Analysis and Design of Scheduling Schemes for Wireless Networks with Unsaturated Traffic

Scheduling schemes assign limited resources to appropriate users,which are critical for wireless network performance.Most current schemes have been designed based on saturated traffic,i.e.,assuming users in networks always have data to transmit.However,the user buffer may sometimes be empty in actual network.Therefore,these algorithms will allocate resources to users having no data to transmit,which results in resource waste.In view of this,we propose new scheduling schemes for onehop and two-hop link scenario with unsaturated traffic.Furthermore,this paper analyzes their key network performance indicators,including the average queue length,average throughput,average delay and outage probability.The two scheduling algorithms avoid scheduling the links whose buffers are empty and thus improve the network resource utilization.For the one-hop link scenario,network provides differentiated services via adjusting the scheduling probabilities of the destination nodes(DNs)with different priorities.Among the DNs with same priority,the node with higher data arrival rate has larger scheduling probability.For the two-hop link scenario,we prioritize the scheduling of relay-to-destination(R-D)link and dynamically adjust the transmission probability of source-to-relay(S-R)link,according to the length of remaining buffer.The experiment results show the effectiveness and advantage of the proposed algorithms.     

Distributed Proportional Fair Scheduling for IEEE802.11 Wireless LANs

In the time varying wireless channel, opportunistic scheduling is one of the important techniques to achieving the rich diversities inherent in wireless communications. However, most existing scheduling schemes require centralized scheduling and little work has been done on developing distributed algorithms The proportional fair scheduling is one of the representative opportunistic scheduling for centralized networks. In this paper, we propose distributed proportional fair scheduling (DPFS) scheme for wireless LAN network. In the proposed DPFS scheme, each receiver estimates channel condition and calculates independently its own priority with probabilistic manner, which can reduce excessive probing overhead required to gather the channel conditions of all receivers. We evaluate the proposed DPFS using extensive simulation and simulation results show that DPFS obtains higher network throughput than conventional scheduling schemes while maintaining fairness among users.     

Proportional Fair Scheduling with Capacity Estimation for Wireless Multihop Networks

In this paper, we investigate the scheduling problem to achieve the proportional fairness among the flows in wireless multihop networks with time-varying channel capacity. Using the signal to interference noise ratio and the outage probability, we present an estimate of time-varying capacity. Then, we achieve the proportional fairness in terms of maximizing the network utility function with consideration of fast fading without measurement of channel state information. Finally, we show that the proposed scheme results in better performance compared to the existing schemes through the simulation results.     

Proportional Fair Space–Time Scheduling for Wireless Communications

We extend the proportional fair (PF) scheduling algorithm to systems with multiple antennas. There are$K$client users (each with a single antenna) and one base station (with$n_R$antennas). We focus on the reverse link of the system, and assume a slow-fading channel where clients are moving with pedestrian speed. Qualcomm's original PF scheduling algorithm satisfies the PF criteria only when the communication is constrained to one user at a time with no power waterfilling. However, the original PF algorithm does not generalize easily when we have$n_R$receive antennas at the base station. In this paper, we shall formulate the PF scheduling design as a convex optimization problem. One challenge is in the optimal power allocation over the multiantenna multiaccess capacity region, which is still an open problem. For practical consideration, we consider multiuser minimum mean-square error processing at the base station. To obtain first-order insight, we propose an asymptotically optimal PF scheduling solution. Using the proposed PF solution for a multiantenna base station, the system capacity is enhanced by exploiting the multiuser selection diversity, as well as the distributed multiple-input multiple-output configuration. It is found that the PF scheduler achieves a good balance between fairness and system capacity gain.     

Channel-Aware Earliest Deadline Due Fair Scheduling for Wireless Multimedia Networks

Providing delay guarantees to time-sensitive traffic in wireless multimedia networks is a challenging issue. This is due to the time-varying link capacities and the variety of real-time applications expected to be handled by such networks. We propose and evaluate the performance of a channel-aware scheduling discipline and a set of policies that are capable of providing such delay guarantees in TDM-based wireless networks. First, we introduce the Channel-Dependent Earliest-Due-Date (CD-EDD) discipline. In this discipline, the expiration time of the head of line packets of users' queues is taken into consideration in conjunction with the current channel states of users in the scheduling decision. This scheme attempts to guarantee the targeted delay bounds in addition to exploiting multiuser diversity to make best utilization of the variable capacity of the channel. We also propose the violation-fair policy that can be integrated with the CD-EDD discipline and two other well-known scheduling disciplines [1, 2]. In this policy, we attempt to ensure that the number of packets dropped due to deadline violation is fairly distributed among the users. The proposed schemes can provide statistical guarantees on delays, achieve high throughput, and exhibit good fairness performance with respect to throughput and deadline violations. We provide extensive simulation results to study the performance the proposed schemes and compare them with two of the best known scheduling disciplines [1, 2] in the literature. Khaled M. F. Elsayed (S90-M95-SM02) received his B.Sc. (honors) in electrical engineering and M.Sc. in engineering mathematics from Cairo University in 1987 and 1990 respectively. He received his Ph.D. in computer science and computer engineering from North Carolina State University in 1995. He is now an Associate Professor in Cairo University, Egypt and is an independent telecommunications consultant. Between 1995 and 1997, he was a member of scientific staff with Nortel Wireless Systems Engineering in Richardson, TX.Dr. Elsayed was the editor for the Internet technology series of the IEEE Communications Magazine from 1998 until 2002. He has served on technical program committees for several IEEE, IFIP, and ITC conferences. He was the technical co-chair for IFIP MWCN 2003 conference in Singapore. He also served as an expert evaluator for the European Commission FP5 and FP6 programmes. His research interest is in the area of performance evaluation of communication networks including IP, wireless and optical networks. Ahmed Khattab received his B.Sc. (honors) and MS.C in Electronics and Communications Engineering from Cairo University in 2002 and 2004 respectively. Since August 2005, he is pursuing his PhD degree at Rice University, Texas. His research interests are in wireless networking and radio resource management.     

Super-Fast Delay Tradeoffs for Utility Optimal Fair Scheduling in Wireless Networks

We consider the fundamental delay tradeoffs for utility optimal scheduling in a general network with time-varying channels. A network controller acts on randomly arriving data and makes flow control, routing, and resource allocation decisions to maximize a fairness metric based on a concave utility function of network throughput. A simple set of algorithms are constructed that yield total utility within$O(1/V)$of the utility-optimal operating point, for any control parameter$V≫0$, with a corresponding end-to-end network delay that grows only logarithmically in$V$. This is the first algorithm to achieve such “super-fast” performance. Furthermore, we show that this is the best utility-delay tradeoff possible. This work demonstrates that the problem of maximizing throughput utility in a data network is fundamentally different than related problems of minimizing average power expenditure, as these latter problems cannot achieve such performance tradeoffs.     

Performance of Random Access Scheduling Schemes in Multi-Hop Wireless Networks

The scheduling problem in multi-hop wireless networks has been extensively investigated. Although throughput optimal scheduling solutions have been developed in the literature, they are unsuitable for multi-hop wireless systems because they are usually centralized and have very high complexity. In this paper, we develop a random-access based scheduling scheme that utilizes local information. The important features of this scheme include constant-time complexity, distributed operations, and a provable performance guarantee. Analytical results show that it guarantees a larger fraction of the optimal throughput performance than the state-of-the-art. Through simulations with both single-hop and multi-hop traffics, we observe that the scheme provides high throughput, close to that of a well-known highly efficient centralized greedy solution called the greedy maximal scheduler.     

一种应用于无线局域网的无源CMOS混频器

针对一种双平衡结构的无源CMOS混频器,分析了它的转换增益、噪声系数和线性等参数,在此基础上,推导了它的电路设计方程.设计了该混频器应用于2.4 GHz无线局域网(WLAN)的电路拓扑,并应用TSMC的0.18 μm CMOS工艺进行了仿真.结果显示,在1.8 V的工作电压下,该混频器具有非常出色的性能指标,转换增益最大为-1.2 dB,噪声系数为6.3 dB,1 dB压缩点为-4 dB,功耗小于1 mW.     

WLAN应用的CMOS低噪声放大器设计

采用TSMC0.25μmCMOS工艺设计了一个IEEE802.11a标准无线局域网(WLAN)应用的5.8GHz差分低噪声放大器(LNA)。阐述了LNA的噪声优化和设计过程。采用Agilent ADS仿真,结果显示:2.5V工作电压下,LNA增益为14.6dB,噪声系数为1.72dB,1dB压缩点为-10.2dBm,功耗16.5mW。     

FHCF: A Simple and Efficient Scheduling Scheme for IEEE 802.11e Wireless LAN

The IEEE 802.11e medium access control (MAC) layer protocol is an emerging standard to support quality of service (QoS) in 802.11 wireless networks. Some recent work shows that the 802.11e hybrid coordination function (HCF) can improve significantly the QoS support in 802.11 networks. A simple HCF referenced scheduler has been proposed in the 802.11e which takes into account the QoS requirements of flows and allocates time to stations on the basis of the mean sending rate. As we show in this paper, this HCF referenced scheduling algorithm is only efficient and works well for flows with strict constant bit rate (CBR) characteristics. However, a lot of real-time applications, such as videoconferencing, have some variations in their packet sizes, sending rates or even have variable bit rate (VBR) characteristics. In this paper we propose FHCF, a simple and efficient scheduling algorithm for 802.11e that aims to be fair for both CBR and VBR flows. FHCF uses queue length estimations to tune its time allocation to mobile stations. We present analytical model evaluations and a set of simulations results, and provide performance comparisons with the 802.11e HCF referenced scheduler. Our performance study indicates that FHCF provides good fairness while supporting bandwidth and delay requirements for a large range of network loads. Pierre Ansel received a multidisciplinary in-depth scientific training in different fields such as Pure and Applied Mathematics, Physics, Mechanics, Computer Science and Economics from the Ecole Polytechnique, Palaiseau, France. Then, he joined the Ecole Nationale Superieure des Telecommunications, Paris, France in 2005 where he went further into electronics, databases, computer network security and high speed networks. He received a multidisciplinary master of sciences degree and an additional master of sciences degree in telecommunications in 2005. He did a summer internship in 2003 in INRIA, Sophia Antipolis, France where he worked on the Quality of Service in 802.11 networks at Planete Group, France. Then in 2004, he joined France Telecom R&D, Issy-les-Moulineaux, France to work on Intranet Security issues. He designed a WiFi security supervision architecture based on WiFi Intrusion Detection Sensors. He is currently a French civil servant and belongs to the French Telecommunications Corps. Qiang Ni received the B.Eng., M.Sc. and Ph.D. degrees from Hua Zhong University of Science and Technology (HUST), Wuhan City, China in 1993, 1996 and 1999 respectively. He is currently a faculty member in the Electronic and Computer Engineering Division,School of Engineering and Design, Brunel University, West London, U.K. Between 2004 and 2005 he was a Senior Researcher at the Hamilton Institute, National University of Ireland, Maynooth. From 1999 to 2001, he was a post-doctoral research fellow in the multimedia and wireless communication laboratory, HUST, China. He visited and conducted research at the wireless and networking group of Microsoft Research Asia Lab during the year of 2000. From Sept. 2001 until may 2004, he was a research staff member at the Planète group of INRIA Sophia Antipolis France. Since 2002, he has been active as a voting member at the IEEE 802.11 wireless LAN standard working group. His current research interests include communication protocol design and performance analysis for wireless networks, cross-layer optimizations, vertical handover and mobility management in mobile wireless networks, and adaptive multimedia transmission over hybrid wired/wireless networks. He has authored /co-authored over 40 international journal/conference papers, book chapters, and standard drafts in this field. He is a member of IEEE. E-mail: Qiang.Ni@ieee.org Thierry Turletti received the M.S. (1990) and the Ph.D. (1995) degrees in computer science both from the University of Nice – Sophia Antipolis, France. He has done his PhD studies in the RODEO group at INRIA Sophia Antipolis. During the year 1995–96, he was a postdoctoral fellow in the Telemedia, Networks and Systems group at LCS, MIT. He is currently a research scientist at the Planete group at INRIA Sophia Antipolis. His research interests include multimedia applications, congestion control and wireless networking. Dr. Turletti currently serves on the Editorial Board of Wireless Communications and Mobile Computing.     

无线局域网中的OFDM收发器ASIC及其设计

本文介绍了目前越来越普及的无线局域网中的正交频分复用(Orthogonal Frequency Division Muhiplex)收发器专用集成电路ASIC芯片的设计和实现。在简要综述了应用于无线局域网收发器技术的ASIC结构和工作原理后，着重分析了其基于面向对象的设计方法，并且给出了实际OFDM收发器ASIC设计中需要关注的几个问题。采用C 语言实现的高层次ASIC设计EDA工具，可以对芯片的算法和结构进行快速仿真验证，简化了OFDM收发器等运算密集型ASIC的设计。     

无线局域网的安全策略

阐述了无线局域网的安全标准与方案,对IEEE802.11,IEEE802.11i和GB15629.11等3种方案进行了比较,并对无线局域网安全方案的发展方向提出了见解.     

用于公共无线接入的无线局域网

随着数据业务的不断增长，人们对无线数据业务的要求越来越高。从市场和技术的角度看，速率高、部暑方便且价格低廉的无线局域网(WLAN)公共无线数据接入服务正当其时。首先介绍了用WLAN提供公共无线接入可采用的三种运营模式。讨论了安全性、鉴权与计费、移动性、网络管理、服务质量等提供公共WLAN服务需要进一步考虑的技术问题，分析了移动运营商的实现方法，最后以诺基亚公司的OWLAN技术方案为例分析了网络的结构和组成。     

CDMA蜂窝移动通信系统中基于Eb/No的无线分组公平调度算法

在第三代移动通信的无线资源管理机制中,分组调度机制在保证预期的服务质量（QoS）和优化无线资源的利用率方面起到了至关重要的作用.至今已经有很多的调度算法被提出,用来有效地提高无线网络资源的利用率.本文提出一种基于Eb/No并且利用功率控制和管理机制的无线分组公平调度算法用来保证QoS,优化资源配置并且达到调度公平性.     

Design of Modified Short Backfire Antennas for Millimeter-Waves Wireless LAN Applications

A set of novel modified short backfire antennas are proposed and designed for the application of millimeter-wave wireless LAN systems, by using the FDTD method. By changing the geometrical parameters and feeding structure, the short backfire antennas can generate different kinds of radiation patterns, including narrow pattern, fan-like pattern and conical patterns. Antenna parameters such as reflection bandwidth, input impedance, and far field radiation pattern are presented for each kind of antennas. The proposed different kinds of antennas are suitable for various purposes of wireless LAN applications.     

通信无线资源调度系统设计

为了达到对空间无线电资源的有效管理,提高频谱资源的利用率,在认知用户可以准确获取空间频谱利用情况和无线资源特征的前提下,提出了短时和长期学习的无线资源体统调度模型。根据认知用户对空间某点的无线信号进行特征提取,得到频谱的利用情况和各个信道的特征参数,如调制方式、带宽、中心频率和功率,根据用户的发射机特性,利用层次分析法结合测量的信道参数,给出可用信道的特征参数,以供认知用户参考。长期对某一固定点进行测量记录后根据历史数据进行复合,作为认知用户机特征参数跳变的根据,以给出合理的建议。     

Fair Resource Allocation in Wireless Networks Using Queue-Length-Based Scheduling and Congestion Control

We consider the problem of allocating resources (time slots, frequency, power, etc.) at a base station to many competing flows, where each flow is intended for a different receiver. The channel conditions may be time-varying and different for different receivers. It is well-known that appropriately chosen queue-length based policies are throughput-optimal while other policies based on the estimation of channel statistics can be used to allocate resources fairly (such as proportional fairness) among competing users. In this paper, we show that a combination of queue-length-based scheduling at the base station and congestion control implemented either at the base station or at the end users can lead to fair resource allocation and queue-length stability.     

Opportunistic Fair Scheduling in Wireless Networks: An Approximate Dynamic Programming Approach

We consider the problem of temporal fair scheduling of queued data transmissions in wireless heterogeneous networks. We deal with both the throughput maximization problem and the delay minimization problem. Taking fairness constraints and the data arrival queues into consideration, we formulate the transmission scheduling problem as a Markov decision process (MDP) with fairness constraints. We study two categories of fairness constraints, namely temporal fairness and utilitarian fairness. We consider two criteria: infinite horizon expected total discounted reward and expected average reward. Applying the dynamic programming approach, we derive and prove explicit optimality equations for the above constrained MDPs, and give corresponding optimal fair scheduling policies based on those equations. A practical stochastic-approximation-type algorithm is applied to calculate the control parameters online in the policies. Furthermore, we develop a novel approximation method—temporal fair rollout—to achieve a tractable computation. Numerical results show that the proposed scheme achieves significant performance improvement for both throughput maximization and delay minimization problems compared with other existing schemes.     

浅析无线局域网的主要标准

本文首先介绍了无线局域网(WLAN)在4G通信系统发展中的重要性,其次介绍了由欧洲的ETSI BRAN项目组制定的HiperLAN/2标准和由IEEE 802.11制定的IEEE 802.11a标准,并比较了这两种WLAN标准的异同,最后总结全文.