dominated by the relatively degraded one of the two-hop channels.Our results based on the simple expressions provide valuable insights into the performance and practical design considerations of MIMO AF networks.     

Compact eight‐port MIMO/diversity antenna with band rejection characteristics

A new compact three‐dimensional multiple‐input‐multiple‐output (MIMO) antenna comprised of eight antenna elements is presented. The unit cell of the proposed MIMO/diversity antenna consists of three elliptical rings connected together in the region close to the feed line and a rectangular‐shaped modified ground plane. To achieve polarization diversity with the proposed eight‐port MIMO configuration, four antenna elements are horizontally arranged and the remaining four are vertically oriented. The proposed antenna has an impedance bandwidth (S₁₁ < ?10 dB) of 25.68 GHz (3.1‐28.78 GHz) with a wireless local area network notch‐band at 5.8 GHz (5.2‐6.5 GHz). In addition to polarization diversity, the proposed antenna provides a reliable link with wireless devices. The prototype antenna design is fabricated and measured for diversity performance. Also, the proposed MIMO antenna provides good performance metrics such as apparent diversity gain, channel capacity loss, envelope correlation coefficient, isolation, mean effective gain, multiplexing efficiency, and total active reflection coefficient.     

Single layer CPSSA array with change polarization diversity in broadband application

The present study proposes a novel broadband circularly polarized (CP) multiple‐input multiple‐output antenna array designed for C‐band applications. The first step was the introduction of a reconfigurable circularly polarized square slot antenna (CPSSA) capable of changing polarization diversity, which could cover impedance bandwidth (BW) from 4.48 to 8.21 GHz with 1.9 GHz of ?3 dB axial ratio (AR) BW. Then, a feed network composed of 90° and 180° couplers, a crossover, and delay lines was presented. The CPSSA with two metalized via‐holes adopted with two ports polarization diversity fed the networks. A number of reconfigurable CP array antennas using the polarization diversity technique have been presented so far. However, given that the proposed layout designed in a single layer had advantages of reduced antenna size and increased antenna gain and ARBW, this approach has received due attention over recent years. Another promising feature of this approach is its capability to change the polarization diversity by rotation of phases in the array feed network using PIN diodes.     

极化MIMO雷达隐身目标检测性能研究*

多输入多输出(MIMO)雷达使用了远距分布的阵元,它利用了信号的空间分集增益来获取更多的目标信息。极化是另一种可以提高雷达系统性能的分集方式。当应对隐身目标时,传统的极化雷达在某些观测角度会遭受到较大的目标雷达截面积(RCS)衰减,而无法获得较好的检测性能。而在一个雷达系统中同时利用这两种分集增益,可以得到一种比传统极化雷达更具优势的新雷达检测系统——极化统计MIMO雷达,它可以更好地应对隐身目标检测。给出了相应的模型,并推导出了该雷达系统的检测性能解析式。将其与传统相控阵及非极化统计MIMO雷达比较,可以看到极化统计MIMO雷达的检测性能更佳。联系到隐身目标的特性,极化MIMO雷达的检测器特性应对它时具有显著优势。最后,以上方法通过仿真得到了验证。     

Ten switched‐beams with 2 × 2 series‐fed 2.4 GHz array antenna and a simple beam‐switching network

This article presents a 2 × 2 series fed 2.4 GHz patch antenna array having multiple beam switching capabilities by using two simple 3 dB/90° couplers to achieve required amplitude and phase excitations for array elements with reduced complexity, cost and size. The beam switching performance with consistent gain and low side lobe levels (SLL) is achieved by exciting the array elements from orthogonally placed thin quarter‐wave (λ_g/4) feeds. The implemented array is capable to generate ten (10) switched‐beams in 2‐D space when series fed elements are excited from respective ports through 3 dB quadrature couplers. The dual polarized characteristics of presented array provide intrinsic interport isolation between perpendicularly placed ports through polarization diversity to achieve independent beam switching capabilities for intended directions. The implemented antenna array on 1.575 mm thick low loss (tan δ = 0.003) NH9450 substrate with ε_r = 4.5 ± 0.10 provides 10 dB return loss impedance bandwidth of more than 50 MHz. The measured beam switching loss is around 0.8 dB for beams switched at θ = ±20°, Ф = 0°, 90°, and 45° with average peak gain of 9.5 dBi and SLL ≤ ?10 dB in all cases. The novelty of this work is the capability of generating ten dual polarized switched‐beams by using only two 3 dB/90° couplers as beam controllers.     

V-BLAST OFDM最大发射分集度分析

V-BLAST OFDM可以利用多径信道的频域选择性改善分集性能.目前相关研究缺乏分集度的理论分析,未能明确给出一种获取最大分集度的方法.针对这一问题,首先分析了V-BLAST系统可获得的最大分集度,然后找出了获得它所必须的条件,最后给出了一种可获得最大分集度的信号发射方法.在两发两收、BPSK调制、M.1225步行测...     

天线相关性对D-MIMO系统极限性能的影响

研究用户设备(UE)天线相关性对多用户分布式多输入多输出(D-MIMO)系统极限性能的影响。与单用户D-MIMO系统中天线相关性会恶化系统性能的传统观点不同,仿真结果表明,在多用户环境下,UE端的天线相关性可以带来系统性能增益,该增益的主要来源是多用户分集和信道能量的聚集效应。     

Transmitter polarization optimization with polarimetric MIMO radar for mainlobe interference suppression

Polarization diverse design of the transmit waveforms based on the property of the target scattering matrix provides better performance than transmitting waveforms with fixed polarizations, especially for mainlobe interference suppression applications. In this work, we propose a radar system combines the advantages of multiple-input–multiple-output (MIMO) systems with the advantages offered by optimally choosing the transmitter polarizations, in order to achieve a better mainlobe interference suppression performance. The polarization diversity is employed in the transmit array, while the receive array adopts 2-D vector sensors to measure the horizontal and vertical components of the received signal. The optimal transmitter polarizations can be obtained by maximizing the output signal-to-interference-plus-noise ratio (SINR) in each coherent processing interval (CPI). In addition, the discrimination method for the target and the interference is studied in this paper, along with the target scattering matrix estimation method. Simulation results demonstrate that interference can be effectively discriminated and suppressed with the radar configuration, and better interference suppression performance is achieved with the optimal transmitter polarizations.