Robert K. Harle

Pedestrian localisation for indoor environments

Location information is an important source of context for ubiquitous computing systems. This paper looks at how a foot-mounted inertial unit, a detailed building model, and a particle filter can be combined to provide absolute positioning, despite the presence of drift in the inertial unit and without knowledge of the users initial location. We show how to handle multiple floors and stairways, how to handle symmetry in the environment, and how to initialise the localisation algorithm using WiFi signal strength to reduce initial complexity. We evaluate the entire system experimentally, using an independent tracking system for ground truth. Our results show that we can track a user throughout a 8725 m2 building spanning three floors to within 0.5m 75% of the time, and to within 0.73 m 95% of the time.

A Survey of Indoor Inertial Positioning Systems for Pedestrians

With the continual miniaturisation of sensors and processing nodes, Pedestrian Dead Reckoning (PDR) systems are becoming feasible options for indoor tracking. These use inertial and other sensors, often combined with domain-specific knowledge about walking, to track user movements. There is currently a wealth of relevant literature spread across different research communities. In this survey, a taxonomy of modern PDRs is developed and used to contextualise the contributions from different areas. Techniques for step detection, characterisation, inertial navigation and step-and-heading-based dead-reckoning are reviewed and compared. Techniques that incorporate building maps through particle filters are analysed, along with hybrid systems that use absolute position fixes to correct dead-reckoning output. In addition, consideration is given to the possibility of using smartphones as PDR sensing devices. The survey concludes that PDR techniques alone can offer good short- to medium- term tracking under certain circumstances, but that regular absolute position fixes from partner systems will be needed to ensure long-term operation and to cope with unexpected behaviours. It concludes by identifying a detailed list of challenges for PDR researchers.

Walk detection and step counting on unconstrained smartphones

Smartphone pedometry offers the possibility of ubiquitous health monitoring, context awareness and indoor location tracking through Pedestrian Dead Reckoning (PDR) systems. However, there is currently no detailed understanding of how well pedometry works when applied to smartphones in typical, unconstrained use. This paper evaluates common walk detection (WD) and step counting (SC) algorithms applied to smartphone sensor data. Using a large dataset (27 people, 130 walks, 6 smartphone placements) optimal algorithm parameters are provided and applied to the data. The results favour the use of standard deviation thresholding (WD) and windowed peak detection (SC) with error rates of less than 3%. Of the six different placements, only the back trouser pocket is found to degrade the step counting performance significantly, resulting in undercounting for many algorithms.

Location Fingerprinting With Bluetooth Low Energy Beacons

The complexity of indoor radio propagation has resulted in location-awareness being derived from empirical fingerprinting techniques, where positioning is performed via a previously-constructed radio map, usually of WiFi signals. The recent introduction of the Bluetooth Low Energy (BLE) radio protocol provides new opportunities for indoor location. It supports portable battery-powered beacons that can be easily distributed at low cost, giving it distinct advantages over WiFi. However, its differing use of the radio band brings new challenges too. In this work, we provide a detailed study of BLE fingerprinting using 19 beacons distributed around a ~600 m2 testbed to position a consumer device. We demonstrate the high susceptibility of BLE to fast fading, show how to mitigate this, and quantify the true power cost of continuous BLE scanning. We further investigate the choice of key parameters in a BLE positioning system, including beacon density, transmit power, and transmit frequency. We also provide quantitative comparison with WiFi fingerprinting. Our results show advantages to the use of BLE beacons for positioning. For one-shot (push-to-fix) positioning we achieve <; 2.6 m error 95% of the time for a dense BLE network (1 beacon per 30 m2), compared to <; 4.8 m for a reduced density (1 beacon per 100 m2) and <; 8.5 m for an established WiFi network in the same area.

Bluetooth Tracking without Discoverability

Outdoor location-based services are now prevalent due to advances in mobile technology and GPS. Indoors, however, even coarse location remains unavailable. Bluetooth has been identified as a potential location technology that mobile consumer devices already support, easing deployment and maintenance. However, Bluetooth tracking systems to date have relied on the Bluetooth inquiry mode to constantly scan for devices. This process is very slow and can be a security and privacy risk. In this paper we investigate an alternative: connection-based tracking. This permits tracking of a previously identified handset within a field of fixed base stations. Proximity is determined by creating and monitoring low-level Bluetooth connections that do not require authorisation. We investigate the properties of the low-level connections both theoretically and in practice, and show how to construct a building-wide tracking system based on this technique. We conclude that the technique is a viable alternative to inquiry-based Bluetooth tracking.

The potential for location-aware power management

This paper explores the use of location-awareness to dynamically optimise the energy consumption of an office. It makes use of high-accuracy location data collected over 60 days randomly selected from a year in a commercial environment to evaluate the potential for energy savings and to motivate techniques that might be used. The results suggest that the energy expended on lighting and fast-response systems could have been cut by 50%; that 75.8% of the average users working day was spent in their office; and that around 140Wh per PC per day could have been saved, compared to a policy that had machines on for the entirety of the working day. We also find inconsistent office usage that would make optimising slow response systems much harder.

RF-Based Initialisation for Inertial Pedestrian Tracking

Location information is an important source of context for ubiquitous computing systems. We have previously developed a wearable location system that combines a foot-mounted inertial unit, a detailed building model and a particle filter to locate and track humans in indoor environments. In this paper we present an algorithm in which a map of radio beacon signal strengths is used to solve two of the major problems with the original system: scalability to large environments and uncertainty due to environmental symmetry. We show that the algorithm allows the deployment of the system in arbitrarily large buildings, and that uncertainty due to environmental symmetry is reduced. This reduction allows a user to be located after taking an average of 38 steps in a 8725 m2 three-storey building, compared with 76 steps in the original system. Finally, we show that radio maps such as those required by the algorithm can be generated quickly and automatically using the wearable location system itself. We demonstrate this by building a radio map for the 8725 m2 building in under two and a half hours.

Optical tracking using commodity hardware

We describe a method for using Nintendo Wii controllers as a stereo vision system to perform 3D tracking or motion capture in real time. Commodity consumer hardware allows a wireless, portable tracker to be created that obtains accurate results for a fraction of the cost of conventional setups. Consequently, tracking becomes viable in situations where cost or space were previously prohibitive. Initial results show an accuracy of plusmn2 mm over a large tracking volume.

Performance of IEEE 802.11a in Vehicular Contexts

A key component of intelligent transportation is the provision of adequate network infrastructure to support vehicle-to-vehicle and vehicle-to-roadside communication. In this paper we report on performance evaluations carried out using the IEEE 802.11a protocol at 5.2 GHz between a moving vehicle and a fixed base station. We concentrate our evaluation on realistic urban speeds and environments, observing that performance at very low speeds is degraded due to the presence of null zones. We vary the modulation scheme and analyse the spread of resulting throughputs. Our results have implications for multimedia and other real-time applications that will utilise vehicle-to-roadside connectivity.

Deploying and evaluating a location-aware system

Location-aware systems are typically deployed on a small scale and evaluated technically, in terms of absolute errors. In this paper, the authors present their experience of deploying an indoor location system (the Bat system) over a larger area and running it for a period exceeding two years.A number of technical considerations are highlighted: a need to consider aesthetics throughout deployment, the disadvantages of specialising sensors for location only, the need for autonomous maintenance of the computational world model, the dangers in coinciding physical and symbolic boundaries, the need to design for space usage rather than space and the need to incorporate feed-back mechanisms and power management. An evaluation of long term user experiences is presented, derived from a survey, logged usage data, and empirical observations. Statistically, it is found that 35% wear their Bat daily, 35% characterise their Bat as useful, privacy concerns are rare for almost 90% of users, and users cite the introduction of more applications and the adoption of the system by other users as their chief incentives to be tracked.Thia paper aims to highlight the need to evaluate large-scale deployments of such systems both technically and through user studies.