Adaptive subcarrier bandwidth and power in OFDM‐based cognitive radio systems for high mobility applications

OFDM‐based cognitive radio systems are spectrally flexible and efficient, but they are vulnerable to intercarrier interference (ICI), especially in high mobility environments. High mobility of the terminal causes large Doppler frequency spread resulting in serious ICI. Such ICI severely degrades the system performance, which is ignored in the existing resource allocation of OFDM‐based cognitive radio systems. In this paper, an adaptive subcarrier bandwidth along with power allocation problem in OFDM‐based cognitive radio systems for high mobility applications is investigated. This adaptive subcarrier bandwidth method should choose the suitable subcarrier bandwidth not only to balance the tradeoff between ICI and intersymbol interference but also to be large enough to tolerate an amount of Doppler frequency spread but less than the coherence bandwidth. The power budget and interference to primary users caused by cognitive radio users are imposed for primary users' protection. With these constraints, a joint optimization algorithm of subcarrier bandwidth and power allocation is proposed to maximize the bandwidth efficiency of OFDM‐based cognitive radio systems in such conditions. Numerical simulation results show that the proposed algorithm could maximize the system bandwidth efficiency and balance this tradeoff while satisfying the constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

A coordinated multi‐point‐based quality of service provision resource allocation scheme with inter‐cell interference mitigation

The paper investigates resource allocation via power control for inter‐cell interference (ICI) mitigation in an orthogonal frequency division multiple access‐based cellular network. The proposed scheme is featured by a novel subcarrier assignment mechanism at a central controller for ICI, which is further incorporated with an intelligent power control scheme. We formulate the system optimization task into a constrained optimization problem for maximizing accepted users' requirements. To improve the computation efficiency, a fast yet effective heuristic approach is introduced for divide and conquer. Simulation results demonstrate that the proposed resource allocation scheme can significantly improve the network capacity compared with a common approach by frequency reuse. Copyright © 2014 John Wiley & Sons, Ltd.     

基于信干噪比的D2D通信功率控制与资源分配

为了优化长期演进(LTE)系统引入设备直传(D2D)通信后带来的同频干扰、系统边缘用户性能恶化问题,提出一种基于信干噪比(SINR)的多小区D2D通信资源分配方案,通过调整信干噪比阈值将部分蜂窝用户(CU)转化为D2D用户并释放频谱资源进而获得较佳的资源分配策略,同时提出一种基于小区间D2D竞争机制的配置算法有效降低小区间干扰.仿真表明,算法能够有效提升系统容量,并提升小区边缘D2D用户公平性.     

DVB-T/H移动接收的信道估计和ICI消除

移动衰落信道中正交频分复用(OFDM)系统的子载波间干扰(ICI)是引起系统性能下降的主要因素.通过对时变信道中ICI的分析,给出了DVB-T/H系统中的一种信道估计和ICI消除算法,并进一步提出改进算法.最后经过仿真并在FPGA上实现,并通过接收机系统的联调与测试,验证了设计的合理性与可靠性.     

A new ICI mitigation method with generalized data‐allocation for OFDM systems

This paper describes an ICI mitigation method based on the generalized data‐allocation of (1, ?β) for orthogonal frequency division multiplexing systems. To improve the performance of the ICI mitigation for the higher‐frequency offset, we propose an efficient search algorithm to generate the sub‐optimal parameter β for maximizing the carrier‐to‐interference ratio (CIR). The CIR and bit error rate performances of the proposed method were derived in this paper. The performances with different carrier frequency offset scenarios were evaluated by computer simulations. According to the simulation results, the performance of the proposed ICI mitigation scheme is better than that of the conventional ICI self‐cancellation scheme and is nearly the same as that of the ICI self‐cancellation scheme for the optimal parameter β. Additionally, the proposed ICI mitigation scheme has a dramatically reduced hardware complexity in comparison with the ICI self‐cancellation scheme for the optimal parameter β. Copyright © 2009 John Wiley & Sons, Ltd.     

Joint user pairing and power allocation in uplink virtual MIMO with imperfect CSI

User pairing strategy for virtual multi-input multi-output （VMIMO） has been widely studied to improve system throughput, but most studies are based on perfect channel state information （CSI） and uniform power allocation. However, perfect CSI is very difficult or even impossible to obtain in practical system. Moreover power allocation has significant impact on algorithm performance. Therefore, in this paper, a low-complex joint user pairing and power allocation algorithm based on aggressive discrete stochastic optimization and Lagrangian dual solution is proposed for uplink VMIMO with imperfect CSI. Simulation results show that the proposed algorithm can achieve desirable throughput performance, and restrict inter-user interference （IUI） efficiently.     

Dynamic and location‐based power allocation mechanism for inter‐cell interference mitigation in 5G heterogeneous cellular network

In this paper, a dynamic and location‐based power allocation mechanism is proposed which could be adopted at both macrocell (MC) and overlaid fixed/mobile small cells (SCs) to mitigate inter‐cell interference (ICI) effects in heterogeneous cellular networks (HetCNs). The proposed Dynamic Power Allocation based on User Location (DPAUL) mechanism allows both MCs and deployed fixed/mobile SCs to dynamically allocate transmit power to its serving base stations (BSs) based on the location of a user in the cell. The paper illustrates the mitigation of dynamic downlink interferences occurring due to the mobility of SCs and users. The mobility of cell and its users is analyzed by introducing the Cell‐User mobility (CUM) model in the network. The proposed DPAUL mechanism is compared with the authors' other ICI mitigation techniques: Dynamic Fixed Region Cooperation (DFRC) and Dynamic Power Allocation Mechanism (DPAM). The network metrics Sumrate, User throughput, Energy‐efficiency, and Outage probability are investigated with allocation of sub 6 GHz and mmWave spectrums at MCs and fSCs/mSCs, respectively.     

An effective suboptimal power loading scheme in OFDM-based cognitive radio systems

Orthogonal frequency division multiplexing (OFDM) is an attractive modulation candidate for Cognitive Radio (CR) networks. Effective and reliable subcarrier power allocation in OFDM-based Cognitive Radio (CR) networks is a challenging problem. This paper focuses on the power allocation for OFDM-based Cognitive Radio (CR) networks. Our objective is to maximize the total transmission rates of Secondary Users (SU) by adjusting the power of subcarrier while the interference introduced to the Primary User (PU) is within a certain range and the total power of subcarrier is not beyond the total power constraint. We investigate the optimal power allocation algorithm for OFDM-based Cognitive Radio (CR) based on convex optimization theory. Then, because of high complexity of the optimal power allocation algorithm, we propose an effective suboptimal power loading scheme. Theory analysis and simulation results show that the performance of the suboptimal power allocation algorithm is close to the performance of the optimal power allocation algorithm, while the complexity of the suboptimal power allocation algorithm is much lower.     

基于MADDPG的无人机辅助通信功率分配算法

针对多无人机(unmanned aerial vehicle, UAV)作为空中基站辅助通信的吞吐量和公平性问题,提出了一种基于多智能体深度确定性策略梯度算法(multi-agent deep deterministic policy gradient algorithms, MADDPG)的功率分配算法,该算法通过联合优化UAV基站的功率分配和用户接入以提高系统吞吐量和公平性。本文首先构建了UAV基站为地面建立通信服务的三维场景,然后通过联合功率、用户关联和UAV位置约束,构建了吞吐量和公平性最大化的问题模型。考虑到该问题的复杂性,本文将所构建的优化问题建模为马尔科夫决策过程(Markov decision process, MDP),通过引入深度确定性策略梯度算法(deep deterministic policy gradient algorithm, DDPG)解决该问题。仿真结果表明,本文提出的基于MADDPG的UAV基站功率分配算法与其他算法相比,可以有效地提升系统的吞吐量和用户的公平性,提高通信的服务质量。     

基于粒子群算法的下行CR-NOMA网络资源分配

将非正交多址接入(Non-orthogonal Multiple Access,NOMA)技术应用于认知无线电(Cognitive Radio,CR)次网络,使次用户的信号在功率域叠加,可以进一步提高次网络的吞吐量。为此,将粒子群算法(Particle Swarm Optimization,PSO)应用于底层模式的CR-NOMA网络进行资源分配,并分为子信道分配和功率分配两个步骤。在子信道分配中,使用结合遗传算法思想的粒子群算法提高算法的全局搜索能力。在此基础上,使用基于罚函数的粒子群算法对子信道功率和信道内用户功率进行分配。仿真结果表明,提出的基于粒子群算法的CR-NOMA网络资源分配相比以往算法能获得更高的次网络吞吐量。     

MIMO空间复用系统的最小BER比特分配

该文基于最小误比特率(BER)准则,提出了多输入多输出(MIMO)空间复用系统的贪婪比特分配算法和基于二分法的比特分配算法。在总比特速率和每个发射天线分配相等功率的约束条件下,通过比特分配优化每个发射天线的调制方式,改善了系统的BER性能。仿真结果表明,与传统的MIMO系统相比,比特分配的MIMO系统可获得显著的信噪比(SNR)增益;与功率分配相比,比特分配在性能损失很小的情况下减少了每个发射天线的功率放大器的动态范围。     

移动OFDM系统中子信道干扰及其均衡算法

移动衰落信道中正交频分复用(OFDM)系统的子信道干扰(ICI)是引起系统性能下降的主要因素。本文分析了ICI对系统性能的影响,结果表明子信道干扰取决于信号能量E_s,子信道数N,和多普勒频移f_d,与信号星座无关。为了消除ICI,我们提出一种基于Jacobi迭代方法的均衡算法。考虑到子信道干扰主要影响相邻子信道的实际情况,兼顾系统性能和算法复杂性,进一步提出改进算法。文章最后给出16QAM调制的OFDM系统性能的仿真结果。     

OFDM-UWB系统基于用户速率的多用户动态资源分配算法

在原有动态资源分配算法基础上,提出了一种基于用户速率需求的动态资源分配算法。该算法在满足用户数据速率需求和服务质量要求(QoS)的前提下,以用户公平性为原则,分步执行子载波和比特分配来降低系统总的发射功率。首先,通过比较不同子载波对用户速率的影响,引入速率影响因子,对子载波进行分配;然后为每个用户子载波分配比特,并根据用户速率需求进行比特调整。为了进一步降低系统的复杂度,提出了一种通过子载波分组来完成子载波比特分配的方法。仿真结果表明,该算法能够降低系统功耗、误码率和系统复杂度。     

Multimedia transmission in MC-CDMA using adaptive subcarrier power allocation and CFO compensation

Multicarrier code division multiple access (MC-CDMA) system is one of the most effective techniques in fourth-generation (4G) wireless technology, due to its high data rate, high spectral efficiency and resistance to multipath fading. However, MC-CDMA systems are greatly deteriorated by carrier frequency offset (CFO) which is due to Doppler shift and oscillator instabilities. It leads to loss of orthogonality among the subcarriers and causes intercarrier interference (ICI). Water filling algorithm (WFA) is an efficient resource allocation algorithm to solve the power utilisation problems among the subcarriers in time-dispersive channels. The conventional WFA fails to consider the effect of CFO. To perform subcarrier power allocation with reduced CFO and to improve the capacity of MC-CDMA system, residual CFO compensated adaptive subcarrier power allocation algorithm is proposed in this paper. The proposed technique allocates power only to subcarriers with high channel to noise power ratio. The performance of the proposed method is evaluated using random binary data and image as source inputs. Simulation results depict that the bit error rate performance and ICI reduction capability of the proposed modified WFA offered superior performance in both power allocation and image compression for high-quality multimedia transmission in the presence of CFO and imperfect channel state information conditions.     

V-MIMO中的协作用户功率分配算法

针对虚拟MIMO(V-MIMO)中源用户与协作用户间的功率分配问题,给出了一种基于源用户功率分配因子的区间搜索算法。该算法通过快速寻找不需要参与协作的用户,将迭代注水功率分配过程中的方程组求解过程转化为源用户功率因子的区间搜索,大大降低了算法的复杂度。瑞利信道下的仿真结果表明,该算法与平均功率分配算法相比,协作容量性能提高显著,与最优功率分配算法相比,性能相当,从整体上提高了系统的性能。     

单频网多播系统中的开环半动态功率分配算法

在单频网多播传输中,传统的全反馈动态功率分配数算法需要根据每个时隙反馈的用户瞬时信道信息进行实时的调整,所以造成了资源分配频率快、上行反馈开销大的缺点。为了克服这个缺点,提出了一个低复杂度、没有用户反馈的单频网多播开环半动态功率分配算法。首先在各小区等功率分配的假设下,根据单频网的形状信息算出各小区等价信道增益,然后再根据这个增益值,实现满足速率需求情况下的各小区功率分配。仿真结果显示,与全反馈的动态功率分配算法相比,该算法以一小部分性能损失为代价,大大减少了单频网的上行反馈和资源分配的开销,因此更适用于实际的单频网多播系统。     

基于改进遗传算法的C-RAN网络动态无线资源分配

针对云无线网络(Cloud Radio Access Network,C-RAN)中传统静态资源分配效率低下以及动态无线资源分配中资源种类单一的问题,提出了一种基于用户服务质量(Qulity of Service,QoS)约束的动态无线资源分配方案,对无线资源从无线射频单元(Remote Radio Head,RRH)选择、子载波分配和RRH功率分配三个维度进行研究.首先,根据传统的C-RAN系统传输模型和QoS约束在时变业务环境下建立了以发射功率为变量,以吞吐量最大为优化目标的优化问题;然后,基于改进的遗传算法,将原优化方案转变为通过优化RRH选择、子载波分配和RRH功率分配来达到提高系统吞吐量的目的;最后,将改进的遗传算法与其他智能算法在种群规模变化下进行了时间复杂度对比.实验结果表明,所提算法具有较低时间复杂度,所提资源分配方案下的平均吞吐量增益为17％.     

基于用户分簇的认知超密集网络资源分配

针对5G时代小基站的密集部署带来的复杂干扰问题,对下行的认知无线电超密集网络下的资源分配进行了研究。为减小网络干扰,提高次用户吞吐量,提出了一种改进的基于用户分簇的资源分配算法。基于基站的覆盖范围,选出用户的强干扰基站,以用户-基站干扰关系建立用户-用户干扰图,按用户受到的平均弱干扰划分优先级对用户分簇,再为簇集群预分配频段,为每个簇分配对应频段中效用最大的信道。该资源分配算法能准确反映用户间的干扰关系,保障资源分配公平性。仿真结果表明,当用户密度与基站密度均较大时,与相同场景的已有算法相比,该改进算法有较好的抗干扰能力,能有效提高次用户的吞吐量。     

MIMO系统一种新的功率分配算法及容量分析

在不额外增加发射功率和带宽消耗的情况下,注水功率分配算法能够获得最大的多输入多输出(MIMO)系统容量.基于拉格朗日乘数法,推导给出了MIMO系统注水功率分配算法的显式解.利用信道冲激响应矩阵的奇异值分解(SVD)算法,推导给出了注水功率分配算法MIMO系统的容量分析公式.利用数字波束形成(DBF)技术,提出了一种新的功率分配算法,推导给出了该算法MIMO系统的容量分析公式.仿真结果表明,提出的功率分配算法的系统容量虽然略低于注水功率分配算法的系统容量,但它的计算复杂度较低.     

OFDM系统频率选择性信道功率分配方案

自适应分配技术根据子信道的瞬时估计值动态地分配传输比特数和发送功率,可以优化正交频分复用（OFDM,Orthogonal Frequency Division Multiplex）系统的整体性能。这里讨论了基于容量优化的自适应比特分配算法,基于误比特率优化的最佳功率分配算法和次佳功率分配算法。仿真结果表明,对不同信道环境下三种算法的特点和性能进行了分析和比较。仿真结果表明,自适应分配技术可以优化系统的容量和误比特率。