Resource Allocation and Adaptive Modulation in Uplink SC-FDMA Systems

In this paper, we study joint power and sub-channel allocation, and adaptive modulation in Single Carrier Frequency Division Multiple Access (SC-FDMA) which is adopted as the multiple access scheme for the uplink in the 3GPP-LTE standard. A sum-utility maximization problem is considered. Unlike OFDMA, in addition to the restriction of allocating a sub-channel to one user at most, the multiple sub-channels allocated to a user in SC-FDMA should be consecutive as well. This renders the resource allocation problem prohibitively difficult and the standard optimization tools (e.g., Lagrange dual approach widely used for OFDMA, etc.) can not help towards its optimal solution. We propose a novel optimization framework for the solution of this problem which is inspired from the recently developed canonical duality theory. We first formulate the optimization problem as binary-integer programming problem, and then transform this binary-integer programming problems into a continuous space canonical dual problem that is a concave maximization problem. Based on the solution of the continuous space dual problem, we derive joint power and sub-channel allocation algorithm whose computational complexity is polynomial. We provide conditions under which the proposed algorithms are optimal. We also propose an adaptive modulation scheme which selects an appropriate modulation strategy for each user. We compare the proposed algorithm with the existing algorithms in the literature to assess their performance. The results show a tremendous performance gain.     

Low complexity margin adaptive resource allocation in downlink MIMO-OFDMA system

We study the downlink multiuser Multiple Input Multiple Output-Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) system for margin adaptive resource allocation where the Base Station (BS) has to satisfy individual Quality of Service (QoS) constraints of the users subject to transmit power minimization. Low complexity solutions involve beamforming techniques for multiuser inter-stream interference cancellation. However, when beamforming is introduced in the margin adaptive objective, it becomes a joint beamforming and resource allocation problem. We propose a sub-optimal twostep solution which decouples beamforming from subcarrier and power allocation. First a reduced number of user groups are formed and then the problem is formulated as a convex optimization problem. Finally an efficient algorithm is developed which allocates the best user group to each subcarrier. Simulation results reveal comparable performance with the hugely complex optimal solution.     

LTE系统上行调度算法研究

无线资源调度是LTE系统研究的一个热点问题。L11E上行链路采用了单载波正交频多址（sc—FDMA）技术,要求在调度时为任一用户分配的RB必须是连续的,使得LTE下行调度算法不能直接应用上行调度。本文对LTE系统上行链路资源调度问题的研究状况进行了概述,分别从信道感知、比例公平、QoS保证三个方面,对现有调度算法进行了分析和比较。重点分析比较了各个算法在保证分配的RB连续的前提下系统性能,并提出了进一步研究的方向。     

Effect of Carrier Frequency Offset on the Channel Capacity in Multiuser OFDM-FDMA Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a very robust transmission procedure in multipath and frequency selective radio channels. A Frequency Division Multiple Access (FDMA) resource allocation technique offers the opportunity of a detailed link adaptation scheme. The combination of these transmission- and multiple access techniques in OFDM-FDMA is an ideal and very strong candidate for the downlink of future fourth generation (4G) mobile communication systems. This technical combination offers high cell capacities by exploiting the inherent multiuser diversity effect of the system. To apply OFDM-FDMA in the uplink, the time and carrier synchronization accuracy becomes very important. Non-ideal synchronization of the user signals to the carrier frequency of the base station leads to intercarrier interferences (ICI). In this paper, an analytical model for the ICI consideration in the uplink of a multiuser OFDM-FDMA based system is derived. The impact of the carrier frequency offset (CFO) on the performance of a cellular multiuser system with respect to different subcarrier allocation schemes is analyzed.

Joint Estimation of the Timing and Frequency Offset for Uplink OFDMA

Inheriting all the advantages of Orthogonal Frequency Division Multiplexing (OFDM), plus the ability to offer a fine level of bit granularity and dynamic subcarrier allocation for multiuser diversity, the Orthogonal Frequency Division Multiple Access (OFDMA) has emerged as a potential candidate for multiple access technique for future broadband wireless networks. However, the benefits of OFDMA come with stringent requirements on synchronization, especially in the uplink. Unless the timing offsets (TOs) and carrier frequency offsets (CFOs) among users in the uplink are kept under tolerable ranges, inter-symbol interference (ISI), inter-channel interference (ICI) and multi-user interference (MUI) will occur, which degrade the overall system performance severely. Accurate estimation of TOs and CFOs is required for each user, so that they can be accounted for at the user’s side or compesated for at the base station. This paper proposes a novel method to estimate jointly TOs and CFOs in the time-domain for multi-user in the OFDMA uplink. The method is shown to offer good accuracy, while maintaining a reasonable complexity compared to conventional estimation schemes.     

考虑用户优先级的OFDMA下行链路自适应子载波分配

针对OFDMA下行链路系统,在总功率以及用户数据速率成比例的约束下,以获取整个系统容量极大化为准则,提出一种考虑用户优先级的自适应子载波分配算法.该算法初始分配时允许每个用户根据用户数据速率的相对比例以及自己的信道状态在所有子载波上独立的进行最优选择,当出现多个用户同时选择一个子载波,即出现冲突时,由平均信道增益的大小来决定用户选择该子载波的优先级.文中分别研究了平均信道增益大者为高优先级以及平均信道增益小者为高优先级的两种冲突解决办法,仿真结果表明,由平均信道增益小的用户来优先选择冲突子载波的算法综合考虑了公平性和频谱效率,与系统容量上限相比,性能损失较小,复杂度低,速度快,能够满足实时要求.     

基于强化学习的802.11ax上行链路调度算法

随着物联网(IoT)时代的到来,无线网络饱和的问题已经越来越严重。为了克服终端密集接入问题,IEEE标准协会(IEEE-SA)制定了无线局域网的最新标准—IEEE 802.11ax。该标准使用正交频分多址(OFDMA)技术对无线信道资源进行了更细致的划分,划分出的子信道被称为资源单元(RU)。为解决密集用户环境下802.11ax 上行链路的信道资源调度问题,该文提出一种基于强化学习的RU调度算法。该算法使用演员-评论家(Actor-Critic)算法训练指针网络,解决了自适应RU调度问题,最终合理分配RU资源给各用户,兼具优先级和公平性的保障。仿真结果表明,该调度算法在IEEE 802.11ax上行链路中比传统的调度方式更有效,具有较强的泛化能力,适合应用在密集用户环境下的物联网场景中。     

子载波交织分配的OFDMA系统

近年来，正交频分多址接入系统做为一种新的多址接入技术受到了极大关注。在OFDMA中，相临的多个子载波被分配给不同的用户来为用户并行低速传输数据。子载波是相互间重叠且正交的，所以避免了载波间干扰的产生。文中介绍了向上链接子载波交织分配的OFDMA系统。     

基于载干比最优的OFDMA切换算法的研究

 正交频分多址接入（OFDMA, Orthogonal Frequency Division Multiple Access）已经成为3G演进策略（LTE, Long Term Evolution）及4G技术的主要多址接入方式.本文研究了现有的OFDMA的切换算法,分析了其存在的不足之处.本文针对OFDMA多址技术特点,提出新型的OFDMA切换算法 (SBA, Sub-carriers Bidirectional Arrayed handover).并通过仿真验证新型切换算法的性能.仿真结果表明,新型OFDMA切换算法保证了用户在切换过程中的信道质量（CIR,Carrier-Interference Ratio）,减少了切换信道的数目,从而提高了OFDMA系统性能.     

下行多用户MIMO-OFDMA/SDMA系统动态资源分配

该文对下行多用户MIMO-OFDMA/SDMA系统动态资源分配算法进行了研究,在满足各种约束条件的前提下,以最大化系统吞吐量为目标建立了相应的优化模型。由于最优解难以获得,将整个优化过程分两步完成,第1步定义了一个用于度量配置多根天线的用户空间兼容性的指标,并根据该指标提出了相应的调度算法;第2步提出了两种次优的资源分配算法。仿真结果表明,所提算法优于传统的随机调度算法,与功率复用策略结合时,所提算法的性能接近于基于用户选择的最优分配算法的性能。     

Evaluation of OFDMA resource allocation algorithms in broadband wireless access networks

Broadband Wireless Access (BWA) is gaining interest due to the increasing demand of high-quality mobile wireless systems. In this context Orthogonal Frequency Division Multiple Access (OFDMA) is one of the most promising and researched physical transmission technologies. In OFDMA, data have to be mapped into a time-frequency matrix before the actual transmission. Efficiency, power consumption, Quality of Service (QoS) and complexity factors should be taken into account by mapping algorithms. In this paper, we focus on the OFDMA resource allocation problem in BWA networks. Through extensive simulation in different scenarios, performance of several resource allocation algorithms is evaluated.     

基于中继的OFDMA网络中可扩展编码视频流传输的权衡优化(英文)

To achieve an optimal trade-off between video quality and energy efficiency in the uplink streaming of multi-user Scalable Video Coding (SVC) videos in relay-based Orthogonal Frequency Division Multiple Access (OFDMA) cellular networks, a cross-layer design framework that jointly selects the Transmission Policy (TP) for SVC video frames, assigns OFDMA subcarriers, and allocates power for each subcarrier is proposed. We apply the dual decomposition method to the problem, and obtain a TP selection subproblem for each SVC video adaptation and a resource allocation subproblem of Joint Subcarrier, Relay and Power Allocation (JSRPA). A second level of dual decomposition is used to divide the JSRPA problem into independent subcarrier subproblems. The proposed Crosslayer Trade-off Optimization (CTO) algorithm is sub-distributed with significantly low complexity. A performance evaluation with typical SVC video traces demonstrates that the proposed algorithm is able to converge and efficiently achieve the optimal trade-off between the video quality and energy consumption at the MSs for uplink SVC streaming.     

Adaptive resource allocation techniques in OFDMA using cross-layer architecture

This paper utilizes the cross-layer architecture to implement adaptive resource allocation in Orthogonal Frequency Division Multiple Access （OFDMA） based on the broadband wireless access system. According to the cross-layer architecture, the information in link layer is used for adaptive resource allocation in OFMDA. A new cross-layer adaptive resource allocation algorithm is developed which can guarantee the users to be in minimum average waiting time in link-layer and get the better spectrum utilization. Numerical results show that our scheme is appealing and can get about half of average waiting time less and 0.5 bps/Hz spectrum utilization more than the scheme in 1EEE802.16a.     

An Adaptive PRB,Power and MCS Allocation Using AMC for MIMO-OFDMA Systems

Long Term Evolution (LTE) is a promising technology for a high communication quality thanks to its radio link flexibility using Adaptive Modulation and Coding (AMC), Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiple Access (OFDMA) technologies. In this paper, we address the adaptive resource allocation problem in down-link transmission of MIMO-OFDMA systems. We aim at maximizing the total system capacity to meet the 4G-technologies promises. In order to reduce the computational complexity, the original optimization problem is divided into sub-optimal ones. Firstly, a recursive Physical Resource Block (PRB) allocation algorithm is developed where the Effective Signal-to-Interference-plus-Noise Ratio (ESINR) metric is investigated to properly characterize the channel condition. Secondly, a power allocation procedure is performed. As all resource blocks allocated to the same user must use the same Modulation and Coding Scheme (MCS) according to the LTE standard requirements, power optimization sub-problem is divided into three steps: power allocation among PRBs, power allocation among antennas and power allocation among users. Finally, a more effective MCS is obtained, which ensures a better system capacity. Simulation results prove the efficiency of the proposed method to maximize the total system capacity with a low complexity even in the case of loaded systems compared to Minimum-MCS (Min-MCS) and Maximum-SINR (Max-SINR) algorithms.     

单小区多用户下行OFDM系统资源分配算法研究

多用户正交频分复用(OFDM)系统中,充分利用多载波系统的多用户分集进行合理无线资源分配,能够显著提高系统容量和最大限度提高频谱利用率。经过广泛的研究,很多有效资源分配算法已经被提出来。重点讨论了单小区多用户OFDM系统关于子载波、比特及功率等无线资源的分配问题,介绍现有的研究成果,包括常见的模型及求解方法,并介绍近期的研究热点,包括多小区系统、多入多出(MIMO)系统等。     

一种多无线电系统中基于公平性和精细化带宽分配的资源分配算法

该文针对以OFDMA(Orthogonal Frequency Division Multiple Access)为多址接入方式的多无线电系统中用户比例公平性和系统效率问题进行了研究,提出一种联合资源分配算法,不仅保证了用户比例公平性下系统的吞吐量,还充分考虑了分配的带宽是子信道带宽整倍数的特点,对分配给每个终端的带宽进行子信道整数倍调整。最后通过仿真对比,从系统吞吐量和公平性两方面给出了算法的性能。     

On the use of NSGA-II for multi-objective resource allocation in MIMO-OFDMA systems

This paper investigates the problem of dynamic subcarrier and bit allocation in downlink of Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiple Access (OFDMA) Systems. Using Singular Value Decomposition, the MIMO fading channel of each subcarrier is transformed into an equivalent bank of parallel Single Input Single Output sub-channels. To achieve the capacity bound, one must solve a multiuser subcarrier allocation and the optimal bit allocation jointly. To alleviate the computational complexity of joint subcarrier and bit allocation, several suboptimal solutions have been proposed. These suboptimal solutions handle subcarrier and bits individually. We propose the use of Non-dominated Sorting Genetic Algorithm (NSGA)-II, which is a multi-objective Genetic Algorithm, for joint allocation of bits and subcarriers, in the downlink of MIMO-OFDMA system. NSGA-II is intended for optimization problems involving multiple conflicting objectives. Here the two conflicting objectives are Rate Maximization and Transmit Power Minimization. The simulation results indicate remarkable improvement in terms of convergence over previous approaches involving Evolutionary algorithms. At the same time capacity achieved by the proposed algorithm is found to be comparable with that of previous algorithms.     

Joint scheduling and resource allocation in uplink OFDM systems for broadband wireless access networks

Orthogonal Frequency Division Multiplexing (OFDM) with dynamic scheduling and resource allocation is a key component of most emerging broadband wireless access networks such as WiMAX and LTE (Long Term Evolution) for 3GPP. However, scheduling and resource allocation in an OFDM system is complicated, especially in the uplink due to two reasons: (i) the discrete nature of subchannel assignments, and (ii) the heterogeneity of the users' subchannel conditions, individual resource constraints and application requirements. We approach this problem using a gradient-based scheduling framework. Physical layer resources (bandwidth and power) are allocated to maximize the projection onto the gradient of a total system utility function which models application-layer Quality of Service (QoS). This is formulated as a convex optimization problem and solved using a dual decomposition approach. This optimal solution has prohibitively high computational complexity but reveals guiding principles that we use to generate lower complexity sub-optimal algorithms. We analyze the complexity and compare the performance of these algorithms via extensive simulations.     

A game-theoretic approach to decentralized optimal power allocation for cellular networks

The rapidly growing demand for wireless communication makes efficient power allocation a critical factor in the network??s efficient operation. Power allocation in cellular networks with interference, where users are selfish, has been recently studied by pricing methods. However, pricing methods do not result in efficient/optimal power allocations for such systems for the following reason. Because of interference, the communication between the Base Station (BS) and a given user is affected by that between the BS and all other users. Thus, the power vector consisting of the transmission power in each BS-user link can be viewed as a public good which simultaneously affects the utilities of all the users in the network. It is well known (Mas-Colell et al., Microeconomic Theory, Oxford University Press, London, 2002, Chap. 11.C) that in public good economies, standard efficiency theorems on market equilibrium do not apply and pricing mechanisms do not result in globally optimal allocations. In this paper we study power allocation in the presence of interference for a single cell wireless Code Division Multiple Access (CDMA) network from a game theoretic perspective. We consider a network where each user knows only its own utility and the channel gain from the base station to itself. We formulate the uplink power allocation problem as a public good allocation problem. We present a game form the Nash Equilibria of which yield power allocations that are optimal solutions of the corresponding centralized uplink network.     

基于带缓存的云接入网络最优能效设计

在云接入网络(Cloud-RAN)中,现有工作大多假定射频拉远头(RRH)不具备缓存功能。然而下一代通信网络具有以内容为中心的特性,因此在Cloud-RAN中考虑带缓存的RRHs也变得有必要。该文考虑在Cloud-RAN中有效设计缓存方案,并通过资源分配有效减轻前程链路负担。假设系统采用正交频分多址接入(OFDMA)技术,通过联合优化子载波(SC)分配,RRH选择与传输功率,最小化系统下行总功耗,并通过拉格朗日对偶分解转化非凸问题,获得最优分配方案。仿真结果表明,比起其它缓存方案,该文提出的优化算法可以有效地提升系统能效,满足未来通信需求。