GPS World, January 2018

MOBILE PRECISION cycle slips see Figures 5 and 8 Only single frequency data was available and while the engines used had been tuned for consumer data they were not specifically designed for this class of data Next Generation Phones Within the next couple of years improved chipsets are expected to be available to consumers that will result in improvements in achievable positioning performance In May 2017 Broadcom provided us with a development kit for its next generation L1 L5 multisystem BCM47755 GNSS chipset This allowed us to assess what may be possible when improved GNSS chipsets are integrated in the next generation of cellular devices The development environment included the GNSS chipset with an external antenna port so both a cell phone equivalent antenna and a precision antenna could be compared This allowed us to evaluate the impact of the antenna performance on the GNSS observables and positioning results The Broadcom GNSS development system communicates via USB to a Samsung S7 phone and publishes data via the Android GNSS measurement API so the equivalent 30 GPS WORLD WWW GPSWORLD COM JANUARY 2018 data flow of an integrated cellular device is maintained see FIGURE 10 In our ION paper we showed the typical phase double difference residuals observed from current Android devices The Broadcom BCM47755 originally provided similar performance although it also supports GPS L5 and Galileo E5A In November 2017 Broadcom provided a firmware update that resolved the sub cycle phase issues With the updated Broadcom software the double difference carrier residuals for GPS L1 on a zero baseline when differencing a precision receiver to a Broadcom BCM47755 are shown in FIGURE 11 The standard deviation is 45 millicycles which is approximately 86 millimeters mm This is substantially better than earlier implementations of the Android GNSS interface see Figure 7 and sufficient to perform RTK ambiguity resolution The rest of the results in this article were obtained with the improved firmware along with a new precision position engine This engine was designed from inception to support GNSS measurements with differing quality and so can more optimally process the Android GNSS FIGURE 11 Precision GNSS to Broadcom BCM47755 zero baseline double difference carrier phase residuals FIGURE 12 Cellular equivalent antenna FIGURE 13 RTK performance for a 35 hour dataset sampled on Nov 22 Broadcom chip at left and precision chip at right A short baseline was used precision antenna FIGURE 15 RTK initialization performance dataset sampled on Nov 22 Broadcom chip at left and precision receiver at right precision antenna FIGURE 14 Number of GPS L1 L5 plus Galileo E1 E5A dual frequency measurements used by the position solution based on the Broadcom chipset precision antenna FIGURE 10 Broadcom BCM47755 development system