Jorge García-Vidal

Wireless Systems and Mobility in Next Generation Internet

WLAN Characterization.- Performance Analysis of Wireless Multihop Data Networks.- On the Shaping Introduced by IEEE 802.11 Nodes in Long-Range Dependent Traffic.- Vehicular Networks.- Measurements of IEEE 802.11g-Based Ad-Hoc Networks in Motion.- TrafficNet: A L2 Network Architecture for Road-to-Vehicle Communication.- WLAN and Sensor Networks Protocols.- A Protocol Stack for Cooperative Wireless Networks.- Cross Layer Routing and Medium Access Control with Channel Dependant Forwarding in Wireless Ad-Hoc Networks.- An Energy-Efficient Low-Latency Multi-sink MAC Protocol for Alarm-Driven Wireless Sensor Networks.- QoS and Routing in Ad-Hoc Networks.- Adaptive QoS Reservation Scheme for Ad-Hoc Networks.- DiffServ in Ad Hoc Networks.- Analytical Evaluation of the Overhead Generated by a Routing Scheme with Subnets for MANETs.- Heterogeneous Networks.- Framework for Resource Allocation in Heterogeneous Wireless Networks Using Game Theory.- On the Performance of Mobile IP in Wireless LAN Environments.- Network Selection Box: An Implementation of Seamless Communication.- Resource Management in Cellular Networks.- Joint Connection and Packet Level Analysis in W-CDMA Radio Interface.- Trunk Reservation in Multi-service Networks with BPP Traffic.- Feasible Load Regions for Different RRM Strategies for the Enhanced Uplink in UMTS Networks.- TCP in Wireless.- On the Interactions Between TCP Westwood and the AODV Routing Protocol.- Stability and Dynamics of TCP-NCR(DCR) Protocol in Presence of UDP Flows.- Mobility Agents.- Optimization Models for Application Migration to Support Mobile Thin Clients.

A Cooperative Vehicular Network Framework

Vehicular Ad Hoc Networks are networks characterized by intermittent connectivity and rapid changes in their topology. This paper addresses car-to-road communications in which vehicles use Access Points (AP) in a Delay Tolerant Network architecture. Results show how the combination of a Delay-Cooperative ARQ mechanism reduces packet losses and in conjunction with a Carry-and-Forward cooperative mechanism improves performance parameters in terms of total file transfer delay and number of AP needed to download files.

A Low Coordination Overhead C-ARQ Protocol with Frame Combining

This paper proposes a low coordination overhead cooperative automatic repeat request (ARQ) scheme with an integrated frame combiner, which exploits space diversity and cooperation between neighbouring nodes. In channels with a strong line of sight (LOS) component and low signal-to- noise ratio (SNR), the maximum achievable throughput of the proposed protocol is many times higher than for other ARQ schemes. For non LOS scenarios, the cooperative ARQ without frame combiner achieves the best efficiency results, and the overhead introduced by the frame combiner mechanisms leads to results which can be even below the classical ARQ mechanism.

Power saving trade-offs in Delay/Disruptive Tolerant Networks

Wireless nodes such as smart-phones in which the WiFi wireless card is continuously on, consume battery energy in just a few hours. Moreover, in many scenarios, an always-on wireless card is useless because there is often no need for transmission and/or reception. This fact is exacerbated in Delay/Disruptive Tolerant Network (DTN) environments, in which nodes exchange Delay Tolerant Objects (DTO) when they meet. Power Saving Management (PSM) techniques enable the lifetime of the nodes to be extended. This paper analyses the trade-offs that appear when wireless nodes periodically turn off the wireless card in order to save battery in DTN environments. The paper shows the conditions in which a node can switch off the battery without impacting the peer-to-peer contact probability, and those in which this contact probability is decreased. For example, it is shown that node lifetime can be doubled while keeping the peer-to-peer contact probability equal to one. But, further increase of the node lifetime quickly decreases peer-to-peer contact probability. Finally, the impact of power savings in DTO dissemination time is also analyzed.

A survey of wireless sensor technologies applied to precision agriculture

This paper gives a state-of-art of wireless sensor network (WSN) technologies and solutions applied to precision agriculture. The paper first considers applications and existing experiences that show how WSN technologies have been introduced in to agricultural applications. Then, a survey in hardware and software solutions is related with special emphasis on technological aspects. Finally, the paper shows how five networking and technological solutions may impact the next generation of sensors. These are: (1) scalar wireless sensor networks; (2) wireless multimedia sensor networks; (3) mobility of nodes; (4) tag-based systems; and (5) smart-phone applications.

Study of internet autonomous system interconnectivity from BGP routing tables

Recently, several authors have proposed models based on power-laws to characterize Internet topologies. Most of these works use the BGP (Border Gateway Protocol) tables published by Oregon Route Views. The adjacency matrix containing AS (autonomous system) connectivity is built from a BGP table. Having access to BGP routing tables from several geographical sites gives a broader vision of ASs connectivity, since several ASs and links may be hidden for an AS due to routing processes policies, while they may be visible to other ASs. We compare BGP tables of different sizes and enrich the adjacency matrix with the union of them. This comparison is based on the AS degree connectivity, clustering coefficient and path length. Our initial results, published in [Proceedings of HPSR2003, Torino, Italy, June 2003], show an increment of 16% in the number of links and 0.7% in the number of ASs and show that a medium-size AS can get a vision similar to a repository such as Route Views. Most of the recent works analyze whether power-law distributions, also called scale-free models, arise on Internet topologies for the whole AS-level graph. However, few ones study whether the AS connectivity of the Internet core follows a power-law distribution. Here we use well-known heuristics to identify AS peeringship and split the Internet core from small regional ISPs and end customers. We will see that the Internet core does not fit a power-law well.

A performance model of a PC based IP software router

We can define a software router as a general-purpose computer that executes a computer program capable of forwarding IP datagrams among network interface cards attached to its I/O bus. This paper presents a parametrical model of a PC based IP software router. Validation results clearly show that the model accurately estimates the performance of the modeled system at different levels of detail. On the other hand, the paper presents experimental results that provide insights about the detailed functioning of such a system and demonstrate the model is valid not only for the characterized systems but for a reasonably range of CPU, memory and I/O bus operation speeds.

Evaluation of a Cooperative ARQ Protocol for Delay-Tolerant Vehicular Networks

This paper evaluates a Cooperative ARQ protocol to be used in delay-tolerant vehicular networks. The scenario consists in cars downloading information from Access Points along a road. The key difference between proposed Cooperative ARQ protocols is when the cooperation takes place. Simply C-ARQ cooperation occurs in a packet-by-packet basis. In this proposal, that we call DC-ARQ (Delayed Cooperative ARQ), the cooperation is delayed until cars are out of the coverage area of the Access Point. The scheme has been evaluated through simulations. A comparison of DC-ARQ with a baseline case in which no cooperation is used has been performed under different vehicle densities scenarios.

Cooperative forwarding in IEEE 802.11-based MANETs

In this paper we introduce a novel cooperative forwarding mechanism for IEEE 802.11-based MANETs. The mechanism has been adapted to operate together with two well known routing protocols: AODV and LUNAR. We evaluate our proposal by means of a prototype, using pedestrian mobility inside a building. Results show that, in dense MANETs, our cooperative forwarding mechanism is a promising technique to achieve robustness, and with a low cost of overhead.

A cooperative-ARQ protocol with frame combining

This article presents a low coordination overhead cooperative Automatic Repeat reQuest (ARQ) scheme with an integrated frame combiner, which exploits space diversity and cooperation between neighbouring nodes. A comparison between cooperation with and without frame combiner is also performed. In channels with a strong Line of Sight (LOS) component and low Signal-to-Noise ratio (SNR), the efficiency of the proposed protocol is many times higher than for other ARQ schemes. For non-LOS scenarios, the cooperative ARQ without frame combiner achieves the best efficiency results, and the overhead introduced by the frame combiner mechanism leads to results that can be even below the classical ARQ mechanism. In AWGN channels, the saturation throughput of the proposed scheme integrated into a IEEE 802.11 DCF based MAC is also studied. When the number of active stations is high, the cooperative ARQ without frame combiner shows to be the best option, while for light network loads, the presented scheme performs better.