Evaluating inter-arrival time in general random waypoint mobility model

In the study of wireless ad hoc networks, the Random Waypoint (RWP) mobility model is extensively used to describe the movement pattern of the hosts. In this paper, we extend our discussion to the general RWP mobility model, where the waypoints may not be uniformly distributed, and hosts may use different distributions to generate their waypoints. In particular, we study a useful property, namely the Inter-Arrival Time (IAT) of hosts to a given area in a network, when the mobility of such hosts is modeled using the random waypoint mobility model. We derive the value of IAT analytically. Three schemes are used to estimate its value. The correctness of our analysis and estimations are verified through simulations. Case studies are also carried out in this paper to show how IAT could be used in the study and applications of mobile wireless networks.     

The critical transmitting range for connectivity in mobile ad hoc networks

In this paper, we have investigated the critical transmitting range for connectivity in mobile ad hoc networks. We have proven that, in the presence of bounded and obstacle free mobility, the CTR in the mobile case is at least as large as the CTR in the case of uniformly distributed points (asymptotically). For the case of RWP mobility, we have proven a more accurate characterization of the CTR and shown that, if the pause time is 0, there is an asymptotic gap between the mobile and uniform scenario. We have verified the quality of our results through simulation. We have also presented a formula that, given the value of the CTR in the uniform case, provides a good approximation of the CTR in the most extreme case of RWP mobility, i.e., when the pause time is set to 0. We want to remark that the approach presented in this paper can be easily extended to other mobility models: If the expression of the pdf f/sub m/ that resembles the long-term node distribution is known and satisfies certain properties, it is sufficient to compute the minimum value of f/sub m/ on R to determine the value of the critical range for connectivity. We believe that the results presented in this paper provide a better understanding of the behavior of a fundamental network parameter in the presence of mobility and, in particular, of RWP mobility. From a practical point of view, our results can be used to improve the accuracy of RWP mobile ad hoc networks simulation, which is commonly used to evaluate the performance of ad hoc networking protocols.     

Analytical modeling of MAC protocol in ad hoc networks

In ad hoc networks, CSMA/CA is a widely used MAC layer protocol. There has been considerable work on the performance evaluation of this protocol. But most work is confined to saturation performance of single‐hop ad hoc networks. In this paper, we employ a linear feedback model to evaluate the performance for CSMA/CA according to the Poisson distributed traffic in both single‐hop and multi‐hop ad hoc networks. To the best of our knowledge, this is the first attempt to analytically evaluate the performance for CSMA/CA protocol under a general assumption about the traffic. This paper also gives analytical results, showing the impact of RTS/CTS. Although RTS/CTS do add the overhead to the system, they become essential when either the hidden terminal problem is dominant, or the traffic is heavy, or the packet length is very large. This paper also shows that the performance degrades dramatically in multi‐hop ad hoc networks when the number of competing nodes increases, which implies that the scalability is still a major problem in ad hoc networks. To validate our analytical results, we have done extensive simulations, and it is observed that the simulation results match the analytical results very well. Copyright © 2006 John Wiley & Sons, Ltd.     

Epoch, length of the random waypoint model in mobile ad hoc networks

In this paper, we derive the probability distribution of the epoch length for the random waypoint model in mobile ad hoc networks. An epoch here is referred to as the movement between two target locations in the mobility model. Such a study is important as the epoch length distribution may be required for the derivation of the link-duration distribution or node spatial distribution for mobile ad hoc networks. The analytical result is then verified via simulation.     

Scalable Routing Protocol for Ad Hoc Networks

In this paper we present a scalable routing protocol for ad hoc networks. The protocol is based on a geographic location management strategy that keeps the overhead of routing packets relatively small. Nodes are assigned home regions and all nodes within a home region know the approximate location of the registered nodes. As nodes travel, they send location update messages to their home regions and this information is used to route data packets. In this paper, we derive theoretical performance results for the protocol and prove that the control packet overhead scales linearly with node speed and as N ^3/2 with increasing number of nodes. These results indicate that our protocol is well suited to relatively large ad hoc networks where nodes travel at high speed. Finally, we use simulations to validate our analytical model.     

An energy-efficient MAC protocol based on IEEE 802.11 in wireless ad hoc networks

Energy efficiency is a measure of the performance of IEEE 802.11 wireless multihop ad hoc networks. The IEEE 802.11 standard, currently used in wireless multihop ad hoc networks, wastes bandwidth capacity and energy resources because of many collisions. Therefore, controlling the contention window size at a given node will increase not only the operating life of the battery but also the overall system capacity. It is essential to develop effective backoff schemes for saving power in IEEE 802.11 wireless multihop ad hoc networks. In this paper, we propose an energy-efficient backoff scheme and evaluate its performance in an ad hoc network. Our contention window mechanism devised by us grants a node access to a channel on the basis of the node’s percentage of residual energy. We use both an analytical model and simulation experiments to evaluate the effective performance of our scheme in an ad hoc network. Our extensive ns-2-based simulation results have shown that the proposed scheme provides excellent performance in terms of energy goodput, end-to-end goodput, and packet delivery ratio, as well as the end-to-end delay.     

The node distribution of the random waypoint mobility model for wireless ad hoc networks

The random waypoint model is a commonly used mobility model in the simulation of ad hoc networks. It is known that the spatial distribution of network nodes moving according to this model is, in general, nonuniform. However, a closed-form expression of this distribution and an in-depth investigation is still missing. This fact impairs the accuracy of the current simulation methodology of ad hoc networks and makes it impossible to relate simulation-based performance results to corresponding analytical results. To overcome these problems, we present a detailed analytical study of the spatial node distribution generated by random waypoint mobility. More specifically, we consider a generalization of the model in which the pause time of the mobile nodes is chosen arbitrarily in each waypoint and a fraction of nodes may remain static for the entire simulation time. We show that the structure of the resulting distribution is the weighted sum of three independent components: the static, pause, and mobility component. This division enables us to understand how the model's parameters influence the distribution. We derive an exact equation of the asymptotically stationary distribution for movement on a line segment and an accurate approximation for a square area. The good quality of this approximation is validated through simulations using various settings of the mobility parameters. In summary, this article gives a fundamental understanding of the behavior of the random waypoint model.     

Network connectivity of one-dimensional MANETs with random waypoint movement

An analysis of network connectivity of one-dimensional mobile ad hoc networks with a particular mobility scheme is presented, focusing on the random waypoint mobility scheme. The numerical results are verified using simulation to show their accuracy under practical network conditions. Observations on RWP properties further lead to approximations and an eventual simple network connectivity formula.     

An analytical study of the communication cost of data-centric storage in mobile ad hoc networks

Data-centric storage is a fundamental data management paradigm in wireless multihop networks. Originally introduced for wireless sensor networks, existing approaches are in principle also applicable in mobile ad hoc networks. However, the mobility of such networks strongly impacts storage performance in general and communication cost in particular. While this is recognized in the research community, a detailed account of the performance in terms of communication cost is lacking.In this article, we provide a detailed study of the communication cost of previously proposed data-centric storage mechanisms that are viable in mobile ad hoc networks. We first introduce a comprehensive analytical model that suitably characterizes the communication cost of data-centric storage mechanisms from the literature. We then use our model to evaluate the considered mechanisms in comparative terms as a function of relevant system parameters, including the amount of considered data, the frequency of data updates and queries, and node speed. Our results give a detailed account of data-centric storage performance and are able to identify the most suitable ranges of operation for each of the considered mechanisms.     

An overview of local capacity in wireless networks

This article introduces a metric for performance evaluation of medium access schemes in wireless ad hoc networks known as local capacity. Although deriving the end-to-end capacity of wireless ad hoc networks is a difficult problem, the local capacity framework allows us to quantify the average information rate received by a receiver node randomly located in the network. In this article, the basic network model and analytical tools are first discussed and applied to a simple network to derive the local capacity of various medium access schemes. Our goal is to identify the most optimal scheme and also to see how does it compare with more practical medium access schemes. We analyzed grid pattern schemes where simultaneous transmitters are positioned in a regular grid pattern, ALOHA schemes where simultaneous transmitters are dispatched according to a uniform Poisson distribution and exclusion schemes where simultaneous transmitters are dispatched according to an exclusion rule such as node coloring and carrier sense schemes. Our analysis shows that local capacity is optimal when simultaneous transmitters are positioned in a grid pattern based on equilateral triangles and our results show that this optimal local capacity is at most double the local capacity of ALOHA based scheme. Our results also show that node coloring and carrier sense schemes approach the optimal local capacity by an almost negligible difference. At the end, we also discuss the shortcomings in our model as well as future research directions.     

Extending Global IP Connectivity for Ad Hoc Networks

Ad hoc networks have thus far been regarded as stand-alone networks without assumed connectivity to wired IP networks and the Internet. With wireless broadband communications and portable devices with appropriate CPU, memory and battery performance, ad hoc connectivity will become more feasible and demand for global connectivity through ad hoc networking is likely to rapidly grow. In this paper we propose an algorithm and describe a developed prototype for connectivity between an ad hoc network running the ad hoc on-demand distance-vector protocol and a wired IP network where mobile IP is used for mobility management. Implementation issues and performance metrics are also discussed.     

An Analytical Model for the Node Degree in Wireless Ad Hoc Networks

Node degree is regarded as an important and convenient metric to measure the connectivity of wireless ad hoc networks. Existing studies are mainly based on the assumption that nodes are static and do not provide closed-form expressions for node degree. In this paper, we investigate three fundamental characteristics of a wireless ad hoc network: Its node degree distribution, its average node degree and its maximum node degree experienced by the nodes during their movement. We introduce a novel mathematical model to derive analytical expressions in the presence of radio channel fading. Furthermore, our results reveal that the node degree distribution follows a binomial distribution regardless of the initial distribution of nodes?? location. The results of this paper are useful to study node connectivity and to improve the algorithmic complexity of incentive protocols.     

Random waypoint mobility model in cellular networks

In this paper we study the so-called random waypoint (RWP) mobility model in the context of cellular networks. In the RWP model the nodes, i.e., mobile users, move along a zigzag path consisting of straight legs from one waypoint to the next. Each waypoint is assumed to be drawn from the uniform distribution over the given convex domain. In this paper we characterise the key performance measures, mean handover rate and mean sojourn time from the point of view of an arbitrary cell, as well as the mean handover rate in the network. To this end, we present an exact analytical formula for the mean arrival rate across an arbitrary curve. This result together with the pdf of the node location, allows us to compute all other interesting measures. The results are illustrated by several numerical examples. For instance, as a straightforward application of these results one can easily adjust the model parameters in a simulation so that the scenario matches well with, e.g., the measured sojourn times in a cell.     

Modeling of Collision Avoidance Protocols in Single-Channel Multihop Wireless Networks

Although there has been considerable work on the performance evaluation of collision avoidance schemes, most analytical work is confined to single-hop ad hoc networks or networks with very few hidden terminals. We present the first analytical model to derive the saturation throughput of collision avoidance protocols in multi-hop ad hoc networks with nodes randomly placed according to a two-dimensional Poisson distribution. We show that the sender-initiated collision-avoidance scheme achieves much higher throughput than the ideal carrier sense multiple access scheme with a separate channel for acknowledgments. More importantly, we show that the collision-avoidance scheme can accommodate much fewer competing nodes within a region in a network infested with hidden terminals than in a fully-connected network, if reasonable throughput is to be maintained. Simulations of the IEEE 802.11 MAC protocol and one of its variants validate the predictions made in the analysis. It is also shown that the IEEE 802.11 MAC protocol cannot ensure collision-free transmission of data packets and thus throughput can degrade well below what is predicted by the analysis of a correct collision avoidance protocol. Based on these results, a number of improvements are proposed for the IEEE 802.11 MAC protocol.     

Gamma random waypoint mobility model for wireless ad hoc networks

Random waypoint (RWP) mobility model is widely used in ad hoc network simulation. The model suffers from speed decay as the simulation progresses and may not reach the steady state in terms of instantaneous average node speed. Furthermore, the convergence of the average speed to its steady state value is delayed. This usually leads to inaccurate results in protocol validation of mobile ad hoc networks modeling. Moreover, the probability distributions of speed vary over the simulation time, such that the node speed distribution at the initial state is different from the corresponding distribution at the end of the simulation. In order to overcome these problems, this paper proposes a modified RWP mobility model with a more precise distribution of the nodes' speed. In the modified model, the speeds of nodes are sampled from gamma distribution. The results obtained from both analysis and simulation experiments of the average speed and the density of nodes' speed indicate that the proposed gamma random waypoint mobility model outperforms the existing RWP mobility models. It is shown that a significant performance improvement in achieving higher steady state speed values that closely model the pre‐assumed average speeds are possible with the proposed model. Additionally, the model allows faster convergence to the steady state, and probability distribution of speed is steady over the simulation time. Copyright © 2012 John Wiley & Sons, Ltd.     

Simulation-based analysis of a multi-hop integrated UMTS and WLAN network

The next generation communication networks will comprise of third-generation (3G) and fourth-generation (4G) cellular and multi-hop ad hoc networks. In particular, the Universal Mobile Telecommunications System (UMTS) and the IEEE 802.11 ad hoc networks will play a significant role. The UMTS can provide Internet service in wide areas with excellent mobility support while IEEE 802.11 can provide high speed last hop connectivity in indoor environment. The performance of the offered end-to-end TCP connection when these two different technologies come together to serve the users is an important aspect to be studied. In this paper, we build an analytical model to model the complete process of TCP packet transfer over this integrated network. The delay and end-to-end throughput are modeled. We also verify the simulation results considering the usual error rate in UMTS channels. Our analytical results match well with the simulation models that are widely used. Apart from modeling the Internet connectivity, our model can be used for multitude of tasks, such as gateway selection, resource reservation, etc., in the next generation cellular multi-hop networks.     

Performance analysis of IEEE 802.11 ad hoc networks in the presence of exposed terminals

The paper evaluates the performance effects of exposed terminals in IEEE 802.11 ad hoc networks in finite load conditions. It derives analytical models for the estimation of channel utilization and media access delay for IEEE 802.11 ad hoc networks in finite load conditions with and without exposed terminals. The simulation results show that the analytical estimated channel utilization and media access delay metrics are fairly accurate.     

Assessing the IEEE 802.11e QoS effectiveness in multi-hop indoor scenarios

The IEEE 802.11e technology is receiving much interest due to the enhancements offered to wireless local area networks in terms of QoS. Other application fields for this technology are wireless ad hoc networks, wireless mesh networks, and vehicular ad hoc networks. In the literature, most of the research works available focusing on the IEEE 802.11e technology offer simulation results alone, being hard to find empirical results of implementations that prove its effectiveness in realistic scenarios. Additionally, we consider that studies of IEEE 802.11e based on simulation platforms have not been thoroughly validated using real-life results. In this work we analyze the performance of the IEEE 802.11e technology in real multi-hop ad hoc networks. With this purpose we first we devise a set of experiments where we compare the results obtained on a small testbed to those from the ns-2 simulation platform. A significant consistency in terms of overall trends is found, although remarkable differences can be appreciated in terms of both delay and throughput results. Afterward we proceed with a full deployment of IEEE 802.11e enabled stations throughout the floor of an university building, performing several experiments using both static and dynamic routing. Experimental results show that QoS can be reasonably sustained for both voice and video traffic in multi-hop ad hoc networks, although dynamic routing protocols can hinder performance by provoking frequent on-off connectivity problems.     

Multipath multihop routing analysis in mobile ad hoc networks

This paper proposes an analytical modeling framework to investigate multipath routing in multihop mobile ad hoc networks. In this paper, a more generalized system has been considered and mathematically analyzed to observe some of the related performance measures of the ad hoc network. Each node in the network is assumed to have finite buffer. The single-path model is approximated to be a multi-node M/M/1/B tandem network, and the multi-path model as a set of multiple parallel paths. This proposed model allows us to investigate issues such as end-to-end delivery delay, throughput and routing reliability in mobile ad hoc networks. Theoretical results have been verified by numerical results. An optimal path selection strategy has been proposed to select a minimized delay path among the available multiple paths between source-destination pair.