Wireless Network Simulation Research Articles

NetTopo: A framework of simulation and visualization for wireless sensor networks

Network simulators are necessary for testing algorithms of large scale wireless sensor networks (WSNs), but lack the accuracy of real-world deployments. Deploying real WSN testbed provides a more realistic test environment, and allows users to get more accurate test results. However, deploying real testbed is highly constrained by the available budget when the test needs a large scale WSN environment. By leveraging the advantages of both network simulator and real testbed, an approach that integrates simulation environment and testbed can effectively solve both scalability and accuracy issues. Hence, the simulation of virtual WSN, the visualization of real testbed, and the interaction between simulated WSN and testbed emerge as three key challenges. In this paper, we present an integrated framework called NetTopo for providing both simulation and visualization functions to assist the investigation of algorithms in WSNs. NetTopo provides a common virtual WSN for the purpose of interaction between sensor devices and simulated virtual nodes. Two case studies are described to prove the effectiveness of NetTopo.

A comparative study on simulation vs. real time deployment in wireless sensor networks

Increasing deployment density and shrinking size of wireless sensor nodes requires small equipped battery size. This means emerging wireless sensor nodes must compete for efficient energy utilization. Medium Access Control (MAC) protocols play a vital role in energy consumption of sensor node as it controls the radio activities. Customized or open source simulators play an important role to measure the performance effectiveness of MAC protocols based on the fact that they are flexible, reduce experimental overhead and cost. Nevertheless, these benefits come at the cost of results accuracy. In this paper, we investigate differences of the behaviour of our agent based S-MAC protocols in real deployment compared to the results produced using our custom based simulator, which ignores the lower layers effects such as packet collision and overhearing. We use network simulator 2 (ns2), an open source simulator, which provides a complete protocol stack. We further try to find and explain the rationale of the variance of results produced by real deployment and that of simulators.

An ultra-wideband impulse radio PHY layer model for network simulation

This paper presents a novel modeling technique of Ultra-Wideband Impulse Radio for the simulation of wireless sensor networks, to evaluate this technology from a systems point of view that includes the effect of communication protocols. The adopted approach, named Maximum Pulse Amplitude Estimation, considers the characteristics of the propagation channel, the transmitter and receiver architectures, the modulation type, the robustness to multiple access interference and the impact of error correction coding. It differs from the state of the art by working at the symbol level instead of developing an analytical model. While this technique increases the processing time, it offers more flexibility in terms of modulations, channel models and receiver architecture. Our approach enabled us to implement the first network simulation model of the UWB PHY specified in the IEEE 802.15.4A standard. It is also the first UWB-IR network simulation model to consider an energy detection receiver. Several channel models have been implemented, offering trade-offs between simulation speed and accuracy. The performance of this energy detection transceiver is compared with MATLAB models. The packet error rate is evaluated as a function of distance with several channel models, and in the presence of interferers. It is shown that our approach leads to results in line with MATLAB models, that the choice of channel model greatly impacts the simulation speed and that the IEEE 802.15.4A UWB PHY allows some limited degree of protection against multiple access interference even when using a low performance energy detection receiver architecture.

Modeling environmental effects on directionality in wireless networks

One method for improving wireless network throughput involves using directional antennas to increase signal gain and/or decrease interference. The physical layer models used in current networking simulators only minimally address the interaction of directional antennas and radio propagation. This paper compares the models found in popular simulation tools with measurements taken across a variety of links in multiple environments. We find that the effects of antenna direction are significantly different from those predicted by the models used in the common wireless network simulators. We propose a parametric model that better captures the effects of different propagation environments on directional antenna systems; we also show that the derived models are sensitive to both the direction of signal gain and the environment in which the antenna is used.

Virtual protocol stack for WSN simulators

In the most recent years, many kinds of simulation packages have been developed for wireless sensor networks. Network developers, engineers, and researchers are frequently using the network simulators for evaluating performance and efficiency of their network protocols. However, the existing wireless network simulators have some drawbacks such as difficulties in programming, lenthy compile time, hard to understand simulator engine, and their reliability issues. In this paper, we present the Virtual Protocol Stack (VPS) for wireless network simulators. The VPS provides two important features; 1) a unified programming interface for developing network protocols, and 2) separation of simulator engine and the network protocols. By using the VPS , developers no longer concern about understanding different simulator engines. By doing so, developers can share their network protocol modules with each other. We implemented and adapted VPS on existing well-known simulation packages, and we observed that VPS well adapted to the different wireless network simulators.

Analytical and Closed-Form Expressions for the Distribution of Path Loss in Hexagonal Cellular Networks

The development of models that predict path loss in a wireless system is worthwhile since they offer valuable information without the need of expensive and time consuming measurements. In the modeling and simulation of cellular systems, a common assumption in path loss calculation is the circular shape of the cells. However, despite its simplicity, this approach has certain drawbacks. This paper proposes an alternative method that considers hexagonal-shaped cells. Exact analytical and approximate closed-form expressions for the path loss statistics are derived. The validity of the circular cell approximation is discussed. Simulated results and comparisons with measurement data in the literature validate the accuracy of the formulation. Finally, we investigate the impact of the size of the cells and the characteristics of the propagation medium on the path loss. The derived expressions simplify the analysis and system-level simulation of wireless networks. Compared to other methods, they give more accurate results in the calculation of path loss when hexagonal-shaped cells are employed.

Simulation of wireless cellular networks with impatient calls

Algorithms for the approximate calculation of the characteristics of wireless telecommunications with a microcellular structure where new and handover calls form queues with limited length have been developed. It is supposed that calls of both types can leave the queues unserved if their waiting time exceeds some threshold values. The results of numerical calculations are presented.

Graph-Theoretic Complexity Reduction for Markovian Wireless Channel Models

Accurate simulation and analysis of wireless networks are inherently dependent on accurate models which are able to provide real-time channel characterization. High-order Markov chains are typically used to model errors and losses over wireless channels. However, complexity (i.e., the number of states) of a high-order Markov model increases exponentially with the memory-length of the underlying channel. In this paper, we present a novel graph-theoretic methodology that uses Hamiltonian circuits to reduce the complexity of a high-order Markov model to a desired state budget. We also demonstrate the implication of unused states in complexity reduction of higher order Markov model. Our trace-driven performance evaluations for real wireless local area network (WLAN) and wireless sensor network (WSN) channels demonstrate that the proposed Hamiltonian Model, while providing orders of magnitude reduction in complexity, renders an accuracy that is comparable to the Markov model and better than the existing reduced state models.

Hardware and software system-level simulator for wireless sensor networks

Wireless Sensor Network is a large-scale network of resource-constrained (energy, memory and processing) sensor nodes that are deployed at different locations, in order to monitor physical or environmental conditions. A design problem is that a lot of sensor node platforms exist, and many MAC-layer and protocol configurations can be used. It is also difficult to explore design space to check for feasibility at early design stage.Focusing on widely used IEEE 802.15.4 standard, our simulator - called IDEA1- enables designers to check, through an easy to use graphical environment, the possible use of actual and future systems. That SystemC simulator is also composed of a library (that is periodically improved) of electrical devices and software stacks. It permits to find which hardware system to choose and which software to develop to best fit application requirements.

Study on minimum hop routing in wireless sensor networks simulation

In order to improve the general performance of Minimum Hop Routing(MHR) wireless sensor networks,with the help of simulation,this paper revealed the shortcomings of traditional MHR wireless sensor networks,dug out the required information at low expenses to improve the traditional MHR wireless sensor networks,discussed the improving policies,and compared the performances of the networks before and after.The theoretical analysis and simulation results imply that it will improve the data transmission reliability,energy-efficiency and general performance if we revise the traditional MHR wireless sensor networks by the information derived from network behaviors with low cost.

Multicast Delivery of File Download Services in Evolved 3G Mobile Networks With HSDPA and MBMS

This article presents and analyzes the multicast transmission problem of file download services to several users simultaneously in 3G mobile networks with MBMS (multimedia broadcast multicast services). MBMS is the second major enhancement in the downlink of the 3G standard after HSDPA (high-speed downlink packet access). Whereas HSDPA supports high speed point-to-point (p-t-p) transmissions up to several Mb/s, with MBMS the same content can be transmitted with a point-to-multipoint (p-t-m) connection to multiple users in a unidirectional fashion. Reliable delivery of files is a challenging task, as an error-free reception of the files is required. In order to increase the robustness of the p-t-m transmission, MBMS adopts new diversity techniques to cope against fast fading and to combine transmissions from multiple cells, and an additional forward error correction (FEC) mechanism at the application layer based on Raptor coding. Moreover, users not able to receive the file after the initial transmission can complete the download in a post-delivery repair phase, in which it is possible to employ both p-t-p and p-t-m connections. The article focuses on the efficient multicast delivery of files in future 3G mobile networks with HSDPA and MBMS. Delivery configurations studied include: only p-t-p transmissions with HSDPA (one for each active user), a single p-t-m transmission with MBMS, and using both jointly in a hybrid approach employing HSDPA for error repair of the MBMS transmission. The approach of minimizing the transmission energy (product of the transmit power times the transmission time) to achieve a target file acquisition probability (percentage of users that successfully receive the file) has been adopted. Radio network simulations have been performed in a typical urban scenario under full background load conditions. This way by minimizing the energy the system capacity is maximized. We investigate the optimum HSDPA and MBMS transmission configurations as a function of the time to deliver the file when used separately, and the optimum trade-off between the initial MBMS file transmission and the HSDPA error repair for the hybrid delivery.

Impact of the Physical Layer Modeling on the Accuracy and Scalability of Wireless Network Simulation

Recent years have witnessed a tremendous growth of research in the field of wireless systems and networking protocols. Consequently, simulation has appeared as the most convenient approach for the performance evaluation of such systems and several wireless network simulators have been proposed in recent years. However, the complexity of the wireless physical layer (PHY) induces a clear tradeoff between the accuracy and the scalability of simulators. Thereby, the accuracy of the simulation results varies drastically from one simulator to another. In this paper, we focus on this tradeoff and we investigate the impact of the physical layer modeling accuracy on both the computational cost and the confidence in simulations. We first provide a detailed discussion on physical layer issues, including the radio range, link and interference modeling, and we investigate how they have been handled in existing popular simulators. We then introduce a flexible and modular new wireless network simulator, called WSNet. Using this simulator, we analyze the influence of the PHY modeling on the performance and the accuracy of simulations. The results show that the PHY modeling, and in particular interference modeling, can have a significant impact on the behavior of the evaluated protocols at the expense of an increased computational overhead. Moreover, we show that the use of realistic propagation models can improve the simulation accuracy without inducing a severe degradation of scalability.

Layered Mobility Model Architecture - LEMMA

This paper presents the
 generic layered architecture for mobility
 models (LEMMA), which can be used to
 construct a wide variety of mobility
 models, including the majority of models
 used in wireless network simulations. The
 fundamental components of the
 architecture are described and analyzed,
 in addition to its benefits. One of the core
 principles stipulates that each mobility
 model is divided in five distinct layers that
 communicate via interfaces. This allows
 their easy replacement and
 recombination, which we support by
 reviewing 19 layers that can form 480
 different mobility models. Some of the
 advanced features provided by the
 architecture are also discussed, such as
 layer aggregation, and creation of hybrid
 and group mobility models. Finally, some
 of the numerous existing studies of the
 different layers are presented.

VGSim: An integrated networking and microscopic vehicular mobility simulation platform

Simulation is the predominant tool used in research related to vehicular ad hoc networks. In this article we first present the key requirements for accurate simulations that arise from the various applications supported by VANETs, and review the current state-of the-art VANET simulation tools. We then present VGSim, an integrated networking and microscopic vehicular mobility simulation platform. VGSim provides full-fledged wireless network simulation with an accurate traffic mobility model. These two components are tightly integrated and can interact dynamically. We discuss the flexibility of VGSim in adopting different mobility models and also present simulation results that empirically validate the modified mobility model we implemented. We discuss how VANET applications can be easily modeled in VGSim, and demonstrate this using two important applications, Accident Alert and Variable Speed Limit.

Self-propagating mal-packets in wireless sensor networks: Dynamics and defense implications

Self-propagating mal-packets have become an emergent threat against information confidentiality, integrity, and service availability in wireless sensor networks. While playing an important role for people to interact with surrounding environment, wireless sensor networks suffer from growing security concerns posed by mal-packets because of sensor networks’ low physical security, lack of resilience and robustness of underlying operating systems, and the ever-increasing complexity of deployed applications. In this paper, we study the propagation of mal-packets in 802.15.4 based wireless sensor networks. Based on our proposed mal-packet self-propagation models, we use TOSSIM, a simulator for wireless sensor networks, to study their propagation dynamics. We also present a study of the feasibility of mal-packet defense in sensor networks. Specifically, we apply random graph theory and percolation theory to investigate the immunization of highly-connected nodes, i.e., nodes with high degrees of connectivity. Our goal is to partition the network into as many separate pieces as possible, thus preventing or slowing down the mal-packet propagation. We study the percolation thresholds of different network densities and the effectiveness of immunization in terms of connection ratio, remaining link ratio, and distribution of component sizes. We also present an analysis of the distribution of component sizes.

High-fidelity and time-driven simulation of large wireless networks with parallel processing

Parallel processing is a promising technique for reducing the execution time of a large and complex wireless network simulation. In this article, a parallel processing technique is presented for time-driven simulations of large and complex wireless networks. The technique explicitly considers the physical-layer details of wireless network simulators such as shadowing and co-channel interference. The technique uses multiple processors interconnected with highspeed links. Principles and issues are elaborated, including workload partitioning, synchronization, and database design. Numerical results from two different wireless network simulators employing the technique are presented to demonstrate the performance of the technique. The results indicate that the technique can significantly improve the run-time performance of time-driven simulations of large and complicated wireless networks of different types.

Wireless network modeling and simulation tools for designers and developers

Modeling and simulation methods are employed by scientists and engineers to gain insight into system behavior that can lead to faster product time-to-market and more robust designs. These advantages come at the cost of model development time and the potential for questionable results because the model represents limited attributes of the actual system. M & S techniques are used to characterize complex interactions and performance at various layers of the protocol stack. This article provides a discussion of M & S for wireless network designers and developers, with particular attention paid to the architectural issues, as well as a discussion of the various communication M & S tools available today. The topics presented span the protocol stack, including radio-frequency-propagation M & S tools, physical-layer and waveform M & S, network-layer M & S, and distributed simulation, as well as waveform generation for test and evaluation.

Impacts of Radio Access Protocols on Cooperative Vehicle Collision Avoidance in Urban Traffic Intersections

This paper p resents the design of a Cooperative Collision Avoidance application, and evaluates its performance with DSRC-recommended 802.11 Medium Access Control (MAC) and with a novel Vehicular Self-Organizing MAC (VeSOMAC) protocol. VeSOMAC is designed as a fully distributed TDMA protocol that relies on an in-band control exchange technique for autonomous TDMA slot allocation among vehicle-mounted wireless communication modules. A hybrid traffic and wireless network simulator has been developed for evaluating both network level and application level performance in the presence of different wireless access protocols. Detailed network and vehicular traffic simulation models have also been developed for evaluating a Cooperative Collision Control (CCA) application, operating in urban traffic intersection scenarios. Simulation results demonstrate that unlike the 802.11 style contention based protocols, a schedule based protocol such as VeSOMAC can offer better vehicle safety performance through smaller and bounded packet latency in vehicular ad hoc networks.

Characterizing 802.11 wireless link behavior

Since wireless signals propagate through the ether, they are significantly affected by attenuation, fading, multipath, and interference. As a result, it is difficult to measure and understand fundamental wireless network behavior. This creates a challenge for both network researchers, who often rely on simulators to evaluate their work, and network managers, who need to deploy and optimize operational networks. Given the complexity of wireless networks, both communities often rely on simplifying rules, which frequently have not been validated using today's wireless radios. In this paper, we undertake a detailed characterization of 802.11 link-level behavior using commercial 802.11 cards. Our study uses a wireless testbed that provides signal propagation emulation, giving us complete control over the signal environment. In addition, we use our measurements to analyze the performance of an operational wireless network. Our work contributes to a more accurate understanding of link-level behavior and enables the development of more accurate wireless network simulators.

Modeling directionality in wireless networks

The physical-layer models commonly used in current networking research only minimally address the interaction of directional antennas and radio propagation. This paper compares the models found in popular simulation tools with measurements taken across a variety of links in multiple environments. We find that the effects of antenna direction are significantly different from the models used by the common wireless network simulators. We propose a parametric model which better captures the effects of different propagation environments on directional antenna systems. We believe that adopting this model will allow more realistic simulation of protocols relying on directional antennas, supporting better design and more valid assessment of those protocols.