Lieven De Strycker

Optical CDMA codes for an indoor localization system using VLC

This paper describes the use of optical Code Division Multiple Access (CDMA) codes for an indoor localization system using Visible Light Communication. VLC uses Intensity Modulation and Direct Detection (IM/DD) so the CDMA codes can be used as baseband signals which makes the driving electronics less complex. In order to keep the installation cost low, a backbone network between the LEDs is not present. This makes it an asynchronous CDMA system where the cross- correlation is random and can in some cases introduces large distance errors. There are two groups of Optical CDMA codes namely uni- and bi- polar. When bipolar codes are used, the receiver should be equipped with an appropriated High Pass Filter (HPF). The results show that there is no large difference in cross- correlation between the codes but bipolar codes can reduce the distance error and so the position error even when there is static surrounding light like e.g. sunlight.

Indoor Multipath Assisted Angle of Arrival Localization

Indoor radio frequency positioning systems enable a broad range of location aware applications. However, the localization accuracy is often impaired by Non-Line-Of-Sight (NLOS) connections and indoor multipath effects. An interesting evolution in widely deployed communication systems is the transition to multi-antenna devices with beamforming capabilities. These properties form an opportunity for localization methods based on Angle of Arrival (AoA) estimation. This work investigates how multipath propagation can be exploited to enhance the accuracy of AoA localization systems. The presented multipath assisted method resembles a fingerprinting approach, matching an AoA measurement vector to a set of reference vectors. However, reference data is not generated by labor intensive site surveying. Instead, a ray tracer is used, relying on a-priori known floor plan information. The resulting algorithm requires only one fixed receiving antenna array to determine the position of a mobile transmitter in a room. The approach is experimentally evaluated in LOS and NLOS conditions, providing insights in the accuracy and robustness. The measurements are performed in various indoor environments with different hardware configurations. This leads to the conclusion that the proposed system yields a considerable accuracy improvement over common narrowband AoA positioning methods, as well as a reduction of setup efforts in comparison to conventional fingerprinting systems.

Distributed, Signal Strength-Based Indoor Localization Algorithm for Use in Healthcare Environments

In current healthcare environments, a trend toward mobile and personalized interactions between people and nurse call systems is strongly noticeable. Therefore, it should be possible to locate patients at all times and in all places throughout the care facility. This paper aims at describing a method by which a mobile node can locate itself indoors, based on signal strength measurements and a minimal amount of yes/no decisions. The algorithm has been developed specifically for use in a healthcare environment. With extensive testing and statistical support, we prove that our algorithm can be used in a healthcare setting with an envisioned level of localization accuracy up to room revel (or region level in a corridor), while avoiding heavy investments since the hardware of an existing nurse call network can be reused. The approach opted for leads to very high scalability, since thousands of mobile nodes can locate themselves. Network timing issues and localization update delays are avoided, which ensures that a patient can receive the needed care in a time and resources efficient way.

AES Data Encryption in a ZigBee Network: Software or Hardware?

This paper describes the experiments which have been conducted to determine the optimal implementation concept for AES (Advanced Encryption Standard) data encryption in a ZigBee network [1,2]. Two concepts have been considered. The first one is a AES128-CBC hardware co-processor embedded on a Spartan 3A FPGA. The second configuration implements the same cryptographic algorithm on the processor which controls the ZigBee nodes. The ZigBee modules in the network contain an 8-bit microcontroller which takes care of the ZigBee protocol stack –and the encryption calculations in the second case. Both approaches are examined and compared. In this paper we show that –in general– a software implementation is feasible in a ZigBee network, though a low-power hardware cryptographic co-processor could prove to be useful in some cases.

A low-power MEMS microphone array for wireless acoustic sensors

In this article we present the design of a low-power MEMS microphone array for wireless sensors. The array is used as part of a device that performs acoustic Angle-Of-Arrival (AOA) measurements. The power consumption of this design is lower than that of comparable designs. Each of the 4 analog channels (each with a microphone and amplifier) can be turned on or off (standby) separately. The power consumption is 1.8 mW per channel, and about 0.13 μW in standby. For a single AOA detection cycle (array activation, audio sampling, AOA computation), the energy consumption is 6.02 mJ. When consecutive AOA detections are performed, the energy cost per detection converges to 3.20 mJ. The AOA accuracy corresponds with the expectations. With a mean error of 4°, this is lower than that of comparable designs.

Time of Arrival Based on Chirp Pulses as a means to Perform Localization in IEEE 802.15.4a Wireless Sensor Networks

This paper introduces the technology Time of Arrival (TOA) based on chirp pulses (according to IEEE 802.15.4a) as a means to perform localization in Wireless Sensor Networks (WSNs) ac ...

A Visible Light Positioning system using Frequency Division Multiple Access with square waves

In this paper, a Visible Light Positioning (VLP) system using Frequency Division Multiple Access (FDMA) with square waves is presented. For the multiple access technology, the properties of square waves in the frequency domain is exploited. Neighboring LEDs will use multiples of the ground frequency of the first LED where the receiver performs a Fast Fourier Transform (FFT) and retrieves the Received Signal Strength (RSS) for every LED. In order to facilitate implementation, the LEDs are transmitting pilot tones in a non-synchronized way to the receiver, and thus requiring no backbone network. The positioning algorithm uses the RSS to perform triangulation and finds the position by taking the least square fit. Practical results show that this VLP system has position errors smaller then 10 cm when an photodiode is used which has a Field Of View (FOV) of 70°. Simulation results show that when a photodiode with a FOV of 90° is applied, the position error can drop to a few centimeter within the entire test bench surface. The key advantage of the system is the use of unsynchronized low bandwidth transmitters, leading to an easy implementation using current high efficiency LED drivers.

Inductive charging of an EDLC powered wristband device for medical measurements

Electronic devices for measuring body parameters in healthcare environments generally exhibit hygienic problems. Furthermore, they require regular battery replacement or recharging. This paper presents an electronic wristband for medical measurements that can be charged wirelessly. Its power supply is equipped with a Qi compatible inductive power receiver, an Electrochemical Double-Layer Capacitor (EDLC) energy buffer and a series of voltage regulators that can be disconnected from the energy buffer by a microcontroller. Because the wireless power receiver was placed behind a display, a study was performed of the effects of the display on receiver coil characteristics and system performance. For the selection of the EDLC, a selection process is presented, making a tradeoff between device autonomy and charging time. The result is a completely sealable and thus sterilizable device that can be charged in less than 5 seconds while being worn on the wrist.

Design of a visible light communication transmitter for the evaluation of a wide range of modulation techniques

In this paper, we describe the development of a dedicated transmitter to be used in Visible Light Communication applications. The transmitter has a high power efficiency, so the communication functionality does not lead to significant power consumption. For this reason, a Trans-Conductance Amplifier (TCA) was designed making use of a class AB amplifier. The final design has an electrical bandwidth from 20 kHz until 25 MHz and is able to power LEDs with a driving current up to 700 mA. Results show that the bandwidth of the driver electronics is much larger than the bandwidth of the commonly used power LEDs that are designed for illumination purposes. Because the transmitter has the ability to implement different modulation techniques, as well digital as analogues in nature, it can be used in a wide range of applications depending on the needs of data rate and bandwidth.

Automated design of an HF RFID loop antenna based on parametric geometry modification

In this paper, we take an innovative approach to the design of RFID loop antennas. As we want to increase the reliability of HF RFID systems, we need to step away from the traditional circular antenna shape. Adapting the shape of the antenna to its environment will improve the reliability of the HF RFID systems with a single loop antenna. We compare various shapes to serve as a reader antenna in a metallic tunnel. The optimized loop antennas are created by an antenna design tool which combines MATLAB® and CST EM Studio®. One of the optimized loop antennas is selected to serve in a practical case. Measurements were performed on this practical case with some promising results.