Self-Stabilizing TDMA Algorithms for Dynamic Wireless Ad Hoc Networks

With the onset of multimedia applications, Quality of Service (QoS) in 802.11-based wireless ad hoc networks has been an essential area to look into. Standard wireless protocols such as IEEE 802.11b and IEEE 802.11e have been deemed unsuitable for multimedia traffic transmission in an ad hoc (multihop) network environment due to the unique network characteristics. As an ad hoc network is infrastructureless and distributed in nature, it gives rise to several challenges in QoS provisioning. In this thesis, we focus on the research of three key areas on QoS in ad hoc networks namely, buffer management in the medium access control (MAC) layer, cross-layer design and flow admission control. Firstly, we study MAC layer buffer management in the IEEE 802.11e protocol. The IEEE 802.11e MAC protocol provides QoS for multimedia traffic by probabilistic priority queueing. Ad hoc networks tend to generate a large volume of network control packets for route maintenance and these control packets are typically queued in the highest priority queue. As a result, higher priority control traffic is always being served, consuming most of the bandwidth and results in poor network performance for data traffic. We examine this problem and propose a dynamic buffer management scheme to mitigate it. By setting different threshold levels in different priority queues, we allow lower priority data traffic to be served when the higher priority control traffic is deemed to be excessive. Simulation of our proposed scheme has shown that our approach yielded better network performance compared to the standard protocol in terms of packet delivery ratio and average delay. Secondly, we study the cross-layer interaction between the MAC and Network layers to identify its impact on QoS. We select the IEEE 802.11e MAC protocol and Ad-hoc On Demand Distance Vector (AODV) routing protocol in our study since they are standardized protocols for wireless networks. In IEEE 802.11e MAC protocol, lower priority traffic has a higher probability of being blocked. Hence, the MAC layer will inform the Network layer of a broken link through the link notification function. In this case, AODV will re-route the paths that traverse this link. As a result, higher priority traffic which shares the same link as the lower priority traffic will undergo the same re-routing procedures. We termed this phenomenon path correlation effect. Under high traffic load, the path correlation effect will be more intense and hence degrade the QoS of higher priority traffic. To break the path correlation effect, we propose a cross-layer design called the Bundled Virtual Circuit (BVC). Our proposed BVC scheme not only addresses the path correlation issues, but also provides priority treatment from the Network layer to the MAC layer. Through our simulations, our proposed cross-layer design approach is proven to provide better network performance than the 802.11e/AODV protocols in terms of packet delivery ratio and delay. Finally, we examine flow admission control at the routing layer in ad hoc networks. Standard routing protocols such as AODV performs routing on a shortest path basis. In the presence of multiple routes, hotspots are likely to form among the intermediate nodes and thus lead to network congestion. In addition, existing routes are not well-protected from the introduction of new routes. We propose a flow admission control algorithm to be used with AODV. Our algorithm allows routes to be created through available bandwidth and congestion estimation. During the route discovery phase, each node will be gauged on its estimated available bandwidth and its backlog of packets in the MAC buffer. If a node does not have sufficient bandwidth, or has too many backlogged packets compared to the requested flow rate, it will not participate in the route discovery process. From simulations, our new scheme is able to provide better network performance than the standard AODV protocol in terms of delay. Our work in this thesis focuses on QoS provisioning in ad hoc networks from the MAC and network layer perspectives. By studying the network characteristics and protocols’ behavior, we investigate the various problems of providing QoS in an ad hoc network environment and propose three different schemes to improve the QoS provisioning at the MAC and network layers. We believe that our work is able to provide some insights to the research area on QoS in ad hoc networks.

Over the past few years, mobile networks have emerged as a promising approach for future mobile IP applications. With limited frequency resources, designing an effective MAC (Medium Access Control) protocol is a hot challenge. IEEE 802.11b/g/a/n networks are currently the most popular wireless LAN products on the market [1]. The conventional IEEE 802.11b and 802.11g/a specification provide up to 11 and 54 Mbps data rates, respectively. However, the MAC protocol that they are based upon is the same and employs a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) protocol with binary exponential back-off. IEEE 802.11 DCF (Distributed Coordination Function) is the de facto MAC protocol for wireless LAN because of its simplicity and robustness [2,3]. Therefore, considerable research efforts have been put on the investigation of the DCF performance over wireless LAN [2]. With the successful deployment of IEEE 802.11a/b/g wireless LAN and the increasing demand for real-time applications over wireless, the IEEE 802.11n Working Group standardized a new MAC and PHY (Physical) layer specification to increase the bit rate to be up to 600 Mbps [3]. The throughput performance at the MAC layer can be improved by aggregating several frames before transmission [3]. Frame aggregation not only reduces the transmission time for preamble and frame headers, but also reduces the waiting time during CSMA/CA random backoff period for successive frame transmissions. The frame aggregation can be performed within different sub-layers. In 802.11n, frame aggregation can be performed either by A-MPDU (MAC Protocol Data Unit Aggregation) or A-MSDU (MAC Service Data Unit Aggregation). Although frame aggregation can increase the throughput at the MAC layer under ideal channel conditions, a larger aggregated frame will cause each station to wait longer before its next chance for channel access. Under errorprone channels, corrupting a large aggregated frame may waste a long period of channel time and lead to a lower MAC efficiency [4]. On the other hand, wireless LAN mobile stations that are defined as the stations that access the LAN while in motion are considered in this chapter. The previous paper analyzed the IEEE 802.11b/g/n MAC performance for wireless LAN with fixed stations, not for wireless LAN with mobile stations [5, 6, 7, 8, 9, 10]. On the contrary, Xi Yong [11] and Ha Cheol Lee [12] analyzed the MAC performance for IEEE 802.11 wireless LAN with mobile stations, but considered only IEEE 802.11 and 802.11g/a wireless LAN specification. So, this chapter summarizes all the reference papers and analyzes the IEEE 802.11b/g/a/n MAC performance for wireless LAN with fixed and mobile stations. In other words, we will present the analytical evaluation of saturation

This paper presents a System on a Chip (SoC) Field-Programmable Gate Array (FPGA) implementation for Media Access Control (MAC) layer of a fast industrial Wireless Local Area Network (iWLAN) protocol, which is used to control industrial robots in factory automation environments. This protocol is a potential technique for industrial wireless communication system by using the Low overhead Packet Division Multiple Access (PDMA) scheme controlled by MAC layer. In our previous research, the MAC layer hardware was implemented and tested on simulation software, but the SoC design for the MAC layer has not been implemented and real tested on the FPGA. In this paper, we have successfully implemented the SoC system for MAC layer of this high-speed wireless communication protocol on the FPGA.

This paper details the medium access control (MAC) layer designed in the PULSERS project for low data rate (LDR) systems, whose main features are low power consumption, low complexity location and relaying capabilities. The MAC developed in PULSERS is based on the IEEE 802.15.4 standard, which, in spite of many virtues, is not the ideal solution for the targeted UWB applications. Thus, the MAC implemented in the project deviates from the standard in a few areas such as the support to peer-to-peer communications, the systematic usage of guaranteed time slots for data transmissions (TDMA), dedicated time slots for ranging or allocation requests, specification of a new ranging procedure, and finally, the definition of a relaying functionality in layer 2. Furthermore, as recent application studies have revealed that mesh networking is necessary for most of the targeted applications, mesh algorithms have also been specified and will be implemented in the next release of the PULSERS MAC layer. The paper first presents the applications targeted in the project. Then, it describes the MAC layer proposal, putting the emphasis on its major specificities in comparison with the IEEE 802.15.4 standard. The expected performances are also provided through OPNET simulation results. Finally, the paper focuses on the localization procedures implemented in the MAC layer, and proposes some enhancements of the current implementation with respect to localization.

11 - Performance Modeling and Analysis over Medium Access Control Layer Wireless Channels

There has been keen interest in the literature recently on the IEEE wireless metropolitan area network (MAN) developed within IEEE 802.16. Through the use of flexible physical layer features and medium access control (MAC) layer mechanisms, this system can be used to deliver broadband voice and data into areas that may have a wide range of population densities, cell radii, propagation environments, and quality of service (QoS) requirements. The physical layer provides flexibilities of time or frequency domain duplexing, multiple bandwidths, adjustable subchannelization, scalable OFDM formats, adaptive coded modulation, and advanced antenna system. The IEEE 802.16 MAC layer offers a connection-oriented service to upper layers of the protocol stack. The QoS of each connection takes one of four levels: constant bit rate grant, real time polling, non-real-time polling, and best effort. The MAC layer also offers packing, fragmentation and ARQ. The MAC privacy sublayer performs authentication, key exchange and encryption of MAC packet data units. The MAC convergence sublayers at the top of the MAC enable Ethernet, ATM, TDM voice and IP (Internet Protocol) services to be offered. This presentation will endeavor to provide a high level overview of the system. It will discuss, from an information theoretic point of view, the key enablers of the system

The performance of traditional TCP congestion control protocol degrades when congestion and contention increase in ad hoc networks that use the IEEE 802.11 DCF. Many of the problems result from medium contention at the media access control (MAC) layer. In this paper, we present a new contention-based congestion control (CBCC) method according to a novel congestion information from MAC layer. This proposal aims to avoid the congestion nodes and guarantee better performance in terms of delay, packet delivery ratio, and throughput. By monitoring the number of one node entry the backoff algorithm, our CBCC scheme can calculate the congestion metric called backoff state ratio, a more accurate metric to characterize the network congestion status. Node uses this indication to determine whether to drop a packet or not. Simulation results show that the algorithm can greatly increase the network throughput and effectively control the network congestion at the MAC layer.

This paper presents a novel cross-layer approach to multiuser H.264/AVC video stream transmission over wireless networks. We consider the joint optimization of three layers of the protocol stacks: the application (APP) layer, the media access control (MAC) layer and the physical (PHY) layer. At the APP layer, the contribution of each packet to the perceptual video quality is evaluated by distortion effect of the packet loss, which is estimated by a Packet Relative Importance Index (PRII). At the MAC layer and the PHY layer, the Gilbert-Elliott (GE) model is employed to describe the time-varying nature of the wireless networks. An objective function for cross-layer optimization is developed based on the layered abstracted parameters from the APP layer, the MAC layer and the PHY layer. Our goal is to maximize the perceptual quality of the video transmitted through the wireless network with constraint of the limited resources. Simulation results show that the proposed scheme performs significantly than the conventional scheduling schemes for video transmission.

In this paper, we address the problem of cross-layer optimization in medium access control (MAC) and network layers for wireless multicasting with multiple cooperative or competitive source nodes in a simple tandem network. We consider scheduled or random access in MAC layer and model network layer operations as network coding or plain routing. We separately look at the cooperative and competitive operation with total and individual performance objectives. We evaluate the resulting cross-layer interactions between MAC and network layers and specify throughput optimization trade-offs intertwined with energy efficiency objectives. We follow a game-theoretic analysis to point at the inefficiency of the non-cooperative equilibrium with selfish nodes competing for limited network resources. In this context, we introduce distributed cooperation stimulation mechanisms to improve the non-cooperative network operation to the cooperative equilibrium performance

The deployment of wireless ad hoc networks faces severe limitations by mutual interference between wireless devices. In this work, we introduce a method to alleviate interference using a medium access control (MAC) layer exploiting multiuser detection (MUD). Instead of interference avoidance, the primary task of such a MAC layer is interference handling. To this end, we first identify link layer requirements for deploying MUD in a decentralized and self-organizing network. Based on these requirements, we propose a MAC protocol supporting MUD. We estimate possible throughput gains of this protocol. Network simulations confirm the analytical results and show remarkable throughput improvements.

최근 무선 인터넷 수요의 증가와 더불어 IEEE 802.11 WLAN의 표준화 작업도 활발히 진행 중이다. 고속처리량을 위한 IEEE 802.11n의 연구 동향은 크게 두 가지로 MAC 계층에서 패킷 간의 Aggregation을 통하여 시스템 처리량을 높인 결과와PHY 계층에서 MIMO 시스템을 적용하여 데이터 전송속도를 높인 결과로 정리될 수 있다. 그러나 아직까지 MAC 계층과 PHY 계층의 연동을 고려하여 IEEE 802.11n의 성능 분석을 보인 결과는 발표되지 않았다. 본 논문에서는 IEEE 802.11n 시스템에서 MAC 계층과 PHY 계층의 연동을 고려하여 성능을 분석한다. MAC 계층에서의 A-MPDU 기법과 PGY 계층에서 MIMO 방식을 적용한다. 결과적으로 기존의 방식에 비해 데이터 전송속도의 증가와 처리량이 향상되었음을 보인다. 또한, MAC과 PRY의 연동을 고려하여 현실성 있는 시뮬레이터인 NS-2를 사용하기로 한다. IEEE 802.11 WLAN(Wireless Local Area Network) standard is currently developing with increased wireless internet demand. Study trends of IEEE 802.11n for high throughput show two aspects, enhanced system throughput using aggregation among packets in MAC(Medium Access Control) layer, and better data rates adapting MIMO(Multiple-Input Multiple-Output) in PRY(Physical) layer. But, no one demonstrates IEEE 802.11n system performance results considering MAC and PRY connection. This paper adapts A-MPDU(Aggregation-MAC Protocol Data Unit) method in MAC layer and MIMO in PRY layer for IEEE 802.11n system. Consequently, Simulation results show enhanced throughput and data rates compared to existing system. Also, We use NS-2(Network Simulator-2) considering MAC and PRY connection for reality.

For the influence of Internet, 802.11 lacks the definition over the MAC (medium access control) layer, user-data are switched via upper protocols and the switching point is located in the network layer. This redundant architecture has shortcomings on efficiency and is not propitious to guarantee QoS (quality of service). In this paper, we propose a novel user-data switching mechanism in the lower layer, viz. the MAC layer in 802.11. This mechanism modifies the traditional finite state machine, the header format of user-data and the communication primitives of MAC layer to achieve the goal of reducing user-data plane. Our simulations show this user-data mechanism can better the relay efficiency and improve the QoS.

In wireless networks all nodes contending to access the medium are supposed to follow the rules of the Medium Access Control (MAC) layer. Wireless Medium Access Control (MAC) protocols such as IEEE 802.11 use a distributed contention resolution mechanism for sharing the wireless channel. The hosts competing for access to the channel are required to wait for a “back off” interval, randomly selected from a specified range, before initiating a transmission. Selfish nodes (or misbehaving nodes) tempt to manipulate their back off parameters to gain more access to the channel, and hence have higher performance than their fair share. Here, the problem of detection of node misbehavior in the MAC layer, with the objective to provide an optimum performance is being considered. This framework captures the presence of uncertainty of attacks.

We propose a combined transport --- medium access control (MAC) layer scheme to provide relativeservice differentiation to Transmission Control Protocol (TCP) flows over a geostationary (GEO) bandwidth on demand (BoD) satellite networks. Our approach involves the joint configuration of TCP-Performance Enhancing Proxy (TCP-PEP) agents at the transport layer and the scheduling algorithm controlling the resource allocation at the MAC layer. The scheme is independent of the TCP variant used in the network. Extensive simulation results show that the two mechanisms exhibit complementary behavior in achieving the desired differentiation throughout the traffic load space: the TCP-PEP agents control differentiation at low system utilization, whereas the MAC scheduler becomes the dominant differentiation factor at high load.

The use of wireless sensor networks (WSNs) is growing up in the last few years. Therefore, new challenges arise every day and one of the emerging challenges in WSNs is the nodes mobility support. This feature increases the application areas of these technologies but also raises new challenges to solve. This paper proposes a new handover mechanism, called Hand4MAC (Handover mechanism for MAC layer supporting continuous communication in mobile wireless sensor networks), to deal with body sensors mobility in scenarios where patients are hospitalized. This approach tries to provide continuous monitoring and communication with these sensor nodes when they move across different access points wireless coverage range. The proposed method for medium access control (MAC) layer considers that nodes remain within the same network. The evaluation study of the proposed algorithm was performed by simulation and evaluated in comparison with the well-known RSSI-based handover algorithm. It was concluded that Hand4MAC performs better and reveals promising results for real deployment.