Received signal strength measurements utilizing signals of opportunity. A feasibility study on the use of RSS for loop-closure in multisensor indoor positioning systems
Publish date: 2014-05-08
Report number: FOI-R--3841--SE
Written in: English
- Multisensor indoor positioning
The aim of this work is to evaluate the feasibility of using received signal strength (RSS) measurements of existing signals in the environment, so-called signals of opportunity, as a sensor in a multisensor soldier positioning system. Radio signals are typically affected by severe multipath propagation and signal attenuation within buildings. RSS measurements on single frequencies are subject to fading, where multipath components are constructively and destructively combined depending on the location. The signal strength in indoor environments, for single frequencies, will have similar values at multiple positions; however, when combining a set of RSS values measured at different frequencies (often transmitted from different locations) they may provide an unique match between location and RSS vector. There is typically no possibility in military applications to create a database with geo-referenced RSS values prior to deployment. Only when a soldier, or another platform, is revisiting an old position during the operation they will be able to know that they are close to a previously visited position. Hence, the soldiers must themselves collect and store RSS values while entering a building, together with location information from the soldier positioning system, and then compare the current RSS values with those stored in the database. When these values are sufficiently close to what is stored in the database, this yields information about the current position which can be used to improve the performance of the integrated multisensor system. Measurements were performed on signals from FM radio, TV, mobile and TETRA base station transmitters. The measurements show how the received RSS is affected by the position. The study also investigates the uncertainties in RSS values that are introduced by the time variation of RSS and also how much shadowing and rotation of the antenna affects the measurements. Indoor positioning based on RSS measurements alone will not be feasible with high enough accuracy and reliability, since the Euclidean distance metric can point at erroneous positions when a position is revisited. However, the erroneous position estimate may be discarded based on information from other sensors when the RSS positioning technique is integrated with a multisensor indoor positioning system. The RSS positioning technique may then be used to aid e.g. a soldier positioning systems accuracy and reliability, for instance by allowing the system to perform loop-closure.