Andrea Zanella

Internet of Things for Smart Cities

The Internet of Things (IoT) shall be able to incorporate transparently and seamlessly a large number of different and heterogeneous end systems, while providing open access to selected subsets of data for the development of a plethora of digital services. Building a general architecture for the IoT is hence a very complex task, mainly because of the extremely large variety of devices, link layer technologies, and services that may be involved in such a system. In this paper, we focus specifically to an urban IoT system that, while still being quite a broad category, are characterized by their specific application domain. Urban IoTs, in fact, are designed to support the Smart City vision, which aims at exploiting the most advanced communication technologies to support added-value services for the administration of the city and for the citizens. This paper hence provides a comprehensive survey of the enabling technologies, protocols, and architecture for an urban IoT. Furthermore, the paper will present and discuss the technical solutions and best-practice guidelines adopted in the Padova Smart City project, a proof-of-concept deployment of an IoT island in the city of Padova, Italy, performed in collaboration with the city municipality.

Experimental comparison of RSSI-based localization algorithms for indoor wireless sensor networks

In this paper, we investigate the actual performance of some of the best known localization algorithms when deployed in real-world indoor environments. Among the plethora of possible localization schemes, we focus on those based on radio signal strength measurements only, since they do not require extra circuitry that would result in higher cost and energy consumption. For a fair comparison, we have first gathered thousands of radio signal strength measurements in two different indoor environments. To estimate the channel model parameters and to compare the different localization algorithms these data have been used.

TCP Westwood: congestion window control using bandwidth estimation

We study the performance of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end rate estimation in a way that is totally transparent to routers and to the destination. Thus, it is compatible with any network and TCP implementation. The key innovative idea is to continuously estimate, at the TCP sender, the packet rate of the connection by monitoring the ACK reception rate. The estimated connection rate is then used to compute congestion window and slow start threshold settings after a congestion episode. Resetting the window to match available bandwidth makes TCPW more robust to sporadic losses due to wireless channel problems. These often cause conventional TCP to overreact, leading to unnecessary window reduction. Experimental studies of TCPW show significant improvements in throughput performance over Reno and SACK, particularly in mixed wired/wireless networks over high-speed links. The contributions of this paper include a model for fair and friendly sharing of the bottleneck link and a Markov Chain performance model in presence of link errors/loss. TCPW performance is compared to that of TCP Reno, and analytic results are validated against simulation results. Internet and laboratory measurements using a Linux TCPW implementation are also reported, providing further evidence of the gains achievable via TCPW.

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad hoc Networks

In this paper, we focus on a vehicular ad hoc network (VANET) that makes use of 802.11-like wireless interfaces for Inter Vehicular Communication (IVC). We propose a distributed position-based broadcast protocol, named Smart Broadcast (SB), that aims at i) maximizing the progress of the message along the propagation line, and ii) minimizing the re-broadcast delay. The protocol is analyzed through a mathematical model that permits to determine the optimal parameter setting for a given scenario. Simulations are then used to validate the mathematical model and to compare SB with other broadcast algorithms.

Long-range communications in unlicensed bands: the rising stars in the IoT and smart city scenarios

Connectivity is probably the most basic building block of the IoT paradigm. Up to now, the two main approaches to provide data access to things have been based on either multihop mesh networks using short-range communication technologies in the unlicensed spectrum, or long-range legacy cellular technologies, mainly 2G/GSM/GPRS, operating in the corresponding licensed frequency bands. Recently, these reference models have been challenged by a new type of wireless connectivity, characterized by low-rate, long-range transmission technologies in the unlicensed sub-gigahertz frequency bands, used to realize access networks with star topology referred to as low-power WANs (LPWANs). In this article, we introduce this new approach to provide connectivity in the IoT scenario, discussing its advantages over the established paradigms in terms of efficiency, effectiveness, and architectural design, particularly for typical smart city applications.

Range-only SLAM with a mobile robot and a Wireless Sensor Networks

This paper presents the localization of a mobile robot while simultaneously mapping the position of the nodes of aWireless Sensor Network using only range measurements. The robot can estimate the distance to nearby nodes of the Wireless Sensor Network by measuring the Received Signal Strength Indicator (RSSI) of the received radio messages. The RSSI measure is very noisy, especially in an indoor environment due to interference and reflections of the radio signals. We adopted an Extended Kalman Filter SLAM algorithm to integrate RSSI measurements from the different nodes over time, while the robot moves in the environment. A simple pre-processing filter helps in reducing the RSSI variations due to interference and reflections. Successful experiments are reported in which an average localization error less than 1 m is obtained when the SLAM algorithm has no a priori knowledge on the wireless node positions, while a localization error less than 0.5 m can be achieved when the position of the node is initialized close to the their actual position. These results are obtained using a generic path loss model for the trasmission channel. Moreover, no internode communication is necessary in the WSN. This can save energy and enables to apply the proposed system also to fully disconnected networks

Long-Range IoT Technologies: The Dawn of LoRa™

The last years have seen the widespread diffusion of novel Low Power Wide Area Network (LPWAN) technologies, which are gaining momentum and commercial interest as enabling technologies for the Internet of Things. In this paper we discuss some of the most interesting LPWAN solutions, focusing in particular on LoRa™, one of the last born and most promising technologies for the wide-area IoT.

Statistical characterization of the service time in saturated IEEE 802.11 networks

In this paper, we propose an analytical model for the service time in saturated IEEE 802.11 DCF networks. We derive a closed-form probability generating function for the packet service time of a cluster of IEEE 802.11 terminals, both for the RTC/CTS and the basic access mode. The probability generating function is inverted by numerical methods, providing the probability distribution function of the service time. Interestingly, it catches certain features of the DCF service time, which cannot be revealed with the second order analysis known in the literature. Finally, this analytical model is validated by means of extensive simulation outcomes.

TCP Westwood: analytic model and performance evaluation

We present a performance model of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end connection bandwidth share estimation, obtained by monitoring the ACK reception rate. An analytic model using Markov Chain techniques is developed in this paper, and then used to assess the performance improvements obtained using TCPW. The model takes into account the estimation and filtering method used in TCPW, as well as the following system parameters, bottleneck link bandwidth, buffer space at the bottleneck router, end-to-end propagation time, and error rate. The model reveals substantial TCPW gains over Reno whenever losses due to link or other errors are taken into consideration. The analytic model accuracy is confirmed by comparing to simulation results.

On the impact of physical layer awareness on scheduling and resource allocation in broadband multicellular IEEE 802.16 systems [Radio Resource Management and Protocol Engineering for IEEE 802.16]

Multicellular networks based on the IEEE 802.16 standard appear to be very promising candidates to provide end users with broadband wireless access. However, they also pose interesting challenges in terms of radio resource management, where several design choices are not specified in the standard, intentionally left open to implementors. For this reason, we focus in this article on scheduling and resource allocation, and investigate how they could operate in a cross-layer fashion. In particular, we describe the principles of joint scheduling and resource allocation for IEEE 802.16 operating in AMC mode, and discuss the critical role played by physical layer considerations, especially intercell interference estimation and channel state awareness, in the obtained performance. This leads to identifying key open issues and possible general solutions