Positioning Using LTE Signals

GNSS is excellent in open-sky conditions, but in many everyday situations such as traveling in urban canyons or being inside buildings, too few GNSS space vehicles (SV) are visible to get a position fix. An alternative is then desirable, and can be provided by positioning using the signals from cellular base stations. Of particular interest are the new signals and positioning possibilities from LTE cellular network operators, since the LTE coverage is expected to be high in cities and other well-populated areas. Furthermore, to accommodate the need for increasing data rates network operators are configuring their LTE downlink bandwidth to be as wide as possible, providing good resolution of different multipath components, which also assists positioning. A portable experimental setup was built to perform measurements and to gather knowledge about the overall performance of positioning with LTE signals. It consists of a universal software radio peripheral (USRP) N210 that is synchronized to a GPS-locked Rubidium frequency standard. A personal computer (PC) acts as an overall system controller and as a recording unit, storing LTE data samples together with GNSS sentences from a u-blox LEA-6T module. A Matlab-based algorithm does the complete post-processing, extracting pseudoranges for the LTE BS, and calculating the position solution.The results of determining the position of a car driven on a route around the town of Rapperswil, Switzerland show the potential of the positioning approach, using only available LTE signals. Even with the basic system the root meansquare (RMS) value of the absolute error in a position using LTE compared to the actual position using GPS is 43 m, demonstrating that the CRS signal of the LTE standard is well suited as a fall-back alternative to GNSS in environmentally challenging situations.