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184
Perfect simulations for random trip mobility models
 In Proc. of the 38th Annual Symposium on Simulation
, 2005
"... The random trip model was recently proposed as a generic mobility model that contains many particular mobility models, including the widelyknown random waypoint and random walks, and accommodates more realistic scenarios. The probability distribution of the movement of a mobile in all these models ..."
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The random trip model was recently proposed as a generic mobility model that contains many particular mobility models, including the widelyknown random waypoint and random walks, and accommodates more realistic scenarios. The probability distribution of the movement of a mobile in all these models typically varies with time and converges to a “steady state " distribution (viz. stationary distribution), whenever the last exists. Protocol performance during this transient phase and in steadystate may differ significantly. This justifies the interest in perfect sampling of the initial node mobility state, so that the simulation of the node mobility is perfect, i.e. it is in steady state throughout a simulation. In this work, we describe implementation of the perfect sampling for some random trip models. Our tool produces a perfect sample of the node mobility state, which is then used as input to the widelyused ns2 network simulator. We further show some simulation results for a particular random trip mobility model, based on a realworld road map. The performance metrics that we consider include various node communication properties and their evolution with time. The results demonstrate difference between transient and steadystate phases and that the transient phase can be long lasting (in the order of a typical simulation duration), if the initial state is drawn from a non steadystate distribution. The results give strong arguments in favor to running perfect simulations. Our perfect sampling tool is available to public at:
Human Mobility Modeling at Metropolitan Scales
"... Models of human mobility have broad applicability in fields such as mobile computing, urban planning, and ecology. This paper proposes and evaluates WHERE, a novel approach to modeling how large populations move within different metropolitan areas. WHERE takes as input spatial and temporal probabili ..."
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Cited by 29 (3 self)
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Models of human mobility have broad applicability in fields such as mobile computing, urban planning, and ecology. This paper proposes and evaluates WHERE, a novel approach to modeling how large populations move within different metropolitan areas. WHERE takes as input spatial and temporal probability distributions drawn from empirical data, such as Call Detail Records (CDRs) from a cellular telephone network, and produces synthetic CDRs for a synthetic population. We have validated WHERE against billions of anonymous location samples for hundreds of thousands of phones in the New York and Los Angeles metropolitan areas. We found that WHERE offers significantly higher fidelity than other modeling approaches. For example, daily range of travel statistics fall within one mile of their true values, an improvement of more than 14 times over a Weighted Random Waypoint model. Our modeling techniques and synthetic CDRs can be applied to a wide range of problems while avoiding many of the privacy concerns surrounding real CDRs.
Fallacies in evaluating decentralized systems
 In Proceedings of IPTPS
, 2006
"... Research on decentralized systems such as peertopeer overlays and ad hoc networks has been hampered by the fact that few systems of this type are in production use, and the space of possible applications is still poorly understood. As a consequence, new ideas have mostly been evaluated using commo ..."
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Cited by 25 (1 self)
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Research on decentralized systems such as peertopeer overlays and ad hoc networks has been hampered by the fact that few systems of this type are in production use, and the space of possible applications is still poorly understood. As a consequence, new ideas have mostly been evaluated using common synthetic workloads, traces from a few existing systems, testbeds like PlanetLab, and simulators like ns2. Some of these methods have, in fact, become the “gold standard ” for evaluating new systems, and are often a prerequisite for getting papers accepted at top conferences in the field. In this paper, we examine the current practice of evaluating decentralized systems under these specific sets of conditions and point out pitfalls associated with this practice. In particular, we argue that (i) despite authors ’ best intentions, results from such evaluations often end up being inappropriately generalized; (ii) there is an incentive not to deviate from the accepted standard of evaluation, even if that is technically appropriate; (iii) research may gravitate towards systems that are feasible and perform well when evaluated in the accepted environments; and, (iv) in the worstcase, research may become ossified as a result. We close with a call to action for the community to develop tools, data, and best practices that allow systems to be evaluated across a space of workloads and environments. 1.
The Random Trip Model: Stability, Stationary Regime, and Perfect Simulation
, 2006
"... We define "random trip", a generic mobility model for random, independent node motions, which contains as special cases: the random waypoint on convex or non convex domains, random walk on torus, billiards, city section, space graph, intercity and other models. We show that, for this model ..."
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Cited by 22 (0 self)
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We define "random trip", a generic mobility model for random, independent node motions, which contains as special cases: the random waypoint on convex or non convex domains, random walk on torus, billiards, city section, space graph, intercity and other models. We show that, for this model, a necessary and sufficient condition for a timestationary regime to exist is that the mean trip duration (sampled at trip endpoints) is finite. When this holds, we show that the distribution of node mobility state converges to the timestationary distribution, starting from origin of an arbitrary trip. For the special case of random waypoint, we provide for the first time a proof and a sufficient and necessary condition of the existence of a stationary regime, thus closing a long standing issue. We show that random walk on torus and billiards belong to the random trip class of models, and establish that the timelimit distribution of node location for these two models is uniform, for any initial distribution, even in cases where the speed vector does not have circular symmetry. Using Palm calculus, we establish properties of timestationary regime, when the condition for its existence holds. We provide an algorithm to sample the simulation state from a timestationary distribution at time 0 (“perfect simulation”), without computing geometric constants. For random waypoint on the sphere, random walk on torus and billiards, we show that, in the timestationary regime, the node location is uniform. Our perfect sampling algorithm is implemented to use with ns2, and is available to download from
Mobility modeling, spatial traffic distribution, and probability of connectivity for sparse and dense vehicular ad hoc networks
 IEEE Trans. Veh. Technol
"... Abstract—The mobility pattern of users is one of the distinct features of vehicular ad hoc networks (VANETs) compared with other types of mobile ad hoc networks (MANETs). This is due to the higher speed and the roadmaprestricted movement of vehicles. In this paper, we propose a new analytical mobil ..."
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Abstract—The mobility pattern of users is one of the distinct features of vehicular ad hoc networks (VANETs) compared with other types of mobile ad hoc networks (MANETs). This is due to the higher speed and the roadmaprestricted movement of vehicles. In this paper, we propose a new analytical mobility model for VANETs based on productform queueing networks. In this model, we map the topology of the streets and the behavior of vehicles at both intersections and different parts of the streets onto different parameters of a BCMP 1 open queueing network comprising M/G/ ∞ nodes. This model represents a sparse situation for VANETs. To include the effect of dense situation on the mobility model, we modify the proposed queueing network as a new one comprising nodes with statedependent service rates, i.e., M/G(n)/ ∞ nodes. With respect to the productform solution property of the proposed queueing networks, we are able to find the spatial traffic distribution for vehicles at both sparse and dense situations. Furthermore, we are able to modify the proposed queueing network to find the lower and upper bounds for the probability of connectivity. In the last part of this paper, we show the flexibility of the proposed model by several numerical examples and confirm our modeling approach by simulation. Index Terms—Connectivity, mobility model, queueing network, spatial traffic distribution, vehicular ad hoc network (VANET). I.
Random waypoint mobility model in cellular networks,” Wireless Networks
, 2007
"... Abstract. In this paper we study the socalled 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 u ..."
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Cited by 20 (4 self)
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Abstract. In this paper we study the socalled 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.
Efficient broadcasting in ad hoc wireless networks using directional antennas
 IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS
, 2006
"... Using directional antennas to conserve bandwidth and energy consumption in ad hoc wireless networks (or simply ad hoc networks) is becoming popular in recent years. However, applications of directional antennas for broadcasting have been limited. We propose a novel broadcast protocol called directio ..."
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Cited by 18 (6 self)
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Using directional antennas to conserve bandwidth and energy consumption in ad hoc wireless networks (or simply ad hoc networks) is becoming popular in recent years. However, applications of directional antennas for broadcasting have been limited. We propose a novel broadcast protocol called directional selfpruning (DSP) for ad hoc wireless networks using directional antennas. DSP is a nontrivial generalization of an existing localized deterministic broadcast protocol using omnidirectional antennas. Compared with its omnidirectional predecessor, DSP uses about the same number of forward nodes to relay the broadcast packet, while the number of forward directions that each forward node uses in transmission is significantly reduced. With the lower broadcast redundancy, DSP is more bandwidth and energyefficient. DSP is based on 2hop neighborhood information and does not rely on location or angleofarrival (AoA) information. Two special cases of DSP are discussed: the first one preserves shortest paths in reactive routing discoveries; the second one uses the directional reception mode to minimize broadcast redundancy. DSP is a localized protocol. Its expected number of forward nodes is Oð1Þ times the optimal value. An extensive simulation study using both custom and ns2 simulators shows that DSP significantly outperforms both omnidirectional broadcast protocols and existing directional broadcast protocols.
On Traffic Load Distribution and Load Balancing in Dense Wireless Multihop Networks
 EURASIP JOURNAL ON WIRELESS COMMUNICATIONS AND NETWORKING
, 2007
"... We study the load balancing problem in a dense wireless multihop network, where a typical path consists of a large number of hops, that is, the spatial scales of a typical distance between source and destination and mean distance between the neighboring nodes are strongly separated. In this limit, w ..."
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Cited by 17 (4 self)
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We study the load balancing problem in a dense wireless multihop network, where a typical path consists of a large number of hops, that is, the spatial scales of a typical distance between source and destination and mean distance between the neighboring nodes are strongly separated. In this limit, we present a general framework for analyzing the traffic load resulting from a given set of paths and traffic demands. We formulate the load balancing problem as a minmax problem and give two lower bounds for the achievable minimal maximum traffic load. The framework is illustrated by considering the load balancing problem of uniformly distributed traffic demands in a unit disk. For this special case, we derive efficient expressions for computing the resulting traffic load for a given set of paths. By using these expressions, we are able to optimize a parameterized set of paths yielding a particularly flat traffic load distribution which decreases the maximum traffic load in the network by 40 % in comparison with the shortestpath routing. Copyright © 2007 E. Hyytiä and J. Virtamo. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1.
GarciaLunaAceves, “Routing Overhead as A Function of Node Mobility: Modeling
 Framework and Implications on Proactive Routing,” Proc. of IEEE MASS’07
, 2007
"... Abstract—The paper presents a mathematical framework for quantifying the overhead of proactive routing protocols in mobile ad hoc networks (MANETs). We focus on situations where the nodes are randomly moving around but the wireless transmissions can be decoded reliablely, when nodes are within commu ..."
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Abstract—The paper presents a mathematical framework for quantifying the overhead of proactive routing protocols in mobile ad hoc networks (MANETs). We focus on situations where the nodes are randomly moving around but the wireless transmissions can be decoded reliablely, when nodes are within communication range of each other. We explicitly present a framework to model the overhead as a function of stability of topology and analytically characterize the statistical distribution of topology evolutions. The OLSR protocol is further singled out for a detailed analysis, incorporating the proposed analytical model. Results are compared against Qualnet simulations for random movements, which corroborate the essential characteristics of the analytical results. The key insight that can be drawn from the analytical results of this paper is that nodal movements will drive up the overhead by a penalty factor, which is a function of the overall stability of the network. I.