Showing papers by "Vassilis Gikas published in 2023"

Testing and Evaluation of Wi-Fi RTT Ranging Technology for Personal Mobility Applications

Abstract: The rapid growth in the technological advancements of the smartphone industry has classified contemporary smartphones as a low-cost and high quality indoor positioning tools requiring no additional infrastructure or equipment. In recent years, the fine time measurement (FTM) protocol, achieved through the Wi-Fi round trip time (RTT) observable, available in the most recent models, has gained the interest of many research teams worldwide, especially those concerned with indoor localization problems. However, as the Wi-Fi RTT technology is still new, there is a limited number of studies addressing its potential and limitations relative to the positioning problem. This paper presents an investigation and performance evaluation of Wi-Fi RTT capability with a focus on range quality assessment. A set of experimental tests was carried out, considering 1D and 2D space, operating different smartphone devices at various operational settings and observation conditions. Furthermore, in order to address device-dependent and other type of biases in the raw ranges, alternative correction models were developed and tested. The obtained results indicate that Wi-Fi RTT is a promising technology capable of achieving a meter-level accuracy for ranges both in line-of-sight (LOS) and non-line-of-sight (NLOS) conditions, subject to suitable corrections identification and adaptation. From 1D ranging tests, an average mean absolute error (MAE) of 0.85 m and 1.24 m is achieved, for LOS and NLOS conditions, respectively, for 80% of the validation sample data. In 2D-space ranging tests, an average root mean square error (RMSE) of 1.1m is accomplished across the different devices. Furthermore, the analysis has shown that the selection of the bandwidth and the initiator–responder pair are crucial for the correction model selection, whilst knowledge of the type of operating environment (LOS and/or NLOS) can further contribute to Wi-Fi RTT range performance enhancement.

A Rigorous and Integrated On-Water Monitoring System for Performance and Technique Improvement in Rowing

Abstract: This paper presents a prototype, on-water rowing monitoring system and its testing results for a single scull boat. The proposed system aims at recording critical kinetic (athlete biomechanics and oar/seat movements) and kinematic (boat position, velocity, acceleration, and attitude) parameters for sport performance evaluation and rowing technique improvement. The data acquisition unit is organized in two parts: the first part aims at logging boat kinematics based on GNSS/INS filtering, while the second one facilitates kinetics data recording using a series of analog sensors (potentiometers, strain gauges) installed on the athlete’s body and the boat seat and oars. Both parts are connected to a central unit featuring analog voltage digitizers and a micro-PC for device handling and data storing. In order to test the performance of the system a series of field trials were undertaken featuring different observation scenarios as well as intentionally induced errors in the rowing technique. Analysis revealed the high performance of the system in terms of sensor completeness and setup procedures as well as operational efficiency. Moreover, system performance evaluation exercised through studying raw data recordings and resultant parameters at stroke cycle and average (standardized) stroke cycle level confirmed the fruitfulness of the proposed approach and system and its potential for implementation on a broad scale. Finally, the data acquired from the proposed system were used to compute the adopted input parameters and performance indicators to characterize the system in terms of functionality and operational efficiency.

Rf-based localization (wifi rtt/lora) in underground quarrying for agent supervision and mapping applications

Abstract: Abstract. Mining and quarrying industry has recently made a shift towards underground exploitation as a viable alternative to traditional open-pit approaches. Thus, emerged the imperative need for localization systems for personnel safety and operations’ monitoring purposes. While there are many approaches taking advantage of the various signals of opportunity (SoO) supported by Internet of Things (IoT) for indoor and underground navigation, the need for a GNSS alternative in such areas is still present in terms of meeting system and user requirements (scale, cost, availability, accuracy, and integrity). The goal of this research is to provide insights regarding different Radio Frequency (RF) technologies operation and evaluate their positioning capabilities (Wi-Fi, BLE and LoRa) in underground industrial facilities such as quarries and mines, following and expanding the tests of previous studies in controlled environment. Furthermore, the multi-sensory approach that this study is pursuing, aims to provide the foundations of a low-cost, scalable and robust positioning system. This system would integrate the characteristics of the aforementioned technologies in order to meet the application-specific user requirements and set the basis for a more efficient mobile mapping system. In this context, technologies’ characterization and comparison is presented, by using data from a real operating underground quarry. The data gathered lead to the conceptualization of the localization scheme, which besides the SoO observables, utilizes their availability status as an additional feature within the quarry as well. The proposed combined approach outperformed the rest, achieving an accuracy bellow 15m for the 85% of the test data, which is sufficient for typical quarrying operations monitoring and management requirements.

Performance assessment of positioning solutions of different mobile devices using kalman filtering

Abstract: Abstract. In this study, the performance of two different smart mobile devices is analysed and compared. These devices are either single-frequency or dual-frequency GNSS carrier frequency-enabled smartphones. Both selected devices are from the same manufacturer. They are the Pixel 3 and Pixel 4 from Google. The smartphones were positioned on six control points in an open sky environment for which ground truth was determined with high-precision geodetic GNSS equipment serving as a reference. For the evaluation, a Kalman filter solution is derived and applied to be able to determine position information epoch-wise. In the first step, the position solution variations on the control points are determined and analyzed. It is seen that high variations may occur, especially in the single-frequency Pixel 3 where high variations were shown. As expected, these deviations are significantly smaller for the dualfrequency Pixel 4. Using the Kalman filter it is then proven that positioning of the few decimeter to meter level is achievable for the dual frequency smartphone. Thus, it has been shown that dual-frequency smartphones have already reached a good level of performance which opens up their use for some applications in surveying and especially in Location-based Services (LBS).