Improving RF Localization Through Measurement and Manipulation of the Channel Impulse Response

For over twenty years, global navigation satellite systems like GPS have provided an invaluable navigation, tracking, and time synchronization service that is used by people, wildlife, and machinery. Unfortunately, the coverage and accuracy of GPS is diminished or lost when brought indoors since GPS signals experience attenuation and distortion after passing through and reflecting off of building materials. This disparity in coverage coupled with growing demands for indoor positioning, navigation, and tracking has led to a plethora of research in localization technologies. To date, however, no single system has emerged as a clear solution to the indoor localization and navigation problem because the myriad of potential applications have widely varying performance requirements and design constraints that no system satisfies. Fortunately, recently-introduced commercial ultra-wideband RF hardware offers excellent ranging accuracy in difficult indoor settings, but these systems lack the robustness and simplicity needed for many indoor applications. We claim that an asymmetric design that separates transmit and receive functions can enable many of the envisioned applications not currently realizable with an integrated design. This separation of functionality allows for a flexible architecture which is more robust to the in-band interference and heavy multipath commonly found in indoor environments. In this dissertation, we explore the size, weight, accuracy, and power requirements imposed on tracked objects (tags) for three broadly representative applications and propose the design of fixed-location infrastructure (anchors) that accurately and robustly estimate a tag’s location, while minimizing deployment complexity and adhering to a unified system architecture. Enabled applications range from 3D tracking of small, fast-moving micro-quadrotors to 2D personal navigation across indoor maps to tracking objects that remain stationary for long periods of time with near-zero energy cost. Each application requires careful measurement of the ultra-wideband channel impulse response, and an augmented narrowband receiver is proposed to perform these measurements. The key design principle is to offload implementation complexity to static infrastructure where an increase in cost and complexity can be more easily absorbed and amortized. Finally, with an eye towards the future, we explore how the increasingly crowded RF spectrum impacts current ultra-wideband system design, and propose an alternative architecture that enables improved coexistence of narrowband and ultra-wideband transmissions.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138642/1/bpkempke_1.pd

Robust, Energy-Efficient, and Scalable Indoor Localization with Ultra-Wideband Technology

Ultra-wideband (UWB) technology has been rediscovered in recent years for its potential to provide centimeter-level accuracy in GNSS-denied environments. The large-scale adoption of UWB chipsets in smartphones brings demanding needs on the energy-efficiency, robustness, scalability, and crossdevice compatibility of UWB localization systems. This thesis investigates, characterizes, and proposes several solutions for these pressing concerns. First, we investigate the impact of different UWB device architectures on the energy efficiency, accuracy, and cross-platform compatibility of UWB localization systems. The thesis provides the first comprehensive comparison between the two types of physical interfaces (PHYs) defined in the IEEE 802.15.4 standard: with low and high pulse repetition frequency (LRP and HRP, respectively). In the comparison, we focus not only on the ranging/localization accuracy but also on the energy efficiency of the PHYs. We found that the LRP PHY consumes between 6.4–100 times less energy than the HRP PHY in the evaluated devices. On the other hand, distance measurements acquired with the HRP devices had 1.23–2 times lower standard deviation than those acquired with the LRP devices. Therefore, the HRP PHY might be more suitable for applications with high-accuracy constraints than the LRP PHY. The impact of different UWB PHYs also extends to the application layer. We found that ranging or localization error-mitigation techniques are frequently trained and tested on only one device and would likely not generalize to different platforms. To this end, we identified four challenges in developing platform-independent error-mitigation techniques in UWB localization, which can guide future research in this direction. Besides the cross-platform compatibility, localization error-mitigation techniques raise another concern: most of them rely on extensive data sets for training and testing. Such data sets are difficult and expensive to collect and often representative only of the precise environment they were collected in. We propose a method to detect and mitigate non-line-of-sight (NLOS) measurements that does not require any manually-collected data sets. Instead, the proposed method automatically labels incoming distance measurements based on their distance residuals during the localization process. The proposed detection and mitigation method reduces, on average, the mean and standard deviation of localization errors by 2.2 and 5.8 times, respectively. UWB and Bluetooth Low Energy (BLE) are frequently integrated in localization solutions since they can provide complementary functionalities: BLE is more energy-efficient than UWB but it can provide location estimates with only meter-level accuracy. On the other hand, UWB can localize targets with centimeter-level accuracy albeit with higher energy consumption than BLE. In this thesis, we provide a comprehensive study of the sources of instabilities in received signal strength (RSS) measurements acquired with BLE devices. The study can be used as a starting point for future research into BLE-based ranging techniques, as well as a benchmark for hybrid UWB–BLE localization systems. Finally, we propose a flexible scheduling scheme for time-difference of arrival (TDOA) localization with UWB devices. Unlike in previous approaches, the reference anchor and the order of the responding anchors changes every time slot. The flexible anchor allocation makes the system more robust to NLOS propagation than traditional approaches. In the proposed setup, the user device is a passive listener which localizes itself using messages received from the anchors. Therefore, the system can scale with an unlimited number of devices and can preserve the location privacy of the user. The proposed method is implemented on custom hardware using a commercial UWB chipset. We evaluated the proposed method against the standard TDOA algorithm and range-based localization. In line of sight (LOS), the proposed TDOA method has a localization accuracy similar to the standard TDOA algorithm, down to a 95% localization error of 15.9 cm. In NLOS, the proposed TDOA method outperforms the classic TDOA method in all scenarios, with a reduction of up to 16.4 cm in the localization error.Cotutelle -yhteisväitöskirj

Doctor of Philosophy

dissertationLow-cost wireless embedded systems can make radio channel measurements for the purposes of radio localization, synchronization, and breathing monitoring. Most of those systems measure the radio channel via the received signal strength indicator (RSSI), which is widely available on inexpensive radio transceivers. However, the use of standard RSSI imposes multiple limitations on the accuracy and reliability of such systems; moreover, higher accuracy is only accessible with very high-cost systems, both in bandwidth and device costs. On the other hand, wireless devices also rely on synchronized notion of time to coordinate tasks (transmit, receive, sleep, etc.), especially in time-based localization systems. Existing solutions use multiple message exchanges to estimate time offset and clock skew, which further increases channel utilization. In this dissertation, the design of the systems that use RSSI for device-free localization, device-based localization, and breathing monitoring applications are evaluated. Next, the design and evaluation of novel wireless embedded systems are introduced to enable more fine-grained radio signal measurements to the application. I design and study the effect of increasing the resolution of RSSI beyond the typical 1 dB step size, which is the current standard, with a couple of example applications: breathing monitoring and gesture recognition. Lastly, the Stitch architecture is then proposed to allow the frequency and time synchronization of multiple nodes' clocks. The prototype platform, Chronos, implements radio frequency synchronization (RFS), which accesses complex baseband samples from a low-power low-cost narrowband radio, estimates the carrier frequency offset, and iteratively drives the difference between two nodes' main local oscillators (LO) to less than 3 parts per billion (ppb). An optimized time synchronization and ranging protocols (EffToF) is designed and implemented to achieve the same timing accuracy as the state-of-the-art but with 59% less utilization of the UWB channel. Based on this dissertation, I could foresee Stitch and RFS further improving the robustness of communications infrastructure to GPS jamming, allow exploration of applications such as distributed beamforming and MIMO, and enable new highly-synchronous wireless sensing and actuation systems

Slocalization: Sub-{\mu}W Ultra Wideband Backscatter Localization

Ultra wideband technology has shown great promise for providing high-quality location estimation, even in complex indoor multipath environments, but existing ultra wideband systems require tens to hundreds of milliwatts during operation. Backscatter communication has demonstrated the viability of astonishingly low-power tags, but has thus far been restricted to narrowband systems with low localization resolution. The challenge to combining these complimentary technologies is that they share a compounding limitation, constrained transmit power. Regulations limit ultra wideband transmissions to just -41.3 dBm/MHz, and a backscatter device can only reflect the power it receives. The solution is long-term integration of this limited power, lifting the initially imperceptible signal out of the noise. This integration only works while the target is stationary. However, stationary describes the vast majority of objects, especially lost ones. With this insight, we design Slocalization, a sub-microwatt, decimeter-accurate localization system that opens a new tradeoff space in localization systems and realizes an energy, size, and cost point that invites the localization of every thing. To evaluate this concept, we implement an energy-harvesting Slocalization tag and find that Slocalization can recover ultra wideband backscatter in under fifteen minutes across thirty meters of space and localize tags with a mean 3D Euclidean error of only 30 cm.Comment: Published at the 17th ACM/IEEE Conference on Information Processing in Sensor Networks (IPSN'18

Étude et positionnement utilisant le réseau de capteur sans fil dans un environnement minier souterrain

La sécurité et la communication posent des problèmes majeurs auxquels il faut remédier dans les environnements hostiles comme les mines souterraines. Pour une communication fiable ainsi que pour tracer la position exacte d’un objet dans les mines souterraines, différentes technologies ont été déployé. Parmi ces dernières, le réseau de capteurs sans fil est considéré comme un outil prometteur pour les applications basées sur la localisation, à savoir, la surveillance des lieux, le repérage des mobiles et la navigation. En fait, les réseaux de capteur sans-fil fournissent une couverture d’une vaste gamme d’équipements fiables, efficaces, tolérants aux défaillances et évolutives. Cependant, les travaux de recherches précédents ont divisé la localisation en deux parties: les méthodes basées sur la portée et celles non-basées sur la portée. Où la première est précise et coûteuse tandis que la deuxième est présentée pour réduire la quantité d’énergie consommée du côté capteur dont les ressources sont limitées. Notre recherche se focalise sur la localisation basée sur la portée utilisant le réseau de capteurs sans fil dans les milieux internes et mines souterrains. Plusieurs techniques ont été proposées pour la localisation comme la réception de l'indicateur de force de signal (RSSI), le temps d'arrivée (TOA), la différence de temps d'arrivée (TDOA), l'angle d'arrivée (AOA). Bien que plusieurs travaux de recherches utilisant ces techniques aient été exécutés, l'approche de localisation à base de temps pour les environnements complexe comme la mine souterraine demeure limitée. Cette thèse offre de nouvelles solutions pour combler l’écart entre la localisation à base de temps et le réseau de capteurs sans fil à haute précision, pour l’environnement minier souterrain. De plus, nous avons utilisé une technologie émergente, à savoir les communications ultra-large bande, pour booster la performance et l'exactitude. Notre travail de recherche est subdivisé en deux principales parties : une partie simulation et une partie pratique. Dans la première, nous avons utilisé MATLAB pour faire les différentes simulations. La deuxième partie consiste en plusieurs mesures pratiques réalisées dans un environnement intérieur ainsi que dans une mine souterraine. Les résultats montrent une amélioration remarquable et une meilleure précision de la technique UWB à base de temps

Indoor Positioning and Navigation

In recent years, rapid development in robotics, mobile, and communication technologies has encouraged many studies in the field of localization and navigation in indoor environments. An accurate localization system that can operate in an indoor environment has considerable practical value, because it can be built into autonomous mobile systems or a personal navigation system on a smartphone for guiding people through airports, shopping malls, museums and other public institutions, etc. Such a system would be particularly useful for blind people. Modern smartphones are equipped with numerous sensors (such as inertial sensors, cameras, and barometers) and communication modules (such as WiFi, Bluetooth, NFC, LTE/5G, and UWB capabilities), which enable the implementation of various localization algorithms, namely, visual localization, inertial navigation system, and radio localization. For the mapping of indoor environments and localization of autonomous mobile sysems, LIDAR sensors are also frequently used in addition to smartphone sensors. Visual localization and inertial navigation systems are sensitive to external disturbances; therefore, sensor fusion approaches can be used for the implementation of robust localization algorithms. These have to be optimized in order to be computationally efficient, which is essential for real-time processing and low energy consumption on a smartphone or robot