Quality-driven cross-layer optimized video delivery over LTE

3GPP Long Term Evolution is one of the major steps in mobile communication to enhance the user experience for next-generation mobile broadband networks. In LTE, orthogonal frequency- division multiple access is adopted in the downlink of its E-UTRA air interface. Although cross-layer techniques have been widely adopted in literature for dynamic resource allocation to maximize data rate in OFDMA wireless networks, application-oriented quality of service for video delivery, such as delay constraint and video distortion, have been largely ignored. However, for wireless video delivery in LTE, especially delay-bounded real-time video streaming, higher data rate could lead to higher packet loss rate, thus degrading the user-perceived video quality. In this article we present a new QoS-aware LTE OFDMA scheduling algorithm for wireless real-time video delivery over the downlink of LTE cellular networks to achieve the best user-perceived video quality under the given application delay constraint. In the proposed approach, system throughput, application QoS constraints, and scheduling fairness are jointly integrated into a cross-layer design framework to dynamically perform radio resource allocation for multiple users, and to effectively choose the optimal system parameters such as modulation and coding scheme and video encoding parameters to adapt to the varying channel quality of each resource block. Experimental results have shown significant performance enhancement of the proposed system.     

Efficient Traffic Scheduling for Real Time VBR MPEG Video Transmission Over DOCSIS-Based HFC Networks

Data-over-cable service interface specifications (DOCSIS), the de facto standard in the cable industry, defines a scheduling service called real-time polling service (rtPS) to provision quality of service (QoS) transmission of real-time variable bit rate (VBR) videos. However, the rtPS service intrinsically has high latency, which makes it not applicable to real-time traffic transport. In this paper, we present a novel traffic scheduling algorithm for hybrid fiber coax (HFC) networks based on DOCSIS that aims to provide QoS for real-time VBR video transmissions. The novel characteristics of this algorithm, as compared to those described in published literatures, include 1) it predicts the bandwidth requirements for future traffic using a novel traffic predictor designed to provide simple yet accurate online prediction; and 2) it takes the attributes of physical (PHY) layer, media access control (MAC) layer and application layer into consideration. In addition, the proposed traffic scheduling algorithm is completely compatible with the DOCSIS specification and does not require any protocol changes. We analyze the performance of the proposed traffic predictor and traffic scheduling algorithm using real-life MPEG video traces. Simulation results indicate that 1) the proposed traffic predictor significantly outperforms previously published techniques with respect to the prediction error and 2) Compared with several existing scheduling algorithms, the proposed traffic scheduling algorithm surpasses other mechanisms in terms of channel utilization, buffer usage, packet delay, and packet loss rate.     

Impacts of Radio Channel Characteristics, Heterogeneous Traffic Intensity, and Near–Far Effect on Rate Adaptive Scheduling Algorithms

Applying adaptive modulation combined with scheduling in a shared data channel can substantially improve the spectral efficiency for wireless systems. This performance gain results from the multiuser diversity, which exploited independent channel variations across multiple users. In this paper, we present a cross-layer analysis to integrate physical-layer channel characteristics, media access control (MAC) layer scheduling strategies, and the network layer issue of heterogeneous traffic intensity across near–far users. Specifically, for radio channel characteristics, we take account of path loss, slowly varying log-normal shadowing and fast-varying Nakagami fading. We also evaluate the impact of selective transmit diversity on the throughput and fairness of wireless data networks. Furthermore, we consider three MAC schedulers: random scheduler, greedy scheduler (GS), and a newly proposed queue-length-based scheduler (QS). By applying the proposed cross-layer analytical framework, the following insights can be gained. First, for the three considered schedulers, channel fluctuations induced by Nakagami fading or log-normal shadowing can improve both total throughput and fairness. Second, using selective transmit diversity can improve throughput, but is unfavorable for the fairness performance. Third, the GS and the QS methods can improve throughput at the expense of unfairness to the far users. However, the throughput improvement from using the GS and the QS decreases as the traffic intensity of the far user increases. In summary, this cross-layer analysis can be used to develop new scheduling mechanisms for achieving better tradeoff between the fairness and throughput for wireless data networks.     

A Cross-Layer Packet Scheduling Scheme for Multimedia Broadcasting via Satellite Digital Multimedia Broadcasting System [Advances in Mobile Multimedia]

In recent years, multimedia content broadcasting via satellite has attracted increased attention. The satellite digital multimedia broadcasting (S-DMB) system has emerged as one of the most promising alternatives for the efficient delivery of multimedia broadcast multicast service (MBMS). The design of an efficient radio resource management (RRM) strategy, especially the packet scheduling scheme, becomes a key technique for provisioning multimedia services at required quality of service (QoS) in S-DMB. In this article, we propose a novel cross-layer packet scheduling scheme that consists of a combined delay and rate differentiation (CDRD) service prioritization algorithm and a dynamic rate matching (DRM)-based resource allocation algorithm. The proposed scheme considers multiple key factors that span from the application layer to the physical layer, aiming at simultaneously guaranteeing diverse QoS while utilizing radio resources efficiently under the system power and resource constraints. Simulation results demonstrate that the proposed cross-layer scheme achieves significantly better performance than existing schemes in queuing delay, jitter, and channel utilization.     

A Unified Approach to QoS-Guaranteed Scheduling for Channel-Adaptive Wireless Networks

Scheduling amounts to allocating optimally channel, rate and power resources to multiple connections with diverse quality-of-service (QoS) requirements. It constitutes a throughput-critical task at the medium access control layer of today's wireless networks that has been tackled by seemingly unrelated information-theoretic and protocol design approaches. Capitalizing on convex optimization and stochastic approximation tools, the present paper develops a unified framework for channel-aware QoS-guaranteed scheduling protocols for use in adaptive wireless networks whereby multiple terminals are linked through orthogonal fading channels to an access point, and transmissions are (opportunistically) adjusted to the intended channel. The unification encompasses downlink and uplink with time-division or frequency-division duplex operation; full and quantized channel state information comprising a few bits communicated over a limited-rate feedback channel; different types of traffic (best effort, non-real-time, real-time); uniform and optimal power loading; off-line optimal scheduling schemes benchmarking fundamentally achievable rate limits; as well as on-line scheduling algorithms capable of dynamically learning the intended channel statistics and converging to the optimal benchmarks from any initial value. The take-home message offers an important cross-layer design guideline: judiciously developed, yet surprisingly simple, channel-adaptive, on-line schedulers can approach information-theoretic rate limits with QoS guarantees.     

Multi-channel-based scheduling for overlay inband device-to-device communications

In this paper, we consider the problem of distributed scheduling for overlay inband device-to-device (D2D) communication systems that employ an orthogonal frequency division multiple access physical layer technology. To improve the spatial reuse gain, we propose a multi-channel-based scheduling algorithm that divides the overall radio resource dedicated to D2D communication into multiple data channels and schedules the links allocated to each channel based on a signal-to-interference-aware priority-based scheduling method. Further, we develop a cross-layer queueing model to analyze the medium-access-control layer performance of the proposed scheduling algorithm and compare the analytic results with the simulation results. We demonstrate that the proposed scheduling algorithm outperforms the existing single one-channel-based algorithm to provide lower packet dropping probability, higher spectral efficiency, and lower packet delay.     

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.     

A cross-layer design of wireless IP systems using effective bandwidth and MQAM adaptive modulation

In this paper, we introduce an effective bandwidth-based call admission control (CAC) with adaptive modulation technique to manage the traffic in a wireless IP-based network. Furthermore, in order to efficiently use the physical resources of the network, we take advantage of an adaptive MQAM (M-ary quadrature amplitude modulation) to match transmission rates to the time-varying channel conditions. This cross-layer architecture has been examined for the self-similar traffic model. The results show that by simultaneous implementation of the effective bandwidth algorithm in the data-link layer and adaptive modulation technique in the physical layer, the performance of the wireless network in terms of the number of rejected calls and system throughput improves.     

Asymptotic loss of real-time traffic in wireless mobile networks with selective-repeat ARQ

We study the issue of quality of service (QoS) for real-time traffic over a wireless channel deploying automatic repeat request (ARQ) error control. An analytical model has been derived to evaluate the queueing related loss and the wireless channel related loss. In contrast to previous work, this model quantifies the interaction between the network layer and the physical layer, and then it enables the admission controllers of wireless networks to improve utilization while satisfying the traffic QoS constraints through cross-layer design techniques.     

A Tutorial on Cross-Layer Optimization in Wireless Networks

This tutorial paper overviews recent developments in optimization-based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channel-aware) scheduling for cellular (single-hop) networks, where easily implementable myopic policies are shown to optimize system performance. We then describe key lessons learned and the main obstacles in extending the work to general resource allocation problems for multihop wireless networks. Towards this end, we show that a clean-slate optimization-based approach to the multihop resource allocation problem naturally results in a “loosely coupled” cross-layer solution. That is, the algorithms obtained map to different layers [transport, network, and medium access control/physical (MAC/PHY)] of the protocol stack, and are coupled through a limited amount of information being passed back and forth. It turns out that the optimal scheduling component at the MAC layer is very complex, and thus needs simpler (potentially imperfect) distributed solutions. We demonstrate how to use imperfect scheduling in the cross-layer framework and describe recently developed distributed algorithms along these lines. We conclude by describing a set of open research problems.     

An adaptive cross-layer mapping algorithm for MPEG-4 video transmission over IEEE 802.11e WLAN

This paper proposes an adaptive cross-layer mapping algorithm to improve the transmission quality of MPEG-4 video stream over an IEEE 802.11e wireless network. Instead of classifying video data to a specific access category in an 802.11e network, we propose an algorithm that dynamically maps MPEG-4 video packets to appropriate access categories according to both the significance of the video data and the network traffic load. Our proposed cross-layer architecture passes information about the significance of video packets from the application layer to the media access control layer. The queue length of a specific access category is used to deduce the network traffic load. We conducted a performance evaluation of our proposed cross-layer approach under both light and heavily loaded network conditions. Our simulation results demonstrate: (a) superior performance of our proposed approach (under both light and heavy loads) over 802.11e (Enhanced Distributed Channel Access (EDCA) and static mapping schemes, (b) not only guarantees prioritized transmission of essential video data but also provides efficient queue length utilization.     

A Low-Complexity QoS-Aware Proportional Fair Multicarrier Scheduling Algorithm for OFDM Systems

Orthogonal frequency-division multiplexing (OFDM) systems are the major cellular platforms for supporting ubiquitous high-speed mobile applications. However, a number of research challenges remain to be tackled. One of the most important challenges is the design of a judicious packet scheduler that will make efficient use of the spectrum bandwidth. Due to the multicarrier nature of the OFDM systems, the applicability and performance of traditional wireless packet-scheduling algorithms, which are usually designed for single-carrier systems, are largely unknown. In this paper, we propose a new quality-of-service (QoS)-aware proportional fairness (QPF) packet-scheduling policy with low complexity for the downlink of multiuser OFDM systems to allocate radio resources among users. Our proposed algorithm is based on a cross-layer design in that the scheduler is aware of both the channel (i.e., physical layer) and the queue state (i.e., data link layer) information to achieve proportional fairness while maximizing each user's packet-level QoS performance. The simulation results show that the proposed QPF algorithm is efficient in terms of average system throughput, packet-dropping probability, and packet delay, while maintaining adequate fairness among users with relatively low scheduling overhead.      

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.      

Optimized video streaming over 802.11 by cross-layer signaling

Seamless video streaming over wireless links imposes strong demands on video codecs and the underlying network. It is not sufficient that only the video codec or only the radio adapts to changes in the wireless link quality; efforts should be applied in both layers, and - if possible - synchronized. Also, the disturbing effect of possible background traffic over the same shared medium has to be taken into account. In this article we present a communication architecture for video streaming over 802.11 that is capable of adapting to changes in the link quality and sharing of the wireless channel in various use scenarios. Experimental results show that substantial improvements in the quality of the video can be obtained by applying link adaptation and cross-layer signaling techniques.     

Adaptive cross-layer protection strategies for robust scalable video transmission over 802.11 WLANs

Robust streaming of video over 802.11 wireless local area networks poses many challenges, including coping with bandwidth variations, data losses, and heterogeneity of the receivers. Currently, each network layer (including physical layer, media access control (MAC), transport, and application layers) provides a separate solution to these challenges by providing its own optimized adaptation and protection mechanisms. However, this layered strategy does not always result in an optimal overall performance for the transmission of video. Moreover, certain protection strategies can be implemented simultaneously in several layers and, hence, the optimal choices from the application and complexity perspective need to be identified. In this paper, we evaluate different error control and adaptation mechanisms available in the different layers for robust transmission of video, namely MAC retransmission strategy, application-layer forward error correction, bandwidth-adaptive compression using scalable coding, and adaptive packetization strategies. Subsequently, we propose a novel adaptive cross-layer protection strategy for enhancing the robustness and efficiency of scalable video transmission by performing tradeoffs between throughput, reliability, and delay depending on the channel conditions and application requirements. The results obtained using the proposed adaptive cross-layer protection strategies show a significantly improved visual performance for the transmitted video over a variety of channel conditions.     

Tracking in Wireless Sensor Networks Using Particle Filtering: Physical Layer Considerations

In this paper, a new framework for target tracking in a wireless sensor network using particle filters is proposed. Under this framework, the imperfect nature of the wireless communication channels between sensors and the fusion center along with some physical layer design parameters of the network are incorporated in the tracking algorithm based on particle filters. We call this approach ldquochannel-aware particle filtering.rdquo Channel-aware particle filtering schemes are derived for different wireless channel models and receiver architectures. Furthermore, we derive the posterior Cramer-Rao lower bounds (PCRLBs) for our proposed channel-aware particle filters. Simulation results are presented to demonstrate that the tracking performance of the channel-aware particle filters can reach their theoretical performance bounds even with relatively small number of sensors and they have superior performance compared to channel-unaware particle filters.     

Scheduling as an important cross-layer operation for emerging broadband wireless systems

Cross-layer scheduling is a promising solution for improving the efficiency of emerging broadband wireless systems. In this tutorial, various cross-layer design approaches are organized into three main categories namely air interface-centric, user-centric and route-centric and the general characteristics of each are discussed. Thereafter, by focusing on the air interfacecentric approach, it is shown that the resource allocation problem can be formulated as an optimization problem with a certain objective function and some particular constraints. This is illustrated with the aid of a customer-provider model from the field of economics. Furthermore, the possible future evolution of scheduling techniques is described based on the characteristics of traffic and air interface in emerging broadband wireless systems. Finally, some further challenges are identified.     

A Dynamic Resource Allocation Scheme for the Downlink Heterogeneous Traffic of Internet Protocol (IP) Based OFDM networks

Radio Resource management mechanisms such as physical-centric radio resource allocation and medium access control (MAC)—centric packet scheduling are expected to play a substantial role in the performance of orthogonal frequency division multiplexing (OFDM) based wireless networks. OFDM provide fine granularity for resource allocation since they are capable of dynamically assigning sub-carriers to multiple users and adaptively allocating transmit power. The current layered networking architecture, in which each layer is designed and operated independently, results in inefficient resource use in wireless networks due to the nature of the wireless medium, such as time-varying channel fading. Thus, we need an integrated adaptive design across different layers, allowing for a cross-layer design. In this paper, a scheduling scheme is proposed to dynamically allocate resources for the downlink data transmission of internet protocol based OFDM networks. Generally to maximize the capacity and user satisfaction improvements in packet data admission, scheduling and policing are necessary. Of the three, efficient scheduling has the greatest impact on increased system capacity or effective spectrum usage. In addition, proper scheduling can greatly improve user satisfaction. The contribution of this work is twofold: first we evaluate current allocation schemes by exploiting the knowledge of channel sate information (CSI) and traffic characteristics in terms of queue state information (QSI) to acquire the system performance on a real time network. Second, the resource allocation scheme is extended by incorporating MAC layer information as well as opportunistic packet scheduling in the time-domain-based on minimum weight cost function. The key factors that affect the overall system performance in terms of system average throughput and delay are identified, evaluated and discussed.     

一种适用于W-CDMA系统的多业务无线资源调度算法

3G系统将以分组交换方式提供语音、数据、视频等具有不同QoS要求的多种业务，资源调度对保证系统服务质量和提高资源利用效率起关键作用．本文提出了一种基于业务类型、当前待发送负荷以及剩余延时限的时间调度策略和基于资源优化的资源调度策略，并使无线链路的传输质量与业务的优先级水平一致．通过系统仿真评价了算法的性能．     

QoS-, Queue-and Channel-Aware Packet Scheduling for Multimedia Services in Multiuser SDMA/TDMA Wireless Systems

With the growing demand for wireless multimedia services and continuing emergence of new multimedia applications, it is necessary for the network to provide various levels of quality of service (QoS) while maximizing the utilization of channel resources. This paper presents an adaptive queuing model and a novel cross-layer packet scheduling algorithm for providing differentiated QoS and effective channel utilization in a space-division-multiple-access/time-division-multiple-access (SDMA/TDMA) system. At the medium access control (MAC) layer, we take into consideration the heterogeneous and bursty nature of multimedia traffic and provide for QoS requirements. At the physical (PHY) layer, we exploit the randomness of the physical channel by incorporating opportunistic scheduling and adopting adaptive modulation and coding (AMC). Performance results obtained by simulations show that by employing the proposed queuing model and packet scheduling algorithm, the system is able to provide for diverse QoS and achieve high throughput.