João Nuno Matos

Increasing the range of wireless passive sensor nodes using multisines

Wireless Sensor Networks (WSNs) usually consist of battery-powered nodes. Therefore, once the batteries deplete, the networks collapse. Passive sensor nodes are immune to this kind of problem because they do not have batteries, but on the other hand, their range is significantly shorter. This paper shows that this range can be enhanced (in a noticeable manner) if the Radio Frequency (RF) source that powers the nodes is set up to radiate a multisine waveform instead of a pure sinusoid, considering the same average power. The passive sensor used to demonstrate the usefulness of combining multiple sinusoidal waveforms is based on a low-power 16-bit microcontroller, and includes circuits for bi-directional wireless binary communication (envelope detection for downlink, backscatter for uplink). The sensor also features a 50Ω antenna port and an interface for debugging and expansion composed of 26 pins. Considering a power source of 2Werp, the maximum range of the wireless sensor (together with a half-wave dipole antenna) is 5.3 meters.

Design of a battery-free wireless sensor node

In this paper, a battery-free wireless sensor designed to harvest energy from electromagnetic waves at 866.6MHz and its detachable antenna system are described, with an emphasis on high frequency front-end design. In addition to having no local power source, the proposed sensor node is programmable, since it integrates a general-purpose microcontroller. Other features of the device are a standard 50Ω port and an interface for debugging and expansion, with of a total of 26 pins. In practice, the proposed system is capable of carrying out communication and processing tasks at up to a distance of 4.1 meters away from a transmitter antenna operating within the limits imposed by local regulatory entities, with respect to radiated power. Uplink communication is achieved using modulated backscattering. The proposed antenna system consists of a printed dipole-based antenna, with an overall efficiency in the order of 96%.

Resonant Electrical Coupling: Circuit Model and First Experimental Results

In this paper, the feasibility of resonant electrical coupling as a wireless power transfer technique is studied. A detailed comparison between this technique and the more popular resonant magnetic coupling based on circuit theory is provided. In this comparison, the strong duality that exists between the two techniques is demonstrated. The analytical results obtained are compared with the results measured with a proof-of-concept prototype.

Printed antenna for DSRC systems with omnidirectional circular polarization

Emerging vehicular communications are a key to combat several mobility issues, like road safety and efficiency. Dedicated short range communications (DSRC) is a wireless technology, operating at 5.9GHz, designed for automotive use. To operate, this technology has two types of devices, one for vehicles and another for roadside. This paper presents the design of an antenna for the vehicle unit of the DSRC system. High bandwidth, omnidirectional radiation pattern with circular polarization and reduced dimensions make this antenna particularly suitable for this application.

Evaluating WiMAX for vehicular communication applications

Road accidents have a dramatic social and economic impact on the society, a situation that fostered the research of mechanisms for increasing road safety. Many of these mechanisms require the ability of the vehicles to communicate among each other and/or with fixed road-side stations. Due to the inherent mobility constraints, wireless technologies play a central role in this type of applications. Despite having been originally developed to delivery last mile wireless broadband access, as an alternative to cable and DSL, WiMAX presents some attractive attributes, such as quality-of-service management and traffic differentiation that are well suited for use in traffic applications. Nevertheless, to the best of our knowledge, no research in this area has considered the use of this technology. Thus, this WIP presents a preliminary study and assessment of the WiMAX technology for vehicular communications usage.

Nonuniform Broadband Circularly Polarized Antenna Array for Vehicular Communications

Road safety applications drive the development of vehicular communications as support to intelligent transport systems. The communications network necessary for this is supported by dedicated short-range communications (DSRC), which is based on roadside units (RSUs) and onboard units. In the RSU, the DSRC physical-layer standards, along with practical issues, require specific radiation patterns of the respective antenna, leading to the use of unusual arrays of antennas. This paper describes a new concept based on a binomial array structure, which simplifies the design of the antenna array while ensuring good performance. The new structure developed for this antenna enabled the design of a feed network using unbalanced power dividers in the same plane as that of the radiating elements, maintaining the favorable characteristics of microstrip antennas. The array thus obtained met the desired specification, in terms of a radiation pattern with a bandwidth greater than 1 GHz.

Behavior of resonant electrical coupling in terms of range and relative orientation

The subjects addressed in this document fall under the topic of wireless power transmission (WPT). Power is transferred using a novel coupling technique based on electrical coupling and resonance across a distance of 5 meters with 40% efficiency. The experimental results obtained so far suggest that the efficiency of the proposed system remains stable when the relative orientation between the transmitter and the receiver is altered. The prototypes used in the experiments measure 16 by 16 cm by 3.7 cm at most. The ratio between the range of the system and the maximum dimension of each prototype is therefore around 30.

WAVE Based Architecture for Safety Services Deployment in Vehicular Networks

Abstract Vehicle manufacturers, highway concessionaries, governments and academic research are cooperating to find the best solution to add safety services relying on vehicle to vehicle communication systems (V2V) and among vehicles and the infrastructure (V2I) located on the roadside. Safety services, such as collision or sudden hard braking warning have delay-critical requirements. This paper proposes a WAVE (Wireless Access for Vehicular Environment) based model and a MAC protocol to disseminate time-critical messages for safety services in highways where the Road Side Units (RSUs) are not present in the instant a safety event is generated and, consequently, the message dissemination is done only through vehicles. The model allows to determine the retransmission slot number and the models feasibility is somewhat evaluated by analysing the maximum number of available slots for a typical scenario.

Printed antenna for on-board unit of a DSRC system

Vehicular communications, among vehicles and between vehicles and infrastructures are based on wireless communication technology known as dedicated short range communications (DSRC), which are in great development with the aim of reduce the traffic problems and improve the road safety. This study is based on the development of a solution to an antenna to be used in the mobile module, usually named On-Board Unit (OBU). The antenna should have characteristics that meet the requirements for new DSRC at 5.9GHz band in Europe. The proposed antenna is a printed monopole with a reduced size that presents an omnidirectional radiation pattern in the horizontal plane and allows communications independently of the direction of vehicles. The wide bandwidth obtained is to enough to encompass the other band for DSRC communications used in Europe, at 5.8GHz, and become more tolerant to manufacturing problems.

A front end to vehicular communications

This paper address the design of a front end for vehicular communications in the 5.9 GHz frequency band. The front end is being developed in accordance with the IEEE 8022.11p standard, which defines the physical layer for WLAN vehicular communications. Also presented are some simulations results, which demonstrate that 802.11p requirements are met. As the work is ongoing there are no practical results. At this time the development of front end is on the PCB design phase. The front encompasses all circuits between antenna and baseband stage, for transmission and reception. The front end will subsequently be integrated into a laboratory prototype used for demonstration purposes.