Capacity and Energy Efficiency of Multi-User Spectrum Sharing Systems with Opportunistic Scheduling

This paper investigates the capacity and energy efficiency of spectrum sharing systems with opportunistic user selection where a secondary network utilizes spectrum bands licensed to a primary network under interference regulation. In spectrum sharing systems, secondary users consume a fraction of their resources in sensing the channels to the primary users to comply with the interference constraints. Although more resources for sensing improve reliability and performance, the throughput loss due to time overhead and energy loss due to power overhead should be properly incorporated in performance evaluation. In this context, we define and derive a new metric ? average capacity normalized by the total energy consumption ? reflecting time and power overhead for spectrum sensing. Based on the developed framework, the optimal normalizedcapacity is investigated. We also propose a simple and practical suboptimal best-n scheme motivated by the infeasibility and high computational complexity of the optimal strategy, where n denotes the number of sensing secondary users. Our analytical and simulation results show that the proposed best-1 scheme is an energy-efficient technique with near optimality in terms of the capacity normalized by the energy consumption.     

Opportunistic Scheduling for Wireless Network Coding

This letter addresses a scheduling problem for wireless network coding (WNC). In our previous work, we have theoretically shown that the optimum number of nodes to be included into a network?coded packet as well as its transmission rate depends on time?varying link condition between a transmitting node and receiving nodes [1]. Based on this observation, this letter designs practical scheme which opportunistically selects scheduled nodes, packets to be coded and an employed modulation level according to time?varying channel conditions and packet length. The numerical results show that the proposed opportunistic scheduling can improve the overall throughput as compared with non?opportunistic approach.     

机会调度模式下的嵌套码研究

将机会调度模式引入嵌套码体系,通过各个收发节点与中继节点的信道状况自适应调整嵌套码的码速率,可以增加信道状况好的链路传输的数据量,提升无线网络的整体吞吐量。仿真结果表明,相比传统非机会调度嵌套码而言,机会调度嵌套码能够有效提升网络吞吐量和误比特性能。     

Opportunistic Beamforming and Scheduling for OFDMA Systems

Orthogonal frequency-division multiple access (OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses three problems in multiuser diversity for OFDMA systems. First, we propose a way to significantly reduce the amount of channel state information (CSI) feedback without sacrificing performance too much, by selective and adaptive feedback. Second, we propose a way to increase the cell throughput and fairness by applying an opportunistic beamforming scheme to orthogonal frequency-division multiplexing. This beamforming scheme increases the frequency fading rate, which increases the multiuser diversity effect. Thirdly, we deal with the issue of fairness and quality-of-service (QoS) in opportunistic systems by proposing a modified proportional fair (PF) scheduler for OFDMA. Key features in the scheduler are that it incorporates QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate the performance of the proposed schemes. The opportunistic beamforming scheme performed well in comparison with several other schemes. The modified PF scheduler was able to give users different QoS, based on their requirements, while still exploiting multiuser diversity     

Cross-Layer MAC Protocol and Holistic Opportunistic Scheduling with Adaptive Power Control for QoS in WiMAX

Providing quality of service (QoS) to different service classes with integrated real-time and non-real-time traffic is an important issue in broadband wireless access networks. Opportunistic MAC (OMAC) is a novel view of communication over spatiotemporally varying wireless link whereby the multi-user diversity is exploited rather than combated to maximize bandwidth efficiency or system throughput. It combines cross-layer design features and opportunistic scheduling scheme to achieve high utilization while providing QoS support to various applications. Channel characteristics, traffic characteristics and queue characteristics are the essential factors in the design of opportunistic scheduling algorithms. In this paper, we propose a cross-layer MAC scheduling framework in WiMAX point-to-multipoint (PMP) systems and a corresponding opportunistic scheduling algorithm with an adaptive power control scheme to provide QoS support to the heterogeneous traffic. Extensive simulation experiments have been carried out to evaluate the performance of our proposal. The simulation results show that our proposed solution can improve the performance of the WiMAX PMP systems in terms of packet loss rate, packet delay and system throughput.     

机会波束成形系统中一种新的调度方案

主要研究机会波束成形系统中的调度算法,将宽带无线IP网络调度算法应用于机会波束成形系统。提出了一个保证用户QoS要求的新方案。数值分析表明,所提的方案较之传统的方案在保证系统吞吐量和用户间公平性的同时,也保证了用户的QoS。     

Adaptive Opportunistic Multicast Scheduling Over Next-Generation Wireless Networks

This paper considers the problem of opportunistic multicast scheduling in wireless time-division multiplexing systems with adaptive modulation and channel coding. The problem is first formulated and an effective scheduling scheme is proposed to maximize the multicast throughput while a desired packet error rate is guaranteed. The proposed scheme dynamically selects multicast rates by considering the configuration of the multicast group and instantaneous network states, and thus it can adapt well to network conditions. Extensive simulation results conclusively demonstrate that, compared to the worst-user multicast scheduling, the proposed approach can increase the wireless channel efficiency by large margins, especially when the channel is operating in a lower signal-to-noise ratio region and/or when the multicast group size increases. Besides, the simulations show that the proposed approach can work well in systems with imperfect channel estimation.     

一种面向移动边缘计算的多用户细粒度任务卸载调度方法

在移动边缘计算中(Mobile Edge Computing,MEC),任务卸载可以有效地解决移动设备资源受限的问题,但是将全部任务都卸载到边缘服务器并非最优.本文提出一种面向移动边缘计算的多用户细粒度任务卸载调度新方法,把计算任务看作一个有向无环图(Directed Acyclic Graph,DAG),对节点的执行位置和调度顺序进行了优化决策.考虑系统的延迟把计算卸载看作一个约束多目标优化问题(Constrained Multi-object Optimization Problem,CMOP),提出了一个改进的NSGA-Ⅱ算法来解决CMOP.所提出的算法能够实现本地和边缘的并行处理从而减少延迟.实验结果表明,算法能够在实际应用程序中做出最优决策.     

Opportunistic Multi-Access: Multiuser Diversity, Relay-Aided Opportunistic Scheduling, and Traffic-Aided Smooth Admission Control

We study multi-access control in opportunistic communication systems, and propose two new schemes to address channel asymmetry and throughput-guaranteed admission control, respectively. We first devise a relay-aided opportunistic scheduling (RAOS) scheme, in which a user can choose to communicate with the base station either directly or using multiple hops (relay transmissions). We develop relay/direct link construction algorithms using either a channel-capacity-based criterion or a throughput-based criterion, and devise opportunistic scheduling schemes accordingly. Our results show that in the presence of channel asymmetry across users, the RAOS scheme performs significantly better than Qualcomm's HDR scheme. Next, we propose a traffic-aided smooth admission control (SAC) scheme that aims to guarantee throughput provisioning. Simply put, in the SAC scheme, the admission decision is spread over a trial period, by increasing gradually the amount of the time resource allocated to incoming users. Specifically, using the modified weighted proportional fair (WPF) scheduling, we devise a QoS driven weight adaptation algorithm, and the weights assigned to new users are increased in a guarded manner. Then an admission decision is made based on the measured throughput within a time-out window. A key feature is that we exploit explicitly the traffic information and throughput requirements in devising the back-off time. Our results show that the proposed SAC scheme works well in opportunistic communication systems.     

Opportunistic Scheduling in Multiuser OFDM Systems with Clustered Feedback

This paper proposes a random access based feedback protocol for multiuser orthogonal frequency division multiple access (OFDMA) systems with clustered feedback, where users are assigned to clusters of subcarriers based on the feedback of channel state information to the base station. To reduce feedback requirements, the proposed protocol employs a contention channel with a fixed number of feedback minislots to carry feedback for each cluster. Users send a feedback message with some probability in the appropriate feedback slot if their average channel quality on a cluster is above a threshold. Both arithmetic and geometric averages are used and compared as channel quality measures. The threshold and feedback probability are jointly adjusted to maximize the estimated average sum rate of all users based on two different limited feedback information. Numerical simulations illustrate that it is possible to achieve multiuser diversity gain despite collisions in the feedback channel and with only a few feedback opportunities.     

无线数据网络中机会调度理论模型的研究

机会通信作为一种对无线通信系统设计具有革命性意义的概念正在受到越来越多的关注.目前对机会调度算法的研究往往采用不同的模型进行性能评价,使得不同算法之间很难直接进行性能比较.本文主要将各种用于机会调度算法研究的理论模型进行分类和比较,对几种典型的机会调度算法在各类理论模型下的性能评价指标、方法和结果进行讨论,最后探讨了该领域未来的发展趋势并给出了一些有待研究的方向.     

Optimal and Approximate Mobility-Assisted Opportunistic Scheduling in Cellular Networks

This paper considers the problem of scheduling multiple users in the downlink of a time-slotted cellular data network. For such a network, opportunistic scheduling algorithms improve system performance by exploiting time variations of the radio channel. We present novel optimal and approximate opportunistic scheduling algorithms that combine channel fluctuation and user mobility information in their decision rules. The algorithms modify the opportunistic scheduling framework of Liu et al., (1993) with dynamic constraints for fairness. These fairness constraints adapt according to the user mobility. The adaptation of constraints in the proposed algorithms implicitly results in giving priority to the users that are in the most favorable locations. The optimal algorithm is an offline algorithm that precomputes constraint values according to a known mobility model. The approximate algorithm is an online algorithm that relies on the future prediction of the user mobility locations in time. We show that the use of mobility information in opportunistic scheduling increases channel capacity. We also provide analytical bounds on the performance of the approximate algorithm using the fundamental inequality of Dyer et al., (1986) for linear programs. Simulation results on high data rate (HDR) illustrate the usefulness of the proposed schemes for elastic traffic and macrocell structures     

无线网络中基于多用户分集的机会调度研究

机会调度(Opportunistic Scheduling,OS)是对无线衰落信道通信的一种现代认识观点。与基于链路/速率自适应的方案不同,机会调度利用无线信道的时空变化特性来提高无线通信系统的性能,而不是减轻它的影响。本文介绍一种引入了业务流参数的机会调度方案,可以保证调度的公平性,并满足不同类型业务流的QoS(Quality of Service)要求。在瑞利衰落信道中的研究数据显示,采用机会调度达到的系统吞吐量要优于轮询(Round-Robin,RR)方案的吞吐量,并保证了不同等级业务流之间的公平性。     

Opportunistic Scheduling with Reliability Guarantees in Cognitive Radio Networks

We develop opportunistic scheduling policies for cognitive radio networks that maximize the throughput utility of the secondary (unlicensed) users subject to maximum collision constraints with the primary (licensed) users. We consider a cognitive network with static primary users and potentially mobile secondary users. We use the technique of Lyapunov optimization to design an online flow control, scheduling, and resource allocation algorithm that meets the desired objectives and provides explicit performance guarantees.     

Opportunistic Scheduling with QoS Constraints for Multiclass Services HSUPA System

This paper focuses on the scheduling problem with the objective of maximizing system throughput, while guaranteeing long‐term quality of service (QoS) constraints for non‐realtime data users and short‐term QoS constraints for realtime multimedia users in multiclass service high‐speed uplink packet access (HSUPA) systems. After studying the feasible rate region for multiclass service HSUPA systems, we formulate this scheduling problem and propose a multi‐constraints HSUPA opportunistic scheduling (MHOS) algorithm to solve this problem. The MHOS algorithm selects the optimal subset of users for transmission at each time slot to maximize system throughput, while guaranteeing the different constraints. The selection is made according to channel condition, feasible rate region, and user weights, which are adjusted by stochastic approximation algorithms to guarantee the different QoS constraints at different time scales. Simulation results show that the proposed MHOS algorithm guarantees QoS constraints, and achieves high system throughput.     

An Opportunistic Channel Quality Feedback Scheme for Proportional Fair Scheduling

In this paper, we propose a channel quality information (CQI) feedback load reduction scheme for proportional fair scheduling (PFS) in wireless systems. The proposed scheme induces select users to feed back CQI only when the probability of selection is high. It is shown that the proposed scheme achieves system throughput comparable to the conventional scheme, where each and every user feeds back its CQIs, with significant feedback load reduction for each of the users.     

高速无线个域网中一种基于效用公平的机会调度算法

基于对无线高速个域网中机会调度的研究,提出了一种适用于WPAN的机会主义时隙调度算法FPTS。该算法充分考虑了信道状态的波动和用户间的公平性,由参数更新模块和调度分配模块组成。参数更新模块根据调度结果更新控制参数,维护用户的公平性和自适应的跟踪信道的变化;调度分配模块负责计算每个用户的公平效用权值,并按照权值向各用户比例分配信道资源。仿真结果表明：所提调度方案能够在保证系统高吞吐量的前提下,获得LLPTS算法更好的公平性和信道使用效率。     

On the BER Performance of Hierarchical M-QAM Constellations With Diversity and Imperfect Channel Estimation

The analytical bit error rate of hierarchical quadrature amplitude modulation formats, which include uniform and nonuniform constellations, over flat Rayleigh fading environments is studied in this paper. The analysis takes into account the effect of imperfect channel estimation and considers diversity reception with both independent identically and nonidentically distributed channels, employing maximal ratio combining.     

多用户JT MIMO系统下行联合功率分配算法

文中提出一种多用户MIMO下行联合发送（简称JTMIMO）技术中的功率分配算法。首先给出了多用户JT MIMO下行链路模型，并导出了下行信道干扰模型和有偏信道信息下的SINR公式。在此基础上，文中提出一种适用于多用户JTMIMO下行链路的联合功率分配算法，仿真验证表明：通过合理分配用户的发送功率，在满足每个用户信干比（SINR）的前提下，最小化总传榆能量具有较好的能量效率。