Luis Felipe Urquiza Aguiar | Universitat Politecnica de Catalunya (original) (raw)

Uploads

Papers by Luis Felipe Urquiza Aguiar

Wireless vehicular communications are a key technology to provide drivers with novel services suc... more Wireless vehicular communications are a key technology to provide drivers with novel services such as collision avoidance, safety warnings and real-time traffic information. Other services are high-speed toll collection, infotainment and wireless ubiquitous connectivity. It is clear that vehicular communications will be a cornerstone of the future transport systems which will significantly change our daily lives. Vehicular ad hoc networks (VANETs) have rapidly emerged and raised novel research challenges such as the design of network protocols adapted to the specific features of VANETs, e.g. the high speed of vehicles. Also, the design of realistic simulation frameworks is an important goal to speed up the development of VANETs. This paper presents the design and evaluation of GBSR-B, a routing protocol based on GPSR that seeks to improve the performance of VANETs over urban scenarios. Our proposal includes a novel algorithm to select the optimal next-hop forwarding node. This paper also presents an alternative to the perimeter mode used in GPSR. We compare our proposal GBSR-B to GPSR and AODV using the network simulator NCTUns 6.0 [1], showing better results in terms of packet losses for different scenarios.

Message encryption does not prevent eavesdroppers from unveiling who is communicating with whom, ... more Message encryption does not prevent eavesdroppers from unveiling who is communicating with whom, when, or how frequently, a privacy risk wireless networks are particularly vulnerable to. The Crowds protocol, a well-established anonymous communication system, capitalizes on user collaboration to enforce sender anonymity. This work formulates a mathematical model of a Crowd-like protocol for anonymous communication in a lossy network, establishes quantifiable metrics of anonymity and quality of service (QoS), and theoretically characterizes the trade-off between them. The anonymity metric chosen follows the principle of measuring privacy as an attacker's estimation error. By introducing losses, we extend the applicability of the protocol beyond its original proposal. We quantify the intuition that anonymity comes at the expense of both delay and end-to-end losses. Aside from introducing losses in our model, another main difference with respect to the traditional Crowds is the focus on networks with stringent QoS requirements, for best effort anonymity, and the consequent elimination of the initial forwarding step. Beyond the mathematical solution, we illustrate a systematic methodology in our analysis of the protocol. This methodology includes a series of formal steps, from the establishment of quantifiable metrics all the way to the theoretical study of the privacy QoS trade-off. tive information about all sorts of individual preferences and behavior across a diversity of services, translates into numerous, increasingly prominent privacy risks. Further, in applications such as reporting of traffic violations,

Keywords-Vehicular ad hoc networks (VANET), network simulators, channel modeling.

This paper proposes an adaptation of the collision probability used in the measure of the availab... more This paper proposes an adaptation of the collision probability used in the measure of the available bandwidth designed for Mobile Ad hoc Networks (MANETs) and which is described in ABE . Instead, we propose a new ABE+ that includes a new function to estimate the probability of losses. This new function has been specially designed for Vehicular Ad hoc Networks, to be suited to the high mobility and variable density in vehicular environments. In this analysis we do not only consider the packet size, but also other metrics, such as, density and speed of the nodes. We include the ABE+ algorithm in the forwarding decisions of the GBSR-B protocol , which is an improvement of the well-known GPSR protocol. Finally through simulations, we compare the performance of our new ABE+ compared to the original ABE. These results show that ABE+ coupled with GBSR-B achieves a good trade-off in terms of packet losses and packet end-to-end delay.

In recent years, the general interest in routing for vehicular ad hoc networks (VANETs) has incre... more In recent years, the general interest in routing for vehicular ad hoc networks (VANETs) has increased notably. Many proposals have been presented to improve the behavior of the routing decisions in these very changeable networks. In this paper, we propose a new routing protocol for VANETs that uses four different metrics. which are the distance to destination, the vehicles' density, the vehicles' trajectory and the available bandwidth, making use of the information retrieved by the sensors of the vehicle, in order to make forwarding decisions, minimizing packet losses and packet delay. Through simulation, we compare our proposal to other protocols, such as AODV (Ad hoc On-Demand Distance Vector), GPSR (Greedy Perimeter Stateless Routing), I-GPSR (Improvement GPSR) and to our previous proposal, GBSR-B (Greedy Buffer Stateless Routing Building-aware). Besides, we present a performance evaluation of the individual importance of each metric to make forwarding decisions. Experimental results show that our proposed forwarding decision outperforms existing solutions in terms of packet delivery.

Many proposals have studied the optimization of the EDCA mechanism used by the IEEE 802.11p MAC l... more Many proposals have studied the optimization of the EDCA mechanism used by the IEEE 802.11p MAC layer to provide QoS. In this work, we focus on the queuing process done by the different Access Categories (ACs). We propose the use of a single common buffer with a prioritized buffer allocation algorithm inspired on the MAX-MIN principle for a fair sharing of a common resource. We test the proposed algorithm with a fixed and a dynamic guaranteed queue size for each AC. Results obtained from simulations in a multihop VANET scenario show that our approach outperforms traditional queuing system used in MAC 802.11p.

Buildings are important elements of cities for VANETs, since these obstacles may attenuate commun... more Buildings are important elements of cities for VANETs, since these obstacles may attenuate communications between vehicles. Consequently, the impact of buildings has to be considered as part of the attenuation model in VANET simulations of urban scenarios. However, the more elaborated the model, the more information needs to be processed during the simulation, which implies longer processing times. This complexity in simulations is not always worth it, because simplified channel models occasionally offer very accurate results. We compare three approaches to model the impact of buildings in the channel model of simulated VANETs in two urban scenarios. The simulation results for our evaluation scenarios of a traffic-efficiency application indicate that modeling the influence of buildings in urban areas as the total absence of communication between vehicles gives similar results to modeling such influence in a more realistic fashion and could be considered a conservative bound in the performance metrics.

This paper proposes a mixed linear and integer optimization model for multi-hop ad-hoc networks t... more This paper proposes a mixed linear and integer optimization model for multi-hop ad-hoc networks to select the positions of the gateways over a certain area. This model mimics the routing behavior of such network and takes into account the maximum bandwidth capacity of the network gateways. We also include a suboptimal solution for the cases in which the complexity or the amount of the data make the optimal solution infeasible. Results in a pedestrian mesh network and in a VANET scenarios show that the model locates gateways in an efficient way and that the suboptimal solution is close to the optimal one in terms of the number of required gateways or the common selected gateways.

Simulation is a very valuable mechanism to study the performance of vehicular ad-hoc networks (VA... more Simulation is a very valuable mechanism to study the performance of vehicular ad-hoc networks (VANETs), due to the high cost and effort involved in the deployment of vehicles in urban scenarios. Accordingly, as in real VANETs, simulations should involve several factors related to realistic topologies, movements, obstacles, error modeling, etc. In this paper we concentrate on evaluating the impact of packet error modeling in VANETs, by measuring losses, end-to-end delay and number of hops in realistic scenarios. For this, we considered three different nodes' densities and three channel capacities. Through simulations in a multi-hop vehicular scenario, we show that a basic packet error model can generate very similar results to the obtained by a realistic packet error model, when the configuration of the former is properly set at a low or medium channel capacity. Nevertheless, we found significant differences between the results of both models when the simulations use a high capacity channel (27 Mbps) even with a low data traffic load.

Keywords-Vehicular ad hoc networks (VANET), network simulators, channel modeling.