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by Marco Fortunato, NSL

6 July 2018

Xiaomi-Mi-8-696x435Figure 1 Xiaomi-Mi-8

During May 2018, the GNSS community waited with bated breath for the release of the first Android dual frequency smartphone, the Xiaomi MI 8, finally seeing its launch on the last day of that month. This new generation of mobile devices is embedded with a Broadcom BCM47755 chip, which can record GNSS signals on both the L1/E1 and L5/E5 frequencies.

This device is an important stepping stone to the revolution that is sweeping the world of GNSS mass-market receivers, which are responding to the newly available signals of Galileo and GPS that allow improved positioning and signal tracking. Google has even released a new Android GNSS Raw Measurement API that is available on some Smartphones providing access to the embedded receivers’ raw data that allows the creation of the traditional GNSS measurements of pseudorange and carrier phase. The FLAMINGO (www.FLAMINGOgnss.com) initiative is championing this revolution with a consortium of Europe's top space companies. Utilising Android raw GNSS measurements and advances in GNSS hardware, systems are being developed for smartphones and IOT to achieve positioning under 50 cm.

 Whilst the Google API is not yet available for dual frequency mobile devices, the performance of Xiaomi MI 8 may still be assessed using the logged NMEA data files, produced from internal position-velocity-time (PVT) calculations. To evaluate the capabilities of the Xiaomi MI 8, we compare the accuracy of the internal PVT solution to that of a Samsung S8, embedded with the older single frequency Broadcom 4774 chipset, and from a geodetic class GNSS receiver (Septentrio PolaRx5e). These devices are placed in a static scenario for a period of 10 minutes.


xiaomiFig1SmFigure 2 Scatter plot (enlarge)

Figure 2 shows the position scatter in a local reference frame for each device. The origin is fixed at the Ground Control Point (GCP), graphically representing the accuracy of the distance from the origin. An R95, i.e. the radius containing 95% of solutions, is presented for each dataset in order to illustrate the GNSS precision.

Of course, the highest accuracy and precision is achieved by the Septentrio PolaRex5e. Considering the mass-market devices, the GNSS dual frequency chipset, as stated by Broadcom, improves both accuracy and precision. This is clearly presented in the figure. The horizontal precision, for example, almost halves: decreasing from 4.92 to 2.75 is observed in the R95. The overall accuracy is presented in Figure 3, where the Root Mean Square Error (RMSE) is considered for the East, North and Up directions. Calculations are made for each individual epoch, with reference to the GCP. These results highlight the significant improvements obtained by the new chipset in the vertical component: a reduction from 12.63 m to 5.11 m is observed between the Samsung S8 and Xiaomi MI 8 respectively. As expected, the geodetic class receiver is still far superior to the performance of both smartphone device. The lower RMSE in the N direction for the Xiaomi MI 8 originates from the greater, with respect to the Septentrio’s solutions, standard deviation of the internal PVT results. This leads to a different mean distance from the precise coordinates.



xiaomiFig1SmFigure 3 RMSE in a local reference system for the dataset collected from Septentrio PolaRx5e, Xiaomi Mi 8 and Samsung S8

A test was also performed in a dynamic scenario in order to evaluate the improvements that can be obtained in real-time navigation. Measurements were taken by a Samsung S8 and Xiaomi MI 8, placed in the pocket of a cyclist’s backpack for 10 minutes.

Figure 4 and 5 illustrate results in two slightly different environments. The pink and white markers represent the Samsung S8 and Xiaomi MI 8 respectively.


XiaomiGig3smFigure 4 (enlarge)

xiaomiFig4SmFigure 5 (enlarge)


Figure 4 demonstrates that, in a slightly closed environment (with proximity to buildings), the Samsung S8 provides more reliable results. Alternatively, in a more open environment (Figure 5), the track reconstructed by the Xiaomi MI 8 is much more representative. This may highlight that the Xiaomi is placing more emphasis on the GNSS PVT solution than the Samsung S8 which may be placing more dependence on other sensors within its navigation solution. These results clearly illustrate the potential of dual frequency receivers. Eventually the Android raw measurements API will be made available for dual frequency smartphones, allowing a more comprehensive analysis. Currently, we can only catch glimpses of the potential of this new GNSS technology. The future will be exciting.





World first: Galileo PRS signal accessed via the cloud

Galileo PRS drone trials at the OSIn another World’s First in the field of Galileo PRS, a team from NSL, QinetiQ and Ordnance Survey performed the first ever end-to-end demonstration of cloud-based authenticated positioning using live Galileo PRS signals. The “EXPLORERS” cloud-based receiver architecture opens up secure PRS services for automated access by European public services. Operation was demonstrated on three representative user platforms: a mobile phone, a drone and a fixed infrastructure deployment.

For further details, please see the Ordnance Survey post here.


SBAS over South Africa delivering outstanding performance

NSL have successfully demonstrated outstanding navigation and positioning improvements for different user communities across South Africa through the use of a new augmentation to GPS.

A new SBAS (Space Based Augmentation System) signal has been transmitting over South Africa immediately providing satellite navigation GPS users with improved accuracy and safety. The ambitious and rather audacious initiative has created an operational system within a 9 month period by developing, installing, implementing and operating GPS reference stations, SBAS processing software, signal uplink systems and safety control systems. NSL are an integral part of the Avanti-led partnership, providing reference stations (our SAGE receivers), uplink control systems and running user community demonstrations.

Set up for the SBAS Africa drone trialsNSL carried out demonstrations for the drone/UAV market and the geomatics/GIS community showcasing the outstanding accuracies of 50cm and better that were being realised by the system.

The drone trials were carried out by NSL and supported by South Africaan company Haevic. 

NSL provided and operated the GNSS equipment, processing the data and analysing results. Haevic provided and operated the vehicles, arranged

Screenshot 2016 04 13 23 44 36Walking a tennis court to demonstrate SBAS Africa accuracy

 the test flights, prepared the drones for the additional equipment and provided market expertise. Trials were performed between the dates of 9-16 March 2016 using three different drones at different locations; Potschefstroom and Klerksdorp in North West Province and Koekenaap in the Western Cape province of South Africa.



GIS trials were carried out in Cape Town in April 2016 by NSL using GIS quality GPS receiver. Real-time mapping activities were demonstrated, again, at the several decimetre level that is suitable for GIS data collection and smaller scale topographic mapping. 

The SBAS-Africa project (http://sbas-africa.avantiplc.com/) is an industry led initiave co-funded by the UK Space Agency (UKSA) under the International Partnership Space Programme (IPSP) has been made possible by a collaboration between the South African National Space Agency (SANSA) and the UK Space Agency (UKSA). The goals have been realised through the highly successful partnership between Avanti Communications, GMV, NSL, Pildo Labs, Adroit Economics, University of Bath, TAS UK, the South African National Space Agency (SANSA), and Ghana Council for Scientific and Industrial Research and the Agency for Aerial Navigation Safety in Africa and Madagascar (ASECNA).