Over the past two decades, Global Navigation Satellite Systems (GNSS) have had a transformational effect on the use of navigation services by non-expert users. SatNavs are now almost standard equipment for the motorist and GNSS plays a large role in applications as diverse as agriculture and surveying. Largely driven by the inclusion of GNSS receivers in smartphones, global shipments are predicted to exceed 1 billion units per annum by 2020. However, the growth of mass-market ‘Location Based Services’ is hindered by the technological limitations of GNSS. Most significantly, GNSS does not provide a robust and accurate position solution to a user trying to navigate where they spend most of their time – indoors.
Accurate indoor positioning is a considerable challenge and is currently the subject of much research. Metre-level accuracies are required if a person is to be reliably directed to an indoor space or point of interest. A single, dominating technology analogous to GNSS does not currently exist to solve this problem. Instead, many approaches have been proposed with varying degrees of accuracy, reliability and practicality. Currently, and for the foreseeable future, a range of positioning technologies will need to be considered by an application designer and matched to the task at hand. There are many examples of the types of technology currently available.
- Radio-based approaches. These include high-sensitivity GNSS, methods based on a cellular phone network and WiFi-based positioning. These methods tend to lack robustness and are inappropriate for emergency or disaster response applications.
- Dead reckoning approaches. These allow indoor navigation to be achieved by measuring the accelerations and rotations of the object to be tracked, i.e. the human body, using miniaturised inertial sensors (accelerometers and gyroscopes). Dead reckoning systems rely on an accurate initial position and orientation from an external source. Over time, sensor errors mean that the position solution quality will decrease.
- Optical approaches. These use image recognition techniques or ‘optical flow’ measurements to estimate either the position or movement of a camera relative to the world. In many cases they suffer from position drift similar to that observed in inertial systems.
- Magnetic field mapping techniques. These use a ‘fingerprint’ magnetic field pattern for a mapped area or measure a low frequency signal from a local beacon. Magnetic methods are prone to unmapped changes in the indoor environment caused by electronic equipment, metallic objects or even changes to the building layout itself. There are significant problems involved in obtaining and maintaining indoor mapping. Mapping provides context for positioning as well as allowing route planning to take place. At present no single source of indoor mapping exists and a major effort is required to bring together and maintain the highly fragmented datasets. Access, privacy and security issues mean that most indoor mapping will need to be maintained by the building operator or through crowdsourcing. As a result, mapping will reflect the biases and priorities of the entity doing the mapping and standards of accuracy and completeness are likely to vary from building to building.
Identifying user groups
We have identified some current and potential user groups for indoor positioning solutions and explored their needs and key characteristics. The types of users we identified were:
Everyday Navigators. The most obvious use for indoor positioning technologies is simply extending existing navigation solutions to work indoors. This extension would facilitate the creation of true end-to-end navigation tools. Generally, these users will require a navigation aid only when traveling through large or complex unfamiliar buildings so they will tend to be infrequent users. For this reason, they won’t be prepared to invest in or even carry specialist equipment, but the size of this user group means that it is justifiable to invest in significant infrastructure in order to support them.
- Blind/Partially Sighted Users. A range of indoor, outdoor and ubiquitous solutions have been adopted for use by the blind and partially sighted. These solutions range in function from crude, high-level navigation, to active object detection and avoidance. Those that are blind or partially sighted need extremely accurate location information in order for any navigation solution to be effective and safe. The potential impact of failure for blind and partially sighted users means that a solution must be extremely robust. Local infrastructure won’t necessarily be present in all environments in which these users wish to navigate, but larger scale infrastructure such as mobile phone masts could be used if sufficiently reliable.
- Surveyors. Creating internal building models requires accurate relative positioning. As this type of activity is often a precursor to infrastructure installation, infrastructure cannot be relied on when completing tasks. As professional users, expensive specialist equipment is acceptable as long as it provides accurate and reliable location solutions within domain specific tolerances.
- Location-Based Gamers. While the needs of gamers vary depending on the specific location-based games they play, there are some commonalities in this user group. The first priority for gamers is a good user experience; if the technology gets in the way of enjoyment it simply will not be used. Issues such as coverage and accuracy may not be important, as long as they are dealt with appropriately within the game.
- Emergency Responders. In emergency situations the environment is variable and it is vital that information is of a known accuracy and delivered in a timely manner. Emergency responders are likely to carry specialised equipment, but cannot rely on infrastructure ‘on the ground’ that may be compromised or simply absent.
By comparing the needs of various user groups with the limitations of each technology we can identify where possible opportunities and pitfalls lie in implementing various indoor positioning technologies.
Blind/partially sighted users, surveyors and emergency responders would all benefit from a robust, accurate solution that does not require infrastructure, but can involve specialist equipment. Comparing these needs to the current solutions suggests a combined approach is necessary. Mid-to-high-end inertial sensors can provide the necessary infrastructure-free accuracy, but another radio-based solution is needed to give initial position and correct drift over time. Even this multi-technology solution may not be sufficiently robust, as it is ultimately still dependent on infrastructure that may not be present.
The way ahead
This analysis reveals that no single currently available indoor positioning technology can fulfil the needs of any of the user groups identified. Three priority areas for future technology development are:
- A high-accuracy, infrastructure-free solution for those willing to use specialist equipment.
- A low-cost solution that uses a suite of cheap sensors to exploit any and all local infrastructure to provide a ‘good enough’ solution for navigation and gaming.
- Development of industry standards for the mass market implementation and use of RF signal based positioning methods.
By comparing a review of current internal positioning solutions with user needs in this area, we have identified specific shortfalls that need to be tackled by future technology developments. With the fast pace of progress in this area it is important to ensure that in the rush to develop technology, the end users are not forgotten.
By Michael Brown, James Pinchin & Chris Hide
Dr Michael Brown and Dr James Pinchin are Research Fellows at the Horizon Digital Economy Research Hub, University of Nottingham.
Dr Chris Hide is a Senior Research Fellow at the Nottingham Geospatial Institute, University of Nottingham.
This work was funded by the RCUK Horizon Digital Economy Research Hub grant, EP/G065802/1.