GNSS Integration

[KE7KUS]

Considerations for adding on-board GNSS via a small GNSS SiP chip like the u-blox ZOE-M8B:

u-blox ZOE-M8B Datasheet

Pro's:

1. Provides SPS accuracy (~3.5m) at extremely low power consumption (<7mA in energy-saving mode).
2. Small form factor (4mmx4mm) could potentially replace the GPS UART header with some clever board re-work - built-in UART interface in chip means relatively easy integration into existing GPS data traces.
3. When used with companion RTC chip, provides accurate long-term date/time retention for firmware use.
4. Adds GNSS logging function when used with external storage (SD card).
5. Provides odometer function which can be accessed by a firmware modification to allow "distance traveled" tracking.
6. Some signal processing hardening against GNSS interference/spoofing.
7. Multi-system compatibility (US GPS, GLONASS, Galileo, etc.) for international applicability.
8. Autonomous GNSS ephemeris downlink/storage (3 days w/ onboard ROM or 6 days w/ external storage (SD card) - enables fast starts from power-off or standby state.
9. Compatible with some position enhancing services (SBAS, D-GPS, etc.)

Con's:

1. Cost ($29 USD/per when purchased in 1 qty or $14 USD/per when purchased in 1000+ qty from DigiKey as of 12/28/21).
2. Requires GNSS antenna integration solution either on the mainboard (performance & space limitations) or into mainboard case (requires external case engineering + GPS antenna port added to main board).
3. ZOE-M8B has no PPS output for precise timing applications (frequency agile/hopping waveforms). Other chips may be substituted which provide PPS output, but potentially at a larger real-estate cost on the board.

Thoughts?