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.     

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.     

Channel-Aware Scheduling for QoS and Fairness Provisioning in IEEE 802.16/WiMAX Broadband Wireless Access Systems

In the last few years, standardization activities within the IEEE 802.16 Working Group have resulted in the publication of specifications for an air interface of Fixed broadband wireless access systems. WiMAX is the commercial name of products compliant with the approved IEEE 802.16 standard. Although the standard suggests the main principles in designing a QoS architecture to support multimedia broadband services, implementation details are left to manufacturers. This article addresses a channel-aware scheduling algorithm conceived for a point-to-multipoint WiMAX architecture. It aims at enabling downlink traffic delivery with differentiated service treatment, even in nonideal channel conditions. A technique to compensate for channel errors is proposed to preserve QoS and fairness of a WF2Q+ based scheduling algorithm. The performance behavior of the proposed algorithm is confirmed by the outputs of a comprehensive simulation campaign.     

Rake-Based Multiuser Detection for Quasi-Synchronous SDMA Systems

In this letter, a Rake-based multiuser detection technique, consisting of multiuser single-path signal separation, time-delay estimation, and multipath combining, is proposed for quasi-synchronous spatial-division multiple-access (SDMA) systems. Time diversity is achieved for performance improvement. In addition, only the upper bounds of the channel length and the time delays are required. Simulation results verify the effectiveness of the proposed technique, as well as its robustness against overestimation of the maximum channel length and the maximum time delay     

Dynamic Resource Allocation for Downlink Multiuser MIMO-OFDMA/SDMA Systems

In this paper, new dynamic resource allocation algorithms are investigated for the downlink of multiuser multiple-input multiple-output orthogonal frequency-division multiple-access and space-division multiple-access (MU-MIMO-OFDMA/SDMA) systems. Firstly, a mathematical formulation of the optimization problem is presented with the objective of maximizing the total system throughput under the constraints of each user’s quality of service (QoS) requirement and the integer modulation orders available on each spatial subchannel. Secondly, since it is difficult to obtain the optimal solution to the joint optimization problem, the whole optimization procedure is divided into two steps, namely, the subcarrier-user scheduling and the resource allocation. In the first step, a new metric is proposed to measure the spatial compatibility of multiple users, each with multiple receive antennas, based on which a new scheduling algorithm is designed to identify the optimal sets of selected users over all subcarriers. In the second step, two dynamic resource allocation algorithms are developed to assign radio resources to the scheduled users subcarrier by subcarrier. Simulation results demonstrate that the proposed algorithms outperform the traditional allocation methods based on random scheduling scheme. Especially, the performance of the algorithm, combined with power reuse strategy, approaches closely to that of the optimal allocation method based on user selection.     

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。     

Joint Subcarrier and Power Allocation in Channel-Aware Queue-Aware Scheduling for Multiuser OFDM

In an orthogonal frequency division multiplexing (OFDM) downlink scenario, we propose joint subcarrier and power allocation for channel-aware queue-aware scheduling while allowing multiple users to share a single OFDM symbol. Our approach is to combine subcarrier and power allocation by optimizing a user's power allocation immediately after the user has been allocated a subcarrier. Simulation results show that joint subcarrier and power allocation yields a significant performance improvement compared to other existing schemes which perform subcarrier allocation with a fixed (uniform) power allocation assumption. Joint subcarrier and power allocation is also extended to band-wise allocation of subcarriers in order to help reduce signaling overhead in time varying channels. We examine the trade-off between increasing the sub-band size and the corresponding degradation in system performance for different values of the channel multipath delay spread.     

Adaptive Max SNR Packet Scheduling for OFDM Wireless Systems

In this paper, we consider scheduling and resource allocation for a downlink in a wireless OFDM system. If each broadcast sub channel is allocated to a user according to max SNR selection, optimal system throughput is obtained for the cost of a significant loss in fairness among users. As a solution to resolve this issue and in an attempt at reaching a compromise between fairness and throughput, we propose to add to the max SNR scheme a weak control based on user QoS requirements. In this work, user latency between two successive channel accesses is considered as a parameter for the control. The feedback of quantized channel state information (CSI) is proposed to reduce the feedback burden. Performance analysis of the proposed scheme has been presented to illustrate the capacity-fairness-feedback trade-off of the considered scheme compared to max SNR and proportional fair algorithms used as benchmark.

Scheduling Algorithms for Packet-Oriented MAC Protocols in Wireless Multimedia Systems

Future generation wireless multimediacommunications will require efficient Medium AccessControl (MAC) protocols able to guarantee suitable Qualityof Service (QoS) levels for different traffic classes whileachieving a high utilization of radio resources. This paperproposes a new scheduling technique to be adopted at the MAClevel in wireless access systems, named Dynamic Scheduling-Time DivisionDuplexing (DS-TDD), that efficiently managesvideo, voice, Web and background traffics. A theoretical approachis proposed in this paper to evaluate the DS-TDD performance withvoice and Web traffics. Simulation results have permitted tohighlight the following promising characteristics of the DS-TDDscheme: (i) a high capacity of real-time traffics isattained with a QoS insensitive to Web and background trafficloads; (ii) a high throughput can be guaranteed whilepreserving the QoS levels of the different traffic classes;(iii) heavier downlink traffic loads do not modify the QoSof uplink traffics. Finally, extensive comparisons with differentscheduling schemes proposed in the literature have permitted tohighlight the better performanceof DS-TDD.     

Media Synchronization and QoS Packet Scheduling Algorithms for Wireless Systems

Wireless multimedia synchronization is concerned with distributed multimedia packets such as video, audio, text and graphics being played-out onto the mobile clients via a base station (BS) that services the mobile client with the multimedia packets. Our focus is on improving the Quality of Service (QoS) of the mobile client's on-time-arrival of distributed multimedia packets through network multimedia synchronization. We describe a media synchronization scheme for wireless networks, and we investigate the multimedia packet scheduling algorithms at the base station to accomplish our goal. In this paper, we extend the media synchronization algorithm by investigating four packet scheduling algorithms: First-In-First-Out (FIFO), Highest-Priority-First (PQ), Weighted Fair-Queuing (WFQ) and Round-Robin (RR). We analyze the effect of the four packet scheduling algorithms in terms of multimedia packet delivery time and the delay between concurrent multimedia data streams. We show that the play-out of multimedia units on the mobile clients by the base station plays an important role in enhancing the mobile client's quality of service in terms of intra-stream synchronization and inter-stream synchronization. Our results show that the Round-Robin (RR) packet scheduling algorithm is, by far, the best of the four packet scheduling algorithms in terms of mobile client buffer usage. We analyze the four packet scheduling algorithms and make a correlation between play-out of multimedia packets, by the base station, onto the mobile clients and wireless network multimedia synchronization. We clarify the meaning of buffer usage, buffer overflow, buffer underflow, message complexity and multimedia packet delay in terms of synchronization between distributed multimedia servers, base stations and mobile clients.     

A TDMA Approach for OFDM-Based Multiuser RadCom Systems

This paper is focused on the multiuser implementation of fusion of radar and communication(RadCom) in internet-of-vehicles(IoV) scenarios.Traditional time-division multiple access(TDMA)technology degrades the velocity detection performance of orthogonal frequency-division multiplexing(OFDM)-based RadCom systems. We propose a new TDMA approach for OFDM-based RadCom systems, where multiuser communication and radar detection are completed synchronously. We consider a continuous-wave TDMA OFDM struc...     

多用户MIMO-OFDMA系统混合业务的跨层分组调度算法

该文提出了一种针对多输入多输出-正交频分多址系统混合业务的跨层分组调度算法。该算法基于物理层的信道状况和媒体接入控制子层用户的排队时延,分别为实时业务用户和非实时业务用户的排队时延构建相应的效用函数,以保障不同业务的服务需求。仿真结果表明:该算法不但能保证实时业务的时延需要,而且能够获得很好的吞吐量,并满足公平性要求。     

Multiuser MIMO-OFDM for Next-Generation Wireless Systems

This overview portrays the evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station's or radio port's coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment in multiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems.     

A Cross-Layer Delay Differentiation Packet Scheduling Scheme for Multimedia Content Delivery in 3G Satellite Multimedia Systems

The design of efficient packet scheduling algorithms, which play a key role in the radio resource management (RRM), is crucial for the multimedia delivery in the satellite digital multimedia broadcasting (SDMB) system. In this paper, a novel packet scheduling scheme, which uses the cross-layer approach in its design, is proposed. This scheme comprises a new service prioritization algorithm and a dynamic rate matching based resource allocation algorithm, aimed at utilizing both the applications' QoS attributes and the physical layer data rate information. The performance of the proposed scheme has been evaluated via simulation. In comparison with existing schemes, the proposed scheme achieves significant performance gain on delay, delay variation and physical channel utilization.      

Resource Allocation in OFDMA Wireless Communications Systems Supporting Multimedia Services

We design a resource allocation algorithm for downlink of orthogonal frequency division multiple access (OFDMA) systems supporting real-time (RT) and best-effort (BE) services simultaneously over a time-varying wireless channel. The proposed algorithm aims at maximizing system throughput while satisfying quality of service (QoS) requirements of the RT and BE services. We take two kinds of QoS requirements into account. One is the required average transmission rate for both RT and BE services. The other is the tolerable average absolute deviation of transmission rate (AADTR) just for the RT services, which is used to control the fluctuation in transmission rates and to limit the RT packet delay to a moderate level. We formulate the optimization problem representing the resource allocation under consideration and solve it by using the dual optimization technique and the projection stochastic subgradient method. Simulation results show that the proposed algorithm well meets the QoS requirements with the high throughput and outperforms the modified largest weighted delay first (M-LWDF) algorithm that supports similar QoS requirements.     

Delay Aware Link Scheduling for Multi-Hop TDMA Wireless Networks

Time division multiple access (TDMA) based medium access control (MAC) protocols can provide QoS with guaranteed access to the wireless channel. However, in multi-hop wireless networks, these protocols may introduce scheduling delay if, on the same path, an outbound link on a router is scheduled to transmit before an inbound link on that router. The total scheduling delay can be quite large since it accumulates at every hop on a path. This paper presents a method that finds conflict-free TDMA schedules with minimum scheduling delay. We show that the scheduling delay can be interpreted as a cost, in terms of transmission order of the links, collected over a cycle in the conflict graph. We use this observation to formulate an optimization, which finds a transmission order with the min-max delay across a set of multiple paths. The min-max delay optimization is NP-complete since the transmission order of links is a vector of binary integer variables. We devise an algorithm that finds the transmission order with the minimum delay on overlay tree topologies and use it with a modified Bellman-Ford algorithm, to find minimum delay schedules in polynomial time. The simulation results in 802.16 mesh networks confirm that the proposed algorithm can find effective min-max delay schedules.     

基于无线Mesh网络的多目标TDMA调度算法

无线mesh网络的迅速发展使其得到了广泛的应用,此类网络的研究中,MAC层的资源优化问题备受关注.本文就无线mesh网络MAC层的时槽分配调度问题,提出了基于NSGA-Ⅱ算法的CNSGA-Ⅱ算法.理论分析和仿真结果表明该算法所得到的Pareto解集具有较好的相对覆盖率和整体前沿扩展性能,能在能耗和时延两个目标参数之间达到较好的平衡状态.     

Delay Analysis of Packet Scheduling with Multi-Users Diversity in Wireless CDMA Systems

There have been a number of studies that investigate efficient packet scheduling schemes to support quality of service of multiple real-time data users and to increase capacity of non-real-time users sharing a wireless channel. We consider the problem of scheduling transmissions of multiple data users sharing the same wireless channel so as to satisfy delay or throughput and present a general packet scheduling, called MBCS (Multi-users Best Channel Scheduling) which takes advantage of the multi-user diversity of a mobile wireless system. In this paper, a queuing model that represents radio resource management for supporting packet data services is developed for the purpose of evaluating the performance of wireless CDMA systems. Numerical results show that delay performance of the proposed scheduler is higher than that of the Single-user Best Channel Scheduler (SBCS) depending on the time-varying channel status.Sungkyung Kim is a Ph. D. student in the collage of information & Communications at University of Korea, Seoul, Korea. She received her B.S. and M.S. degree in electrical engineering from Korea University in 1999 and in 2001, respectively. From March 2001 to August 2004, she worked at the Electronics Telecommunications Research Institute, Daejeon, Korea, as a member of research engineer. Her research interests include MAC protocol, radio resource control, packet scheduling, and system performance evaluation at system level in wireless access networks.Chung Gu Kang received his B.S. degree in Electrical Engineering from the University of California, San Diego in 1987 and his M.S. and Ph.D. degrees both in Electrical and Computer Engineering from the University of California, Irvine, in 1989 and 1993, respectively. While working on his Ph.D. dissertation from June 1991 to May 1992, he also was with the Aerospace Corporation in El Segundo, California, as a part-time member of technical staff (MTS). After graduation in 1993, he joined Rockwell International in Anaheim, California, where he has been working on the signaling system no. 7 and other telecommunication systems development. Since March 1994, he has been with College of Information & Communications at the Korea University, Seoul, Republic of Korea, as a full professor. His research interests include next generation mobile radio communication system and broadband wireless networks, with special emphasis on physical layer/medium access control layer design and performance analysis. During the academic year of 2000, he has been a visiting scholar at Center for Wireless Communication and also a visiting professor at Department of Electrical & Computer Engineering in University of California at San Diego (UCSD). He is a member of IEEE COMSOC, IT, and VT, and a member of KICS and KITE.     

A Service Differentiated MAC Protocol for OFDM/TDMA Wireless Systems

1IntroductionAkey goal to achievein next generation wireless net-works is to develop an efficient method to allocate thescarce bandwidth resources among users of differenttypes of traffic in a wireless multi media network. Theentityincharge of performingthat taskisthe MACpro-tocol , which must be able to support various classes oftraffic while guaranteeing their required Quality of Ser-vice (QoS) .Ref .[1] proposes a MACprotocol for ultrahigh-speed radio access system. The new protocol isb…     

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。