Advances in Vehicular Ad-hoc Networks (VANETs): challenges and road-map for future development

Recent advances in wireless communication technologies and auto-mobile industry have triggered a significant research interest in the field of vehicular ad-hoc networks (VANETs) over the past few years. A vehicular network consists of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications supported by wireless access technologies such as IEEE 802.11p. This innovation in wireless communication has been envisaged to improve road safety and motor traffic efficiency in near future through the development of intelligent transportation system (ITS). Hence, governments, auto-mobile industries and academia are heavily partnering through several ongoing research projects to establish standards for VANETs. The typical set of VANET application areas, such as vehicle collision warning and traffic information dissemination have made VANET an interesting field of mobile wireless communication. This paper provides an overview on current research state, challenges, potentials of VANETs as well as the ways forward to achieving the long awaited ITS

Impact of clustering on the BER performance of ad hoc wireless networks

Ad hoc wireless networks are characterized by multi-hop radio communications. The spatial distribution of the nodes is seldom perfectly regular. In particular, in a realistic ad hoc wireless network communication scenario, the nodes are likely to be clustered, i.e., to configure themselves in subgroups such that the nodes inside each subgroup are relatively close to each other with respect to the distance between different subgroups. In this paper, we consider a very simple clustering scenario, defined as “uniformly clustered,” which allows to derive a parameterized analytical description. The proposed clustering model, although simple and idealistic, allows to gain insights valid also in a more general case with non-regular clustering. In particular, the obtained results highlight the fact that a single long hop can significantly degrade the network communication performance and quantify this performance degradation. Topology-dependent power control is then proposed, and its advantages are evaluated

Performance of ad hoc wireless networks with Aloha and PR-CSMA MAC protocols

In this paper, bit error rate (BER) performance and connectivity characteristics of multi-hop ad hoc wireless networks are analyzed under a circuit-switched network communication scheme characterized by the creation of a multi-hop communication route, through intermediate relay nodes, for each source-destination pair. The proposed transmission scheme is packetized yet it does not employ retransmissions: in this sense, it can be considered as a hybrid scheme between circuit switching and packet switching. The ideal limiting performance under the assumption of no inter-node interference (INI) is evaluated. In particular, the concept of minimum spatial energy density is introduced, and quantified with a precise expression in the case of uncoded binary phase shift keying (BPSK) transmission. A realistic scenario with INI is then considered, and two different medium access control (MAC) protocols are proposed: Aloha and "per-route" carrier sense multiple access (PR-CSMA). In both cases, the BER performance is analyzed. Results show that MAC and physical layers are strictly interrelated, and designing one without considering the other may lead to wrong choices in ad hoc wireless network design

Impact of mobility on the BER performance of ad hoc wireless networks

In this paper, the authors quantify the impact of mobility on the bit error rate (BER) performance of ad hoc wireless networks. Analytical expressions, relating the BER at the end of a multihop route with the mobility characteristics of the nodes and the switching strategy, are derived on the basis of a rigorous detection-theoretic approach. In particular, two network switching scenarios are considered: 1) opportunistic non-reservation-based switching (ONRBS), where a message flows from source to destination by opportunistically choosing the available shortest consecutive links and 2) reservation-based switching (RBS), where, after the creation of a multihop route from source to destination, the message is “forced” to flow over the reserved links, regardless of their actual lengths. The network performance is evaluated for both an ideal case (without interference) and a realistic case (with interference). The improved robustness against mobility offered by ONRBS, with respect to RBS, is analyzed and quantified. In particular, two node mobility models, known as direction-persistent (DP) and direction-non-persistent (DNP), are considered, and it is shown that DP mobility causes a much more profound degradation in the end-to-end route BER than DNP mobility. This conclusion is more pronounced in ad hoc wireless networks employing RBS. Overall, the results show that if the medium access control (MAC) protocol is not efficient in canceling or mitigating the interference, then the role of the switching/routing strategy in network performance is quite minor

Minimum number of neighbors for fully connected uniform ad hoc wireless networks

Determining the minimum number of neighboring nodes required to guarantee full connectivity, i.e., to ensure that a node can reach, through multiple hops, any other node in the network, is an important problem in ad hoc wireless networks. In this paper, we consider reservation-based wireless networks with stationary and uniform (on average) node spatial distribution. Assuming that any communication route is a sequence of minimum length hops, we show that, in an ideal case without inter-node interference (INI) and on the basis of a suitable definition of transmission range, the minimum number of neighbors required for full connectivity is, on average, π. Full connectivity is guaranteed if the transmitted power (in the case of fixed node spatial density) or, equivalently, the node spatial density (in the case of fixed transmitted power) are larger than critical minimum values. In a realistic case with INI, we prove that there are situations where full connectivity cannot be guaranteed, regardless of the number of neighbors or the transmitted power

A communication-theoretic approach to ad hoc wireless networking

The remarkable surge in research on ad hoc wireless networks is largely due to their potential in offering insfrastructureless communications. While initially studied adopting a "conventional" networking approach, based upon years of research experience on wired computer networks (with virtually error-free communication links), the presence of unreliable wireless communication links necessitates a communication-theoretic foundation for the design and analysis of wireless ad hoc networks. Such a novel comprehensive "bottom-up" perspective was, for the first time, presented in OK Tonguz et al. (2006). In this paper, we summarize the communication-theoretic framework, where the impact of physical layer on the network performance and its interaction with higher layers is taken into account. The main goal of this paper is to provide the reader with the intuition behind the comprehensive approach, rather than the mathematical details of the approach

Circuit-switched wireless sensor networks: a discrete-time communication model for performance analysis

We consider a novel discrete-time model to analyze the performance of circuit-switched sensor networks. In particular, we assume that a node, after reserving a multi-hop communication route to the desired destination, holds it for a time interval defined as reserved channel utilization interval (RCUI) and utilizes it for an effective channel utilization interval (ECUI). A realistic network communication scenario with inter-node interference (INI) and a reservation-based medium access control (MAC) protocol with finite numbers of (active) routes (FNR) in the network is first considered, and the average interference power is evaluated through a novel combinatorial analysis. Results are presented in terms of effective transport capacity and channel utilization ratio (CUR). In particular, we show that for very low values of the packet generation rate at each node, activation of the maximum possible number of routes guarantees no loss, in terms of effective transport capacity, with respect to an ideal (no INI) scenario. However, this comes at the expense of a very low utilization: in other words, once a multi-hop route has been reserved, its effective utilization time must be a few orders of magnitude lower than the duration of the reservation interval