LIAD: Adaptive bandwidth prediction based Logarithmic Increase Adaptive Decrease for TCP congestion control in heterogeneous wireless networks

In this paper, we present a Lemma to achieve the upper bound of coverage for broadcasting relay in military ad hoc based wireless communications in critical battle field environment. Then, a scalable random directional broadcasting relay (RDBR) scheme based on the theorem presented in the Lemma is presented, so that a source node is able to effectively determine the forwarding nodes, especially when the density of nodes is high. The numerical results show that the proposed RDBR scheme associated with relative forwarding distance and angle is able to increase the successful delivery ratio up to 10% compared to conventional distance based broadcasting approaches.

An efficient broadcasting scheme in support of military ad hoc communications in battle field

The presence of multi-hop topologies within all types of wireless communications is becoming more and more common, and this tendency is expected to be maintained in the near future. Although they were originally conceived to compensate the lack of subjacent infrastructure in certain scenarios, these deployments have attracted the interest of different actors in the wireless communications value chain (including network operators) and thus it is logical to think that their relevance will gradually increase. In fact, there already exist some standardization initiatives which corroborate this point to some extent. Furthermore, other additional factors, such as the rapid growth which has been seen in wireless sensor technologies, also strengthen the use of these topologies.. 


In spite of the growing activity in the multi-hop deployment field, it is still necessary to establish, in a quantitative way, their potential benefits, both for the end-users of the communication systems, as well as for the operators, considering, in addition, the high degree of heterogeneity which will characterize wireless networks in the future. 


On the other hand, as far as algorithms and protocols to be used over this type of topology are concerned, and despite the intense research which has been conducted into them, there is still a large number of issues to be tackled. First, the simple fact that their initial requirements and challenges have been modified can, and must, influence their basic principles. In addition, it becomes necessary to address their validation on real platforms and, on the other hand, to ensure that simulation-based evaluations of their performance make use of realistic models which accurately reflect the conditions which are observed in real scenarios. 


This dissertation tackles, on the one hand, the quantitative evaluation of the improvements which are achievable when using multi-hop topologies to extend legacy network deployments. One first aspect which is logical to consider is the increase in the coverage which is brought about. In this sense, a two-fold approach has been followed, employing both an analytical as well as a simulation-based analysis, to establish what the gain is. Two network models have been used, being complementary to each other; the first one assumes a complete lack of network planning for the deployment of the access elements, while the second one assumes an optimum distribution of them. Although their characteristics are completely different, the results are somehow similar for both cases. Furthermore, it can be concluded that, despite the coverage extension which can be obtained, it is indeed possible to establish a reasonable limit on the maximum number of hops to be used, since the improvement becomes less relevant for higher values. This aspect could influence the design of routing techniques to be used over this type of topology. 


Furthermore, other additional benefits have been also analyzed, using a network deployment in which the presence of heterogeneity (multi-access) is evident. The multi-hop extensions have been integrated within a generic access selection algorithm which enables the modification of the weights which are assigned to the different entities (both the end-user terminals and the network) as well as to the set of parameters and constraints to be considered when selecting the most appropriate access alternative. It is concluded that for both the end-users, who improve their perception of the quality of service, and the network, which is able to increase the overall amount of traffic possible to be handled, multi-hop extensions are certainly beneficial. 


In addition, the dissertation also tackles the improvement of the routing techniques which are traditionally employed over multi-hop networks, which are based on minimizing the number of hops between the two sides of the communication. To accomplish this, and using the Cross-Layer Optimisation paradigm, an improved version of the DSR protocol is proposed, namely SADSR. It uses information about the subjacent link qualities to modulate the route selection algorithm. It is worth highlighting that a fully empirical (on a real platform) validation has been conducted, addressing one of the most pressing demands within this field. The results obtained allow us to infer that the proposal made in the framework of this dissertation is clearly outperforming the original DSR version. 


Although the added value provided by empirical validations is unquestionable, they also have some limitations. First, they normally do not favour the establishment of large topologies, or to undertake repetitive experiments aimed at finding an average behaviour. In this sense, a simulation-based analysis is also used so as to compare the SADSR with the original DSR version as well as with other proposals which have recently attracted interest from the scientific community. The results obtained by the validation carried out on a real platform are confirmed, since the performance brought about by the SADSR is somewhat higher than that of the other strategies. 


In order to perform the previous analysis the use of a realistic channel model, able to capture with a high degree of accuracy the behaviour exhibited on real platforms, is mandatory. To fulfil this requirement, the dissertation also tackles the design, implementation, and integration within the Network Simulator platform of BEAR, a channel model based on auto-regressive filtering. It is mainly characterized by being able to emulate the bursty presence of errors which is observed over real channels. The design is based on an extensive set of measurements which is used to assess the validity of the proposal.

Contribución a la mejora de las prestaciones en redes de acceso inalámbricas no convencionales

Performance analysis of ad-hoc routing in heterogeneous clustered multi-hop wireless networks

The point coordination function (PCF) of the IEEE 802.11 WLAN facilitates deterministic frame transfer by a polling mechanism. This enables to support quality of service. Despite this benefit the PCF could be inefficient at low-to-medium traffic loads because it always polls all stations regardless of their actual demand. To overcome this drawback, we introduce a novel polling scheme where all stations simultaneously report their status by sending orthogonal signals, and a BS identifies and polls only those stations having data to send. The feasibility of orthogonal signalling is evaluated in a realistic channel model where multipath fading and additive white Gaussian noise are applied. Moreover, channel utilization of the proposed scheme is investigated analytically, and compared with other schemes through simulation. The evaluation results show that the proposed scheme considerably outperforms other schemes at low-to-medium traffic loads.

A polling method using orthogonal signalling for Wireless Local Area Networks

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

This paper shows an important enhancement of TCP behavior over the IEEE 80211b 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)

Smart Enhancement of TCP Performance Over Lossy WLAN Channels 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.

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

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 will 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 will discuss 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.

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

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.

José Ángel Irastorza

Papers

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

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

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

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

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