Vasileios Lakafosis

Serendipity: enabling remote computing among intermittently connected mobile devices

Mobile devices are increasingly being relied on for services that go beyond simple connectivity and require more complex processing. Fortunately, a mobile device encounters, possibly intermittently, many entities capable of lending it computational resources. At one extreme is the traditional cloud-computing context where a mobile device is connected to remote cloud resources maintained by a service provider with which it has an established relationship. In this paper we consider the other extreme, where a mobile devices contacts are only with other mobile devices, where both the computation initiator and the remote computational resources are mobile, and where intermittent connectivity among these entities is the norm. We present the design and implementation of a system, Serendipity, that enables a mobile computation initiator to use remote computational resources available in other mobile systems in its environment to speedup computing and conserve energy. We propose a simple but powerful job structure that is suitable for such a system. Serendipity relies on the collaboration among mobile devices for task allocation and task progress monitoring functions. We develop algorithms that are designed to disseminate tasks among mobile devices by accounting for the specific properties of the available connectivity. We also undertake an extensive evaluation of our system, including experience with a prototype, that demonstrates Serendipitys performance.

Progress Towards the First Wireless Sensor Networks Consisting of Inkjet-Printed, Paper-Based RFID-Enabled Sensor Tags

This paper discusses the evolution towards the first integrated radio-frequency identification (RFID)-enabled wireless sensor network infrastructure using ultra-high frequency/radio frequency (UHF/RF) RFID-enabled sensor nodes and inkjet-printed electronics technologies on flexible and paper substrates for the first time ever. The first sections highlight the unique capabilities of inkjet printed electronics as well as the benefits of using paper as the ultra-low-cost, conformal and environmentally friendly substrate for the mass-scale ubiquitous implementation of the first RFID-enabled wireless sensing applications. Various inkjet-printed antenna configurations are presented for enhanced-range compact RFID-enabled sensing platforms in “rugged” environments up to 7 GHz, followed by the discussion of their 2-D integration with integrated circuit (IC) and sensors on paper. This integration is extended to a power-scavenging “smart-shoe” batteryless integrated RFID module on paper that could be used for autonomous wearable sensing applications with enhanced range. The paper concludes discussing the details for establishing for the first time an asynchronous wireless link between the aforementioned RFID-tags and a widely used commercial wireless sensor network (WSN) mote using a simplified protocol; a paramount step that could potentially create ubiquitous ultra-low-cost sensor networks and large-scale RFID implementations eliminating the need of expensive RFID reader infrastructure and linking RFIDs to the mature level of WSNs.

Inkjet Printed, Self Powered, Wireless Sensors for Environmental, Gas, and Authentication-Based Sensing

In this paper, inkjet-printed flexible sensors fabricated on paper substrates are introduced as a system-level solution for ultra-low-cost mass production of UHF Radio Frequency Identification (RFID) Tags and wireless sensor nodes in a “green” approach that could be easily extended to other microwave and wireless applications. The authors briefly touch up the state-of-the-art area of fully integrated wireless sensor modules on paper and show several active and power scavenging platforms to power on wireless sensors that could potentially set the foundation for the truly convergent wireless sensor ad hoc networks of the future.

Paper-Based RFID-Enabled Wireless Platforms for Sensing Applications

In this paper, the feasibility of inkjet printing of circuit and microwave structures on paper-based substrates is investigated for the first time in the implementation of a complete low-cost wireless platform for sensors. First, the system-level design of the module including the amplifier characterization were carried out to ensure optimum performance of the sensor modules in the UHF bands used in RF identification communication. These results were then used to design two different antenna structures, which are printed on paper along with their respective circuit layouts using inket-printing technology. Different techniques were investigated for the assembly of circuit components on the silver printed layouts. Finally, wireless link measurements on the assembled prototypes verified the good performance on the wireless and sensing sides.

RF Fingerprinting Physical Objects for Anticounterfeiting Applications

Rendering typical RF identification (RFID) tags physically unique and hard to near-exactly replicate by complementing them with unique RF certificates of authenticity (RF-CoAs) can prove a valuable tool against counterfeiting. This paper introduces a new robust RFID system with enhanced hardware-enabled authentication and anticounterfeiting capabilities that relies on the near-field RF effects between a 5 × 5 antenna array and the uniquely modified substrate of the RF-CoAs. A microcontroller-enabled, low-power, and low-cost reader is used to accurately extract the near-field response (“RF fingerprint”) of the certificates meant to complement typical RFID tags in the 5-6-GHz frequency range. The RF characterization of all the readers components, with an emphasis on the accuracy provided, has been performed. The state diagram of the fast and accurate reader operation is outlined. Rigorous performance and security test results are presented and verify the unique features of this technology.

Inkjet-printed graphene-based wireless gas sensor modules

In this paper we demonstrate the use of graphene as the basis for design and development of low-cost, self-powered, battery-less, wireless sensor solutions utilizing thin films produced from environmentally friendly, water-based, inkjet printed graphene oxide (GO) ink. The in-house developed novel sensor material demonstrates good response to ammonia gas (NH3), yielding a 6% normalized resistance change within 15 minutes of exposure to a concentration of 500 ppm. In addition, excellent recovery time is achieved using the RGO thin films, with over 30% of material recovery observed within 5 minutes without exposure to high temperature or any UV treatments. Finally, we present in this work important distinctive characteristics in the behavior of the RGO sensor when exposed to different types of gases, including the hard-to-detect CO gas, that can be exploited in order to further enhance the applicability of the material. The introduction of mass producible, stable, environmentally friendly, inkjet-printable GO on organic paper/kapton substrates lays the foundation for the development of a wide range of new low-cost, high performance graphene-based devices, such as inkjet-printed diodes, capacitors and transistors.

Performance Enhancement of the RFID Epc Gen2 Protocol by Exploiting Collision Recovery

Maximizing the Radio Frequency Identification (RFID) performance is one of the main challenges in application domains, such as logistics and supply chain management, where the undesired effect of Tag collisions can significantly degrade the speed of the inventory process. The dominating UHF EPC Class-1 Generation2 (EPC Gen2) protocol only specifies collision avoidance algorithms but makes no provision for collision resolution. In this paper, performance enhancement of the EPC Gen2 standard exploiting Tag collision recovery is demonstrated, for the first time, in real time with measurements. Three simple and effective approaches to handle successful Tag acknowledgments of recovered collided packets are proposed and implemented on a software-defined Reader and programmable Tags. The attained benefits over the conventional EPC Gen2 MAC scheme are significant: the throughput per time slot is increased by 72% while the overall time required to inventory the Tag population is reduced by 26%. The effectiveness of the proposed approach and the validity of the achieved results are confirmed by the good agreement with simulations reported in the literature.

From single-to multihop: The status of wireless localization

The solutions reviewed in this article, which have been proposed to solve the problem of providing reliable localization coordinate estimates in both single and multihop wireless network environments, are regarded as some of the most prominent ones. Although all these proposed solutions are addressing localization needs in different physical environments with exclusively single-hop or additionally multihop connectivity to reference nodes and have been either hardware implemented or just computer simulated, an attempt to summarize their characteristics in a somewhat comparative fashion is also shown.

A battery-less, wireless mote for scavenging wireless power at UHF (470–570 MHz) frequencies

In this paper, a novel power scavenging mote to harness wireless power in the UHF frequencies between 470 and 570 MHz is presented. A broadband monopole antenna prototype inkjet printed on a paper based substrate is used transduce the incident wireless power from its Electromagnetic wave form to a RF AC signal. A conjugately matched voltage multiplier and RF transformer are used to rectify and store the RF input power in a low leakage capacitor for powering on a microcontroller unit and wireless transceiver end-device thereby making the entire operation of this mote battery-less.

Concealable, low-cost paper-printed antennas for WISP-based RFIDs

Paper-based, inkjet-printed antennas are proposed in this paper as replacement for the typical antennas used on the WISP RFID tag. These antennas are designed to be as concealable as possible. The designs presented exploit meandered techniques in order to achieve significantly reduced dimensions. In particularly, text-based meandered line techniques are applied to obtain both decreased size and concealment. The inkjet printing has been chosen to provide a substrate, which suits the aim of concealment for the final device. Moreover, this paper shows how the inkjet printing techniques perfectly match the text-based design proposed in terms of high applicability. A comparison with the normal antennas mounted on the WISP is performed.