三小区多用户MIMO系统中干扰对齐优化算法

针对三小区多用户MIMO干扰信道系统,通过一个启发性例子,联合设计发射预编码矩阵和接收赋形矩阵,给出基于特征向量闭式解的干扰对齐优化算法,相比已有干扰对齐算法,用户端可使用更少的天线资源获得相同的自由度性能,且只需本小区内用户协作共享信道信息;并归纳出普适场景下系统配置与可达自由度之间的关系：设定每个小区中的基站配置M根天线和K个用户,用户配置N根天线,各个基站对本小区中每个用户都发送d个数据流,当M=N≥2 Kd时,所提算法总共可获得3 Kd个自由度。所提算法可以完全消除小区间干扰和用户间干扰,相比传统的正交化干扰抑制算法,系统容量得到了明显地提升。     

Delay spread reduction effect of beam antenna and adaptively controlled beam facing access system in urban line-of-sight street microcells

The paper presents theoretical and experimental investigation results of the delay spread reduction effect of beam antennas in urban line-of-sight (LOS) street microcells. The 95% delay spread cumulative probability in a 600 m LOS cell length is reduced to 70% when the 3 dB beamwidth of the base station (BS) antenna is in the range from 80/spl deg/ to 140/spl deg/, compared with that (420 ns) in omnidirectional antennas. An adaptively controlled beam facing access (ABFA) system in which the beam antennas are used in both the base and mobile stations is further proposed. The beam direction of the BS antenna is fixed along the street, but that of the mobile station (MS) antenna is adaptively controlled as the maximum received power is obtained. Using ABFA, the 95% delay spread cumulative probability in the 300 m LOS microcell is reduced to less than 70 ns, when the antenna beam-width lies in the range from 20/spl deg/ to 140/spl deg/ in the BS and about 80/spl deg/ in the MS.     

RIGOROUS FULL-WAVE ANALYSIS OF THE BASE-STATION ANTENNAS

Rigorous analysis of the Base-Station (BS) antennas with reflector is made in this letter. The wire-grid modeling of BS antenna is established. In order to improve the solution accuracy and efficiency, some efficient techniques such as three-term sinusoidal interpolation basis function and discrete wavelet transform are used. Numerical examples considered here are the typical vertically polarized and the dual-polarized BS antennas. The calculated results for the vertically polarized BS antenna are in good agreement with the measured data, which show that the analysis modeling used is accurate and reliable.     

Evaluation of exposure levels generated by cellular systems: methodology and results

During the past years, the number of antenna installations has considerably increased mainly as a consequence of the great diffusion of cellular systems. While the emissions of mobile terminals principally concern cellular system users, the exposure due to base stations (BSs) is permanent and spread over the entire territory. In this paper, a flexible approach for the evaluation of exposure levels generated by cellular systems BSs is proposed. Both a conceptual method for the evaluation of the overall exposure level and a site specific method for the computation of the field in the surroundings of BS antennas are proposed. This last method is based on a combination of three different propagation models which enable an accurate evaluation of the field both close to the antenna and farther off. The validity of the approach is checked by comparison with measurements in single-antenna and multiantenna cases.     

Generalized multiuser orthogonal space-division multiplexing

This paper addresses the problem of performing orthogonal space-division multiplexing (OSDM) for downlink, point-to-multipoint communications when multiple antennas are utilized at the base station (BS) and (optionally) all mobile stations (MS). Based on a closed-form antenna weight solution for single-user multiple-input multiple-output communications in the presence of other receiver points, we devise an iterative algorithm that finds the multiuser antenna weights for OSDM in downlink or broadcast channels. Upon convergence, each mobile user will receive only the desired activated spatial modes with no cochannel interference. Necessary and sufficient conditions for the existence of OSDM among the number of mobile users, the number of transmit antennas at the BS, and the number of receive antennas at the MS, are also derived. The assumption for the proposed method is that the BS knows the channels for all MS's and that the channel dynamics are quasi-stationary.     

Angle of Arrival Statistics for a 3-D Cylinder Model

In this paper, a three-dimensional (3-D) geometric model is considered to simultaneously describe angle of arrival (AoA) of multipath waves in the azimuth and elevation planes. The model is suitable in a macrocellular environment with a low MS antenna and an elevated base station (BS), where scatterers are distributed in a cylinder with the radius of the cell and the height of the BS. Closed-form expressions for the probability density functions in the angles are provided as seen from the mobile station (MS). Results show that the azimuth AoA depends on the ratio of the distance between the BS and the MS to the radius of the cell whereas the elevation AoA depends on the height of the BS, the radius of the cell and the distance between the BS and the MS. Monte-Carlo simulations are performed to examine the accuracy of the proposed model.     

An External Calibration Scheme for DBF Antenna Arrays

A novel calibration scheme is presented that is especially suited for complex digital beamforming (DBF) antenna arrays at millimeter-wave frequencies. Calibration data is extracted by sampling the field of each radiator at certain locations near the array by fixed probe antennas. A scalable calibration model for evaluation of the measured data is described. First tests are performed on a small passive array representing a unit cell of larger arrays. The calibration scheme is subsequently applied to and tested on a 64 element DBF transmit antenna array.      

A Low Complexity Correlation Algorithm for Compressive Channel Estimation in Massive MIMO System

Channel state information is essential for base station (BS) to fully exploit the merits of massive multiple input multiple output, which consumes large amount of pilot overhead attributed to tremendous number of BS antennas. Accordingly, huge computational complexity of correlation operation tends to be an obstacle for the implementation of compressive channel estimation algorithms, especially for greedy algorithms. In this paper, pilot overhead problem lightens by exploiting common support property due to the close space of BS antenna array. Furthermore, a low complexity correlation algorithm is proposed for each iteration of greedy algorithm, which exploits the inherent of pilot distribution and sensing matrix composed of pilot sequence. Complexity of proposed algorithm related to pilot distribution is also investigated. Performance analysis and simulation results prove that the proposed algorithm maintains the same performance, while achieves much less computational complexity than the original greedy algorithm.     

Analysis of Eccentered Dipole Antenna for Borehole Radar

A dipole antenna in a borehole may be placed away from the center of the borehole, and this eccentricity produces additional complicated electromagnetic fields, which may influence borehole radar signals. In this paper, we analyze an eccentric dipole antenna in a borehole for borehole radars. Our approach is an extended version of the pseudoanalytical formulation that was previously applied for analyzing an induction logging tool and a dielectric logging tool. The proposed equations are suitable for modeling the finite dipole antenna, utilizing a method-of-moments. The eccentricity of the radar sonde has two consequences. First, it modifies the antenna characteristics such as its impedance, and second, it changes the electromagnetic field inside the borehole, owing to the change of the structure of the cylindrical layers. These two changes are evaluated by the proposed algorithm and two types of experiments. The first one is a measurement of the input impedance of a monopole antenna which is in cylindrical layers on a ground plane in air. The second one is about the transmission between two antennas, one of which is eccentered in cylindrical layers. This experiment was done in granite at a field test site and on a ground plane in air. In the field experiments, we controlled the position of the radar sonde in a borehole and made the antenna eccentered artificially. We found that a 4-cm displacement resulted in changes of 4 dB in amplitude and 4 ns in time delay. Comparing the experimental and calculated data obtained by the present method shows the validity of the proposed analytical formulation.      

机械调整式极化跟踪器

在低剖面动中通天线系统中,辐射器多为平板阵列或柱形抛物面的形式,由于天线高度限制,无法通过旋转天线面板的方式进行极化跟踪,需要独立的极化跟踪调整机构,针对此提出了一种新型机械调整式极化跟踪器,具有结构紧凑和可靠性高的特点。通过电机驱动波导关节及OMT实现上行极化调整。基于极化波合成的工作原理,提出了系统设计方案,并描述了核心器件的设计方法。给出仿真与实测结果,且二者吻合较好。     

Massive MIMO异构网的高能效资源分配

为满足第五代移动通信系统高频谱效率和高能量效率的需求,提出一种工作在不同频段下行两层异构网中的高能量效率资源分配方法,考虑用户数据率需求和基站最大发射功率。天线和传输带宽是影响系统能量效率的关键因素。通过研究宏基站和小基站的天线资源和带宽分配发现:当系统天线数很大时,发射功耗的影响可以忽略不计;给定带宽分配因子时,达到宏基站或微基站最大发射功率的天线分配因子几乎可以达到最高能效;给定天线分配因子时,系统平均总功耗是关于带宽分配因子的下凸函数,存在全局最优带宽分配因子使能效最高。仿真结果表明,与给定带宽和天线资源的异构网和小小区网络相比,所提出的异构网可以显著提高系统能量效率,而且在大量用户、高数据率需求时能效提升更明显。      

Radiation characteristics of uniform and nonuniform dielectricleaky-wave antennas

An approach based on a waveguide model for analyzing the uniform and nonuniform dielectric leaky-wave structures is proposed for which the Galerkin solution method is applied. In the first part of the paper the far-field radiation of the uniform antenna is determined theoretically and experimentally in the Ku band and also the dependence of beamwidth and sidelobe level as function of strip width and frequency is demonstrated. In addition, an analysis of the antenna with a tapered-strip distribution-is presented. The second part describes a novel tapering procedure, performed by changing the width of the uniform antenna, for obtaining the radiation pattern with lower sidelobe levels. Sinusoidally and exponentially shaped dielectric leaky-wave structures are analyzed as nonuniform antennas. Finally, the radiation and scanning characteristics of these antennas are theoretically presented     

Composite right/left-handed transmission line based compact resonant antennas for RF module integration

Several electrically small resonant antennas employing the composite right/left-handed transmission line (CRLH-TL) are presented for integration with portable RF modules. The proposed antenna designs are based on the unique property of anti-parallel phase and group velocity of the CRLH-TL at its fundamental mode. In this mode, the propagation constant increases as the frequency decreases, therefore, a small guided wavelength can be obtained at a lower frequency to provide the small /spl lambda//sub g//2 resonant length used to realize a compact antenna design. Furthermore, the physical size and the operational frequency of the antenna depend on the unit cell size and the equivalent transmission line model parameters of the CRLH-TL, including series inductance, series capacitance, shunt inductance and shunt capacitance. Optimization of these parameters as well as miniaturization techniques of the physical size of unit cell is investigated. A four unit-cell resonant antenna is designed and tested at 1.06 GHz. The length, width and height of the proposed antenna are 1/19/spl lambda//sub 0/, 1/23/spl lambda//sub 0/ and 1/83/spl lambda//sub 0/, respectively. In addition, a compact antenna using a 2-D three by three mushroom like unit cell arrangement is developed at 1.17 GHz, showing that an increased gain of 0.6 dB and higher radiation efficiency can be achieved over the first prototype antenna. The same design is applied in the development of a circularly polarized antenna operating at 2.46 GHz. A 116/spl deg/ beamwidth with axial ratio better than 3 dB is observed. The physical size of the proposed mushroom type small antenna and the circularly polarized antenna is 1/14/spl lambda//sub 0/ by 1/14/spl lambda//sub 0/ by 1/39/spl lambda//sub 0/ and 1/10/spl lambda//sub 0/ by 1/10/spl lambda//sub 0/ by 1/36/spl lambda//sub 0/, respectively.     

A distributed-feedback antenna oscillator

In this paper, a new design of the active transmitting antenna array, called the distributed-feedback antenna oscillator, is proposed. The active array is formed by serially connecting several unit cells to a closed loop. Each unit cell contains an amplifier and a two-port antenna, with an overall insertion gain larger than 0 dB and a phase delay equal to a multiple of 360°. The signal traveling on the loop is amplified and radiated in each unit cell. The radiation fields from all the antennas are then combined in free space. A four-element feedback antenna oscillator operating at 10 GHz is demonstrated by using two-port aperture-coupled microstrip antennas. Simulation results show that multiple oscillation modes with different frequencies and different radiation beams may be excited in the antenna oscillator. By experiment, it is found that each oscillation mode can be built by tuning the biases of the oscillator. The measured radiation pattern for each mode agrees very well with the predicted one. For a single-mode operation with a broadside pattern, bandstop filters of a simple geometry are designed and embedded in the oscillator to suppress the unwanted oscillation modes. Finally, the influence of the bias condition on the radiation power of the single-mode oscillator is investigated     

基于蘑菇状谐振器的谐波抑制的微带贴片天线

提出了一种基于耦合谐振器的微带贴片天线谐波抑制的方法。通过在微带天线馈线与地板之间增加蘑菇状电磁带隙（EBG）单元的谐振器,有效地抑制了天线的2次和3次谐波,减少了谐波辐射对周围微波器件的干扰。对天线的等效电路模型进行了详细分析和研究,通过改变参数令谐振器工作在天线的谐波频率上,从而抑制天线的谐波辐射。为了对理论分析进行验证,我们加工了实物模型并进行测试,测试的数据显示微带天线的2次谐波减少了11.6dB,3次谐波减少了8.4dB。     

基于容量相关字典的5G毫米波大规模天线单元选择算法

针对传统天线选择算法在大规模天线阵列应用中的局限性,该文在多用户场景下提出一种基于容量相关字典的5G毫米波大规模天线随机选择算法。该算法通过特定环境中不同位置处的多用户与基站的交互,快速提取大规模天线单元间容量的强弱相关特性,并建立相关字典;在天线选择时,先搜索最优信道容量单元连接射频链路,再随机选择相关字典中与最优单元容量相关大的天线单元接入其余射频链路。该方法大大降低了传统天线选择算法应用的复杂度,只与环境有关且较为稳定,当新用户加入时也无需重新建立相关字典。该方法通过损失一部分性能来换取较低的复杂度,适用于天线单元多的大规模天线阵列。此外,该文在室内开放式办公室开展了26 GHz视距和非视距下的大规模天线信道测试,分析了不同场景下的天线阵列行间单元间的容量相关性,并对该算法的系统信道容量性能进行了实验验证。     

Robust Tomlinson-Harashima Precoders for Multiuser MISO Downlink with Imperfect CSI

In this paper, we consider robust non-linear precoding for the downlink of a multiuser multiple-input single-output (MISO) communication system in the presence of imperfect channel state information (CSI). The base station (BS) is equipped with multiple transmit antennas and each user terminal is equipped with a single receive antenna. We propose two robust Tomlinson-Harashima precoder (THP) designs. The first design is based on the minimization of the total BS transmit power under constraints on the mean square error (MSE) at the individual user receivers. We show that this problem can be solved by an iterative procedure, where each iteration involves the solution of a pair of convex optimization problems that can be solved efficiently. A robust linear precoder with MSE constraints can be obtained as a special case of this robust THP. The second design is based on the minimization of a stochastic function of the sum MSE under a constraint on the total BS transmit power. We formulate this design problem as an optimization problem that can be solved by the method of alternating optimization, the application of which results in a second-order cone program that can be numerically solved efficiently. Simulation results illustrate the improvement in performance of the proposed precoders compared to other robust linear and non-linear precoders in the literature.     

Subcarrier Wise Scheduling Methods for Multi-antenna and Multi-carrier Systems

In this paper, multiuser scheduling algorithms are evaluated for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) networks. These scheduling schemes allocate M [number of transmit antennas at base station (BS)] number of independent data streams from BS to the M most favourable users experiencing the highest signal-to-interference-plus-noise-ratio (SINR). Here, SINR is used to convey the channel state information (CSI) to the BS. We have investigated the system throughput and feedback overhead attained by these scheduling schemes for different scenarios as: (a) the maximum CSI is sent to the BS by every user and (b) the maximum CSI sent to the BS corresponding to every BS antenna. The overall feedback overhead incurred by MIMO-OFDM system increases linearly with number of users, number of subcarriers and number of transmit antennas. Hence, to reduce the feedback overhead, a scheme is proposed where users with SINR values greater than or equal to a predefined threshold value are only allowed to feedback the channel state information to BS. The relation between system throughput and various thresholds is also studied. The achievable system throughput results are validated by comparing the probability density function of achieved SINR values by different scheduling schemes.

     

Merging multicarrier CDMA and oscillating-beam smart antenna arrays: exploiting directionality, transmit diversity, and frequency diversity

In this paper, a novel merger of multicarrier code-division multiple access (MC-CDMA) and smart antenna arrays is introduced. Here, a group of Q carriers in the MC-CDMA system is applied to its own M-element smart antenna array at the base station (BS). The smart antennas are located in close proximity to one another. We generate a transmit diversity gain at the receiver by carefully moving (oscillating) the antenna array's pattern. The pattern oscillation is achieved by applying appropriate time-varying phases to array elements of each smart antenna. The beam pattern oscillation ensures a mainlobe at the position of the intended user and small oscillations in the beam pattern. This beam pattern oscillation leads to a time-varying channel with a controllable coherence time; hence, a transmit diversity benefit, in the form of a time diversity benefit, is available at the receiver. Employing MC-CDMA with the proposed smart antenna at the BS, we achieve: 1) directionality which creates high network capacity via space-division multiple access; 2) a transmit diversity gain which supports high performance at the receiver in the mobile unit; and 3) increased capacity and performance via MC-CDMA's ability to support both CDMA and frequency diversity benefits, respectively.     

大规模MIMO相关信道下的联合天线分组和天线选择

在大规模多输入多输出系统中,针对密集部署的大型天线阵列之间的强相关性会抑制天线选择增益效果的问题。在系统下行链路场景下建立空间相关信道模型,提出了基于天线分组的天线选择算法。根据瞬时信道相关矩阵将天线阵列划分为若干组,保证各组内天线之间相关性较强。在完成天线分组的基础上,基于信道矩阵列范数准则在各组发射天线与接收天线之间构成的子信道矩阵中选择天线,进而构造有效发射天线与接收天线之间的信道矩阵。仿真分析了所提天线选择算法对系统遍历和速率的影响,结果表明,在基站天线数为32、接收天线数为2、选择天线数为2、天线相关因子为0.9的假设下,当信噪比为10 dB时,与基于相邻天线分组的天线选择算法相比,所提算法使系统和速率约提高了27.5%,且所提算法若要与最优天线选择算法达到相同的和速率,仅需将其信噪比提升1～2 dB即可。