José Ángel Irastorza

Coverage extension by means of non-conventional multi-hop communications

This paper analyzes the benefits that can be obtained by using opportunistic multi-hop extensions in terms of coverage extension of traditional network deployments. We assume that there are some devices acting as relaying entities, so as to allow others reaching an Access Element, in those situations in which a direct connection is not possible. Two different network deployments are used for this analysis: in the first one, an a priori planning is not assumed and, therefore, the Access Elements are randomly deployed, thus leading to a rather poor connectivity; on the other hand, in the second case, the Access Elements are placed according to an array deployment, thus maximizing the covered area. The paper finds analytical expressions for the probability of a user to be disconnected, i.e. she is not able to reach an Access Element, or the outage probability, for both scenarios, when either one or two hop paths can be used. These results are assessed, first, and complemented later, by means of an extensive simulation-based analysis, which brings about the possibility of extending the results when more than two hops are considered. The results provide helpful insights for aiding network dimensioning processes, since they allow establishing sensible bounds on the maximum number of hops which should be used to connect to the network; in the two complementary deployments which are used throughout the paper, there was not much additional benefit for paths longer than three/four hops, regardless of the probability for a user terminal to behave as a forwarding node.

Smart Enhancement of TCP Performance Over Lossy WLAN Channels Through the Combined Use of Link Layer Techniques

This paper shows an important enhancement of TCP behavior over the IEEE 802.11b Wireless Local Area Network (WLAN) if a combination of a Forward Error Correction (FEC) scheme and a Snoop agent is added to the idle Repeat reQuest (RQ) mechanism inherently used by such technology. The FEC scheme has been improved with some smart cross-layer optimizations, and its operation adapts to the channel conditions. Besides, the aim of the Snoop agent is to back up the FEC, overcoming the deficiencies of its adaptation, which are mainly due to the high variability of the channel inside a typical office environment. A complete experimental approach has been followed, and exhaustive measurement campaigns have been carried out over a real platform to derive a large number of performance parameters. Both methods have been implemented as modules belonging to a generic layer-two Performance Enhancing Proxy (PEP).

Beyond Management in Ad Hoc, Heterogeneous WPAN Environments: an Experimental Approach

This paper presents a hierarchical management architecture which has been designed to work over next generation WPAN environments. In this sense, it copes with e.g. ad hoc networks (likely to play a fundamental role within future wireless networks) as well as with low capacity devices, such as sensors and actuators (thus, highlighting the heterogeneity that also characterize these environments). The architecture uses both a traditional-management operation (based on SNMP) and a proprietary one. Furthermore, security concerns have also been considered. One of the main contributions of the paper is that it gives some insights about the implementation of the management architecture and on how the different pieces of information are managed. In particular, the paper discusses the following aspects: network topology, ad hoc routing mechanisms, sensors, and terminal status. The main goal of the implementation is to assess the feasibility of the proposed scheme over the high dynamic environments which have been targeted

Manager Selection over a Hierarchical/Distributed Management Architecture for Personal Networks

In spite of having been the focus of several works, traditional management architectures, usually based on a centralized model, are not suitable for the particular characteristics of personal networks and their underlying multi-hop topologies. A hierarchical/distributed approach is proposed in this work, which also analyzes different strategies to optimally select the nodes taking the manager role. In order to assess the benefits and drawbacks of these mechanisms, a proprietary simulator was developed, and different metrics were studied (probability for a node to take part on the management architecture, number of hops needed to reach a manager, and fairness of the distribution of the management burden). A novel heuristic is proposed to enhance one of the analyzed strategies, and it is shown to outperform the rest of algorithms.

Fostering the simulation-based evaluation of management architectures over multi-hop topologies

This paper discusses a simulation based approach to evaluate legacy management frameworks over new personal networking architectures. After implementing a real demonstrator, gathering a broad range of devices, technologies, and services supported by this type of environments, we were able to assess the feasibility of a hierarchical management framework, validating its correct behavior. However, we realized that this demonstrator does not allow carrying out a thorough and systematic evaluation of more complex scenarios, mimicking potential real environments, especially in terms of network dimensions and mobility restrictions. Hence, we propose to extend the analysis performed over the real platform by means of the Network Simulator framework. Finally we obtain preliminary measurements to validate the approach, which aims at being the starting point to address management modeling and evaluation over multi-hop networks.

Stabilizing TCP performance over bursty wireless links through the combined use of link-layer techniques

Improving TCP performance over wireless fidelity (WiFi) networks is recognized as a crucial issue, specially in those links prone to suffer from high bit error rate (BER) and bursty error losses. This paper shows how TCP throughput over a real IEEE 802.11b wireless local area network (WLAN) in a lossy office environment is stabilized by a combination of an adaptive forward error correction (FEC) scheme in conjunction with a Snoop agent, both added to the idle repeat request (RQ) mechanism inherently used by such technology. The most innovative aspects of this work are that these techniques operate simultaneously and they have been tested over a real scenario.