Collision and Fade Localization within Packets for Wireless LANs

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.

Besides avoiding inter-symbol interference and leading to high capacity, wireless orthogonal frequency division multiplexing (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 dominate layered networking architecture, in which each layer is designed and operated independently, results in inefficient and inflexible 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. In this paper, we focus on resource allocation and scheduling in wireless multiuser OFDM networks based on joint physical and medium access control (MAC) layer optimization. An adaptive cross-layer design for the downlink multiuser OFDM systems, to maximize the weighted sum capacity of all users, where each user has multiple heterogeneous traffic queues simultaneously is proposed. A packet dependent (PD) scheduling scheme is employed at the MAC layer, which determines the packet transmission order by assigning different weights to different packets, and is shown by simulations more efficient than the previous methods where all packets in a queue have the same weight. The weight design in PD scheduling considers the delay, size and quality of service (QoS) priority level of packets. Each user weight employed in resource allocation at the physical (PHY) layer is obtained by summing up the weights of selected packets for the user. We also deeply investigate the various resource scheduling schemes for comparisons.

The wireless environment is built everywhere, especially IEEE 802.11 WLANs. More users use wireless network for searching information in Internets, TV program streaming, and video/voice conference. The packets include not only traditional data but also interactive multimedia data. There is an extension to IEEE 802.11 standards called IEEE 802.11e, improving the QoS capabilities on WLANs. This protocol enhances QoS data as above applications and features. The contribution, Cross-Layer Adaptive Video Prioritization (CAVP), in this thesis paper is divided into two parts. First, it provides MAC-Layer adaptive prioritization (MAP) to prioritize the packet which has the information of video frames at the Medium Access Control (MAC) Layer of IEEE 802.11e. In IEEE 802.11e, the priority of packets is very important, and it affects the order of received packets and the probability of successfully-received packet. The method to prioritize packets is estimating the access time of each access category (AC) for the arrived packet and putting the packet into the AC which has the minimal access time. Second, Video Frame Prioritization (VFP) prioritizes the video packet. Because the importance of video frames is different, we set the initial priority at Application Layer by choosing the maximal PSNR-difference frame as the highest priority frame. The maximal PSNR-difference frame critically influences the overall video sequences. These two parts of our contribution can greatly improve the quality of video streaming. The cross-layer design, CAVP, involves MAC Layer and Application Layer. The information of a packet arrived at MAC Layer is gotten from Application Layer. The benefit of cross-layer design is effectively using the information of different layers and combining their feature. In simulations, we use the popular simulator ns-2 as the experiment platform. We design several scenarios to show that our cross-layer design improves the quality of video streaming. The result shows that our cross-layer design proposal not only greatly increases PSNR of video but also improves the video in vision after the wireless transmission.

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

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.

Video transmission over 802.11 wireless networks poses many challenges. Bandwidth demands and timing constraints are two major challenges for real time video transmission over wireless. To increase network throughput as well as overall network capacity, the use of cross layer design approach is required. One of such design approaches includes physical (PHY) and medium access control (MAC) layers considerations and is explored in this paper. This survy paper describes a detailed study of the MAC and PHY layer considerations for good wireless video transmission performance. The ultimate solution for the problem of real time video transmission is to study the different methods of adapting parameters for achieving the delay constraints in real time environment. The best techniques available in literature are studied for adapting the parameters which are suitable for real time video transmission. This study focuses on adaptive retry limit (ARL) parameter for MAC layer and PHY layer parameter like Enhanced Adaptive Forward Error Correction (EnAFEC) for real time video transmission that can be supported by a wireless network. The new scheme for optimizing the wireless network's MAC and PHY layer parameters is proposed in this work.

This paper gives an overview of the European level standard proposal for smart wireless body area networks (WBAN). Under the mandate of European Telecommunication Standards Institute ETSI, a technical committee TC SmartBAN was formed in 2013. The goal of the TC SmartBAN is to define a standard for low power devices and networks to be used in short range links supporting, e.g., healthcare, wellness and sport relating applications operating around a human body. The main focus areas were in physical and medium access control layers' specifications as well as efficient data presentation format for information delivery. Moreover, experimental measurement campaigns to characterize radio channel occupancy in the specified SmartBAN frequency range have been carried out. The actual work is divided into several, parallel Work Items (WI). Within this paper, a short overview of the ETSI TC SmartBAN work is given. The components of the SmartBAN standard are described in their own dedicated papers.

This paper proposed the use of physical (PHY) and medium access control (MAC) cross-layer approach to obtain two goals outlined by the next-generation V2X (NGV) ’s project authorisation request (PAR) of IEEE 802.11bd group, namely having twice the MAC layer throughput and able to operate in a high mobility scenario of up to 500 km/h. At the PHY layer, we suggested utilising mid-ambles channel estimation (MCE), dual-carrier modulation (DCM), and multiple-input multiple-output space-time block coding (MIMO-STBC). At the MAC layer, we suggested an aggregate MAC protocol data unit (A-MPDU) aggregation technique, choosing an appropriate contention window (CW) value, and setting a limit for re-transmissions. We designed a model utilising a cross-layer approach then we simulated the performance of normalised system throughput for two types of V2X applications, namely safety-related (high reliability) and non-safety (high throughput) V2X applications. To better portray the high-mobility scenario, we used the enhanced highway line of sight (LOS) channel model. Our simulation results showed two times normalized throughput performance improvement for both V2X applications in a high mobility environment, as requested by the NGV standard’s PAR.

The large amount of unlicensed bandwidth available in the millimeter-wave has enabled very high data rate wireless applications. The IEEE 802.15 Task Group 3c has completed standardization efforts for multi-gigabit data rate communications on both the physical (PHY) and medium access control (MAC) layers. This paper presents a performance evaluation of the PHY and MAC layers of the newly published standard. Packet error rate (PER) and PHY throughput are simulated for different modes based on a typical 60 GHz channel model. The theoretical MAC throughput is calculated for different packet sizes and modes under different link conditions. The link adaptation mechanism is used to analyze the operating range versus data rate. The results show that very high data rates can be achieved over low distances.

Since the inception of IEEE 802.11 wireless local area networks (WLANs) in 1997, wireless networking technologies have tremendously grown in the last few decades. The fundamental IEEE 802.11 physical (PHY) and medium access control (MAC) protocols have continuously been enriched with new technologies to provide the last mile wireless broadband connectivity to end users. Consequently, several new amendments of the basic IEEE 802.11 gradually came up in the forms of IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g. More recently, IEEE 802.11n, IEEE 802.11ac, and IEEE 802.11ad are introduced with enhanced PHY and MAC layers that boost up physical data rates to the order of Gigabit per second. So, these amendments are generally known as high throughput WLANs (HT-WLANs). In HT-WLANs, PHY layer is enhanced with multiple-input multiple-output antenna technologies, channel bonding, short guard intervals, enhanced modulation and coding schemes. The MAC sublayer overhead is reduced by introducing frame aggregation and block acknowledgement technologies. However, several existing studies reveal that, many a time, the aforesaid PHY and MAC enhancements yield negative impact on various upper layer protocols, that is end-to-end transport and application layer protocols. As a consequence, a large number of researchers have focused on improving the coordination among PHY/MAC and upper layer protocols. In this survey, we discuss impact of HT-WLAN PHY and MAC layer enhancements on various transport and application layer protocols. This paper also summarizes several research works that use aforesaid enhancements effectively to boost up data rate of end-to-end protocols. We also point out limitations of the existing researches and list down different open challenges that can be meaningfully explored for the development of the next generation HT-WLAN technologies.

Recent V2X communication technology provides safety and service information in real time for autonomous driving. It has been researched more improved performance rather than legacy wireless access in vehicular environments (WAVE) through high data rate and low packet latency. However, quality of service(QoS) cannot currently be guaranteed, because original physical and medium access control(MAC) layer have been optimized for low mobility. This paper focuses on the implementation of enhanced MAC layer of WAVE and proposes a new channel access method for QoS.

With the emergence of ultra-reliable and low latency communication (URLLC) services, link adaptation (LA) plays a pivotal role in improving the robustness and reliability of communication networks via appropriate modulation and coding schemes (MCS). LA-based resource management schemes in both physical and medium access control layers can significantly enhance the system performance in terms of throughput, latency, reliability, and quality of service. Increasing the number of retransmissions will achieve higher reliability and increase transmission latency. In order to balance this trade-off with improved link performance for URLLC services, we study a joint subcarrier and power allocation problem to maximize the achievable sum-rate under an appropriate MCS. The formulated problem is mixed-integer nonconvex programming which is challenging to solve optimally. In addition, a direct application of standard optimization techniques is no longer applicable due to the complication of the effective signal-to-noise ratio (SNR) function. To overcome this challenge, we first relax the binary variables to continuous ones and introduce additional variables to convert the relaxed problem into a more tractable form. By leveraging the successive convex approximation method, we develop a low-complexity iterative algorithm that guarantees to achieve at least a locally optimal solution. Simulation results are provided to show the fast convergence of the proposed iterative algorithm and demonstrate the significant performance improvement in terms of the achievable sum-rate, compared with the conventional LA approach and existing retransmission policy.

Modern random access avoids scheduling overheads and greatly improves the transmission efficiency of small packets. The major challenge is the random collision, and slotted ALOHA (SA)-based methods were proposed to cancel collisions via the receiving time slot diversity. Based on power-domain multiple access (PDMA), some nonorthogonal multiple access (NOMA) SA methods increased the active user number. This article refines PDMA-based methods at the first step, including: 1) the existing NOMA irregular repetition SA is enhanced and 2) NOMA coded SA is proposed. However, PDMA-based methods require accurate sensing and power control to separate multiple users in the power domain, which is not friendly to low-cost devices. This article proposes a NOMA SA method named spreading SA (SSA), which does not rely on any sensing or power control. Both physical and medium access control layers are considered, and the outage model, instead of the collision model, is proposed to be used for NOMA SA. SSA uses random nonorthogonal code spreading to reduce collisions as a relatively large number of codes can be employed. Compared with the power domain, the code domain gains a much higher degree of freedom. It can be utilized without any coordination with the help of blind detection technologies. Moreover, collision resolution diversity SSA (CRDSSA) is proposed to further improve the user loading. The simulation results validate the analysis and show that the proposed SSA-based methods support a higher user loading and much higher flexibility than existing NOMA SA works in most cases.

The focus of this chapter is twofold: information dissemination from infrastructure nodes deployed along the roads, the so-called Road-Side Units (RSUs), to passing-by vehicles, and content downloading by vehicular users through nearby RSUs. In particular, in order to ensure good performance for both content dissemination and downloading, the presented study addresses the problem of RSU deployment and reviews previous work that has dealt with such an issue. The RSU deployment problem is then formulated as an optimization problem, where the number of vehicles that come in contact with any RSU is maximized, possibly considering a minimum contact time to be guaranteed. Since such optimization problems turn out to be NP-hard, heuristics are proposed to efficiently approximate the optimal solution. The RSU deployment obtained through such heuristics is then used to investigate the performance of content dissemination and downloading through ns2 simulations. Simulation tests are carried out under various real-world vehicular environments, including a realistic mobility model, and considering that the IEEE 802.11p standard is used at the physical and medium access control layers. The performance obtained in realistic conditions is discussed with respect to the results obtained under the same RSU deployment, but in ideal conditions and protocol message exchange. Based on the obtained results, some useful hints on the network system design are provided.

This paper presents an overview of the physical layer (PHY) and medium access control layer (MAC) requirements for a new class of high-speed wireless local area networks (WLANs) operating in the 5 GHz Unlicensed National Information Infrastructure (UNII) bands at data rates of 6-54 Mbps.