Low-cost precise vehicular positioning in urban environments

Accurate Collaborative Globally-Referenced Digital Mapping with Standard GNSS

“…The rover GNSS receiver is one among several sensors housed in an integrated perception platform called the University of Texas Sensorium [ 6 ]. Designed for connected and automated vehicle research, the Sensorium is a self-contained sensor housing that can be mounted atop any standard passenger vehicle.…”

“…Development of an extensive dense reference network in support of CDGNSS consumer vehicular positioning in urban areas, as suggested in [ 38 ], could be an expensive affair. PPP is a low-cost alternative to CDGNSS that requires only a sparse network of reference stations across the globe, but is not considered a viable option for urban GNSS positioning in this paper because the constant cycle slips and outages experienced in urban areas [ 6 ] make it difficult for PPP’s float carrier phase ambiguity estimates to converge [ 7 ], in which case PPP degrades to code-phase positioning accuracy.…”

“…However, when the LOS signal is comparable to or weaker than other rapidly-decorrelating echoes, the combined carrier-phase is uniformly random. In a GNSS receiver, the phase lock loop’s phase-lock indicator indicates whether a sufficiently strong LOS signal is available, enabling carrier lock [ 6 ]. The simulator’s phase-lock indicator is asserted only if (1) the tracked Doppler frequency does not deviate significantly from a second-order polynomial, and (2) the strongest received echo is attenuated by more than 25 dB with respect to an unattenuated signal.…”

“…Meanwhile, GNSS position estimates are obtained in the global frame and do not exhibit any distance-dependent drift. Accordingly, GEOSLAM ingests standard GNSS position estimates from a software-defined GNSS receiver, called GRID/pprx [ 6 , 61 ], in a tightly-coupled architecture to create a globally-referenced map, enable cooperative multi-session mapping, and constrain the drift of visual SLAM. Since the stereo camera setup is triggered by the same clock that drives digitization of the GNSS samples (see Figure 7 ), it is possible to produce GNSS measurements synchronized with the camera image epochs.…”

“…Maps anchored by these measurements may not exhibit lane-level consistency with each other. One possible solution is to create digital maps with decimeter-accurate carrier-phase differential GNSS (CDGNSS) systems [ 6 ]. However, at current prices, such systems can only be installed on a limited fleet of specialized mapping vehicles.…”