Analytical performance evaluation of downlink beamforming with power control by transmit power limited channel inversion

We investigate the transmission performance of a downlink BPSK transmission system which uses beamforming combined with cross-polarised antenna arrays and power control in a Rayleigh fading environment to fulfil QoS requirements of real time services. A power control method termed “power control by transmit power limited channel inversion” is applied in the system. Power limitation in the downlink and the effect on the bit error rate performance is especially interesting for mobile stations at the cell borders of a cellular communication system. For this non-linear transmit model we derive analytical formulas for the average transmit power and the bit error rate performance. The exact validity of the results is verified by Monte-Carlo simulations. We also show the interaction of power control and beamforming, and the dependency of the gain in transmit power from the SNR, an effect that is not visible without transmit power limited power control.     

Joint transmit beamforming and power control in multi-user MIMO downlink using a game theoretic approach

This study addresses the problem of jointly optimizing the transmit beamformers and power control in multi-user multiple-input multiple-output (MIMO) downlink. The objective is minimizing the total transmission power while satisfying the signal-to-noise plus interference ratio (SINR) requirement of each user. Before power control, it uses the maximum ratio transmission (MRT) scheme to determine the beamformers due to its attractive properties and the simplicity of handling. For power control it introduces a supermodular game approach and proposes an iterated strict dominance elimination algorithm. The algorithm is proved to converge to the Nash equilibrium. Simulation results indicate that this joint optimization method assures the improvement of performance.     

Joint beamforming and power control in downlink multiuser multiple‐input multiple‐output systems

In this paper, we study joint beamforming and power control for downlink multiple‐input multiple‐output systems with multiple users and target values for signal‐to‐interference plus noise ratios (SINRs). We formulate this as a constrained optimization problem of minimizing total interference subject to constraints on the beamforming vector norms, target SINRs, and total transmit power. Necessary and sufficient conditions satisfied by the optimal beamformer and power allocation are presented, and a new algorithm for joint beamforming and power control is proposed. This adapts the beamforming vectors and transmit powers incrementally, and it stops when the specified SINR targets are achieved with minimum powers. The proposed algorithm is illustrated with numerical results obtained from simulations, which study its convergence and compare it with other similar algorithms. Copyright © 2013 John Wiley & Sons, Ltd.     

CDMA系统下行链路性能优化的递阶算法研究

不对称的多媒体传输是未来宽带无线通信的主要模式，本文基于目前下行链路多种传输技术的特点，提出了一种递阶优化算法进行下行链路性能的优化，用功率控制（PC）、波束成形（BF）和发射分集（TD）三种要素进行系统建模，并根据移动用户的接收服务质量（QoS）要求构建效用函数进而进行性能优化，从向达到一种效能最佳的传输目标。文后给出了仿真实验并与常规的BF和TD算法进行了性能比较。     

CDMA系统中联合功率控制、波束赋形与多用户检测

应用功率控制、波束赋形和多用户检测可以有效地消除和减少CDMA系统中的干扰。本文结合波束赋形和多用户检测的特性，提出一种应用波束赋形增益和多用户相关矩阵的解相关算法。基于算法的复杂性，提出一种区分聚集用户进行多用户检测的的算法。由于波束赋形能够消减主瓣波束之外的多用户干扰，对聚集移动台采用解相关检测达到减少运算量和消除多用户干扰的目的。对算法进行了仿真分析，证明了本算法的优越性。     

Principles of minimum variance robust adaptive beamforming design

Robustness is typically understood as an ability of adaptive beamforming algorithm to achieve high performance in the situations with imperfect, incomplete, or erroneous knowledge about the source, propagation media, and antenna array. It is also desired to achieve high performance with as little as possible prior information. In the last decade, several fruitful principles to minimum variance distortionless response (MVDR) robust adaptive beamforming (RAB) design have been developed and successfully applied to solve a number of problems in a wide range of applications. Such principles of MVDR RAB design are summarized here in a single paper. Prof. Gershman has actively participated in the development and applications of a number of such MVDR RAB design principles.     

User clustering and robust beamforming design in multicell MIMO-NOMA system for 5G communications

In this paper, we present a robust beamforming design to tackle the weighted sum-rate maximization (WSRM) problem in a multicell multiple-input multiple-output (MIMO) – non-orthogonal multiple access (NOMA) downlink system for 5G wireless communications. This work consider the imperfect channel state information (CSI) at the base station (BS) by adding uncertainties to channel estimation matrices as the worst-case model i.e., singular value uncertainty model (SVUM). With this observation, the WSRM problem is formulated subject to the transmit power constraints at the BS. The objective problem is known as non-deterministic polynomial (NP) problem which is difficult to solve. We propose an robust beamforming design which establishes on majorization minimization (MM) technique to find the optimal transmit beamforming matrix, as well as efficiently solve the objective problem. In addition, we also propose a joint user clustering and power allocation (JUCPA) algorithm in which the best user pair is selected as a cluster to attain a higher sum-rate. Extensive numerical results are provided to show that the proposed robust beamforming design together with the proposed JUCPA algorithm significantly increases the performance in term of sum-rate as compared with the existing NOMA schemes and the conventional orthogonal multiple access (OMA) scheme.     

A downlink beamforming assisted by locally positioned communication devices

Recently, multiple cell types with overlapping coverage have been deployed simultaneously to increase cellular network capacity. Cross‐tier interference is one of the key technical challenges in the use of this method. A simple and practical beamforming scheme assisted by locally positioned communication devices for the downlink of a multi‐cell wireless hierarchical cell structure system is proposed in this paper to maximize the capacity of the embedded small cell and simultaneously ensure minimal impact on the performance of existing macrocells. The locally positioned communication devices can be implemented with low complexity and at low cost and can continuously provide helpful and accurate information to base stations for the proper configuration of geographical cell coverage, allowing neighboring cells to cooperate effectively with each other. Simulation results verify that the proposed scheme can provide a significant gain over conventional systems not using the proposed algorithm. Copyright © 2013 John Wiley & Sons, Ltd.     

多小区多用户无线网络下行链路协同波束成形设计

在频率复用的多小区多用户无线网络中,为了获得较好的和速率性能,研究了降低同频干扰的协同波束成形设计问题。博弈论分析结果表明,性能最优的协同波束成形矢量是自私和利他策略的线性组合。提出了一种最大化和速率的波束成形矢量迭代算法,给出了基于信道状态统计量的组合系数的估计方法。最后,仿真评估了波束成形算法的性能,表明了所提迭代算法的收敛性。     

Beamforming and power allocation in the downlink of MIMO cognitive radio systems based on multiobjective optimization

In this paper, power allocation and beamforming are considered in a multiple input multiple output (MIMO) downlink cognitive radio (CR) communication system, which a base station (BS) serves one primary user (PU) and one secondary user (SU). In order to design the CR system, a constrained multiobjective optimization problem is presented. Two objectives are the signal to noise plus interference ratios (SINRs) of PU and SU. Since PU has a spectrum license for data communication, a constraint in the optimization problem is that the SINR of PU must be greater than a predefined threshold based on the PU demand requirement. Another constraint is a limitation on power in BS. By considering the mentioned model, three iterative algorithms are proposed. At each iteration of all algorithms, the receiver beamforming vectors are derived based on the maximization of PU and SU SINRs, by assuming that the allocated powers and BS beamforming vectors are known. Also, power is assigned to users such that the constraint of power limitation is satisfied. The difference between the algorithms is in the obtaining of transmitter beamforming parameters. We evaluate the performance of the proposed algorithms in terms of bit error rate (BER) in simulations. Also, the computational complexity of the proposed algorithms is obtained.     

多用户MIMO下行收发联合波束成形

针对随机波束成形(RBF)只有在包含大量用户的系统中才能获得较好性能的局限性,提出了一种新的收发联合波束成形方案,用于多用户多入多出(MIMO)下行链路传输。该方案有效地结合了RBF与接收天线合并技术。分析及仿真结果表明,即使在用户数为中等甚至较小时仍然能获得较高的和速率性能。由于每个用户的反馈开销没变,从而使获得同样和速率时系统的总反馈开销明显减少。仿真结果还显示,所提方案的和速率性能不仅优于原RBF,也比RBF结合最大比合并或者等增益合并的性能有明显改善,同时还保持了最优的随用户数变化的增长速度。     

一种加载量迭代搜索的稳健波束形成

当阵列的导向矢量并不精确已知时,自适应波束形成有较大的性能损失.为提高波束形成的稳健性,对角加载成为一种常用的方式.但困扰这类方法的核心问题是合适的加载量如何确定.粗估导向矢量经对角加载后得到修正的导向矢量,如果加载量合适,则修正后的导向矢量接近真实导向矢量,即与噪声子空间的正交性变好.基于以上分析,构造修正导向矢量向信号子空间和噪声子空间投影的加权代价函数来评价加载量的合适与否,进而提出一种迭代搜索合适加载量的方法.计算机仿真验证了方法的有效性,与同类方法对比显示其优越性.     

基于鲁棒稳定的闭环激磁电源幅值回路设计

保证系统鲁棒稳定,同时满足系统性能指标要求始终是控制设计的目标。该文根据转台测角系统对激磁电源稳定性和性能指标的要求,提出了采用H优化控制理论,以鲁棒稳定为基础的闭环激磁电源幅值回路设计的方法,讨论了H控制器的求解过程。经四个转台长期使用验证该设计方法的有效性和合理性,完全满足了高精度转台的需要。     

分布式卫星系统的上/下行功率联合控制

为了能合理地控制功率以提高分布式卫星系统的系统效能,研究了其上下行功率联合控制问题。通过分析分布式卫星系统的特征及其功率控制问题的难点,建立了合理的分布式卫星系统功率控制模型和控制方案的具体框架;通过改进现有的上行功率预测和单级调整算法,提出了基于预置、预测和多级调整算法的上下行功率联合控制方法,并给出了控制方法的流程图;最后将所提方法与传统上行控制算法、单级补偿算法和预测算法进行了仿真比较,表明在上下行不同降雨百分比条件下,所提方法能更好地满足功率门限需求;在广州、长春两地不同实测雨衰曲线下,所提方法均能够更准确跟踪雨衰变化;业务与通信网区切换时,所提方法也能快速完成切换和保持动态跟踪,能够较好满足分布式卫星系统的功率控制准确性、时效性等应用需求。     

Multiuser beamforming based on max SINR for downlink spatial multiplexing MIMO

In this article, a method based on max signal interference noise ratio (SINR) criterion is proposed, to mitigate the interuser interference for downlink multiuser spatial multiplexing multi-input multi-output (MIMO) systems.Unlike the zero forcing (ZF) scheme in which the SNR is decreased when the interference is eliminated completely, max SINR method makes a compromise between noise and interuser interference.When the number of substreams is larger than the difference between the number of base station antennas and the sum of interference mobile station antennas, the ZF is infeasible.An existing coordinated TX-RX block diagonalization (COOR BD) method uses preprocessing at the receiver to cancel the interuser interference.However, it cannot obtain more receive diversity gain because of the preprocessing.Analysis and simulation show that the max SINR scheme has better performance than the ZF method.Moreover, when the ZF is infeasible, the max SINR scheme can obtain more receive diversity gain than COOR BD in the two-user case.     

Robust adaptive beamforming for large-scale arrays

For a large-scale adaptive array, heavy computational load and high-rate data transmission are two challenges in the implementation of an adaptive digital beamforming system. Moreover, the large-scale array becomes extremely sensitive to array imperfections. First, based on a restructured recursive linearly constrained minimum variance algorithm and a gradient-based optimization method, a new robust recursive linearly constrained minimum variance (RRLCMV) algorithm is proposed in this paper. The computational load of the RRLCMV algorithm is on the order of o(N), which is less than that of the conventional gradient-based robust adaptive algorithm. Then, a new efficient parallel robust recursive linearly constrained minimum variance (PRRLCMV) adaptive algorithm is proposed by appropriately partitioning the RRLCMV algorithm into a number of operational modules. It can be easily executed in a distributed-parallel-processing fashion, sequentially and in parallel. As a result, the PRRLCMV algorithm provides an effective solution that can alleviate the bottleneck of high-rate data transmission and reduce the computational cost. Finally, an implementation scheme of the PRRLCMV algorithm based on a distributed-parallel-processing system is also proposed. The simulation results demonstrate that the new PRRLCMV algorithm can significantly reduce the degradation due to various array errors.     

MIMO下行链路联合波束成形稳健性设计

针对MIMO下行链路中的发射/接收波束成行器,提出了一种对非精确CSI稳健的联合设计方案。方案采用的设计准则是在总发射功率受限的条件下最小化系统和MSE。根据此非凸和非线性优化问题的最优解条件,通过交替地计算每个用户的最优解来近似地获得原问题最优解。仿真结果表明,与非稳健性方法相比,该方案能有效地减少非精确CSI引起的性能损失。     

一种改进均方误差性能的新型鲁棒性波束形成算法

结合信干噪比最大化和均方误差最小化两个优化目标,提出一种新型的鲁棒性波束形成算法.该方法考虑信号估计误差,在传统的最小方差的代价函数中引入信号协方差矩阵的估计误差,并在波达角估计误差的约束下,将鲁棒性波束形成器转换成基于支持向量机形式的波束形成器,通过一种高效的新型支持向量机训练算法计算阵列权值;然后以均方误差最小化为目标来修正阵列权值.仿真结果表明:该方法降低了波束形成器对信号估计误差的敏感度,提高了其抑制非平稳干扰的能力,且具有更好的均方误差性能.     

Distributed energy efficient beamforming algorithm for multicell multiuser downlink system

A distributed energy efficient beamforming algorithm was studied for multicell multiuser downlink communication system.Firstly,the energy efficient optimization problem was first considered as the maximization of the ratio between the system sum rate and the system power consumption.The fractional programming optimization target was then transformed into a subtractive form via using the fractional programming theorem.Secondly,the problem was decomposed into some subproblems that can be solved respectively by introducing the concept of the interference temperature in cognitive radio networks.Finally,an effective distributed energy efficient beamforming algorithm was proposed by exploiting the Lagrangian duality theorem and optimization theorem.Compared to the classical energy efficient optimization algorithm,the proposed algorithm can achieve an obvious energy efficiency performance gain.     

Robust beamforming for multicell downlink TDD massive MIMO system based on QoS

In view of multicell downlink time division multiplexing (TDD) massive multiple-input multiple-output (MIMO) systems which had imperfect channel state information (CSI),the beamforming problem that minimized the total transmit power and signal leakage power based on quality of service (QoS) was studied.First,the objective problem was approximated as a standard convex optimization problem.Then,by using the duality of uplink and downlink,an inner and outer layer iterative algorithm was proposed.Numerical results show that,comparing with other typical downlink multicell massive MIMO beamforming algorithms,the proposed algorithm has obvious advantages in terms of complexity and energy efficiency.