Domenico Giustiniano

Micro aerial vehicle networks: an experimental analysis of challenges and opportunities

The need for aerial networks is growing with the recent advance of micro aerial vehicles, which enable a wide range of civilian applications. Our experimental analysis shows that wireless connectivity among MAVs is challenged by the mobility and heterogeneity of the nodes, lightweight antenna design, body blockage, constrained embedded resources, and limited battery power. However, the movement and location of MAVs are known and may be controlled to establish wireless links with the best transmission opportunities in time and space. This special ecosystem undoubtedly requires a rethinking of wireless communications and calls for novel networking approaches. Supported by empirical results, we identify important research questions, and introduce potential solutions and directions for investigation.

Measuring transmission opportunities in 802.11 links

We propose a powerful MAC/PHY cross-layer approach to measuring IEEE 802.11 transmission opportunities in WLAN networks on a per-link basis. Our estimator can operate at a single station and it is able to: 1) classify losses caused by noise, collisions, and hidden nodes; and 2) distinguish between these losses and the unfairness caused by both exposed nodes and channel capture. Our estimator provides quantitative measures of the different causes of lost transmission opportunities, requiring only local measures at the 802.11 transmitter and no modification to the 802.11 protocol or in other stations. Our approach is suited to implementation on commodity hardware, and we demonstrate our prototype implementation via experimental assessments. We finally show how our estimator can help the WLAN station to improve its local performance.

OpenVLC: software-defined visible light embedded networks

Though there has been a lot of interest in Visible Light Communication (VLC) in recent years, a reference platform based on commercial off-the-shelf components is still missing. We believe that an open-source platform would lower the barriers of entry to VLC research and help the VLC community gain momentum. In this paper we take an initial step toward the goal of a VLC reference platform - OpenVLC, and present our design and implementation. Built around a credit-card-sized embedded Linux platform with an LED front-end, OpenVLC offers a basic physical layer, a set of essential medium access primitives, as well as interaction with Internet protocols. We investigate the performance of OpenVLC and show how it can be used along with standard networking diagnostics tools.

Detection of Reactive Jamming in DSSS-based Wireless Communications

Reactive jammers have been shown to be a serious threat for wireless communication. Despite this, it is difficult to detect their presence reliably. We propose a novel method to detect such sophisticated jammers in direct sequence spread spectrum (DSSS) wireless communication systems. The key idea is to extract statistics from the jamming-free symbols of the DSSS synchronizer to discern jammed packets from those lost due to bad channel conditions. Our contribution is twofold. First, we experimentally evaluate new empirical models utilizing the preamble symbols of IEEE 802.15.4 packets, thus enabling the accurate prediction of the packet delivery ratio (PDR). We show that the chip error rate-based metric is superior to metrics used in the literature, offering an accurate and reactive indicator of the true PDR. Our second contribution is the design and evaluation of a detection technique relying on this metric to detect reactive jammers. We build a software-defined radio testbed and show that our technique enables the error-free detection of reactive jammers that jam all packets on links with a PDR above 0.3. To the best of our knowledge, our detector is the first to detect reactive jamming attacks targeting the physical layer header of DSSS packets, and does not require any modifications of the wireless communication system.

An open source research platform for embedded visible light networking

Despite the growing interest in visible light communication, a reference networking platform based on commercial off-the-shelf components is not available yet. An open source platform would lower the barriers to entry of VLC network research and help the VLC community gain momentum. We introduce OpenVLC, an open source VLC research platform based on software-defined implementation. Built around a creditcard- sized embedded Linux platform with a simple opto-electronic transceiver front-end, OpenVLC offers a basic physical layer, a set of essential medium access primitives, as well as interoperability with Internet protocols. We investigate the performance of OpenVLC and show examples of how it can be used along with standard network diagnostics tools. Our software-defined implementation can currently reach throughput on the order of the basic rate of the IEEE 802.15.7 standard. We discuss several techniques that researchers and engineers could introduce to improve the performance of OpenVLC and envision several directions that can benefit from OpenVLC by adopting it as a reference platform.

A software-defined sensor architecture for large-scale wideband spectrum monitoring

Todays spectrum measurements are mainly performed by governmental agencies which drive around using expensive specialized hardware. The idea of crowdsourcing spectrum monitoring has recently gained attention as an alternative way to capture the usage of wide portions of the wireless spectrum at larger geographical and time scales. To support this vision, we develop a flexible software-defined sensor architecture that enables distributed data collection in real-time over the Internet. Our sensor design builds upon low-cost commercial off-the-shelf (COTS) hardware components with a total cost per sensor device below

Characterizing 802.11n aerial communication

100. The low-cost nature of our sensor platform makes the sensing approach particularly suitable for large-scale deployments but imposes technical challenges regarding performance and quality. To circumvent the limits of our solution, we have implemented and evaluated different sensing strategies and noise reduction techniques. Our results suggest that our sensor architecture may be useful in application areas such as dynamic spectrum access in cognitive radios, detecting regions with elevated electro-smog, or simply to gain an understanding of the spectrum usage for advanced signal intelligence such as anomaly detection or policy enforcement.

Experimental assessment of 802.11 MAC layer channel estimators

In Search And Rescue missions, Unmanned Aerial Vehicles (UAVs) equipped with cameras allow for efficient scanning of large areas. Yet, delivering high resolution images to rescuers also requires high-speed communication. In this paper, we investigate the potential and challenges of wireless communication between UAVs in such scenarios. Our fleet of UAVs supports both a high-bandwidth network for bulk data transfer (802.11n) as well as a long-range radio for control messages (XBee-PRO 802.15.4). Extensive experiments show that 802.11n performs poorly in highly mobile scenarios, as the throughput between UAVs drops far below the theoretical maximum as soon as they become airborne. We consider several potential causes and present an analysis of their impact in isolation.

Now or later?: delaying data transfer in time-critical aerial communication

We evaluate two approaches for estimating the proportions of frame losses at an 802.11 station due to collisions and interference. These methods use only local 802.11 measurements available in basic access mode. We implement the estimators on an experimental testbed using off-the-shelf hardware to investigate implementation requirements and to evaluate performance in real wireless environments. We And that the estimators are accurate and of potential practical utility.

Detection of reactive jamming in DSSS-based wireless networks

Search and rescue missions are entering a new era with the advent of small scale unmanned aerial vehicles (UAVs) with communication capabilities and embedded cameras. Yet, delivering high resolution images of the supervised surface to rescuers is time-critical. To help resolving this problem, we study how UAVs can take advantage of their controlled mobility to derive the optimum strategy for data transmission. Driven by real-world aerial experiments with both airplanes and quadrocopters equipped with 802.11n technology, we show that the UAV should not necessarily transmit as soon as a wireless link is established. Instead, it should wait until it reaches a suitable distance to the receiving UAV, only to transmit when the time to move to the new location and transmit is minimal. We then apply the principle of delayed gratification, where the UAV attempts to solve the tradeoff between postponing until it reaches this minimum and the impatience to deliver as much data as soon as possible, before any physical damage on-the-fly may occur. Our empirical-driven simulations demonstrate that the optimal distance of transmission greatly depends on the interplay of actual throughput, data size, UAV cruise speed, and failure rate, and that state-of-the-art UAVs can already benefit from our approach.