Downlink synchronization of LTE base stations for opportunistic ToA positioning

Long Term Evolution (LTE) signals are a very good complement to Global Navigation Satellite Systems (GNSS) in urban environments, due to their attractive positioning capabilities. However, the network-based positioning methods defined in the LTE standard hinder the use of these signals for ranging in an opportunistic way. This is mainly due to the lack of synchronization between LTE base stations (BSs) in most of current network deployments. To circumvent this limitation, this paper proposes a method to synchronize LTE BSs using time-delay and frequency tracking loops and a-priori known receiver position. The main considerations on the use of this method for opportunistic time-of-arrival (ToA) positioning are discussed. Using real LTE signals emulated in the laboratory, positioning results are obtained with a software receiver under a dynamic trajectory, validating the use of the proposed synchronization for opportunistic ToA positioning.