Opportunistic Use of Metropolitan RF Beacon Signals for Urban and Indoor Positioning

In GPS-challenged environments such as dense urban and indoors, ranging with local radio signals is being explored for positioning (multilateration) as an alternate/supplement to GPS. Local radio signals such as broadcast and wireless communications signals are strong with good coverage. In particular, it offers horizontal penetration through windows and alleys, less attenuated than vertical traverse through roofs and buildings by GPS. Dedicated radio beacons have an extra advantage for being synchronous in transmission with well-structured signals designed for timing and ranging as compared to other signals of opportunity. In this paper, we investigate an example radio beacon signal, namely, Metropolitan Broadcast System (MBS) by NextNav (Sunnyvale, CA), and its opportunistic use for positioning by passive users who do not have access to encrypted data payloads. Formation of pseudoranges from time of arrival (TOA) measurements of dedicated beacon signals is presented, which is shown to be simpler than with non-cooperative asynchronous signals of opportunity. A positioning mechanism wherein both time of transmit (TOT) and location of transmitter (LOT) are unknown is formulated as simultaneous localization and mapping of emitting radio sources (SLAMERS). To illustrate, three examples are presented, namely, acquisition and tracking of in-the-air MBS signals, mobile positioning with mixed signals of opportunity, and simulation performance of SLAMERS.