Giorgio Corbellini

LED-to-LED visible light communication networks

Visible Light Communication (VLC) with Light Emitting Diodes (LEDs) as transmitters and receivers enables low bitrate wireless adhoc networking. LED-to-LED VLC adhoc networks with VLC devices communicating with each other over free-space optical links typically achieve a throughput of less than a megabit per second at distances of no more than a few meters. LED-to-LED VLC adhoc networks are useful for combining a smart illumination with low-cost networking. We present and evaluate a software-based VLC physical layer and a VLC medium access control layer that retain the simplicity of the LED-to-LED approach. The design satisfies the requirement that LEDs should always be perceived as on with constant brightness. In each VLC device, in addition to an LED, only a low-cost microcontroller is required for handling the software-based communication protocol. The results of our performance measurements confirm recent claims about the potential of LED-to-LED VLC adhoc networks as a useful technology for sensor networks, smart and connected consumer devices, and the Internet-of-Things.

Connecting networks of toys and smartphones with visible light communication

Light emitting diodes are low-cost and energy- efficient. They are replacing incandescent bulbs as the primary source of illumination in residential and public environments. The brightness of LEDs can be modulated at a high rate, which enables the combination of illumination and wireless communication, imperceptible to humans. Such systems using LEDs as transceivers are called visible light communication systems. LEDs have also been extensively used in consumer electronics such as toys and smartphones, but primarily for reasons other than communication. We show various use cases of devices connected with VLC. Since LEDs can also be used as light receivers in VLC systems, adding microcontrollers to devices (if not already embedded) enables low-cost implementation of a wireless communication interface with VLC. This article reports on experience with several prototypes of practical VLC systems.

An LED-to-LED Visible Light Communication system with software-based synchronization

An LED can emit and receive light and provides therefore a simple building block for a Visible Light Communication (VLC) system. We describe a microcontroller-based system and report on its effectiveness in a testbed. The key idea is to use a microcontroller to provide synchronization so that the receiver can lock to the transmitted signal in a fast and efficient way. Further we propose a combined light emission and light measurement approach to receive with an LED while emitting light. The proposed system enables new entertaining applications by creating the illusion (for a human observer) that both transmitting and receiving LEDs are always switched on.

Continuous synchronization for LED-to-LED visible light communication networks

Off-the-shelf Light Emitting Diodes (LEDs) and low-cost microcontrollers provide the foundation for networking using the visible light as communication medium. These networks require fast and stable synchronization and a distributed protocol to handle shared medium access. We present and evaluate a physical layer and a distributed, contention-based medium access control protocol that enables reliable communication over room-range distances; both are implemented in software using low-cost commercial off-the-shelf building blocks. Experiments with a testbed consisting of embedded devices equipped with only LEDs demonstrate the scalability of this approach. The performance evaluation indicates that Visible Light Communication is a reliable solution for more than ten devices to bring low-cost and non-complex connectivity to a large number of devices.

Using consumer LED light bulbs for low-cost visible light communication systems

LED-to-LED Visible Light Communication (VLC) based on Light Emitting Diodes (LEDs) and microcontrollers provide a foundation for networking using visible light as communication medium. We describe a low-complexity smart LED light bulb prototype that is based on existing consumer light bulbs and hence can be replicated with minimal effort. The protocol software employed for these smart light bulbs is consistent with earlier VLC protocols originally developed for communication between single LEDs. Using VLC with consumer light bulbs leads to improvements in communication range, field of view, and throughput compared to existing VLC communication systems based on single LEDs. VLC-enabled light bulbs are an important contribution to the vision of all-optical networks, i.e., a multi-hop network of light bulbs in which light bulbs deployed inside buildings and communicate with each other using free space optics only.

RFID shakables: pairing radio-frequency identification tags with the help of gesture recognition

A novel approach for pairing RFID-enabled devices is introduced and evaluated in this work. Two or more devices are moved simultaneously through the radio field in close proximity of one or more RFID readers. Gesture recognition is applied to identify the movements of the devices, to mark them as a pair. This application is of interest for social networks and game applications in which play patterns with RFID-enabled toys are used to establish virtual friendships. In wireless networking, it can be used for user-friendly association of devices. The approach introduced here works with off-the-shelf passive RFID tags, as it is software-based and does not require hardware or protocol modifications. Every RFID reader constantly seeks for tags, thus, as soon as one tag is in its vicinity, the reader reports the presence of the tag. Such binary information is used to recognize the movement of tags and to pair them, if the gesture patterns match each other. We show via experimental evaluation that this feature can be easily implemented. We determine the required gesture interval duration and characteristics for accurate gesture and matching detection.

Acoustic data transmission to collaborating smartphones — An experimental study

The acoustic capabilities (i.e. microphone) and the fast processors of modern smartphones allow for the transmission of data to groups of such devices through the audio channel. We discuss an acoustic data transmission system for broadcast communication to a multitude of smartphones without the need of a radio access point. Acoustic data transmission is particularly attractive in scenarios that involve sound systems (e.g., movie theaters or open-air film festivals). We discuss different techniques to hide data in sound tracks and how to form a microphone array from a collection of smartphones in the same location. Collaborating smartphones share (using their radio interfaces to form an ad hoc network) the received data streams to jointly correct errors. With a testbed of up to four smartphones, we demonstrate how the robustness and reliability of a downlink broadcast via an acoustic communication system can be improved by collaboration between spatially distributed devices. With field tests in different scenarios, we investigate the potential gain of the collaboration in a real environment.

Two-Way Communication Protocol using Bluetooth Low Energy Advertisement Frames

Bluetooth Low Energy (BLE) is a wireless personal area network technology designed to provide low-power connectivity to smartphones and wearable devices. To transmit bidirectional data, devices must first discover each other and then start a pairing process. Usually, the pairing process requires manual intervention that might result in undesirable user experiences. If security and privacy requirements allow, communication sessions could be limited to the advertisement channels only, without pairing the devices. Further, the use of only advertisement channels without pairing devices enables scenarios in which different radio systems can also join the communication. For example, the nRF24L01+ radio system can be programmed to communicate using the advertisement channels defined by BLE. This is relevant because the nRF24L01+ radio system is a popular technology for the Internet-of-Things and for location-based services with wearable devices in smart cities. This paper evaluates a two-way communication protocol between the nRF24L01+ and BLE devices, using only advertisement frames. We show a practical protocol implementation and use an experimental testbed to evaluate its performance. The evaluation shows that it is possible to build a simple and reliable communication protocol that works in both directions.

Resource-constrained medium access control protocol for wearable devices

This work introduces a customized medium access control protocol, referred to as DrxMAC, for resource-constrained radio devices. The protocol is based on a time-slotted communication scheme with a simple automated slot allocation based on device identities. DrxMAC deploys an in-slot listen-before-talk approach to maximize the slot usage when multiple devices share a slot. The objective of our protocol is to minimize the use of the memory footprint and battery consumption. Further, it should be scalable even without support of a network infrastructure. DrxMAC is evaluated with a testbed implementation on Nordic Semiconductors nRF24LE1 radio system on a chip. This system is often used for low-latency, low-throughput communication in consumer electronics such as wearables, wireless keyboards, or game controllers. It has recently been used in a large roll-out of wearable beacon devices that enable new personalized applications in entertainment theme parks. Such theme parks are controlled environments and can serve as model environment for smart cities. We believe that introducing adhoc networking for the wearable devices (as enabled by DrxMAC) will open the path towards new applications not only for theme parks but related applications in smart cities. We argue that our customized protocol approach improves the coverage range of such wearables and outperforms existing state-of-art protocols in terms of resource and energy efficiency. We compare different configurations and existing standard protocols proposed for sensor networks and the Internet-of-Things, and analyze the performance of our DrxMAC testbed implementation with focus on packet delivery ratio and energy consumption.

Poster: A Hybrid Indoor Audio Localization System

User localization with mobile devices remains a challenging research problem if the environment or required accuracy prevent the use of satellite navigation (GPS). In this paper, we present a hybrid system that performs real time localization on a mobile device, using the audio signals emitted by nearby loudspeakers. Such an approach is useful in controlled environments with background music and sound, such as shopping centers, malls, or entertainment theme parks (Fig. 1). Two known audio identification methods are used in combination: (1) watermarking [1] with hidden location markers and (2) fingerprinting [2] with sound matches in a database. Based on the performance of the two methods in terms of accuracy and energy consumption, a particle filter-based hybrid combination [3] of CRC-based watermarking and fingerprinting is proposed. Our localization scheme runs as stand-alone mobile application and enables a user to identify the current location. It also respects the user’s privacy as it runs locally on a mobile device. We present the testbed implementation and experimental evaluation in an indoor environment with respect to the presence of noise, interference, user mobility, and power consumption. This implementation is the first step towards fine-grained localization using sound in the future.