Secure routing in mobile wireless ad hoc networks

We discuss several well known contemporary protocols aimed at securing routing in mobile wireless ad hoc networks. We analyze each of these protocols against requirements of ad hoc routing and in some cases identify fallibilities and make recommendations to overcome these problems so as to improve the overall efficacy of these protocols in securing ad hoc routing, without adding any significant computational or communication overhead.     

Neighbor discovery in wireless networks with sectored antennas

Directional antennas offer many potential advantages for wireless networks such as increased network capacity, extended transmission range and reduced energy consumption. Exploiting these advantages requires new protocols and mechanisms at various communication layers to intelligently control the directional antenna system. With directional antennas, many trivial mechanisms, such as neighbor discovery, become challenging since communicating parties must agree on where and when to point their directional beams to communicate.In this paper, we propose a fully directional neighbor discovery protocol called Sectored-Antenna Neighbor Discovery (SAND) protocol. SAND is designed for sectored-antennas, a low-cost and simple realization of directional antennas, that utilize multiple limited beamwidth antennas. Unlike many proposed directional neighbor discovery protocols, SAND depends neither on omnidirectional antennas nor on time synchronization. SAND performs neighbor discovery in a serialized fashion allowing individual nodes to discover all potential neighbors within a predetermined time. SAND guarantees the discovery of the best sector combination at both ends of a link, resulting in more robust and higher quality links between nodes. Finally, SAND reliably gathers the neighborhood information in a centralized location, if needed, to be used by centralized networking protocols. The effectiveness of SAND has been assessed via simulation studies and real hardware implementation.     

Service discovery in mobile ad hoc networks: an overall perspective on architectural choices and network layer support issues

Service discovery is indispensable to ad hoc networking where establishing a stand-alone and self-configurable communication environment is the main objective. In this paper, we first discuss possible service discovery architectures along with the required network support for their implementation in mobile ad hoc networks. We then propose a distributed service discovery architecture that relies on a virtual backbone for locating and registering available services within a dynamic network topology. Our proposal consists of two independent components: (i) formation of a virtual backbone and (ii) distribution of service registrations, requests, and replies. The first component creates a mesh structure from a subset of a given network graph that includes the nodes acting as service brokers and also a subset of paths (which we refer to as virtual links) connecting them. Service broker nodes (SBNs) constitute a dominating set, i.e. all the nodes in the network are either in this set or only one-hop away from at least one member of the set. The second component establishes sub-trees rooted at service requesting nodes and registering servers for efficient dissemination of the service discovery control messages. Extensive simulation results are provided for comparison of performance measures, i.e. latency, success rate, and control message overhead, when different architectures and network support mechanisms are utilized in service discovery.     

Maximum lifetime broadcast communications in cooperative multihop wireless ad hoc networks: Centralized and distributed approaches

We investigate the problem of broadcast routing in energy constrained stationary wireless ad hoc networks with an aim to maximizing the network lifetime measured as the number of successive broadcast sessions that can be supported. We propose an energy-aware spanning tree construction scheme supporting a broadcast request, considering three different signal transmission schemes in the physical layer: (a) point-to-point, (b) point-to-multipoint, and (c) multipoint-to-point. First we present a centralized algorithm that requires global topology information. Next, we extend this to design an approximate distributed algorithm, assuming the availability of k-hop neighborhood information at each node, with k as a parameter. We prove that the centralized scheme has time complexity polynomial in the number of nodes and the distributed scheme has a message complexity that is linear in the number of nodes. Results of numerical experiments demonstrate significant improvement in network lifetime following our centralized scheme compared to existing prominent non-cooperative broadcasting schemes proposed to solve the same lifetime maximization problem in wireless ad hoc networks. Due to lack of global topology information, the distributed solution does not produce as much advantage as the centralized solution. However, we demonstrate that with increasing value of k, the performance of the distributed scheme also improves significantly.     

The rise and fall of spatio-temporal clusters in mobile ad hoc networks

Cluster detection has been widely applied to the problem of efficient data delivery in highly dynamic mobile ad hoc networks. By grouping participants who meet most often into clusters, hierarchical structures in the network are formed which can be used to efficiently transfer data between the participants. However, data delivery algorithms which rely on clusters can be inefficient in some situations. In the case of dynamic networks formed by encounters between humans, sometimes called Pocket Switched Networks (PSNs), cluster based data delivery methods may see a drop in efficiency if obsolete cluster membership persists despite changes to behavioural patterns. Our work aims to improve the relevance of clusters to particular time frames, and thus improve the performance of cluster based data delivery algorithms in PSNs. Furthermore, we will show that by detecting spatio-temporal clusters in PSNs, we can now improve on the data delivery success rates and efficiency of data delivery algorithms which do not use clustering; something which has been difficult to demonstrate in the past.     

An analytical study of the communication cost of data-centric storage in mobile ad hoc networks

Data-centric storage is a fundamental data management paradigm in wireless multihop networks. Originally introduced for wireless sensor networks, existing approaches are in principle also applicable in mobile ad hoc networks. However, the mobility of such networks strongly impacts storage performance in general and communication cost in particular. While this is recognized in the research community, a detailed account of the performance in terms of communication cost is lacking.In this article, we provide a detailed study of the communication cost of previously proposed data-centric storage mechanisms that are viable in mobile ad hoc networks. We first introduce a comprehensive analytical model that suitably characterizes the communication cost of data-centric storage mechanisms from the literature. We then use our model to evaluate the considered mechanisms in comparative terms as a function of relevant system parameters, including the amount of considered data, the frequency of data updates and queries, and node speed. Our results give a detailed account of data-centric storage performance and are able to identify the most suitable ranges of operation for each of the considered mechanisms.     

On the stability of paths, Steiner trees and connected dominating sets in mobile ad hoc networks

We propose algorithms that use the complete knowledge of future topology changes to set up benchmarks for the minimum number of times a communication structure (like paths, trees, connected dominating sets, etc.) should change in the presence of a dynamically changing topology. We first present an efficient algorithm called OptPathTrans that operates on a simple greedy principle: whenever a new source–destination (s–d) path is required at time instant t, choose the longest-living s–d path from time t. The above strategy when repeated over the duration of the s–d session yields a sequence of long-lived stable paths such that number of path transitions is the global minimum. We then propose algorithms to determine the sequence of stable Steiner trees and the sequence of stable connected dominating sets to illustrate that the principle behind OptPathTrans is very general and can be used to find the stable sequence of any communication structure as long as there is a heuristic or algorithm to determine that particular communication structure in a given network graph. We study the performance of the three algorithms in the presence of complete knowledge of future topology changes as well as using models that predict the future locations of nodes. Performance results indicate that the stability of the communication structures could be considerably improved by making use of the knowledge about locations of nodes in the near future.     

Forecasting user demand for wireless services: A socio-economic approach for Europe

This article reports the findings of a study for the European Commission to forecast demand for mobile communications services up to 2020. The study used a socio-economic approach including scenarios to explore the future and an original methodology for estimating traffic volumes under different socio-economic conditions. This article describes the objectives, outlines the methodology and summarises the results of the study. The study’s findings lay the foundation for a European consensus for calculating future spectrum requirements and are an important part of the process in the lead up to the World Radiocommunication Conference in 2007.     

Biased choice of a mobile telephony tariff type:: Exploring usage boundary perceptions as a cognitive cause in choosing between a use-based or a flat rate plan

Most mobile network operators provide newly acquired or existing customers with the possibility to choose between a monthly flat rate for unlimited voice calls and pay-per-minute price schemes. Consumers who maximize their utility should select the tariff type that leads to the lowest invoice amount given their anticipated service usage volume. However, previous research looking at users of fixed network telephony, broadband Internet access and other services suggests that a significant share of consumers prefers a flat rate to use-dependent price plans even though their invoice will be higher. One cognitive explanation for such biased choices is that consumers consider the ratio of the likelihood of calling enough to justify a flat rate to the probability of not calling enough to save money with a fixed price (= “ratio rule”) when choosing between the two tariff types. In this assessment they overestimate the first likelihood in proportion to the second one. Drawing on a sample of 203 mobile telephony customers in Germany the present study shows that mobile users are biased in favor of a flat rate because they overestimate their future call usage and behave in line with the “ratio rule” when choosing a tariff type. Correlates of cognitively biased tariff choices are explored. With regard to pricing practices it is concluded that managers should not follow the temptation to exploit the overestimation bias in designing pricing and advertising policies pushing customers into fixed price schemes, which do not fit their actual calling patterns.