IEEE 802.15.4a CSS-based Localization System for Wireless Sensor Networks

Abstract—This demonstration shows IEEE 802.15.4a CSS-based localization system for wireless sensor networks. IEEE 802.15.4a CSS technology can provide high accurate ranging functionality to a sensor node. However, as it measures a distance based on Time-of-Flight(TOF) of RF signal, the system needs well designed ranging and report protocol. So, in this demonstration we show our ranging protocol and location calculation server. I

Cooperative localization with 802.15.4a CSS radios: Robustness to node failures

Cooperative positioning is a solution for location-aware applications where GPS-aided localization is unfeasible. In this paper, we provide a qualitative comparison between cooperative and non-cooperative localization under node-failure scenarios, in a typical indoor environment using off-the-shelf 802.15.4a radios. From our analysis, we observe the improved robustness and coverage offered by the cooperative approach in node-failure scenarios

A Three-Tiered Architecture for Large-Scale Wireless Hospital Sensor Networks

International audienceThe Utra Wide Band physical layer specified by the IEEE 802.15.4a standard [1] presents numerous advantages comparing with its original IEEE 802.15.4 standard, namely high accuracy positioning ability, high data rate up to 27 mbps, extended communication range, low power consumption and low complexity. Actually, many research and development activities focus on the design of UWB sensor nodes entities. However nodes interactions or network configuration are neglected. For that, we propose in this paper to investigate the use of UWB for large scale Wireless Hospital Sensor Networks (WHSNs) to benefit from the advantages offered by the UWB technology. This evolving networking paradigm promises to revolutionize healthcare by allowing inexpensive, non-invasive, pervasive and ubiquitous, ambulatory health monitoring. We present the design of new system architecture, based on IEEE 802.15.4a compliant sensors, suitable for health monitoring application in high dense hospital environment. The proposed system architecture is intended to support large-scale deployment and to improve the network performance in terms of energy efficiency, real-time guarantees and Quality-of-Service (QoS)

Optimization of positioning capabilities in wireless sensor networks : from power efficiency to medium access

In Wireless Sensor Networks (WSN), the ability of sensor nodes to know its position is an enabler for a wide variety of applications for monitoring, control, and automation. Often, sensor data is meaningful only if its position can be determined. Many WSN are deployed indoors or in areas where Global Navigation Satellite System (GNSS) signal coverage is not available, and thus GNSS positioning cannot be guaranteed. In these scenarios, WSN may be relied upon to achieve a satisfactory degree of positioning accuracy. Typically, batteries power sensor nodes in WSN. These batteries are costly to replace. Therefore, power consumption is an important aspect, being performance and lifetime of WSN strongly relying on the ability to reduce it. It is crucial to design effective strategies to maximize battery lifetime. Optimization of power consumption can be made at different layers. For example, at the physical layer, power control and resource optimization may play an important role, as well as at higher layers through network topology and MAC protocols. The objective of this Thesis is to study the optimization of resources in WSN that are employed for positioning purposes, with the ultimate goal being the minimization of power consumption. We focus on anchor-based positioning, where a subset of the WSN nodes know their location (anchors) and send ranging signals to nodes with unknown position (targets) to assist them in estimating it through distance-related measurements. Two well known of such measurements are received signal strength (RSS) and time of arrival (TOA), in which this Thesis focuses. In order to minimize power consumption while providing a certain quality of positioning service, in this dissertation we research on the problems of power control and node selection. Aiming at a distributed implementation of the proposed techniques, we resort to the tools of non-cooperative game theory. First, transmit power allocation is addressed for RSS based ranging. Using game theory formulation, we develop a potential game leading to an iterated best response algorithm with sure convergence. As a performance metric, we introduce the geometric dilution of precision (GDOP), which is shown to help achieving a suitable geometry of the selected anchor nodes. The proposed scheme and relative distributed algorithms provide good equilibrium performance in both static and dynamic scenarios. Moreover, we present a distributed, low complexity implementation and analyze it in terms of computational complexity. Results show that performance close to that of exhaustive search is possible. We then address the transmit power allocation problem for TOA based ranging, also resorting to a game theoretic formulation. In this setup, and also considering GDOP as performance metric, a supermodular game formulation is proposed, along with a distributed algorithm with guaranteed convergence to a unique solution, based on iterated best response. We analyze the proposed algorithm in terms of the price of anarchy (PoA), that is, compared to a centralized optimum solution, and shown to have a moderate performance loss. Finally, this dissertation addresses the effect of different MAC protocols and topologies in the positioning performance. In this direction, we study the performance of mesh and cluster-tree topologies defined in WSN standards. Different topologies place different constraints in network connectivity, having a substantial impact on the performance of positioning algorithms. While mesh topology allows high connectivity with large energy consumption, cluster-tree topologies are more energy efficient but suffer from reduced connectivity and poor positioning performance. In order to improve the performance of cluster-tree topologies, we propose a cluster formation algorithm. It significantly improves connectivity with anchor nodes, achieving vastly improved positioning performance.En les xarxes de sensors sense fils (WSN), l'habilitat dels nodes sensors per conèixer la seva posició facilita una gran varietat d'aplicacions per la monitorització, el control i l'automatització. Així, les dades que proporciona un sensor tenen sentit només si la posició pot ésser determinada. Moltes WSN són desplegades en interiors o en àrees on la senyal de sistemes globals de navegació per satèl.lit (GNSS) no té prou cobertura, i per tant, el posicionament basat en GNSS no pot ésser garantitzat. En aquests escenaris, les WSN poden proporcionar una bona precisió en posicionament. Normalment, en WSN els nodes són alimentats amb bateries. Aquestes bateries són difícils de reemplaçar. Per tant, el consum de potència és un aspecte important i és crucial dissenyar estratègies efectives per maximitzar el temps de vida de la bateria. L'optimització del consum de potència pot ser fet a diferents capes del protocol. Per exemple, en la capa física, el control de potència i l'optimització dels recursos juguen un rol important, igualment que la topologia de xarxa i els protocols MAC en les capes més altes. L'objectiu d'aquesta tesi és estudiar l¿optimització de recursos en WSN que s'utilitzen per fer posicionament, amb el propòsit de minimitzar el consum de potència. Ens focalitzem en el posicionament basat en àncora, en el qual un conjunt de nodes coneixen la seva localització (nodes àncora) i envien missatges als nodes que no saben la seva posició per ajudar-los a estimar les seves coordenades amb mesures de distància. Dues classes de mesures són la potència de la senyal rebuda (RSS) i el temps d'arribada (TOA) en les quals aquesta tesi està focalitzada. Per minimitzar el consum de potència mentre que es proporciona suficient qualitat en el posicionament, en aquesta tesi estudiem els problemes de control de potència i selecció de nodes. Tenint en compte una implementació distribuïda de les tècniques proposades, utilitzem eïnes de teoria de jocs no cooperatius. Primer, l'assignació de potència transmesa és abordada pel càlcul de la distància amb RSS. Utilitzant la teoria de jocs, desenvolupem un joc potencial que convergeix amb un algoritme iteratiu basat en millor resposta (best response). Com a mètrica d'error, introduïm la dilució de la precisió geomètrica (GDOP) que mostra quant d'apropiada és la geometria dels nodes àncora seleccionats. L'esquema proposat i els algoritmes distribuïts proporcionen una bona resolució de l'equilibri en l'escenari estàtic i dinàmic. Altrament, presentem una implementació distribuïda i analitzem la seva complexitat computacional. Els resultats obtinguts són similars als obtinguts amb un algoritme de cerca exhaustiva. El problema d'assignació de la potència transmesa en el càlcul de la distància basat en TOA, també és tractat amb teoria de jocs. En aquest cas, considerant el GDOP com a mètrica d'error, proposem un joc supermodular juntament amb un algoritme distribuït basat en millor resposta amb convergència garantida cap a una única solució. Analitzem la solució proposada amb el preu de l'anarquia (PoA), és a dir, es compara la nostra solució amb una solució òptima centralitzada mostrant que les pèrdues són moderades. Finalment, aquesta tesi tracta l'efecte que causen diferents protocols MAC i topologies en el posicionament. En aquesta direcció, estudiem les topologies de malla i arbre formant clusters (cluster-tree) que estan definides als estàndards de les WSN. La diferència entre les topologies crea diferents restriccions en la connectivitat de la xarxa, afectant els resultats de posicionament. La topologia de malla permet una elevada connectivitat entre els nodes amb gran consum d'energia, mentre que les topologies d'arbre són més energèticament eficients però amb baixa connectivitat entre els nodes i baix rendiment pel posicionament. Per millorar la qualitat del posicionament en les topologies d'arbre, proposem un algoritme de formació de clústers.Postprint (published version

Indoor positioning using symmetric double-sided two-way ranging in a welding hall

We introduce a method by which to locate sensors in a 2.4 GHz wireless network. We tested our system in a rough welding hall, where plasma cutters and welding machines commonly cause radio interference. Indoor positioning is a challenge because standardized GPStype global-positioning technologies are not available. There is therefore a need for extra infrastructure, such as wireless sensors, but moreover there is no standardized communication between sensors. Therefore, it is reasonable to investigate alternative technologies. We found that a reliable positioning system could be created by using Chirp Spread Spectrum (CSS) modulation. Also, we studied which CSS parameters affect the transfer data rate in order to determine the most reliable speed for both top and average transfer

Cooperative localization by dual foot-mounted inertial sensors and inter-agent ranging

The implementation challenges of cooperative localization by dual foot-mounted inertial sensors and inter-agent ranging are discussed and work on the subject is reviewed. System architecture and sensor fusion are identified as key challenges. A partially decentralized system architecture based on step-wise inertial navigation and step-wise dead reckoning is presented. This architecture is argued to reduce the computational cost and required communication bandwidth by around two orders of magnitude while only giving negligible information loss in comparison with a naive centralized implementation. This makes a joint global state estimation feasible for up to a platoon-sized group of agents. Furthermore, robust and low-cost sensor fusion for the considered setup, based on state space transformation and marginalization, is presented. The transformation and marginalization are used to give the necessary flexibility for presented sampling based updates for the inter-agent ranging and ranging free fusion of the two feet of an individual agent. Finally, characteristics of the suggested implementation are demonstrated with simulations and a real-time system implementation.Comment: 14 page

무선통신 기반 원점 복귀를 위한 상대좌표 추정에 관한 연구

Localization Systems based on wireless communications are required to complete the deployment of reference nodes and it is essential to deploy three or more reference nodes before providing localization service. Also, It is difficult to provide accurate direction to users because of accumulated error of inertial sensor with time and influence of external magnetic field. This paper presents the localization system for estimating relative coordinates without pre-deployment of the reference nodes based on UWB(Ultra Wide Band) ranging communication. The proposed localization system which consists of a mobile node composed of three nodes estimates relative coordinates of the reference node and azimuth. Also, In the process of estimating relative coordinates of the reference node, errors are minimized through a RE (Rounding Estimation) technique and Kalman filter. Experimental results show the feasibility and validity of proposed system.1. 서 론 1.1 연구배경 1 1.2 논문구성 3 2. 관련이론 2.1 거리추정 방법 4 2.1.1 RSSI(Received signal strength indication) 4 2.1.2 ToA(Time of Arrival) 4 2.1.3 TDoA(Time Difference of Arrival) 6 2.2 위치추정 방법 8 2.2.1 무선통신 기반 위치추정 시스템 8 2.2.2 영상 기반 위치추정 시스템 9 2.3 잡음제거를 위한 필터링 알고리즘 11 2.3.1 이동평균 필터 11 2.3.2 저주파 통과 필터 11 2.3.3 칼만 필터 12 2.4 위치 추정을 위한 무선 통신방법 13 2.4.1 IR-UWB(Impulse Radio–Ultra Wide Band) 13 2.4.2 CSS(Chirp Spread Spectrum) 14 2.5 좌표의 회전 변환 14 3. 제안한 위치추정 시스템 3.1 개요 16 3.2 제안한 시스템 16 3.2.1 세 개의 노드로 구성된 이동노드의 배치 16 3.2.2 제안한 위치 추정 시스템의 흐름 18 4. 실험 및 분석 4.1 실험장비 22 4.2 Prototype 24 4.3 RE 기법 신뢰도 실험 26 4.4 실내 환경에서 방위각 실험 No.1 27 4.5 실내 환경에서 방위각 실험 No.2 28 5. 결론 5.1 결론 및 향후 응용분야 29 참고문헌 3

Accuracy and Delay: An Inherent Trade-off in Cooperative UWB Navigation

Location-aware applications and wireless sensor networks are becoming essential in our daily lives from a commercial, and public perspectives. The need of localization information to drive the applications is a key requirement. New technologies have emerged to tackle the problem of the limitations of the Global Positioning System (GPS) solutions. Ultra-wideband (UWB) is one of those emerging RF-technologies. The thrive in search for better accuracy involves improved ranging algorithms, higher transmission powers, and the use of cooperation among nodes. The goal of this thesis is to investigate the trade-off between medium access control (MAC) delay and accuracy for UWB systems based on hands-on experience and practical implementation with state-of-the-art equipment, based on two-way-ranging and a spatial time division multiple access scheme (STDMA).Paper A investigates the connection between accuracy and MAC delay for noncooperative scenarios. We quantify, by means of lower bounds how traditional methods to improve accuracy such as increased number of anchors, and increased communication range comes at a significant cost in terms of delay. Techniques such as selective ranging and eavesdropping help alleviate the trade-off and reduce the MAC delay in favor of mobile networks with tolerable accuracies. Paper B extends the work for cooperative scenarios, where nodes cooperate with each other by means of shared information. This sharing has an impact not only on the position accuracy but also on the MAC delay which we quantify by means of lower bounds, both for the accuracy and MAC delay. Once again, selective ranging is evaluated to reduce the MAC delay for finite cooperative networks. We show how indiscriminate cooperation leads to large MAC delays, which has a direct impact on the update rate for high mobility scenarios. Finally, Paper C unifies all findings by including derivations of the accuracy and MAC delay lower bounds for noncooperative and cooperative networks, evaluating selective ranging and eavesdropping to cope with the tradeoff in different conditions. Numerical evaluations are included for several distinct operations. Furthermore, we characterize the trade-off behavior for dense-location aware networks for both noncooperative and cooperative cases by means of scaling laws. We conclude by introducing a delay/accuracy parameter which can uniquely quantify the trade off between accuracy and MAC delay as a function of the agent and anchor density. Noncooperative eavesdropping shows to outperform cooperative networks in terms of accuracy with reasonable delays. Finally, in terms of scaling, we found that, under certain conditions, standard cooperative positioning exhibits the worst possible trade-off among the considered strategies