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Розглянуто один з протоколів синхронного множинного доступу з контролем несівної за додаткового припущення про використання процедур розв’язання конфліктів на фізичному рівні. Наведені результати аналізу обслуженого навантаження та пропускної спроможності. It’s considered one of the protocols of the synchronous multiple access with carrier control and additional assumption of conflict resolution procedures in the physical layer. The results of analysis of handled load and bandwidth are mentioned. Рассмотрен один из протоколов синхронного множественного доступа с контролем несущей с дополнительным предположением применения процедуры разрешения конфликтов на физическом уровне. Приведены результаты анализа обслуженной нагрузки и пропускной способности.

The IEEE 802.11 distributed coordinated function (DCF) adopts carrier sense multiple access with collision avoidance (CSMA/CA) as its medium access control (MAC) protocol. CSMA/CA is designed such that the transmission from any one station does not have priority over any other. In a congested environment with many DCF stations, this design makes it difficult to protect channel resources for certain stations such as when products are used for presentation at exhibitions, which should be protected based on priority. On the other hand, The IEEE 802.11 enhanced distributed channel access (EDCA) provides a quality-of-service (QoS) mechanism for DCF. However in EDCA, transmission opportunities are allocated based on not individual stations but on the defined traffic type of applications. This paper proposes a distributed dynamic resource allocation method that enables control of flexible bandwidth allocation to each specific station. The proposed method controls the priority level and can coexist with conventional CSMA/CA. Moreover, the proposed method improves the system throughput. Specifically, under the coexistence environment with DCF stations, the proposed method is able to obtain up to over 300% higher user throughput characteristic compared to the case in which the proposed method is not introduced. In addition, under non-coexistence environment, all the proposed stations achieve 70% higher throughput than DCF stations when the number of stations in a network is 50.

International audience; In wired networks, systems are usually optimized to offer the maximum throughput of point-to-point and generally well identified transmissions. In the first widespread wireless networks such as IEEE 802.11, the model of point-to-point communication still applies; the transmissions are between the wireless nodes and the access point, which usually serves as a gateway to the Internet. Yet this model is no longer valid with more recent wireless systems such as Wireless Sensor Networks (WSNs) and Vehicular Ad Hoc NETworks (VANETs). In such networks, communication is between one node and its neighbors and simultaneous transmissions or, in other words spatial reuse, is required to insure good performance. Thus performance is directly linked to the density of successful simultaneous transmissions. Another important remark concerning wireless networks, past and present, is that most of these communications systems use Carrier Sense Multiple Access (CSMA) techniques. Previous studies, such as [1], show that in CSMA networks, the density of successful transmissions is greatly influenced by the carrier sense detection threshold, which is one of the main parameters of CSMA. In this paper, we use a simple stochastic model for CSMA to experiment an adaptive scheme which tunes the carrier sense threshold to the density of network nodes. This model uses a Matern selection process with a random pattern of nodes distributed as a Poisson Point Process (PPP). Each node in the process receives a random mark and the nodes that have the smallest mark in their neighborhood are elected for transmission, mimicking the election process of CSMA. The analysis in this paper indicates that an adaptive technique can be based on the average waiting times of packets. Alternatively, this technique can also be based on the number of neighboring nodes.

Backoff-free fragment retransmission (BFFR) scheme enhances the performance of legacy MAC layer fragmentation by eliminating contention overhead. The eliminated overhead is the result of backoff executed before a retransmission attempt is made when fragment transmission failure occurs within a fragment burst. This paper provides a mathematical analysis of BFFR energy efficiency and further assesses, by means of simulations, the energy efficiency, throughput and delay obtained when BFFR is used. The validity of the new scheme is evaluated in different scenarios namely, constant bit rate traffic, realistic bursty internet traffic, node mobility, rigid and elastic flows and their combinations at different traffic loads. We also evaluate and discuss the impact of BFFR on MAC fairness when the number of nodes is varied from 4 to 10. It is shown that BFFR has advantages over legacy MAC fragmentation scheme in all the scenarios.

This paper proposes and investigates a distributed adaptive contention window adjustment algorithm based on the transmission history for wireless LANs called the transmission-history-based distributed adaptive contention window adjustment (THAW) algorithm. The objective of this paper is to reduce the transmission delay and improve the channel throughput compared to conventional algorithms. The feature of THAW is that it adaptively adjusts the initial contention window (CWinit) size in the binary exponential backoff (BEB) algorithm used in the IEEE 802.11 standard according to the transmission history and the automatic rate fallback (ARF) algorithm, which is the most basic algorithm in automatic rate controls. This effect is to keep CWinit at a high value in a congested state. Simulation results show that the THAW algorithm outperforms the conventional algorithms in terms of the channel throughput and delay, even if the timer in the ARF is changed.

We show that CSMA is able to spontaneously synchronize transmissions in a wireless network with constant-size packets, and that this property can be used to devise efficient synchronized CSMA scheduling mechanisms without message passing. Using tools from queuing theory, we prove that for any connected wireless networks with arbitrary interference constraints, it is possible to implement self-synchronizing TDMA schedules without any explicit message passing or clock synchronization besides transmitting the original data packets, and the interaction can be fully local in that each node decides when to transmit next only by overhearing its neighbors' transmissions. We also provide a necessary and sufficient condition on the emergence of self-synchronization for a given TDMA schedule, and prove that such conditions for self-synchronization can be checked in a finite number of steps for a finite network topology.

Multi-hop wireless networks employing random access protocols have been shown to incur large discrepancies in the throughputs achieved by the flows sharing the network. Indeed, flow throughputs can span orders of magnitude from near starvation to many times greater than the mean. In this paper, we address the foundations of this disparity. We show that the fundamental cause is not merely differences in the number of contending neighbors, but a generic coordination problem of CSMA-based random access in a multi-hop environment. We develop a new analytical model that incorporates this lack of coordination, identifies dominating and starving flows and accurately predicts per-flow throughput in a large-scale network. We then propose metrics that quantify throughput imbalances due to the MAC protocol operation. Our model and metrics provide a deeper understanding of the behavior of CSMA protocols in arbitrary topologies and can aid the design of effective protocol solutions to the starvation problem.

Denna rapport behandlar prestandaproblem i den nyligen standardiserade Mesh kommunikationsstandarden (IEEE 802.11s). I denna rapport, undersöker och förbättra vi ett förhållande som resulterar i reduktion av genomströmningen i en kedja av noder topologi. IEEE802.11s är mycket lovande med många fördelar för både IoT-systemen och trådlösa nätverk i båda hemmet och arbete.Vi arbetar med frågan om orättvisa när CSMA/CA tillämpas, vilket orsakar genomströmningsreduktion på grund av paketförluster och indikerar svältning. Vi analyserar konsekvenserna av Collision Avoidance (CA) mekanism och föreslår en ersättning för CA som är både rättvist och samtidigt kan upprätthålla undvikande av kollisioner. Vi implementera detta i en simulator och resultatet visar på betydligt högre end-to-end-genomströmning än standard CSMA/CA och inga paketförluster på grund av buffertspill. This thesis rapport deals with the performance issues of the newly standardized Wireless mesh protocol (IEEE 802.11s). In this thesis, we work on improving the conditions that results in throughput degradation in a chain of nodes topology. The mesh standard is very promising with many advantages for both IoT systems and home wireless networks.We work on the issue of unfairness when CSMA/CA is applied, which causes throughput degradation due to packet loss and indicates starvation. We analyze the implication of the Collision Avoidance (CA) mechanism and propose a replacement for the CA that is both fair and able to maintain collision avoidance. We implement this in a simulator and the result shows significantly higher end-to-end throughput compared to the original CSMA/CA and no packet loss due to buffer overflow.

Currently, with the rapid development of Internet of Things (IoT), users demand more and more personalized and diversified business categories, radio spectrum increasingly tense. With the exploiting of Transmission Control Protocol/Internet Protocol (TCP / IP) protocol, network achieves the objects of the intelligent identifying, locating, tracking, monitoring and managing a network. Multichannel random access mechanism maximizes the utilization of constrained spectrum resources and allocating scarce channel resources to disparate hierarchical according to business priorities with various qualitiy of service (QoS) requirements. In this paper, we propose a MAC design combining them together in one unit system under three-dimensional probability CSMA (Carrier Sense Multiple Access) adopting the average cycle analysis method to analysis. Through the paper, precise mathematical value of system throughput is got by rigorous derivations under many circumstances. The correctness of the theory and model is demonstrated with simulation results and effectiveness illustrated. In the offline phase, simulation results verify that the proposed algorithm can improves the controllability of the system, the channel utilization, system security, and reliability of packet transmission and meet the different priorities of different QoS requirements.

Growing demands of high bandwidth and data rates in wireless networks haveinspired the US Federal Commission Council (FCC) to free the licensed 60 GHzspectrum for emerging technologies. Typically, wireless networks operate at 2.4,3.6 or 5 GHz but these frequency bands have become more populous by virtue ofrising acceptance and demands across the globe. This craved a desire to incorporatewireless networks over 60 GHz. Potential challenges posed due to directionaldeafness, lack of signal penetration and higher attenuation due to oxygen absorptionhave to be overcome to realize the full potential of communications in this frequencyrange. In this thesis we focus on the design of efficient medium access control(MAC) protocols that overcome the aforementioned challenges posed by thetransmission medium at 60 GHz. Specifically, we conducted performance comparisonof memory-guided directionalMAC(MDMAC) against traditional carriersense multiple access (CSMA) based MAC protocols. Our simulation results onthe open source simulator Prowler demonstrate that the network throughput ofMDMAC is relatively higher than what can be achieved with traditional CSMAprotocols (which assumes a omnidirectional pattern for transmission/receptionof signals). Futher it has been observed that in the case of MDMAC protocol decreasein antenna beamwidth increases the network throughput. We then lookedat the impact of deploying relays on the performance of MDMAC protocol. Wefound that in the presence of relays having a larger beamwidth leads to higher networkthroughput as against the case when beamwidth is small (Note: Usage ofrelays helps improve the transmission range of any communication). This couldbe attributed to the fact that when the beamwidth is large the probability of findinga relay node is much higher than the case when beamwidth is small. Howeverhaving smaller beamwidth increases the network throughput of MDMAC. Thesetwo conflicting trends in network throughput with respect to beamwidth suggestthat there exists an optimal value for beamwidth that maximizes the networkthroughput.

This paper presents Carrier Sense Multiple Access (CSMA) communication models based on SoC design methodology. Such a model can be used to support the modeling of the complex wireless communication systems. Therefore, the use of such communication model is an important technique in the construction of high-performance communication. SystemC has been chosen because it provides a homogeneous design flow for complex designs (i.e. SoC and IP-based design). We use a swarm system to validate CSMA designed model and to show how advantages of incorporating communication early in the design process. The wireless communication created through the modeling of CSMA protocol that can be used to achieve communication between all the agents and to coordinate access to the shared medium (channel)., {"references":["Ibrahim Aref. Wireless Extension to the Existing SystemC Design\nMethodology. PhD thesis, School of Engineering, University of\nGlasgow, University of Glasgow, Glasgow, UK, February 2011.","H. Bidgoli. The Handbook of Computer Networks. John Wiley and\nSons, 2008.","D. Black and J. Donovan. SystemC: From the Ground-up. Kluwer\nAcademic Publishers, first edition, 2004.","N. Bombieri, F. Fummi, and D. Quaglia. System/network design-space\nexploration based on tlm for networked embedded systems. ACM\nTransactions on Embedded Computing Systems, 9(4), Mar. 2010.","L. Cai and D. Gajski. Transaction level modelling in system level\ndesign. CECS Technical Report 03-10, 2003.","L. Cai, S. Verma, and D. Gajski. Comparison of specc and systemc\nlanguages for system design. Technical report, Center for Embedded\nComputer Systems, University of California, Irvine, 2003.","R. Domer, D. Gajski, and A. Gerstlauer. Specc methodology for highlevel\nmodelling. IEEE Electronic Design Processes Workshop EDP\n2002, 2002.","B. A. Forouzan. Data Communications and Networking. McGraw-Hill\nScience/Engineering/Math, fourth edition, 2006.","F. Fummi, P. Gallo, S. Martini, G. Perbellini, M. Poncino, and F.\nRicciato. A timing-accurate modeling and simulation environment for\nnetworked embedded systems. Annual ACM IEEE Design Automation\nConference, pages 42–47, 2003.\n[10] F. Fummi, S. Martini, and G. Perbellini. Heterogeneous co-simulation of\nnetworked embedded systems. Proceedings of the Design, Automation\nand Test in Europe Conference and Exhibition (DATE), 3, 2004.\n[11] F. Fummi, D. Quaglia, and F. Stefanni. A systemc-based framework for\nmodeling and simulation of networked embedded systems. Forum on\nSpecfication, Verification and Design Languages, pages 49–54,\nSeptember 2008.\n[12] D. Gajski, J. Zhu, R. Domer, A. Gerstlauer, and S. Zhao. Spec C:\nSpecification Language and Methodology. 2000.\n[13] A. Ghosh, S. Tjiang, and R. Chandra. System modeling with systemc. In\nASIC, 2001.\n[14] S. Glisic and P. Leppänen. Wireless Communications TDMA versus\nCDMA. Kluwer Academic Publishers, 1997.\n[15] IEEE_Computer_Society. Ieee standard systemc language reference\nmanual. IEEE Std 1666-2005, pages 1–423, Mar. 2006.\n[16] OSCI. SystemC User's Guide. Open SystemC Initiative, 2002.\n[17] H. Parunak. Engineering swarming systems. Kluwer, 2004.\n[18] S. Chen and H. Fang. Modeling and control of scalable engineering\nswarm. the 6th World Congress on Intelligent Control and Automation,\nJune 2006.\n[19] F. Stefanni, D. Quaglia, and F. Fummi. Systemc simulation of\nnetworked embedded systems. Springer Netherlands, 36:201–211, May\n2009.\n[20] J. Torregoza and W. Hwang. Multi-channel multitransceiver routing\nprotocol for wireless mesh network.The 9th International Conference on\nAdvanced Communication Technology, pages 484–488, Feb. 2007.\n[21] R. Walstrom, J. Schneider, and D. Rover. Teaching system-level design\nusing specc and systemc. Proceedings of the IEEE International\nConference on Microelectronic Systems Education (MSE), 2005.\n[22] W. Yue and Y. Matsumoto. Performance Analysis of Multi-Channel and\nMulti-Traffic on Wireless Communication Networks. Kluwer Academic\nPublishers, first edition, 2002."]}

The aim of this paper is to present a model for the throughput of the 1-persistent CSMA protocol in underwater networks, where the typically large propagation delay with respect to the packet transmission time requires to take into account the spatial distribution of the nodes. Our model is developed based on the analysis carried out in [1] for the non-persistent CSMA protocol. Our results show that the 1-persistent CSMA model developed by Tobagi and Kleinrock is still valid as an approximation, with a few small adjustments, even though it considers an equal propagation delay for all pairs of nodes in the network. The proposed model is validated against simulation results based on the network simulator OMNeT++. TRUE pub

En este trabajo se realizará un profundo estudio sobre la capa de acceso al medio (MAC) de la tecnología WIFI (Wireless – fidelity) así como de las técnicas de control de acceso que se emplean para el control de los usuarios que acceden al sistema. Para llevar a cabo el estudio del sistema propuesto, el trabajo ha sido estructurado en los siguientes bloques principales. 1. Estudio teórico. Se estudiarán los tipos de protocolos de acceso al medio existentes para redes inalámbricas y se abarcará el estudio fundamental del protocolo de contienda CSMA. Para poder comprender su funcionamiento, el trabajo se basará en el estándar WIFI 802.11[1] , el cual recoge las definiciones e influencia de los parámetros fundamentales que rigen el acceso al canal inalámbrico compartido. La capa de acceso al medio (MAC) está basada en el protocolo de acceso de la DCF el cual hace referencia a CSMA . Es en esta capa del nivel de enlace, donde nos centraremos para estudiar los parámetros fundamentales como: contador de backoff, ventana de contención, slot time o espacio entre tramas (SIFS). Tras el estudio de dichos parámetros, procederemos a comprobar su influencia en las prestaciones del sistema mediante los siguientes datos objetivos. Tasa de descarte de paquetes. Goodput de la línea. Throughput de la línea. Número de usuarios en el sistema. 2. Modelado teórico. Mediante el modelo teórico basado en el estudio de Giuseppe Bianchi [2] sobre el análisis de las prestaciones de la DCF, se obtendrán unos resultados teóricos sobre las prestaciones que el estándar WIFI 802.11 ofrece. Por otra parte, proporcionará una base de trabajo enfocada a las simulaciones que se realizarán posteriormente. 3. Simulación de parámetros bajo estudio. Tras el estudio teórico, se procederá a realizar una simulación mediante el software NS2 (Network Simulator), desarrollado para el ámbito de las redes telemáticas [2]. Dicha simulación permitirá programar en lenguaje propio TCL, una red inalámbrica que opera bajo el protocolo CSMA y a su vez, redefinir los valores de las variables que influyen en las prestaciones finales del sistema descrito. El objetivo fundamental de la simulación mediante un software especializado es, obtener un modelo visual y representativo de la influencia, tanto conjunta como individual, de los parámetros anteriormente descritos, para determinar la repercusión de cada uno de ellos en las prestaciones finales. 4. Comparativa de modelos. Como parte final del trabajo desarrollado, se concluirá validando los resultados obtenidos en las simulaciones, contrastándolos con el modelo teórico expuesto y visualizando, numérica y gráficamente la variación en las prestaciones del protocolo de contienda CSMA tanto de forma teórica como práctica. Ingeniería de Sistemas de Comunicaciones

Cataloged from PDF version of article. In this paper, we introduce BilMesh, an indoor 802.11 b/g mesh networking testbed we established, and we report about our performance experiments conducted on multi-hop topologies with single-radio and multi-radio relay nodes. We investigate and report the effects of using multi-radio, multi-channel relay nodes in the mesh networking infrastructure in terms of network and application layer performance metrics. We also study the effects of physical channel separation on achievable end-to-end goodput perceived by the applications in the multi-radio case by varying the channel separation between the radio interfaces of a multi-radio relay node. We have observed that the difference between TCP and UDP goodput performances together with the delay and jitter performance depends on the hop count. We also observed that assigning overlapping channels with a central frequency separation of 5-15 MHz may render the CSMA mechanism used in 802.11 MAC ineffective and hence reduce the overall network performance. Finally, we provide some suggestions that can be considered while designing related protocols and algorithms to deal with the observed facts. (C) 2013 Elsevier Ltd. All rights reserved.

The popularity of the wireless networks is so great that we will soon reach the point where most of the devices work based on that, but new challenges in wireless channel access will be created with these increasingly widespread wireless communications. Multi-channel CSMA protocols have been designed to enhance the throughput of the next generation wireless networks compared to single-channel protocols. However, their performance analysis still needs careful considerations. In this thesis, a set of techniques are proposed to model and analyse the CSMA protocols in terms of channel sensing and channel access. In that respect, the performance analysis of un-slotted multi-channel CSMA protocols is studied through considering the hidden terminals. In the modelling phase, important parameters such as shadowing and path loss impairments are being considered. Following that, due to the high importance of spectrum sensing in CSMA protocols, the Double-Threshold Energy Detector (DTED) is thoroughly investigated in this thesis. An iterative algorithm is also proposed to determine optimum values of detection parameters in a sensing-throughput problem formulation. Vehicle-to-Roadside (V2R) communication, as a part of Intelligent Transportation System (ITS), over multi-channel wireless networks is also modelled and analysed in this thesis. In this respect, through proposing a novel mathematical model, the connectivity level which an arbitrary vehicle experiences during its packet transmission with a RSU is also investigated.

Network traffic model is a critical problem for urban applications, mainly because of its diversity and node density. As wireless sensor network is highly concerned with the development of smart cities, careful consideration to traffic model helps choose appropriate protocols and adapt network parameters to reach best performances on energy-latency tradeoffs. In this paper, we compare the performance of two off-the-shelf medium access control protocols on two different kinds of traffic models, and then evaluate their application-end information delay and energy consumption while varying traffic parameters and network density. From the simulation results, we highlight some limits induced by network density and occurrence frequency of event-driven applications. When it comes to realtime urban services, a protocol selection shall be taken into account - even dynamically - with a special attention to energy-delay tradeoff. To this end, we provide several insights on parking sensor networks., Comment: ACM International Workshop on Wireless and Mobile Technologies for Smart Cities (WiMobCity) (2014)

We consider extended wireless networks characterized by a random topology of access points (APs) contending for medium access over the same wireless channel. Recently, stochastic geometry has emerged as a powerful tool to analyze random networks adopting MAC protocols such as ALOHA and CSMA. The main strength of this methodology lies in its ability to account for the randomness in the nodes' location jointly with an accurate description at the physical layer, based on the SINR, that allows considering also random fading on each link. In this paper, we extend previous stochastic geometry models of CSMA networks, developing computationally efficient techniques to obtain throughput distributions, in addition to spatial averages, which permit us to get interesting insights into the impact of protocol parameters and channel variability on the spatial fairness among the nodes. Moreover, we extend the analysis to a significant class of topologies in which APs are not placed according to a Poisson process.

A multi-frame Neighbor Discovery Protocol over a DTN network with RFID Devices is proposed. This protocol is based on a Sift-distribution (s-Persistent) in order to differentiate the access probability to slots among RFID devices. Moreover, our approach has been considered in a mono-frame and multi-frame scenario. Our s-Persistent approach is applied in a simulated test and in a real test-bed in order to see the effectiveness of the proposal in comparison with a well-known technique such as p-Persistent protocol. Performance Evaluation has been evaluated in terms of number discovered neighbors under different numbers of nodes and frames. Obtained results shows that s-Persistent performs better than p-Persistent increasing the number of discovered neighbors.

In Low power and Lossy Networks (LNNs), routing has been considered as a main design and development challenge. This has led to the open design of the IPv6 routing protocol for LLNs called RPL. The protocol allows creating groups (instances) of multiple loop-free routing topologies over a physical network. The purpose of forming an optimized tree routing topology is to drive packets from the nodes to the collection point or sink which is the root of the tree. In this paper, we take advantage of extracted routing information to support high performance transmission of priority packets by proposing a QoS-aware cross-layer mechanism. The mechanism is explained and its performance is evaluated through simulation experiments. Simulation results show that the proposed mechanism provides high Packet Reception Ratio with low Packet Delivery Latency for priority traffic.

International audience; Duty-cycling technique has been widely adopted in MAC protocols for wireless sensor networks to conserve energy. However, low duty-cycle also leads to limited throughput in most of existing solutions. In this paper, we propose iQueue-MAC to provide immediate yet energy-efficient throughput enhancement for dealing with burst or heavy traffic. Combined with CSMA/CA, iQueue-MAC makes use of queue length of each sensor node and allocates suitable TDMA slots to them for packets transmission. During light traffic period, no extra slots will be allocated; iQueue-MAC acts like other low duty-cycle MACs to conserve power. While in burst or heavy traffic period, iQueue-MAC senses the build up of packet queues and dynamically schedules adequate number of slots for packet transmission. We have implemented iQueue-MAC on STM32W108 chips that offer IEEE 802.15.4 standard communication. We set up several real- world experimental scenarios, including a 46 nodes multi-hop test-bed for simulating a general application, and conducted numerous experiments to evaluate iQueue-MAC, in comparison with other traffic adaptive duty-cycle protocols, such as multi- channel version RI-MAC and CoSenS. Results clearly show that iQueue-MAC outperforms multi-channel version of RI-MAC and CoSenS in terms of packet delay and throughput.

This paper proposes a carrier-sensing multiple access protocol for asynchronous multiple-packet reception (MPR), which enables wireless receivers to correctly decode partially time-overlapping packets. Unlike previous studies, which require back-off nodes to constantly monitor the channel, our design requires only that each node sense the number of transmitting nodes after the completion of the back-off period for determining whether to begin transmission in the next time slot. In addition, we develop an analytical model to evaluate relevant parameters and performance metrics of the proposed protocol. Our model relies on the channel-sensing probability of a node in a randomly chosen slot, rather than channel-accessing probability adopted in previous models for asynchronous MPR. The results are validated through numerical study under a variety of network conditions. We also show that the proposed protocol is quite robust to imperfect estimation in channel sensing, and is more energy-efficient than other similar threshold-based protocols.

Traffic safety applications using vehicle-to-vehicle (V2V) communication is an emerging and promising area within the ITS environment. Many of these applications require real-time communication with high reliability. To meet a real-time deadline, timely and predictable access to the channel is paramount. The medium access method used in 802.11p, CSMA with collision avoidance, does not guarantee channel access before a finite deadline. The well-known property of CSMA is undesirable for critical communications scenarios. The simulation results reveal that a specific vehicle is forced to drop over 80% of its packets because no channel access was possible before the next message was generated. To overcome this problem, we propose to use STDMA for real-time data traffic between vehicles. The real- time properties of STDMA are investigated by means of the highway road simulation scenario, with promising results., 28 pages, 18 figures, International Journal of Network Security & Its Applications, International Journal of Network Security & Its Applications (IJNSA), Vol.5, No.2, March 2013

In this paper we consider a multi-hop wireless network, where a source transmits data to a destination node, through a route composed of multiple relays which are randomly distributed over a line. Priority-based Carrier-Sense Multiple Access (P-CSMA), a novel Medium Access Control (MAC) protocol, is proposed. According to the protocol, when accessing the radio channel different levels of priority are assigned to nodes, depending on their positions in the route: nodes closer to the destination have higher priority with respect to those closer to the source. The priority in the access to the channel is managed by assigning to nodes different durations of the sensing phase. This mechanism speeds up the transmission of packets which are already in the route, making the transmission flow more efficient. Results show that P-CSMA outperforms existing contention-basedMAC protocols, like p-persistent CSMA and Slotted ALOHA. A mathematical model to derive the performance in terms of packet success probability and average throughput is also provided. The model represents an effective tool for the performance analysis of multi-hop CSMA-based wireless networks, when accounting for interference, due to the hidden terminal node problem.

International audience; In this paper we compare the spatial throughput of Aloha and Carrier Sense Multiple Access (CSMA) in Wireless multihop Ad-Hoc Networks. In other words we evaluate the gain offered by carrier sensing (CSMA) over the pure statiscal collision avoidance which is the basis of Aloha. We use a Signal-to-Interference-and-Noise Ratio (SINR) model where a transmission is assumed to be successful when the SINR is larger than a given threshold. Regarding channel conditions, we consider both standard Rayleigh and negligible fading. For slotted and non-slotted Aloha, we use analytical models as well as simulations to study the density of successful transmissions in the network. As it is very difficult to build precise models for CSMA, we use only simulations to compute the performances of this protocol. We compare the two Aloha versions and CSMA on a fair basis, i.e. when they are optimized to maximize the density of successful transmissions. For slotted Aloha, the key optimization parameter is the medium access probability, for non-slotted Aloha we tune the mean back-off time, whereas for CSMA it is the carrier sense threshold that is adjusted. Our study shows that CSMA always outperforms slotted Aloha, which in turn outperforms its non-slotted version.

The main objective of this thesis is to analyze the performance of wireless networks under various scenarios: stationary, mobile, single-hop and multi-hop networks. Our main focus in the first two parts of this thesis is on the geometric placement of simultaneous transmitters in the network. In the first part, we study the impact of the placement of transmitters, by the medium access control scheme, on the performance of single-hop wireless network. We establish a general framework and study the optimal placement of transmitters in the network. Later we compare this optimal placement with placements obtained by random point processes such as Poisson point process, ALOHA, node coloring and CSMA. Our analysis allows us to evaluate the per- formance gains of a highly managed medium access control that would be required to implement the optimal placement of transmitters. For instance, we show that the capacity of this highly managed medium access control cannot be more than twice the capacity of a low managed medium access control such as ALOHA. Later, we use analytical methods to evaluate the heuristics for optimizing the capacity and coverage in an existing cellular network by optimally locating additional base stations. In the second part, we extend our analysis to multi-hop wireless network where we evaluate the optimum transmission range and network throughput capacity with various medium access control schemes. Our analyses in the first two parts of this thesis allow us to gain perspectives into the theoretical limits on the performance of an optimized medium access control in single-hop and multi-hop wireless network. In the last part, we shift our focus to capacity-delay tradeoff in mobile wireless network. We propose a georouting scheme and study its scaling properties. Using a realistic mobility model and the information available at mobile nodes, our scheme achieves a delay which is bounded by a constant with network capacity that increases quasi-linearly when the number of nodes in the network increases and approaches infinity., L'objectif principal de cette thèse est d'analyser la performance des réseaux sans fil selon divers scénarios: réseaux fixes, réseaux mobiles, réseaux mono-saut, et réseaux multi-sauts. Dans les deux premières parties de cette thèse, nous nous focalisons sur le placement géométrique des émetteurs simultanés dans le réseau. Dans la première partie, par l'intermédiaire d'une méthode d'accès au médium, nous étudions l'impact de l'emplacement des émetteurs sur la performance du réseau sans fil mono-saut. Nous établissons une structure générale et nous étudions l'emplacement des émetteurs dans le réseau. Ensuite, on compare ces résultats aux résultats obtenus à l'aide d'un par processus ponctuels aléatoires tels que le processus ponctuel de Poisson, ALOHA, le coloriage des nœuds et CSMA. Notre analyse nous permet d'évaluer les gains en performance d'une méthode d'accès au médium efficace qui serait nécessaire pour mettre en œuvre le déploiement optimal des émetteurs. Par exemple, nous montrons que la capacité garantie par une méthode d'accès très complexe est au plus deux fois la capacité d'un contrôle d'accès avec une faible complexité comme ALOHA. Plus tard, nous utilisons des méthodes analytiques pour évaluer les heuristiques pour l'optimisation de la capacité et de la couverture d'un réseau cellulaire existant de façon optimale via l'ajout de stations de base supplémentaires. Dans la deuxième partie, nous étendons notre analyse à un réseau sans fil multi-sauts où nous évaluons la portée de transmission optimale et la capacité du réseau avec différentes méthodes d'accès au médium. Nos analyses dans les deux premières parties de cette thèse nous permettent d'avoir des perspectives par rapport aux limites théoriques de la performance d'une méthode optimisée d'accès au médium pour les réseaux sans fil mono-saut et multi-sauts. Dans la dernière partie, nous concentrons nos efforts sur l'étude du compromi entre les délais et la capacité dans le réseau mobile sans fil. Nous proposons un routage géographique et nous étudions ses propriétés de passage l'échelle. En se basant sur un modèle de mobilité réaliste et des informations disponibles au niveau des nœuds mobiles, notre méthode de routage permet d'obtenir des délais qui sont bornés par une constante lorsque la capacité du réseau augmente de façon quasi-linéaire et quand le nombre de nœuds dans le réseau augmente et tend vers l'infini.

In IEEE 802.11p VANET networks the transmission scheduling is distributed and asynchronous. The number of simultaneous transmitters is thus closely related to the CSMA/CA mechanism which limits the spatial reuse of the channel. The capacity is bounded by a constant $C$ whatever the number of nodes and the type of routing schemes. This paper aims to evaluate the spatial reuse of a VANET (using CSMA/CA) and to deduce its maximum capacity. The proposed model is an extension of a classical \textit{packing problem}. We prove formally that the intensity of the maximum number of simultaneous transmitters (the maximal spatial reuse) converges to a constant and propose a simple estimate of this constant. Realistic simulations show that the theoretical capacity offers a very tight bound on the real capacity of the network.

Wireless Sensor Networks (WSN) are emerging because of the developments in wireless communication technology and miniaturization of the hardware. WSN consists of a large number of low-cost, low-power, multifunctional sensor nodes to monitor physical conditions, such as temperature, sound, vibration, pressure, motion, etc. The MAC protocol to be used in the sensor networks must be energy efficient and this should aim at conserving the energy during its operation. In this paper, with the focus of analyzing the MAC protocols used in wireless Adhoc networks to WSN, simulation experiments were conducted in Global Mobile Simulator (GloMoSim) software. Number of packets sent by regular nodes, and received by sink node in different deployment strategies, total energy spent, and the network life time have been chosen as the metric for comparison. From the results of simulation, it is evident that the IEEE 802.11 protocol performs better compared to CSMA and MACA protocols., {"references":["Ian F. Akyildiz, Weilian Su, Yogesh sankara subramaniam, and Erdal Cayirc, \"Survey on Sensor Networks\", IEEE Communications\nMagazine, pp. 102-114, August 2002.","Edoardo S. Biagioni, and Galen Sasaki, \"Wireless Sensor Placement for\nReliable and Efficient Data Collection, 36th Annual Hawaii International Conference on System Sciences (HICSS'03) vol. 5,pp.10,2003.","Kenan Xu, Glen Takahara, and Hossam Hassanein, \"On the robustness\nof grid-based deployment in wireless sensor networks\", Proceedings of\nthe International conference on wireless Communications and mobile\ncomputing, IWCMC '06, 2006.","Ilker Demirkol, Cem Ersoy and Faith Alagoz, \"MAC Protocol for\nWireless Sensor Networks:A Survey\", IEEE Communications\nMagazine, pp.115-121, April 2006.","Kleinrock, L., and Tobagi, F.A, \" Packet Switching in Radio Channels:\nPart I- Carrier Sense Multiple-Access Modes and Their Throughput-\nDelay Characteristics\", IEEE Transactions on communications, 23(12):\npp.1400-1416, 1975.","Karn P, \" MACA - A New Channel Access Protocol for Packet Radio\",\nProceedings of the ARRL/CRRL Amateur Radio Ninth Computer\nNetworking Conference, pp. 134-140, 1990.","Guido R. Hiertz, Sebastian Max, Rui Zhao, Dee Denteneer, and Lars\nBerlemann, \" Principles of IEEE 802.11s\", 6th International Conference\non Computer Communications and Networks (ICCCN), pp. 1002-1007,\n2007.","Carrier Sense Multiple Access (CSMA), Available at\nhttp://en.wikipedia.org/wiki / Carrier_sense_multiple_access.","Wei Ye, John Heidemann, and Deborah Estrin, \" Medium Access\nControl with Coordinated Adaptive Sleeping for Wireless Sensor\nNetworks\", IEEE /ACM Transactions On Networking, Vol. 12, No. 3,\npp. 493-506, June 2004.\n[10] TelosB Mote Specification, Available at www.willow.co.uk."]}

International audience; In this paper, we propose a simple theoretical model to compute the maximum spatial reuse feasible in a VANET. We focus on the ad hoc mode of the IEEE 802.11p standard. Our model offers simple and closed formulae on the maximum number of simultaneous transmitters, and on the distribution of the distance between them. It leads to an accurate upper bound on the maximum capacity. In order to validate our approach, results from the analytical models are compared to simulations performed with the network simulator NS-3. We take into account different traffic distributions (traffic of vehicles) and we study the impact of this traffic on capacity.

Underwater Acoustic Sensor Networks (UW-ASNs) have recently been proposed as a way to explore and observe the ocean, which covers two-thirds of the Earth's surface. In particular, we consider a SEA Swarm (Sensor Equipped Aquatic Swarm) architecture for short-term ad hoc real-time aquatic exploration, such as oil and chemical spill monitoring, submarine detection, and surveillance, by deploying drifting sensor nodes (e.g., UCSD Drogues) to the venue of interest that form a swarm and move as a group with the ocean oceanic current. Each sensor monitors local underwater activities and reports critical data or events in real-time using acoustic multi-hop routing to a distant data collection center, e.g., surface buoys or Autonomous Underwater Vehicles (AUVs).As SEA Swarm architecture adopts acoustic links as a means of communication, it is accordingly confronted with long propagation delays, low bandwidth, and high transmission power consumption. To put SEA Swarm architecture into practical use and alleviate these limitations, we propose the Delay-aware Opportunistic Transmission Scheduling (DOTS) algorithm to increase channel utilization by harnessing both temporal and spatial reuse. Extensive simulation results show that DOTS outperforms existing solutions, S-FAMA, DACAP, and CS-ALOHA in a line topology, in a highly competitive medium access star topology, and in a random topology with an underwater mobility by harnessing temporal and spatial reuse. Furthermore, in a SEA Swarm architecture, a sensor cloud that drifts with water currents and enables 4D (space and time) monitoring of local underwater events such as contaminants, marine life and intruders, is escorted at the surface by drifting sonobuoys that collect the data from underwater sensors via acoustic modems and report it in real-time via radio to a monitoring center. Thus, to realize SEA Swarm architecture, designing an efficient anycast routing algorithm for reliable underwater sensor event reporting to any one of the surface sonobuoys is imperative. Major challenges are the ocean current and the limited resources (bandwidth and energy). We address these challenges and propose two hydraulic pressure based anycast routing protocols, namely HydroCast and VAPR, which exploit the measured pressure levels to route data to surface buoys. The proposed routing protocols are validated via extensive simulations.