GPS World, January 2018

MOBILE PRECISION significant improvement in accuracy for Android based devices However as performance differences were observed between different mobile devices significantly more data needs to be collected over a larger set of devices to review the repeatability of these preliminary results from existing Android devices The Broadcom BCM47755 development kit for a dual frequency GNSS chipset intended for future phones has allowed us to review the potential position performance that may be achievable in a handset in a few years By connecting this nextgeneration GNSS chipset to a GNSS antenna typical of a cellular device and comparing the performance from a precision GNSS antenna weve shown for the first time that it is possible to produce precision positions from a static cellular class GNSS device in ideal conditions at the centimeter level with both an RTK solution and a PPP solution However due to the significantly higher measurement noise and high multipath from the cellular devices GNSS antenna the convergence times to reach centimeter level remain a challenge although using dual frequency phase data from a cellular GNSS chipset with a PPE and RTX service the position is very rapidly sub meter Future work wi l l focus on analyzing how the performance changes when operating in the normal user environment The effects on the measurements of user motion body masking and de tuning of the antenna when the device is held need to be quantified The Nexus 9 tablet used in this article does not have integrated cellular The Broadcom development kit connects to the phone via a cable and is also 34 GPS WORLD WWW GPSWORLD COM JANUARY 2018 FIGURE 25 PPE engine on a Samsung S7 with a Broadcom BCM4775 evaluation kit not integrated into the handset We will be evaluating what may happen with a more integrated unit to make sure emissions from devices with integrated cellular very close to the GNSS antenna do not result in further degradation As the position performance is very sensitive to the quality of the antenna from both multipath and cycle slips due to low C N O and deep fades well also evaluate how well the performance of the PCB based GNSS antenna which is part of the BCM47755 evaluation kit matches current handsets Acknowledgment This article further develops work first shown in an ION GNSS 2017 paper On the Path to Precision Observations with Android GNSS Observables Manufacturers Trimble trimble com CenterPoint RTX is the satellite orbit and clock corrections service used here enabling a PPP like positioning with ambiguity fixing providing better than 4 cm with typically less than 10 minutes convergence RTX Fast functionality in Europe and parts of California uses regional atmospheric models to provide better than 4 cm horizontal in typically less than one minute When precision and professional receivers and RTK engines are mentioned in this article they are Trimble devices the BD940 receiver in some cases A Trimble Zephyr 3 antenna was used in many tests shown here FIGURE 23 Code RTX performance the dataset sampled Nov 20 and corresponding RTK and RTX phase solutions cell phone GNSS antenna FIGURE 24 CDF plots for the different PPE position solutions for cell antenna dataset