The table below highlights a few key aspects of the signals supported by the M10. It omits details such as modulation, code frequency / chipping rate, primary PRN / code length, etc. Nevertheless, GLONASS and B1I are clearly the odd ones out because of their differing frequencies and use of FDMA. The other signals have all been designed to co-exist on the same central frequency, simplifying receiver design and improving performance. The BeiDou B1C and Galileo E1 signals also benefit from modern signal designs, including individual data and pilot components.
| Constellation | Signal | Frequency | Technique | Components |
|---|---|---|---|---|
| GPS | L1 C/A | 1575.42 MHz | CDMA | Data |
| GLONASS | L1OF | 1598.0625 - 1605.375 MHz | FDMA | Data |
| BeiDou | B1I | 1561.098 MHz | CDMA | Data |
| BeiDou | B1C | 1575.42 MHz | CDMA | Data + Pilot |
| Galileo | E1 | 1575.42 MHz | CDMA | Data + Pilot |
| SBAS | L1 C/A | 1575.42 MHz | CDMA | Data |
| QZSS | L1 C/A | 1575.42 MHz | CDMA | Data |
| QZSS | L1S | 1575.42 MHz | CDMA | Data |
There is a useful online tool called GNSS View which can be used to determine the visible GNSS satellites at any given time.
The longest running GNSS, and one most likely to be included in the best performing M10 configurations.
Very likely to be used alongside the Galileo + BeiDou signals.
GLONASS currently uses FDMA, instead of CDMA like the other systems. The system is recognised as being less accurate than its rivals; GPS, BeiDou, and Galileo.
M10 configurations should probably use GPS + Galileo + BeiDou B1C, instead of GPS + Galileo + GLONASS. The processing burden is lower for the M10, and the results are likely to be more accurate.
The MAX-M10M-00B Integration manual claims that tracking and reacquisition sensitivity for acquired signals is approximately at the same level for BeiDou B1I and B1C.
BeiDou B1I
Faster TTFF and higher start-up sensitivity. BeiDou B1I signals are acquired significantly faster and at a lower signal level than BeiDou B1C signals.
Better availability. Higher start-up sensitivity results in a larger number of BeiDou satellites tracked and used in navigation solution especially at low signal level.
BeiDou B1C
Concurrent reception of 4 GNSSs with GPS L1 C/A, Galileo E1, BeiDou B1C, and GLONASS L1OF.
No additional frequency band required for BeiDou B1C in multiGNSS constellations, resulting in a lower power consumption during acquisition and tracking phases.
Notes
Galileo is one of the most accurate GNSS systems, and should always be one of the constellations used in addition to GPS.
Suggest GNSS configurations including GPS + Galileo + BeiDou B1C.
SBAS can perform two different roles, firstly as a satellite based Differential GPS (DGPS).
CFG-SBAS-USE_DIFFCORR = 1Secondly, SBAS satellites (geostationary, not MEO) can also be used to calculate positions.
CFG-SBAS-USE_RANGING = 0By all means use SBAS for corrections, but don’t use it as supplementary satellites for position fixes.
Quasi-Zenith Satellite System (QZSS) is a regional navigation satellite system that transmits additional GPS L1 C/A signals for the Pacific region covering Japan and Australia.
The M10 is able to receive and track these signals concurrently with GPS signals, resulting in better availability, especially under challenging signal conditions. It is akin to a few extra GPS satellites in Japan and Australia.
Individual signals are enabled using CFG-SIGNAL keys which are described in the u-blox M10 SPG 5.30 Interface description.
You need to be sure that your selection will not overwhelm the M10 with too many signals, which also relates to update rates.
Popular devices within the speed sailing community:
| Constellations / Signals | Motion | ESP-GPS |
|---|---|---|
| GPS + GLONASS | ❓ | ✅ |
| GPS + Galileo | ❓ | ✅ |
| GPS + Galileo + GLONASS | ✅ | ✅ |
| GPS + Galileo + BeiDou B1C | ❌ | ✅ |
| GPS + Galileo + BeiDou B1C + GLONASS | ❌ | ✅ |
n.b. It is not known whether the Motion with M10 uses GPS + Galileo, or GPS + GLONASS when running at 10 Hz.
High numbers of satellites are good, but approaching the limit of 32 may not be ideal:
It is sometimes worth limiting the number of satellites being tracked, or used in the PVT solution:
The default for u-blox Standard Precision GNSS (SPG) chipsets is to use up to 32 satellites for the PVT solution, including M8 / M9 / M10 chipsets. It should be noted that the M9 will enforce a maximum of 16 satellites at rates >= 10 Hz.
It is possible to change this limit, which will cause the GNSS chip to reduce its processing payload. The chip will still track all of the available signals, but will only use a limited number of satellites / signals for the PVT solution.
CFG-NAVSPG-INFIL_MAXSVS - default is 32The GNSS chip will automatically choose the best selection of satellites / signals. This is based on the Carrier-to-Noise-Density Ratio (C/N₀), and their positions in the sky; both in terms of the elevation angle, and their impact on Dilution of Precision (DOP).
Limiting the number of satellites in this way can often makes sense, especially where lots of satellites tend to be visible (e.g. BeiDou in Asia). The benefits of additional satellites typically start to diminish once into the twenties.
The Motion GPS limits the number of satellites to 24 when logging at 5 Hz, and 18 when logging at 10 Hz.
Satellites at a low elevation angle have an increased risk of both multipath, and ionospheric delay / distortion. The default elevation mask for u-blox SPG products is 5°, including M8 / M9 / M10 chipsets.
Specifying an elevation mask of 10° to 15° is relatively common in marine environments. Eliminating these low elevation signals before the internal selection engine even evaluates them leaves it to focus on the more reliable signals.
CFG-NAVSPG-INFIL_MINELEV - default is 5°Specifying 10° or 15° is likely to be beneficial when speed sailing, especially in environments with cliffs, buildings, or ships.
References:
The online GNSS View can be used to see the effects of different mask angles.
30 to 35 dB-Hz may be suitable for open sky environments. If you have perfect signal conditions, raising the threshold will filter out marginal multi-path and weak signals, saving processing power and potentially increasing accuracy.
The default minimum C/N₀ setting for u-blox SPG products is 6 dBHz, including M8 / M9 / M10 chipsets. You can proactively filter out weak signals by reducing the minimum C/N₀ to a floor value such as 30 or 35 dB-Hz.
CFG-NAVSPG-INFIL_MINCNO - default is 6 dBHzOnce the weak signals are dropped, the engine will dynamically balance the highest C/N₀ streams against those providing the lowest math residuals and the best spatial distribution (Dilution of Precision, DOP).
Enable the UBX-NAV-SAT binary message to stream data for all tracked satellites. Read the array of satellites, extracting their C/N₀ and PRN codes. Run a quick sorting algorithm on your host microcontroller to pick your fixed number of top signals. Feed those specific satellite measurements into your custom navigation algorithm or localized filtering loop.