Joint resource allocation for lifetime-aware cooperative multi-carrier DF system

In this paper,we study the problem of optimal resource allocation for lifetime maximization in an orthogonal-frequencydivision multiplexing(OFDM)system with decode-and-forward relay.The goal is to minimize total energy cost of the system by jointly optimizing power allocation,subcarrier pairing and relay selection.We present a heuristic solution that is composed of two parts.The first part is an optimal power allocation approach to allocate power to a subcarrier pair of the source and the relay.The second part is a modified Hungarian algorithm to make subcarrier pairing and relay selection.Evaluations show that the presented scheme outperforms other schemes in the total transmitted data and the network lifetime.     

保证公平的最大化中继OFDMA系统容量策略

基于正交频分多址(OFDMA)解码-转发中继的系统资源分配方法不能兼顾系统容量与用户公平度。针对该问题,提出一种新的子载波与功率资源分配算法,其中包括子载波分配与配对以及功率分配2个过程。在子载波分配与配对过程中,设计新的同步子载波差值最小配对方法,以最大程度匹配两跳链路配对的子载波。在功率分配过程中,通过拉格朗日方法调整每个子载波对的功率,进一步提高系统传输速率。仿真结果表明,将该策略运用于不同的OFDMA子载波分配算法中能够较好地兼顾系统容量与用户间公平度。     

中继OFDMA系统容量公平资源分配算法研究

针对OFMDA解码-转发中继系统的资源分配问题,提出了一种以系统总功率和用户间的数据速率比例公平为约束条件,以最大化系统总速率为目标的资源分配算法。该资源分配问题为非线性最优化问题,联合求解所有变量复杂度很高,通过次优化的方法降低计算复杂度。算法包括：子载波分配和功率分配。子载波分配是以功率平均分配为前提,对基站-中继站和中继站-用户链路的子载波按照信道条件进行配对,并根据比例公平约束将配对的子载波分配给相应的用户。功率分配是对每个用户利用Lagrange方法调整每个子载波的功率,进一步提高系统的数据速率。算法仿真分析表明,该算法既能同时满足多用户不同数据速率的要求,又能提高系统的数据速率。     

Resource allocation for physical-layer security in OFDMAdownlinkwith imperfect CSI

We investigate the problem of resource allocation in a downlink orthogonal frequency-division multiple access (OFDMA) broadband network with an eavesdropper under the condition that both legitimate users and the eavesdropper are with imperfect channel state information (CSI). We consider three kinds of imperfect CSI: (1) noise and channel estimation errors, (2) feedback delay and channel prediction, and (3) limited feedback channel capacity, where quantized CSI is studied using rate-distortion theory because it can be used to establish an informationtheoretic lower bound on the capacity of the feedback channel. The problem is formulated as joint power and subcarrier allocation to optimize the maximum-minimum (max-min) fairness criterion over the users’ secrecy rate. The problem considered is a mixed integer nonlinear programming problem. To reduce the complexity, we propose a two-step suboptimal algorithm that separately performs power and subcarrier allocation. For a given subcarrier assignment, optimal power allocation is achieved by developing an algorithm of polynomial computational complexity. Numerical results show that our proposed algorithm can approximate the optimal solution.     

协同OFDM系统联合中继选择、子载波配对和功率分配算法

研究了协同OFDM系统中的资源分配问题,提出了一种联合中继选择、子载波配对和功率分配的算法.首先在假定等功率分配的情况下,对中继节点进行选择并对子载波进行配对,然后在此基础上对选定的子载波对进行功率分配.分析结果显示所提算法是一种计算复杂度比较低,且系统容量接近最优容量的算法.     

Data traffic scheduling algorithm for multiuser OFDM system with adaptive modulation considering fairness among users

Orthogonal frequency division multiplexing (OFDM) is regarded as a very promising digital modulation technique for achieving high rate transmission. However, the increasing number of wireless data users and the deployment of broadband wireless networks have brought about issues of fairness among users and system throughput. In this paper, we propose an efficient scheduling algorithm to maximize system throughput while providing a level of fairness among users for non-real-time data traffic in the downlink of a multiuser OFDM system. We establish a practical scheduling procedure to implement our scheme considering fairness among users and also formulate the resource allocation problem for rate, power, and subcarrier allocation as an integer program that maximizes system throughput. Next, we present a computationally efficient heuristic algorithm for a problem based on the Lagrangian relaxation procedure. Through the computing simulation, we show that the proposed scheme performs better than other schemes in terms of both system throughput and fairness among users.     

基于子载波选择配对及功率优化分配的多跳中继系统研究

为了提升OFDM协作通信系统的网络覆盖率及网络容量,提出了一种基于子载波选择配对及功率优化分配的多跳中继OFDM系统优化算法。首先,通过在OFDM的系统模型上进行中继配对和非中继配对的性能分析,将子载波选择配对转换为一个整数规划问题,并采用基于匈牙利算法的规划方法进行配对矩阵的计算。接着,根据OFDM系统的功率分配问题,通过KKT条件对中继功率及电源功率进行优化,从而实现中继系统的功率优化分配 。最终的仿真结果表明,与统计质量QoS保证的资源分配方案以及OFDM中继系统异构服务的资源分配算法相比,所提出的方法在提高网络覆盖率和容量上均表现出更好的效果。     

Game Theoretic subcarrier and power allocation for wireless OFDMA networks

This paper proposes a bargaining game theoretic resource(including the subcarrier and the power) allocation scheme for wireless orthogonal frequency division multiple access(OFDMA) networks.We define a wireless user s payoff as a function of the achieved data-rate.The fairness resource allocation problem can then be modeled as a cooperative bargaining game.The objective of the game is to maximize the aggregate payoffs for the users.To search for the Nash bargaining solution(NBS) of the game,a suboptimal subcarrier allocation is performed by assuming an equal power allocation.Thereafter,an optimal power allocation is performed to maximize the sum payoff for the users.By comparing with the max-rate and the max-min algorithms,simulation results show that the proposed game could achieve a good tradeoff between the user fairness and the overall system performance.     

Subcarrier and power allocation for OFDMA-based multicast cellular networks using a coalitional game

The subcarrier and power allocation problem for orthogonal frequency-division multiple access (OFDMA)-based multicast cellular networks is investigated in this paper. Due to the intrinsic heterogeneity of the channel gains experienced by different multicast users, the conventional multicast schemes are highly conservative and spectrally inefficient. To address this issue, a novel multicast formulation is proposed where multiuser diversity inherent in OFDMA can be adaptively exploited by clustering users within a multicast group into smaller subgroups based on their channel gains. Subcarriers and power are then dynamically allocated to these subgroups to maximize the total multicast rate of the system. Coalitional game theory is adopted to model the group formation in which users can autonomously form coalitions with other users to compete for network resources. A low-complexity algorithm is proposed for the multicast coalitional game to reach multicoalitional equilibrium in which a sub-optimal performance can be obtained. Simulation results demonstrate that the proposed scheme outperforms the conventional unicast and multicast schemes while achieving a sub-optimal performance comparable to the exhaustive search scheme.     

一种子载波配对和功率分配联合最优算法

在基于正交频分复用的多载波两跳中继系统中有两个关键的问题亟需解决:子载波间的功率分配和子载波配对.子载波功率分配和配对之间存在复杂的耦合关系,通过现有的方法对子载波功率分配和配对进行联合优化比较困难.在深入研究这种耦合关系的基础上,针对解码转发,利用凸优化思想,提出一种功率受限下的子载波配对和功率分配联合最优算法.仿真结果表明,本算法可以有效提升中继系统的系统容量.     

认知中继网络中的功率分配算法

无人机（Unmanned aerial vehicle, UAV）通信是当前无线通信领域的研究热点。为了保证地面移动端与UAV通信的可靠性,提出了基于空时块码（Space-time block code, STBC）的协作中继传输方案。为了提升频谱效率,本文利用认知无线电技术,于协作中继处分别采用放大转发(Amplify-and-forward, AF)和解码转发(Decode-and-forward, DF)两种协议进行传输,在主用户通信服务质量得到保证和认知用户传输功率受限的条件下,建立以认知中继网络的吞吐量最大化为目标函数的优化问题。采取拉格朗日乘子法与Karush-Kuhn-Tucker (KKT)条件相结合的方案来实现优化问题中最优功率的分配。最后,仿真结果不仅验证了所提方案的有效性,还表明了DF中继协议下认知中继网络的吞吐量优于AF中继协议。     

OFDMA中继系统比例公平资源调度方案研究

针对放大-转发OFDMA中继系统的多用户比例公平资源分配问题, 在独立功率约束条件下,提出一种联合的子载波和功率分配的调度方案。方案将该资源分配问题的计算转化为对其对偶问题的计算,通过计算对偶问题间接获得原问题的解。对于对偶问题的计算采用次梯度方法。在每次迭代计算过程中,利用Hungarian算法进行最佳的子载波配对,子载波对的用户分配采用比例公平原则,利用改进的注水算法进行功率调整。仿真分析表明,在多用户比例公平的原则下所提方案的频谱效率得到明显提高。     

基于认知OFDM系统的功率分配算法

在正交频分复用的认知无线电系统中,授权用户会受到认知用户频带内子载波带外功率泄漏的干扰。针对这一问题,提出了一种基于幂函数分布的次优化功率分配方案,通过线性约束的凸优化数值运算,有效降低了最优方案中运算的复杂度。给出了在认知用户发射功率约束条件下的信道吞吐量分析。仿真结果表明,所提出的方案在满足授权用户干扰门限约束条件下,提高了现有功率分配方案的认知用户信道吞吐量。     

电力线通信系统中跨层的用户调度和资源分配

针对多用户多业务基于正交频分多址的电力线通信系统,提出一种在数据链路控制层进行用户调度和在物理层进行资源分配的多层多目标最优的跨层资源分配算法,其用户调度根据所有用户的服务质量(QoS)满意程度、QoS要求、业务包模型、信道状态信息和队列状态信息,从所有用户中选出要服务的用户和确定这些用户的最优跨层参数;其资源分配则根据所有调度用户的QoS要求、最优跨层参数和信道状态信息,先把功率按地窖注水原理分给每个子载波,再把每个子载波最优地分给调度用户并采用逐比特加载查表算法调整其上分配的功率和比特。最后在典型的电力线信道环境下对算法进行仿真,结果表明新算法在系统资源大范围变化时也能保障用户的服务质量,同时有效地提高系统资源的利用。     

认知中继网络功率分配的优化算法

本文研究了认知中继网络的功率分配策略。在基于AF(amplify-and-forward)和DF(decode-and-forward)中继模式下,考虑认知用户传输功率受限以及主用户干扰容限等因素,建立了认知中继网络吞吐量的非凸函数和凸函数优化模型;并利用拉格朗日乘子得到最优解。仿真结果表明,所提算法在认知用户传输功率受限以及主用户干扰容限下优化了认知中继网络的吞吐量。     

JCCA resource allocation for video transmission in relay-enhanced OFDMA system

Resulting from the rapid growth of wireless video services in the recent years, radio resource is often inadequate in the high data rate communication environment. Under the circumstance, it is important to make full use of limited resource for efficient video transmission. Hence, we propose a joint content and channel aware (JCCA) resource allocation algorithm in relay-enhanced OFDMA system. It can maximize accumulation of allocated subcarriers’ contribution for transmitting video data so as to improve overall quality of users’ received video under resource constrained conditions. As it is described in this work, the algorithm is implemented by packet scheduling, path selection and subcarrier allocation, in which time-varying data content and channel state are jointly considered at the same time. And the two implementation schemes, JCCAG and JCCAL, are designed for JCCA resource allocation algorithm. JCCAG is executed for allocating subcarriers through global search among all subcarriers’ contribution. For reducing complexity of JCCAG, subcarriers are allocated according to the corresponding contribution towards each user on the basis of local search in JCCAL. In the simulation, we make comparison between the JCCA resource allocation algorithm and others for video transmission in relay-enhanced OFDMA system. And the comparison results are evaluated through objective and subjective criterion, respectively. It is demonstrated that the proposed algorithm can perform better in improving overall quality of users’ received video.     

OFDMA 协同网络中基于QoS 保证的资源分配算法

针对正交频分多址(OFDMA)协作通信系统,为了解决数据传输速率最大化并提供尽力而为业务与实时业务的服务质量(QoS)保证问题,提出新型资源分配算法.通过以总功率受限为约束条件,定义基于数据速率、时延和丢包率的效用函数,并以在协作传输中以最大化效用函数为目标进行中继选择和子载波分配.通过中继和用户上的子载波和功率分配方案的设计,从而最大化网络数据传输速率并最小化时延与丢包率,为多种业务提供服务质量保证.采用最优化理论与方法求解效用函数,得到了资源分配结果.仿真结果验证了算法收敛,并给出功率分配结果,以及网络吞吐量和时延性能指标情况,验证了算法的有效性.     

MIMO two-way relay channel with superposition coding and imperfect channel estimation

This paper deals with the superposition coding (SPC) scheme in multiple-input multiple-output two-way relay channels subject to imperfect channel estimation. In this scenario, two multiple antenna terminals, which are unable to communicate directly, exchange information with each other via a multiple antenna relay. We determine the impact of the channel estimation error degradation on the achievable rate region for two main SPC techniques: (a) SPC without channel state information (CSI) at the users, (b) SPC with an imperfect CSI at the users where a waterfilling power allocation is employed. We demonstrate that imperfect CSI significantly improves the achievable rate at low signal-to-noise ratios (SNRs) while it becomes less critical at high SNRs. In addition, a SPC power allocation technique that incorporates the average channel statistics and does not require any instantaneous CSI is also investigated. We show how the available power is split between the two bi-directional (superimposed) data flows in order to maximize the system performance and to support fairness as well as to maximize the achievable sum-rate.     

Subcarrier allocation in multi-hop orthogonal frequency division multiple access wireless networks

Orthogonal frequency division multiplexing (OFDM) has been widely considered as a key technique for next generation mobile communication systems. Meanwhile, relaying technologies can improve users’ quality of service, increase network capacity and enlarge cellular coverage at a low cost. In this paper, we focus on subcarrier allocation and utilization in multi-hop OFDM access (OFDMA) wireless networks, and propose two efficient subcarrier allocation schemes aiming to increase network throughput and subcarrier utilization. The first scheme selects suitable links for data transmission from base stations to terminals at the beginning. Then, interference-free links are included into the same group for network resource reuse. For the purpose of global optimization, we propose a Tabu-based searching algorithm as the second subcarrier allocation scheme. Simulation results demonstrate that our proposed algorithms outperform other schemes in both network throughput and subcarrier utilization.     

Utility-based downlink power allocation in multicell wireless packet networks

This paper introduces a utility-based radio resource management technique in multicell wireless packet networks. In terms of allocation of base station (BS) downlink transmit power and assignment of resource to users in each cell, we formulate a problem of maximizing system utility which is defined as the sum of cell utilities. The problem, however, is not solvable due to its non-convex property. Thus, we propose a heuristic algorithm based on an intuition obtained from analyzing a simple two-cell problem. Though the heuristic approach also incurs signaling overhead for power coordination between neighboring base stations, it is much less than that of the original approach. Simulation results show the performance of our proposed algorithm compared with two competitive schemes: optimal and maximum power allocation schemes. As expected, the optimal allocation scheme shows the best performance but can not be employed in a real network due to intractable complexity. Our heuristic algorithm performs reasonably well with very low complexity.