Multipath assisted positioning for pedestrians using LTE signals

The rapid growth of available services depending on location awareness has led to a more and more increasing demand for positioning in challenging environments. Global navigation satellite system (GNSS) based positioning methods may fail or show weak performance in indoor and urban scenarios due to blocking of the signals and multipath propagation. In contrast, cellular radio signals provide better reception in these scenarios due to a much higher transmit power. Also, they offer high coverage in most urban areas. However, they also undergo multipath propagation, which deteriorates the positioning performance. In addition, there are often only one or two base stations within communication range of the user. Both of these problems can be solved by means of a multipath-assisted positioning approach. The idea is to exploit multipath components (MPCs) arriving at the receiver via multiple paths due to scattering or reflections. Such approaches highly depend on the ability to resolve the MPCs at the receiver. This is why multipath-assisted positioning schemes typically assume ultra-wideband systems. Today's cellular radio systems work with much smaller bandwidths, though. The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard uses bandwidths up to 20 MHz. The aim of this paper is to show by means of measurements that multipath-assisted positioning is possible using 3GPP-LTE signals with only two base stations. We apply an advanced signal processing algorithm to track MPCs arriving at the mobile terminal, and to estimate the position of the mobile terminal. Since each of the MPCs can be regarded as being sent from some physical or virtual transmitter, we estimate the positions of transmitters in addition. Assuming only the starting position and direction of the mobile terminal to be known, the results show that the root mean square positioning error of the mobile terminal is always below 1.8 meters. In 90% of the cases, it is below 1.25 meters.