Angela Sara Cacciapuoti

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.

Correlation-Aware User Selection for Cooperative Spectrum Sensing in Cognitive Radio Ad Hoc Networks

This paper develops a solution for the problem of uncorrelated user selection in mobile cognitive radio ad hoc networks, with the objective to increase the performance of cooperative spectrum sensing. For this, a fully distributed user selection algorithm is developed by adaptively selecting uncorrelated cognitive radio users, which is able to account for dynamic changes in the network topology and in the channel conditions. Since the proposed user selection is based on the evaluation of the correlation experienced by the cognitive radio users, it is mandatory to have a parameter able to measure the correlation among them. For this, a spatial correlation coefficient is proposed to express the correlation characteristics of mobile cognitive radio users in different environments. Performance evaluation is conducted through simulations, and the results reveal the benefits of adopting the proposed correlation-aware user selection for cooperative spectrum sensing.

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.

Optimal Primary-User Mobility Aware Spectrum Sensing Design for Cognitive Radio Networks

A key issue of the spectrum sensing functionality in Cognitive Radio (CR) networks is the ability of tuning the sensing time parameters, i.e., the sensing time and the transmission time, according to the Primary User (PU) network dynamics. In fact, these parameters influence both the spectrum sensing efficiency and the PU interference avoidance. This issue becomes even more challenging in presence of PU mobility. In this paper, an optimal spectrum sensing design for mobile PU scenarios is proposed with the aim to achieve the following important features: i) to determine the optimal mobility-aware transmission time, i.e., the transmission time value that jointly maximizes the spectrum sensing efficiency and satisfies the PU interference constraint; ii) to determine the optimal mobility-aware sensing time threshold, i.e., the maximum sensing time value assuring efficient spectrum sensing. First, closed-form expressions of both the optimal transmission time and the optimal sensing time threshold are analytically derived for a general PU mobility model. Then, the derived expressions are specialized for two widely adopted mobility models, i.e., the Random Walk mobility Model with reflection and the Random Way-Point mobility Model. Practical rules for the sensing parameter tuning are provided with reference to the considered mobility models. The analytical results are finally validated through simulations.

Primary-user mobility impact on spectrum sensing in Cognitive Radio networks

In this paper, the effects of the primary-user (PU) mobility on spectrum sensing in Cognitive Radio (CR) networks are studied. To this aim, first, the spectrum sensing problem is reformulated to account for the PU mobility. Then, the effects of the PU mobility are studied with the objective to determine the parameters that affect the spectrum sensing functionality. For this, two performance metrics are analytically derived: i) the detection capability, which measures the PU mobility impact on the CR user detection probability; ii) the mobility-enabled sensing capacity, a new metric that measures the expected transmission capacity achievable by a CR user in the presence of PU mobility. The mathematical analysis is carried out in different scenarios, by using mobility and spectrum occupancy models. The results show that the detection capability is affected by five parameters: the PU protection range, the network region size, the PU mobility model, the CR spatial distribution, and the number of PUs that use the same spectrum band. Moreover, it is shown that the sensing capacity can significantly increase in the presence of PU mobility if the PU protection range is smaller than the network region size. The mathematical results are derived by considering the dynamic PU traffic, and validated through simulations.

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.

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.

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.

Cooperative Spectrum Sensing Techniques with Temporal Dispersive Reporting Channels

Cooperative approaches have been proposed as an effective way to improve the spectrum sensing accuracy. Generally, cooperative spectrum sensing techniques require two successive stages: sensing and reporting. The reporting channels are usually assumed ideal. In this paper, we remove this assumption and we investigate the effects of reporting channels affected by temporal dispersion on cooperative spectrum sensing. To this aim, we propose two fusion schemes: a Widely Linear scheme and a Linear one. For both the schemes, closed-form expressions of the detection and the false alarm probabilities are derived. The performance are also evaluated numerically, and the results show that the Widely Linear detector outperforms the Linear one in operative conditions of practical interest. Moreover, for the sake of completeness, a theoretical comparison of the proposed detectors is carried out for reporting channels affected by multipath frequency non-selective fading. Surprisingly, the analysis proves that the two detectors perform exactly the same under this assumption. Therefore, there is not anymore advantage in using the Widely Linear scheme, which exhibits higher, although limited, computational complexity. The theoretical analysis is validated numerically.

Human-mobility enabled networks in urban environments: Is there any (mobile wireless) small world out there?

In the last 10 years, new paradigms for wireless networks based on human mobility have gained the attention of the research community. These paradigms, usually referred to as Pocket Switched Networks or Delay Tolerant Networks, jointly exploit human mobility and store-and-forward communications to improve the connectivity in sparse or isolated networks. Clearly, understanding the human mobility patterns is a key challenge for the design of routing protocols based on such paradigms. To this aim, we anonymously collected the positions of almost two thousand mobile phone users, spread over a metropolitan area greater than 200km^2 for roughly one month. Then, with a multi-disciplinary approach, we estimated the mobility patterns from the collected data and, assuming Wi-Fi connectivity, we inferred the contact events among the devices to evaluate the connectivity properties of a human mobility-enabled wireless network. In a nutshell, the contribution of the paper is threefold: (i) it confirms some of the results obtained in smaller environments, such as the power-law distribution for contact and inter-contact times, allowing us to estimate the distribution parameters with high statistical significance; (ii) it addresses the feasibility of the transmission opportunities provided by human mobility to build a city-wide connected network for different forwarding strategies classes; (iii) it shows uncovered characteristics of the connectivity properties of human mobility, such as the presence of the small world phenomenon in wide-scale experiments.