Cross-Layer Protocols for WSNs

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.

In this paper, we propose a detailed energy survey of the physical, data link, and network layer by analytical techniques. We also show the impact of regular sleep periods on node energy consumption and present a comparison analysis of single-hop vs. multi-hop communications in the energy realm. A detailed energy expenditure analysis of not only the physical layer but also the link and network layer provides a basis for developing new energy efficient wireless sensor networks. Regular, coordinated sleeping extends the lifetime of sensor nodes, but systems can only benefit from sleeping in terms of transmitted packets if the data arrival rate to the system is low. Energy efficiency is the driving motivation for it can be considered the most important factor for wireless sensor networks because of the power constraints set by battery operation. Radio solutions in the lower ISM bands are attractive because of their relatively easy implementation and low power consumption. However, the data rates of these commercial radios are also relatively low, limiting transmittable frame sizes to a few tens of octets along with strict duty cycle requirements. From the analysis we extract key parameters of selected MAC protocols and show that some traditional mechanisms, such as binary exponential backoff, have some inherent problems. We also argue that single-hop communications has up todo% lower energy consumption than multi-hop forwarding within the feasible transmission distances of an ISM radio. Index Terms-Energy efficiency, Wireless sensor net- works, Medium access control (MAC) protocols, multi-hop communications a duty cycIe (Z), (3), which is normally 10% for the 434MHz band and 1% for the 868MHz band. The duty cycle is defined as the ratio, expressed as a percentage, of the maximum transmitter on-time, relative to a one hour period. When a sensor network is expected to work continuously, this duty cycle has to be taken into account and it can affect the energy efficiency of a network. In this paper we perform cross-layer analysis by pre- senting topology, medium access control (MAC) and ra- dio transceiver energy consumption models that work in unison. The hear topology model represents a common network after network layer route discovery has been accomplished. We use an energy consumption model for the transmission and reception of MAC frames originally presented in (4), develop a coordinated sleep group energy consumption model, and analytically investigate the effect of sleep on sensor networks using three MAC protocols. From the analysis we show that although in an ideal scenario multi-hop communications perform better than single-hop communications, realistic energy models and especially the MAC protocol design have a significant impact. We propose a multi-group sleep model for our nanoMAC protocol, and show that reg- ular sleep periods have a significant, energy reducing impact on node energy consumption with low traf!fic rates. The radio transceiver energy model takes into account several important radio parameters and we use the RFM TRlOOO and RFM radio designers guide (5) for realistic transceiver parameters. The main metric used is absolute energy, consumption per useful transmitted bit. This means only the MAC or thc network protocol data unit (PDU) will be considered and all the other communicated bits, headers, control frames, preambles, etc. are considered as overhead. The rest of the paper is organized as follows. Some related work is discussed in Section IT and in Section 111 we look at the radio propagation energy model. Section TV presents the network topology and energy

One of the most novel applications of wireless sensor networks in recent years has been in the field of biomedical research. Biomedical sensor networks are formed by tiny wireless sensor nodes, embedded inside the body. The communication protocol used in such networks must prevent the formation of hotspots in the network and at the same time route data efficiently, while conserving energy. In this paper we propose a cross-layer medium access control (MAC) protocol and routing protocol co-design for biomedical sensor networks. The cross-layer interactions among the network and MAC layers help optimise the overall performance of the in vivo network. Extensive simulations have been done to show that the proposed Biocomm protocol performs much better than the other existing MAC and routing protocols in terms of preventing the formation of hotspots, reducing energy consumption of nodes and preventing network congestion when used in an in vivo network. A variation of Biocomm, Biocomm-D has been proposed for delay-sensitive biomedical sensor network applications.

Contrary to present conjectures, our medium access control (MAC) based performance studies revealed that battery capacity may not be used as the sole means for achieving energy-based fairness and system longevity for wireless mobile multi-hop ad hoc and sensor networks. Moreover, energy conservation may be attained only if valuable MAC (and PHY) input is passed to the network layer. Hence, we propose two schemes, the objective of which is to enhance the operation of existing power-based multi-path routing protocols via cross-layer designs and optimal load assignments. Our proposed schemes, namely, energy-constrained path selection (ECPS) and energy-efficient load assignment (E2LA), employ probabilistic dynamic programming techniques and utilize cross-layer interactions between the network and MAC layers. To the best of the authors' knowledge, this is the first time that MAC-originated information is used as the basis for achieving energy-efficient routing.

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.

Multiuser diversity refers to a kind of diversity present across different users in a fading environment. This diversity can be exploited by scheduling transmissions so that users transmit when their channel conditions are favorable. Exploiting multiuser diversity access, called also opportunistic access, conducts to a system efficiency that rises with the number of users. Different opportunistic IEEE 802.11 Medium Access Control (MAC) approaches have been proposed. The efficiency study of these approaches by NS-2 simulation is necessary for a performance comparison. The implementation of any opportunistic IEEE 802.11 MAC approach in NS-2 is based on using different cross-layer interactions between the physical layer and the link layer components which are the interface queue and the MAC sub layer. In this paper, we introduce the work that has been done to create a model for implementing these interactions. We also give the different functions we have implemented in NS-2 on the basis of this model. Any opportunistic approach can thus be implemented using these functions. Our contribution is providing an NS-2 extension that can be used to implement protocols exploiting multiuser diversity. We explain how to use our NS-2 extension by giving two examples showing the implementation of new opportunistic MAC protocols.

Intrusion Detections Systems(IDSs) in ad hoc net- works monitor other devices for intentional deviation from protocol, i.e., misbehavior. This process is complicated due to limited radio range and mobility of nodes. Unlike conventional IDSs, it is not possible to monitor nodes for long durations. As a result IDSs suffer from a large number of false positives. Moreover other environmental conditions like radio interference and congestion increase false positives, complicating classification of legitimate nodes and attackers. We present a scheme that helps in accurate diagnosis of malicious attacks in ad hoc networks. Our scheme employs cross- layer interactions based on observations at various networking layers to decrease the number of false positives. Our simulations show that our scheme is more effective and accurate than those based on isolated observations from any single layer. I. INTRODUCTION Mobile ad hoc networks (MANETs) are comprised of a dy- namic set of cooperating peers, which share their wireless ca- pabilities with other similar devices to enable communication with devices not in direct radio-range of each other, effectively relaying messages on behalf of others. Conventional methods of identification and authentication are not available, since the availability of a Certificate Authority (CA) or a Key Distribu- tion Centre (KDC) cannot be assumed. Consequently, mobile device identities or their intentions cannot be predetermined or verified. Communication protocols are though designed for fairness in contention resolution provide no enforcement mechanism to ensure it. Protocols are fair to the extent to which the de- vices conform to the protocol specifications. Wireless Medium Access Control(MAC) Protocols like 802.11 that employ dis- tributed contention resolution for gaining access to the shared wireless channel are susceptible to attack from selfish nodes trying to gain an unfair share of the medium. The various networking layers from the lowest physical layer to the application layer were designed for with the tacit assumption that devices comprising the network will be protocol conformant. Herein lie several security threats, some arising from short- comings in the protocols, and others from the lack of con- ventional identification and authentication mechanisms. These inherent properties of ad hoc networks make them vulnerable, and malicious nodes can exploit these vulnerabilities in the networking layers for selfish or even malicious motives. Selfish nodes can slightly deviate from the MAC protocol specifi- cation for contention resolution in order to gain an unfairly large share of the bandwidth. More harmful attacks like packet dropping, routing disruption, jamming attacks or other forms of Denial-of-Service (DOS) at any of the networking layers can severely disrupt MANET communications. Traditionally, intrusion detection involves looking at events and activities in individual layers of the modeled OSI stack. Various pattern matches at the Transport layer, for example, can indicate SYN attacks. However, sophisticated attacks that simultaneously exploit vulnerabilities at multiple layers of the communication proto- cols will be especially hard to detect. By using observations of both external and internal events at multiple layers of the OSI our approach will be to use observations both external and internal from various layers of the OSI stack for a more accurate evaluation of bad nodes and good nodes. In this paper we show the results of looking specifically at malicious RTS activity in the 802.11 MAC layer when combined with packet dropping at the Network layer. Robust IDS and response systems will depend on accurate classification of attacks and identification of attackers. In order for devices to establish and maintain trust relations - and evolve reputations, there is a need to balance the intrusion de- tection effort with the individual node's primary function. The goal is to maximize the probability that malicious behavior will be correctly detected (True Positives), while minimizing the probability that good nodes will be falsely accused (False Positives).

This paper presents SECANT (Spectrum Efficient Communications and Advanced Networking Technology) as a novel multiuser communication protocol that integrates advanced physical (PHY) layer techniques for adaptive multiple access and interference management. SECANT supports concurrent multiple access (MA) transmissions to common receivers and parallel peer-to-peer (P2P) transmissions in the network. SECANT combines multiuser multiple-input multiple output (MU-MIMO), multiuser detection (MUD), and interference alignment (IA) methods at the PHY layer such that spectrum efficiency can be improved in both interference and signal spaces. An adaptive medium access control (MAC) mechanism is developed to enable spectrum efficiency gains at the PHY layer by managing concurrent transmissions and interference levels. Numerical results indicate significant spectrum efficiency gains (>14 times for fully loaded, and >56 times for 25% loading) that can be achieved over conventional single antenna systems with static MAC protocols.

The interference in coexisting wireless local area networks (WLANs), can be viewed as a layered space-time (LST) structure, in which the number of access points (APs) is equal to the number of transmit antennas. Thus, the interference that is caused by APs from different vendors is equivalent to the interference between transmit antennas in LST architecture. This analogy can be further extended to the WLANs receiver strategy, so that receiver structures derived for LST architectures can be directly applied to mitigate against the interference between vendors. Therefore, in this paper, we propose the LST architecture receivers in the physical layer (PHY) to mitigate against the interference in coexisting WLANs. To improve the bit error rate (BER) performance further, a cross-layer design in both the PHY and medium access control (MAC) layers is also proposed. It is shown that the proposed receivers demonstrate superior performance to the standard receiver for WLANs.

The data link layer provides the reliable means to transfer data between network nodes by detecting and possibly correcting errors that may occur in the physical layer. This layer has the important task of creating and managing data frames. There are usually two sublayers, Logical Link Control (LLC) layer and Medium Access Control (MAC) layer. LLC layer defines the service to the network layer and MAC defines how the communication medium is accessed by multiple nodes. This chapter lists the services that the WirelessHART data link layer provides to the upper network layer. It further describes in more detail the LLC and MAC layers. We describe the message format and its flow control, error detection, and security. We also describe how to maintain slot synchronization with TDMA, schedule slots to listen for packets from neighbors and propagate packets from the network layer. Please refer to the TDMA Data Link Layer Specification (HCF_SPEC-75) for more details.

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.

This paper proposes the design of enabling technologies for practical wireless communication systems operating in the TV white space (TVWS). The main objective of this paper is to cover a macro perspective on the system design blocks including: (a) targeted use case applications and governing regulations, (b) channelization, physical (PHY) layer and medium access control (MAC) layer designs, and (c) achievable throughput and range. It is the intention of this paper to serve as a general guideline for designing wireless communication systems operating in TVWS. The core system design addresses both PHY and MAC layer issues with realistic system considerations. In the PHY layer, a channelization design that fits into the area-specific TV channels and a transceiver that enables data exchange in the TV bands are designed. In the MAC layer, a cognitive engine that manages access to vacant TV channels and MAC functionalities that facilitate effective medium access are also proposed. As a result, the system is capable of supporting up to a typical throughput of 80 Mbps, and a maximum number of 40 users, assuming all users performing the most bandwidth-hungry application in the use case scenario. The corresponding operating range is found reach up to 400 m.

Below the Media Access Control (MAC) layer is the Physical (PHY) layer which deals with the actual transmission of the bits received from the MAC layer above into electromagnetic signals. This layer is optimized to implore power management in wireless networks. Power management is a crucial issue in wireless and mobile networks. In this paper, we propose an Adaptive Context-Aware Rate Selection (ACARS) algorithm to handle the issue of power consumption in wireless networks. This algorithm is implemented by optimizing the PHY layer to transmit efficiently as the number of nodes changes and we estimate the Signal-to-Noise Ratio (SNR) to the PHY layer. Results show that by using the appropriate power management technique, ACARS is reliable and efficient for power consumption in wireless networks which is a high demand for vehicular networks.

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.

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