多用户自适应调制及功率分配

为了满足新一代无线通信系统的高数据速率、高频谱效率的通信要求,本文提出了基于正交频分复用(OFDM)技术的自适应调制、子载波分配及功率分配方法,它采用的多址方式是码分多址(CDMA).通过上行信道返馈获知下行信道参数,在一定服务质量要求(QoS)、一定传输速率下,通过本文的优化分配算法,使系统的频谱利率最高,所有子载波的发射功率之和最小.将本方法应用在下行同步信道环境下,系统具有较快的收敛速度;与非自适应OFDM比较,用户发射功率有较大降低,是一种工程可适用方案.     

Exponential Diversity Achieving Spatio–Temporal Power Allocation Scheme for Fading Channels

In this paper, we analyze optimal (in space and time) adaptive power transmission policies for fading channels when the channel-state information (CSI) at the transmitter (CSIT) and the receiver (CSIR) is available. The transmitter has a long-term (time) average power constraint. There can be multiple antennas at the transmitter and at the receiver. The channel experiences Rayleigh fading. We consider beamforming and space-time coded systems with perfect/imperfect CSIT and CSIR. The performance measure is the bit error rate (BER). We show that in both coded and uncoded systems, our power allocation policy provides exponential diversity order if perfect CSIT is available. We also show that, if the quality of CSIT degrades then the exponential diversity is retained in the low SNR region but we get only polynomial diversity in the high SNR region. Another interesting conclusion is that in case of imperfect CSIT and CSIR, knowledge of CSIT at the receiver is very important. Finally, for the optimal power control policy of the uncoded system we find the error-exponents which provide the rate versus diversity-order tradeoff for this policy. This tradeoff is of an entirely different nature than the well-known Zheng-Tse tradeoff.     

Optimal Power Allocation for Distributed Detection Over MIMO Channels in Wireless Sensor Networks

In distributed detection systems with wireless sensor networks, the communication between sensors and a fusion center is not perfect due to interference and limited transmitter power at the sensors to combat noise at the fusion center's receiver. The problem of optimizing detection performance with such imperfect communication brings a new challenge to distributed detection. In this paper, sensors are assumed to have independent but nonidentically distributed observations, and a multiple-input/multiple-output (MIMO) channel model is included to account for imperfect communication between the sensors and the fusion center. The J-divergence between the distributions of the detection statistic under different hypotheses is used as a performance criterion in order to provide a tractable analysis. Optimization of performance with individual and total transmitter power constraints on the sensors is studied, and the corresponding power allocation scheme strikes a tradeoff between two factors, the communication channel quality and the local decision quality. For the case with orthogonal channels, under certain conditions, the power allocation can be solved by a weighted water-filling algorithm. Simulations show that the proposed power allocation in certain cases only consumes as little as 25% of the total power used by an equal power allocation scheme while achieving the same performance.      

基于动态反馈与功率分配的干扰对齐方法

在多用户MIMO系统中,信道状态的精确性严重影响干扰对齐技术的性能。该文针对信道状态信息(CSI)有限反馈导致的干扰泄露问题,提出一种基于动态反馈与功率分配的干扰对齐方法。首先从理论上分析了系统和速率与信道状态反馈比特分配和功率分配之间的关系,得到了在动态反馈和功率分配条件下系统和速率的解析表达式;在此基础上,以系统容量提升为目标,对反馈比特分配和功率分配优化问题进行建模;并根据信道的准静态特性利用库恩塔克条件(KKT)对该问题进行求解,得到功率和反馈比特分配方案。仿真结果表明,与单独考虑信道状态动态反馈条件下的干扰对齐技术相比,提出的方法能够有效减少干扰泄漏强度,提高系统和速率。     

时变信道下基于有效容量的OFDMA系统资源分配方案

该文给出时变信道下多用户正交频分多址接入(OFDMA)系统的有效容量表达式。为了最大化系统平均有效容量,该文利用泰勒近似得到了渐近可达的多用户调度准则,根据用户移动速度、业务时延敏感特性和有效容量的关系调度用户。仿真结果表明,该方案能够更好地提高移动用户有效容量。     

功率约束条件下MIMO-OFDM下行广播信道自适应资源分配

该文分析了功率约束条件下MIMO-OFDM系统广播信道的发送优化问题,提出了两种不同准则下的多用户传输策略和功率分配方案,即最优空间距离OSD-DPC(Optimal Space Distance Dirty Paper Coding)方案和最大化信噪比波束成形MSNR-DPC(Max Signal to Noise Ratio Dirty Paper Coding)方案。数据结果表明,两种传输策略与理论上的最优传输方案性能非常接近,可以显著提高功率约束条件下的系统性能与容量。     

Capacity Optimizing Power Allocation in Interference Channels

The interference channel is an essential model in both wireline and wireless communication systems. This article addresses transmit power allocation in interference channels with total transmit power constraint. The optimum power allocation maximizing the sum rate in two user interference channels can be derived analytically. However, the non-convexity of the optimization problem makes it prohibitively complex to obtain the optimum solution either analytically or numerically in general K user scenarios. After reviewing several conventional suboptimum power allocation schemes including equal power allocation, greedy power allocation and waterfilling power allocation, an iterative waterfilling algorithm is proposed and discussed. The performance of various power allocation schemes is evaluated through simulations, which suggests that the proposed iterative waterfilling outperforms other suboptimum power allocation schemes in certain scenarios.     

LTE—A异构网络中CoMP—JP在不同功率分配方案下的性能对比

为解决异构网络中的干扰问题,研究了存在LTE-A异构网络中进行相干协作多天线传输,并使用迫零预编码时不同功率分配片案对系统性能的影响。包括按最大数据率分配、按公平性分配和等功率分配,并进行了相应的仿真分析。结果表明,三种功率分配方案对宏用户的影响差别并不大,主要差别体现存微用户上;宏用户的数据率主要受到微小区与宏用户位置关系的影响,而这种彰响本质上是由微基站的单机站功率约束造成的。     

Joint User Association and Power Allocation for Millimeter-Wave Ultra-Dense Networks

Mobile Networks and Applications - To meet the demand of various high-speed data rate services as well as serving an exponential increment of mobile devices, millimeter-Wave (mmWave) communication...     

Optimizing the Power Allocation for Rayleigh Block-Fading Channels with Outage Capacity Constraints

This letter studies the power distribution over K blocks of coded information to support a certain rate in Rayleigh- fading channels given the causal channel state information at the transmitter (CSIT). For K = 2, we shall show that since the channel in the future is random, the optimal power policy tends to pour all the power for the first block, which disables the time diversity. By introducing outage capacity as a constraint, time-diversity can be unleashed by stochastically distributing the power among the blocks. For K = 2, we derive the stochastic- optimal power allocation in closed-form for the transmit power minimization problem subject to an outage capacity constraint. For K > 2, we propose to minimize the power by constraining the upper bound of the outage probability, and in so doing, the problem is convex which permits to derive the optimal power policy. Numerical results demonstrate that the proposed power policy exploiting CSIT gives significant power reduction when compared to an equal-power policy.     

Power Control and Allocation for MIMO Broadcast Channels in Cognitive Radio Networks

This paper considers multiple-input multiple-output broadcast channels in cognitive radio networks which consist of a cognitive base station (CBS), K secondary users (SUs) and N primary users (PUs). The multiantenna-based CBS concurrently operates with the PUs. The channel state information for SUs is assumed to be perfectly known at the CBS. To ensure the quality of service of PUs and maximize sum-rate capacity of SUs, two problems are considered: (1) What is the optimal power control of CBS? (2) What are the optimal power allocations of SUs? A two-level game is presented to jointly consider the benefits of power control of CBS and power allocations of SUs. Under this game model, the corresponding game algorithms are also proposed. Finally, numerical simulation results are provided to examine the performance of our proposed algorithms.     

Optimized Power Allocation for a Cooperative NOMA System with SWIPT and an Energy-Harvesting User

ABSTRACT

This paper investigates the solution to an optimisation problem to minimise the total transmission power at the transmitter in a cooperative non-orthogonal multiple access (NOMA) system with simultaneous wireless information and power transfer (SWIPT) and an energy-harvesting user. First, we formulate the optimisation problem to obtain the minimum transmission power at the transmitter under the constraints of minimum signal-to-interference-plus-noise ratio and minimum energy harvesting. Since the problem is not convex, we transform it into a bi-level optimisation problem. Then, conditions to guarantee the feasibility of the problem are provided, and we derive the analytical optimal solution via the Lagrange method meeting Karush–Kuhn–Tucker optimality conditions to solve the lower-level variables of the inner convex problem. Second, we use particle swarm optimisation to find the approximately optimal values of the upper-level variables. Next, we present two baseline schemes based on orthogonal multiple access (OMA) and equal power splitting for performance comparison with the proposed cooperative NOMA system with SWIPT. Finally, simulation results show that cooperative NOMA with SWIPT can reduce the transmit power at the transmitter, compared to two baseline schemes: OMA and EPS.     

MIMO Systems with Transmit Antenna Selection and Power Allocation over Correlated Channels

In this paper, we present a comprehensive performance analysis of multiple-input multiple-output (MIMO) systems with transmit antenna selection (TAS) and stochastic power allocation (SPA) for the spatially correlated fading channels. Two best transmit antennas that maximize the instantaneous received signal-to-noise (SNR) are selected to transmit the Alamouti scheme and maximal-ratio combining (MRC) is applied at the receiver. With correlation matrices available to the transmitter, SPA is applied on these selected antennas. Two different methods are given to derive the explicit upper bounds on the bit-error rate (BER) performance. Finally we present numerical results to verify our analysis. It is shown that the TAS/SPA scheme can achieve high performance in spatially correlated channels.     

采用发送功率加权分配策略的群小区架构容量与覆盖分析

随着用户对高速率、高质量无线通信业务需求的不断增长,以及对多入多出、空时码、分布式天线等多天线信号处理技术的深入研究,探讨面向未来移动通信系统的小区构建方法成为必然的需求。该文介绍了一种广义分布式小区架构群小区,群小区架构适应先进的物理层技术,能够充分利用多天线技术带来的优势,并且可以解决未来移动通信系统由于载频提高导致小区变小带来的频繁切换问题。该文介绍了群小区架构的概念、构建方法以及基于群小区架构的滑动切换策略,重点分析了群小区架构采用下行发送功率加权分配策略下的容量性能和覆盖性能。理论分析和仿真结果证明,与当前的小区架构相比较,群小区架构可以有效地提高系统容量,扩大覆盖范围。     

Joint Beamforming and Power Allocation for Multiple Access Channels in Cognitive Radio Networks

A cognitive radio (CR) network refers to a secondary network operating in a frequency band originally licensed/allocated to a primary network consisting of one or multiple primary users (PUs). A fundamental challenge for realizing such a system is to ensure the quality of service (QoS) of the PUs as well as to maximize the throughput or ensure the QoS, such as signal-to-interference-plus-noise ratios (SINRs), of the secondary users (SUs). In this paper, we study single-input multiple output multiple access channels (SIMO-MAC) for the CR network. Subject to interference constraints for the PUs as well as peak power constraints for the SUs, two optimization problems involving a joint beamforming and power allocation for the CR network are considered: the sum-rate maximization problem and the SINR balancing problem. For the sum-rate maximization problem, zero-forcing based decision feedback equalizers are used to decouple the SIMO-MAC, and a capped multi-level (CML) water-filling algorithm is proposed to maximize the achievable sum-rate of the SUs for the single PU case. When multiple PUs exist, a recursive decoupled power allocation algorithm is proposed to derive the optimal power allocation solution. For the SINR balancing problem, it is shown that, using linear minimum mean-square-error receivers, each of the interference constraints and peak power constraints can be completely decoupled, and thus the multi-constraint optimization problem can be solved through multiple single-constraint sub-problems. Theoretical analysis for the proposed algorithms is presented, together with numerical simulations which compare the performances of different power allocation schemes.     

A Novel Nonlinear and Non-iterative Precoding Technique for Single and Multi User MIMO Systems

Wireless Personal Communications - A modification of the well known linear and iterative based precoder intended for both single and multi-user multiple-input multiple-output (MIMO) has been...     

大规模MIMO系统中联合用户分组和联盟博弈的动态导频分配方案

大量研究表明,大规模MIMO系统中的小区边缘用户比中心用户更易遭受导频污染的影响。因此,该文提出一种联合用户分组和联盟博弈(JUG-AG)的动态导频分配方案来减轻系统导频污染。根据用户信号强度将所有用户分为A,B两组,把接收基站信号强度弱的小区边缘用户记为A组,剩余用户则为B组。A组用户使用相互正交的导频,B组用户则借助联盟博弈来重复使用剩余的正交导频。在B组用户的联盟博弈中,用户被分成若干个互不相交的用户子联盟,属于不同子联盟的用户分配不同的相互正交导频序列,而属于同一子联盟中的用户使用相同的导频序列。与已有的导频分配方案相比,该文提出的JUG-AG方案更灵活,可以用于所有用户随机分布的场景。而且,该算法通过循环搜索可以获得整体最优解。仿真结果表明JUG-AG方案能够有效降低上行链路中用户信号检测的平均均方根误差(RMSE),而且可以提高用户的平均服务速率。

     

VLC网络中兼具功率与时隙分配的自适应干扰管理机制

为了更好解决目前可见光通信(visible light communication,VLC)中干扰管理方案存在的动态优化问题,提出了一种兼具优化功率分配与时隙分配的自适应干扰管理机制。首先,在每个时隙依据用户的位置建立每个用户的接入点(access point,AP)协作集,寻找所有由最多数量互不干扰用户组成的极大独立集,以此自适应地避免同频干扰;在每个时隙为每个极大独立集采用改进的线性注水功率分配算法为信道自适应地分配发送功率,以此优化每个极大独立集的用户和速率;基于用户和速率、速率公平性及时延公平性的归一化优先因子,选出具有最大优先因子的候选极大独立集,其中包含的用户在该时隙被调度。通过仿真且与代表性文献中的算法比较可得,本文提出的自适应干扰管理与优化资源分配方案在网络频谱利用率、能效、用户速率公平性与时延公平性方面具有明显优势。     

Low Complexity User Selection and Power Allocation for Uplink NOMA Beamforming Systems

Wireless Personal Communications - In this paper, we develop user selection and power allocation methods for NOMA systems equipped with multi-antenna to enhance the sum capacity of the uplink. The...