Marcello Caleffi

Reactive routing for mobile cognitive radio ad hoc networks

Although more than a decade has passed from the proposal of the Cognitive Radio paradigm, in these years the research has mainly focused on physical and medium access issues, and few recent works focused on the problem of routing in cognitive networks. This paper addresses such a problem by evaluating the feasibility of reactive routing for mobile cognitive radio ad hoc networks. More specifically, we design a reactive routing protocol for the considered scenario able to achieve three goals: (i) to avoid interferences to primary users during both route formation and data forwarding; (ii) to perform a joint path and channel selection at each forwarder; (iii) to take advantage of the availability of multiple channels to improve the overall performance. Two different versions of the same protocol, referred to as Cognitive Ad-hoc On-demand Distance Vector (CAODV), are presented. The first version exploits inter-route spectrum diversity, while the second one exploits intra-route spectrum diversity. An exhaustive performance analysis of both the versions of the proposed protocol in different environments and network conditions has been carried out via numerical simulations. The results state the suitability of the proposed protocol for small mobile cognitive radio ad hoc networks.

OPERA: Optimal Routing Metric for Cognitive Radio Ad Hoc Networks

Two main issues affect the existing routing metrics for cognitive radio ad hoc networks: i) they are often based on heuristics, and thus they have not been proved to be optimal; ii) they do not account for the route diversity effects, and thus they are not able to measure the actual cost of a route. In this paper, an optimal routing metric for cognitive radio ad hoc networks, referred to as OPERA, is proposed. OPERA is designed to achieve two features: i) Optimality: OPERA is optimal when combined with both Dijkstra and Bellman-Ford based routing protocols; ii) Accuracy: OPERA exploits the route diversity provided by the intermediate nodes to measure the actual end-to-end delay, by taking explicitly into account the unique characteristics of cognitive radio networks. A closed-form expression of the proposed routing metric is analytically derived for both static and mobile networks, and its optimality is proved rigorously. Performance evaluation is conducted through simulations, and the results reveal the benefits of adopting the proposed routing metric for cognitive radio ad hoc networks.

CAODV: Routing in mobile ad-hoc cognitive radio networks

This paper deals with the routing in cognitive mobile ad hoc networks. We propose to modify the widely adopted Ad-hoc On-demand Distance Vector (AODV) protocol [1] in order to assure its functionality in the considered scenario. The resulting protocol, referred to as the Cognitive Ad-hoc On-demand Distance Vector (CAODV) protocol, has been designed according to three guidelines: i) to avoid regions of primary users activity during both route formation and packet discovery without requiring a dedicated common control channel; ii) to perform a joint path and channel selection at each forwarder to minimize the route cost; iii) to take advantage of the availability of multiple channels to improve the overall performances. The performances of CAODV have been evaluated by means of numerical simulations, and the experimental results confirm its effectiveness for cognitive mobile ad hoc networks.

M-DART: multi-path dynamic address routing

The paper proposes a Distributed Hash Table (DHT)-based multi-path routing protocol for scalable ad hoc networks. Specifically, we propose a multipath-based improvement to a recently proposed DHT-based shortest-path routing protocol, namely the Dynamic Address RouTing (DART). The resulting protocol, referred to as multi-path DART (M-DART), guarantees multi-path forwarding without introducing any additional communication or coordination overhead with respect to DART. The performances of M-DART have been evaluated by means of numerical simulations across a wide range of environments and workloads. The results show that M-DART performs the best or at least comparable with respect to widely adopted routing protocols in all the considered scenarios. Moreover, unlike these protocols, it is able to assure satisfactory performances for large networks by reducing the packet loss by up to 75%. Copyright

Augmented Tree-based Routing Protocol for Scalable Ad Hoc Networks

In ad hoc networks scalability is a critical requirement if these technologies have to reach their full potential. Most of the proposed routing protocols do not operate efficiently with networks of more than a few hundred nodes. In this paper, we propose an augmented tree-based address space structure and a hierarchical multi-path routing protocol, referred to as augmented tree-based routing (ATR), which utilizes such a structure in order to solve the scalability problem and to gain good resilience against node failure/mobility and link congestion/instability. Simulation results and performance comparisons with existing protocols substantiate the effectiveness of the ATR.

A theoretical model for opportunistic routing in ad hoc networks

Traditional routing strategies for multi-hop wireless networks forward packets by selecting at the sender side the next hop for each packet. Recently, such a paradigm has been called into question by a new approach, namely the Opportunistic Routing. It exploits the broadcast nature of wireless transmissions to take advantage from spatial diversity by routing the packets according to the propagation conditions, i.e. by selecting the next hop at the receiver side. Although numerous opportunistic algorithms and protocols have been proposed in the last years, very few works have used an analytical approach to analyze the opportunistic routing behavior so as to provide a guideline for future protocol design. In this paper, we propose an analytical model to describe any routing procedures operating according to the opportunistic paradigm. It applies in a very general multi-hop scenario and is not restricted to any specific network topology or opportunistic protocol. The model requires the knowledge of both the delivery ratios and node priority, which is based on the adopted routing metric (Expected Transmission Count (ETX), geographic distance, etc). In this paper we exploit such a model to derive a closed-form expression of the average number of data-link transmissions needed to successfully deliver a packet.

Joint path and spectrum diversity in cognitive radio ad-hoc networks

AbstractThe uncertain availability of the spectral resource imposes unique challenges in cognitive radio networks. One of the critical issues is to counteract the performance degradation experienced by cognitive users (CUs) due to the activity of primary users (PUs). Since the activity of PUs varies both in frequency and space domain, diversity techniques can represent an efficient way to address this issue. In this article, it is proposed to jointly exploit path and spectrum diversity for effective use of spectrum in cognitive radio ad-hoc networks (CRAHNs). By jointly exploiting both the diversities, CUs can switch dynamically to different paths and spectrum bands for communicating with each other in presence of frequency- and space-varying PU activity. This idea is adopted in a routing protocol, referred to as Dual Diversity Cognitive Ad-hoc Routing Protocol, and simulation results reveal the effectiveness of introducing joint path and spectrum diversity in CRAHNs.

Decision Maker Approaches for Cooperative Spectrum Sensing: Participate or Not Participate in Sensing?

Cooperative spectrum sensing techniques are mainly based on two different decision approaches, according to the role of the decision maker: i) in the Combining Decision approach, the decision maker combines the sensing information collected from its cooperators, without participating in the sensing of the monitored band; ii) in the Sensing & Combining Decision approach, the decision maker combines both the sensing information of its cooperators and its own local sensing information. The choice of the decision approach deeply affects the performance of any cooperative spectrum sensing technique. However, the key issue of choosing the decision approach that guarantees the higher detection accuracy independently of the underlying cooperative sensing architecture is still an open problem. For this, in this paper, the criteria for an effective decision-approach selection are analytically derived with the object of maximizing the detection accuracy in presence of realistic channel propagation effects. Specifically, through a theoretical analysis, it is proven that the detection accuracy exhibits a threshold behavior as a function of the adopted decision approach. Closed-form expressions of such a threshold are analytically derived and practical insights for the decision approach choice are provided. Finally, the theoretical analysis is validated through simulations.

A reliability-based framework for multi-path routing analysis in mobile ad-hoc networks

Unlike traditional routing procedures that, at the best, single out a unique route, multi-path routing protocols discover proactively several alternative routes. It has been recognised that multi-path routing can be more efficient than traditional one mainly for mobile ad hoc networks, where route failure events are frequent. Most studies in the area of multi-path routing focus on heuristic methods, and the performances of these strategies are commonly evaluated by numerical simulations. The need of a theoretical analysis motivates such a paper, which proposes to resort to the terminal-pair routing reliability as performance metric. This metric allows one to assess the performance improvement gained by the availability of route diversity. More specifically, resorting to graph theory, we propose an analytical framework to multi-path route discovery processes against route failures for mobile ad hoc networks. Moreover, we derive a useful bound to easily estimate the performance improvements achieved by multi-path routing with respect to any traditional routing protocol. Finally, numerical simulation results show the effectiveness of this performance analysis.

Human-mobility enabled wireless networks for emergency communications during special events

Abstract During social gatherings or emergency situations, infrastructure-based communication networks have difficulty operating given either increased traffic demand or possible damage. Nevertheless, current communication networks still rely on centralized networking paradigms. The adoption of a peer-to-peer communication paradigm would be better adapted to these needs, especially if it relies on the mobile phones that people normally carry, since they are automatically distributed where the communication needs are. However a question arises: can the spatio-temporal distribution of mobile phones enable a partially-connected ad hoc network that allows emergency communications to happen with an acceptable delay? To try to answer this question, we defined a methodology composed of three steps. First, the positions of seven hundred humans, spread over a metropolitan area, have been anonymously traced during a special gathering event. Then, with a multi-disciplinary approach, we have inferred the contact events from the humans’ traces. Finally, we have assessed the effectiveness of an ad hoc network established by the mobile phones to disseminate emergency information to the population in a timely fashion. The results reveal that the humans’ mobility can effectively enable emergency communications among a significant subset of mobile phones, although the connectivity of the network strictly depends on the number of cooperating devices and on the maximum allowed delay.