Cross-layer Scheduling Algorithms for IEEE 802.16 Based Wireless Mesh Networks

Wireless mesh network (WMN) is emerging as an important networking architecture for future wireless communications. The mesh mode supported in IEEE 802.16 protocol provides a TDMA solution for WMN, in which scheduling is an important issue. In this paper, we discuss the issues on how to satisfy a set of bandwidth requests in IEEE 802.16 WMNs using minimal radio resources (or solving minimal schedule length problem). In consideration of transmission overhead and adaptive modulation and coding (AMC), two cross-layer scheduling algorithms are proposed, namely max-transmission and priority-based algorithms. In particular, they are proposed based on a physical interference model, instead of a protocol interference model as suggested in the literature. For the priority-based algorithm, we study several priority criteria based on different cross-layer information. An iterative scheme for QoS traffic is introduced to guarantee fairness when traffic load exceeds the network capacity. Simulation results show that our algorithms outperform the existing schemes based on protocol model, and they also ensure better fairness among different nodes.     

IEEE 802.16/WiMAX-based broadband wireless access and its application for telemedicine/e-health services

In this article we investigate the application of IEEE 802.16-based broadband wireless access (BWA) technology to telemedicine services and the related protocol engineering issues. An overview of the different evolutions of the IEEE 802.16 standard is presented and some open research issues are identified. A survey on radio resource management, traffic scheduling, and admission control mechanisms proposed for IEEE 802.16/WiMAX systems is also provided. A qualitative comparison between third-generation wireless systems and the IEEE 802.16/WiMAX technology is given. A survey on telemedicine services using traditional wireless systems is presented. The advantages of using IEEE 802.16/WiMAX technology over traditional wireless systems, as well as the related design issues and approaches are discussed. To this end, we present a bandwidth allocation and admission control algorithm for IEEE 802.16-based BWA designed specifically for wireless telemedicine/e-health services. This algorithm aims at maximizing the utilization of the radio resources while considering the quality of service requirements for telemedicine traffic. Some performance evaluation results for this scheme are obtained by simulations     

Wireless cars: A cyber-physical approach to vehicle dynamics control

A non-conventional drive-by-wireless technology for guidance and control of a redundantly actuated electric car supported by an on-board wireless network of sensors, actuators and control units is proposed in this article. Several optimization-based distributed feedforward control schemes are developed for such powertrain infrastructures. In view of the limitations of the commercial off-the-shelf wireless communication technologies and the harshness of the in-vehicle environments, a pressing design and implementation aspect, in addition to the robustness against information loss, refers to fulfilling the hard real-time computational requirements. In this work, we address such problems by introducing several distributed event-based control schemes in conjunction with adaptive scheduling at the protocol level. Hereby we obtain a simple tuning mechanism to compromise between the outcome accuracy and computation efficiency (i.e., communication traffic intensity). Using simulative evaluations, we demonstrate the viability of the proposed algorithms and illustrate the impact of external interferences in an IEEE 802.15.4 based wireless communication solution.     

MiFi: a framework for fairness and QoS assurance for current IEEE 802.11 networks with multiple access points

In this paper, we present a framework for providing fair service and supporting quality of service (QoS) requirements in IEEE 802.11 networks with multiple access points (APs). These issues becomes critical as IEEE 802.11 wireless LAN are widely deployed in nationwide networks, linking tens of thousands of "hot-spots" for providing both real-time (voice) and non real-time (data) services to a large population of mobile users. However, both fairness and QoS guarantees cannot be supported in the current 802.11 standard. Our system, termed MiFi, relies on centralized coordination of the APs. During any given time of the "contention-free" period only a set of non-interfering APs is activated while the others are silenced. Moreover, the amount of service granted to an AP is proportional to its load and the system's performance is optimized by employing efficient scheduling algorithms. We show that such a system can be implemented without requiring any modification of the underlying MAC protocol standard or the behavior of the mobile stations. Our scheme is complementary to the emerging 802.11e standard for QoS and guarantees to overcome the hidden node and the overlapping cell problems. Our simulations establish that the system supports fairness and hence can provide QoS guarantees for real-time traffic, while maintaining a relative high throughput.     

Providing Real-Time Service in CDMA Wireless Networks

Medium Access Control (MAC) protocol design plays a very important role in the design of wireless networks. In this paper, we propose a new MAC protocol to provide real-time service for a CDMA wireless network. This protocol has been designed based on the distributed queuing random access protocol for CDMA wireless networks (DQRAP/CDMA). As real-time scheduling schemes have been introduced into the protocol design, the new protocol has an ability to accommodate real-time traffic in the CDMA wireless networks. A series of simulation experiments have been carried out to evaluate the performance of the proposed protocol. The results reveal that the proposed protocol can efficiently provide real-time service to the traffic composed of time constrained messages in the CDMA wireless networks.     

A bandwidth allocation/sharing/extension protocol for multimediaover IEEE 802.11 ad hoc wireless LANs

We propose a novel bandwidth allocation/sharing/extension (DBASE) protocol to support both asynchronous traffic and multimedia traffic with the characteristics of variable bit rate (VBR) and constant bit rate (CBR) over IEEE 802.11 ad hoc wireless local area networks. The overall quality of service (QoS) will be guaranteed by DBASE. The designed DBASE protocol will reserve bandwidth for real-time stations based on a fair and efficient allocation. Besides, the proposed DBASE is still compliant with the IEEE 802.11 standard. The performance of DBASE is evaluated by analysis and simulations. Simulations show that the DBASE is able to provide almost 90% channel utilization and low packet loss due to delay expiry for real-time multimedia services     

Infrastructure-based MAC in wireless mobile ad-hoc networks

The IEEE 802.11 standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in an ad-hoc environment, the Point Coordination Function (PCF), defined in the standard, cannot be readily used. This is due to the fact that there is no central authority to act as a Point Coordinator (PC). Peer-to-peer ad-hoc mode in the IEEE 802.11 standard only implements the Distributed Coordination Function (DCF). In this paper, an efficient and on-the-fly infrastructure is created using our proposed Mobile Point Coordinator (MPC) protocol. Based on this protocol, we also develop an efficient MAC protocol, namely MPC–MAC. Our MAC protocol extends the IEEE 802.11 standard for use in multi-hop wireless ad-hoc networks implementing both the DCF and PCF modes of operation. The goal, and also the challenge, is to achieve QoS delivery and priority access for real-time traffic in ad-hoc wireless environments while maintaining backward compatibility with the IEEE 802.11 standard. The performance of MPC–MAC is compared to the IEEE 802.11 DCF-based MAC without MPC. Simulation experiments show that in all cases the use of PCF benefits real-time packets by decreasing the average delay and the discard ratio. However, this may come at the expense of increasing the average delay for non-real-time data. On the other hand, the discard ratio for both real-time and non-real-time packets improves with the use of PCF. Therefore, our MPC–MAC outperforms the standard DCF IEEE 802.11 MAC protocol in multi-hop ad-hoc environments.     

E‐MAC: an elastic MAC layer for IEEE 802.11 networks

We present a system for real‐time traffic support in infrastructure and ad hoc IEEE 802.11 networks. The proposed elastic MAC (E‐MAC) protocol provides a distributed transmission schedule for stations with real‐time traffic requirements, while allowing a seamless coexistence with standard IEEE 802.11 clients, protecting best‐effort 802.11 traffic from starvation by means of admission control policies. Our scheduling decisions are based on an ‘elastic’ transmission opportunity (TXOP) assignment which allows for efficient wireless resource usage: whenever a real‐time station does not use the assigned TXOP, the other real‐time stations can take over the unused access opportunity, thus preventing the well‐known inefficiencies of static time division multiple access (TDMA) schemes. Unlike other TDMA‐based solutions for 802.11, E‐MAC does not require a tight synchronization among the participating clients, thus allowing its implementation on commodity WLAN hardware via minor software changes at the client side, and no changes at the access points (APs). We studied the performance of our mechanism via ns‐2 simulations and a mathematical model, showing that it outperforms IEEE 802.11e in terms of throughput, delay, and jitter. We finally provide a proof of concept through the results obtained in a real testbed where we implemented the E‐MAC protocol. Copyright © 2011 John Wiley & Sons, Ltd.     

Improving protocol capacity for UDP/TCP traffic with model-based frame scheduling in IEEE 802.11-operated WLANs

In this paper, we develop a model-based frame scheduling scheme, called MFS, to enhance the capacity of IEEE 802.11-operated wireless local area networks (WLANs) for both transmission control protocol (TCP) and user datagram protocol (UDP) traffic. In MFS each node estimates the current network status by keeping track of the number of collisions it encounters between its two consecutive successful frame transmissions, and computes accordingly the current network utilization. The result is then used to determine a scheduling delay to be introduced before a node attempts to transmit its pending frame. MFS does not require any change in IEEE 802.11, but instead lays a thin layer between the LL and medium access control (MAC) layers. In order to accurately calculate the current utilization in WLANs, we develop an analytical model that characterizes data transmission activities in IEEE 802.11-operated WLANs with/without the request to send/clear to send (RTS/CTS) mechanism, and validate the model with ns-2 simulation. All the control overhead incurred in the physical and MAC layers, as well as system parameters specified in IEEE 802.11, are figured in. We conduct a comprehensive simulation study to evaluate MFS in perspective of the number of collisions, achievable throughput, intertransmission delay, and fairness in the cases of TCP and UDP traffic. The simulation results indicate that the performance improvement with respect to the protocol capacity in a WLAN of up to 300 nodes is 1) as high as 20% with the RTS/CTS and 70% without the RTS/CTS in the case of UDP traffic and 2) as high as 10% with the RTS/CTS and 40% without the RTS/CTS in the case of TCP traffic. Moreover, the intertransmission delay in MFS is smaller and exhibits less variation than that in IEEE 802.11; the fairness among wireless nodes in MFS is better than, or equal to, that in IEEE 802.11.     

Sticky CSMA/CA: Implicit synchronization and real-time QoS in mesh networks

We propose a novel approach to QoS for real-time traffic over wireless mesh networks, in which application layer characteristics are exploited or shaped in the design of medium access control. Specifically, we consider the problem of efficiently supporting a mix of Voice over IP (VoIP) and delay-insensitive traffic, assuming a narrowband physical layer with CSMA/CA capabilities. The VoIP call carrying capacity of wireless mesh networks based on classical CSMA/CA (e.g., the IEEE 802.11 standard) is low compared to the raw available bandwidth, due to lack of bandwidth and delay guarantees. Time Division Multiplexing (TDM) could potentially provide such guarantees, but it requires fine-grained network-wide synchronization and scheduling, which are difficult to implement. In this paper, we introduce Sticky CSMA/CA, a new medium access mechanism that provides TDM-like performance to real-time flows without requiring explicit synchronization. We exploit the natural periodicity of VoIP flows to obtain implicit synchronization and multiplexing gains. Nodes monitor the medium using the standard CSMA/CA mechanism, except that they remember the recent history of activity in the medium. A newly arriving VoIP flow uses this information to grab the medium at the first available opportunity, and then sticks to a periodic schedule, providing delay and bandwidth guarantees. Delay-insensitive traffic fills the gaps left by the real-time flows using novel contention mechanisms to ensure efficient use of the leftover bandwidth. Large gains over IEEE 802.11 networks are demonstrated in terms of increased voice call carrying capacity (more than 100% in some cases). We briefly discuss extensions of these ideas to a broader class of real-time applications, in which artificially imposing periodicity (or some other form of regularity) at the application layer can lead to significant enhancements of QoS due to improved medium access.     

Performance Evaluation of the IEEE 802.16 MAC for QoS Support

The IEEE 802.16 is a standard for broadband wireless communication in metropolitan area networks (MAN). To meet the QoS requirements of multimedia applications, the IEEE 802.16 standard provides four different scheduling services: unsolicited grant service (UGS), real-time polling service (rtPS), non-real-time polling service (nrtPS), and Best Effort (BE). The paper is aimed at verifying, via simulation, the effectiveness of rtPS, nrtPS, and BE (but UGS) in managing traffic generated by data and multimedia sources. Performance is assessed for an IEEE 802.16 wireless system working in point-to-multipoint (PMP) mode, with frequency division duplex (FDD), and with full-duplex subscriber stations (SSs). Our results show that the performance of the system, in terms of throughput and delay, depends on several factors. These include the frame duration, the mechanisms for requesting uplink bandwidth, and the offered load partitioning, i.e., the way traffic is distributed among SSs, connections within each SS, and traffic sources within each connection. The results also highlight that the rtPS scheduling service is a very robust scheduling service for meeting the delay requirements of multimedia applications     

Provisioning of Parameterized Quality of Service in 802.11e Based Wireless Mesh Networks

There has been a growing interest in the use of wireless mesh networks. Today’s wireless technology enables very high data rate up to hundreds of Megabits per second, which creates the high demand of supporting real-time multimedia applications over wireless mesh networks. Hence it is imperative to support quality of service (QoS) in wireless mesh networks. In this paper, we design a framework to provide parameterized QoS in 802.11e based wireless mesh networks. Our framework consists of admission control algorithms and scheduling algorithms, which aim at supporting constant bit-rate (CBR) traffic flows, as well as variable bit-rate (VBR) traffic flows. We first present deterministic end-to-end delay bounds for CBR traffic. We then prove that the delay of VBR traffic can be bounded if the traffic flow conforms to a leaky-bucket regulator. We further study different admission control algorithms for VBR traffic. Our simulation results show that, by taking advantage of statistical multiplexing, much more traffic flows can be admitted.     

A Dynamic Adaptation Mechanism for Traffic Conditions in Wireless Sensor Network

As overall network traffic pursue to expand, a lot of low-power medium access control protocols have been proposed to deal with burst traffic in wireless sensor network. Although most of them provide low throughput but do not well optimize the energy consumption. In this paper, we propose a new hybrid carrier sense multiple access with collision avoidance (CSMA/CA) and time division multiple access (TDMA) protocol that arranges nodes into two categories of priority according to their traffic rate and data transmission delay. Nodes that have continuous data should send its data during the contention free period, those one will be classified as low priority and its data will be scheduling using TDMA. Others nodes who have a random data should transmit it immediately during the contention access period (CAP) using a fuzzy logic algorithm, based on their queue length and implemented in the CSMA/CA algorithm. Therefore, the proposed scheme dynamically changes the CAP length to ensure that nodes can complete its transaction during the same super-frame. Simulation results are done using the network simulator tools (NS-2) and have improved good efficiency regarding the IEEE 802.15.4 standard. The mechanism has improved the energy consumption, minimised the packet loss probability, increased the throughput variation in the network and also minimised the average end to end delay.     

Scheduler for IEEE 802.16 networks

The IEEE 802.16 standard was designed to support real-time and bandwidth demanding applications with quality of service (QoS). Although the standard defines a QoS signaling framework and five service levels, scheduling disciplines for these service levels are unspecified. In this paper, we propose a scheduling scheme for the uplink traffic which is fully standard-compliant and can be easily implemented in the base station. Simulation results show that this scheme is able to meet the QoS requirements of the service flows.     

Dynamic bandwidth management in IEEE 802.11-based multihop wireless networks

In this paper, we propose a new protocol named dynamic regulation of best-effort traffic (DRBT) which supports quality of service (QoS) throughput guarantees and provides a distributed regulation mechanism for best-effort traffic in multihop wireless networks. By adapting dynamically the rate of best-effort traffic at the link layer, DRBT increases the acceptance ratio of QoS flows and provides a good use of the remaining resources through the network. Our protocol also provides an accurate method to evaluate the available bandwidth in IEEE 802.11-based ad hoc networks which is able to differentiate QoS applications from best-effort traffic. Through extensive simulations, we compare the performance of our proposal scheme with some others protocols like QoS protocol for ad hoc real-time traffic for instance.     

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.     

Busy tone contention protocol: a new high‐throughput and energy‐efficient wireless local area network medium access control protocol using busy tone

Design of an efficient wireless medium access control (MAC) protocol is a challenging task due to the time‐varying characteristics of wireless communication channel and different delay requirements in diverse applications. To support variable number of active stations and varying network load conditions, random access MAC protocols are employed. Existing wireless local area network (WLAN) protocol (IEEE 802.11) is found to be inefficient at high data rates because of the overhead associated with the contention resolution mechanism employed. The new amendments of IEEE 802.11 that support multimedia traffic (IEEE 802.11e) are at the expense of reduced data traffic network efficiency. In this paper, we propose a random access MAC protocol called busy tone contention protocol (BTCP) that uses out‐of‐band signals for contention resolution in WLANs. A few variants of this protocol are also proposed to meet the challenges in WLAN environments and application requirements. The proposed BTCP isolate multimedia traffics from background data transmissions and gives high throughput irrespective of the number of contending stations in the network. As a result, in BTCP, admission control of multimedia flows becomes simple and well defined. Studies of the protocol, both analytically and through simulations under various network conditions, have shown to give better performance in comparison with the IEEE 802.11 distributed coordination function. Copyright © 2011 John Wiley & Sons, Ltd.     

HSDPA系统中一种感知用户终端缓存状态的QoE保障调度算法

针对HSDPA系统中现有调度算法无法满足实时业务QoE的缺点,提出一种保障实时业务QoE的调度算法。该算法根据用户反馈的信道质量信息和在基站获取到的用户终端缓存状况信息。确定用户的优先级并据此调度优先级最高的用户,进而保证实时业务的吞吐量和QoE需求。仿真结果表明,与轮询调度算法、比例公平调度算法相比,提出的调度算法不仅能够保证实时业务的QoE需求,而且能满足非实时业务基本的吞吐量需求。     

QoS-oriented packet scheduling for wireless multimedia CDMA communications

In the third-generation (and beyond) wireless communication systems, there will be a mixture of different traffic classes, each having its own transmission rate characteristics and quality-of-service (QoS) requirements. In this paper, a QoS-oriented medium access control (MAC) protocol with fair packet loss sharing (FPLS) scheduling is proposed for wireless code-division multiple access (CDMA) communications. The QoS parameters under consideration are the transmission bit error rate (BER), packet loss, and delay requirements. The MAC protocol exploits both time-division and code-division statistical multiplexing. The BER requirements are guaranteed by properly arranging simultaneous packet transmissions and controlling there transmit power levels, whereas the packet loss and delay requirements are guaranteed by proper packet scheduling. The basic idea of FPLS is to schedule the transmission of multimedia packets in such a way that all the users have a fair share of packet loss according to their QoS requirements, which maximizes the number of the served users under the QoS constraints. Simulation results demonstrate effectiveness of the FPLS scheduler, in comparison with other previously proposed scheduling algorithms.     

QoS for wireless sensor networks: Enabling service differentiation at the MAC sub-layer using CoSenS

Providing service differentiation in wireless sensor networks while proposing simple and highly scalable solution is a challenging problem. We retain the use of CSMA/CA as access protocol because of its simplicity, versatility and good scalability properties. We developed CoSenS, a Collect then Send burst Scheme, on top of it to address its weaknesses while facilitating the implementation of scheduling policies. In this article, we propose a simple and scalable service differentiation solution; we implement fixed priority and earliest deadline first on top of CoSenS. The simulation analysis shows that our solution self-adapts to the traffic variation and greatly enhances end-to-end delay, reliability and deadline meet ratio for urgent traffic while not degrading best effort traffic compared to IEEE 802.15.4 original protocol and IEEE 802.15.4 implementing these scheduling policies. Additionally, CoSenS is implemented and tested on motes. The real experimentation results validated our simulation analysis.