Scenario - GNSS Scan with ROSE¶

Introduction¶

The LoRa Cloud™ Services enable the use of scanned GNSS signal measurements for determining the location of an end device. Here, we review the requirements for processing an assisted GNSS scan or autonmous GNSS scan by the LR111x device and returning the location data to the application server.

When using the assisted GNSS scan, the assistance (aiding) position is used by the LoRa Cloud GNSS solver, and must be within +/-150km of the actual position of the device.

The aiding position is taken from the NAV message (in the case of the LoRa Edge™ Tracker Reference Design) or from the application server. If both of these are absent, it is roughly estimated by the Doppler solver within the LoRa Cloud™ Modem & Geolocation Services.

The LoRa Cloud™ Modem & Geolocation Services issue an aiding position downlink whenever at least one of the following conditions are met:

1. No aiding position is contained in the NAV message from the device.

2. The Doppler error flag from the device is set for at least one observation inside the NAV message.

3. The aiding position inside the NAV message is present, but with more than a 150km two-dimensional error when compared to the gnss_aiding_position passed in the API call from the application server.

4. The aiding position inside the NAV message is present, but with more than a 150km two-dimensional error when compared to the position solution computed by the solver.

The device can detect that its aiding position is wrong based on the available satellites and the current time. For aiding position errors greater than 400-500km from the actual device location, the device will set the Doppler error flag and will limit the GNSS scan to search only for strong satellite signals, to avoid wasting energy.

Compatibility¶

The Semtech radio must be an LR111x.

Prerequisites/Dependencies¶

Common:

• The device application must have performed an assisted GNSS scan.

• The device application must have initialized the LoRa Basics™ Modem streaming feature on the LR111x via the modem_stream_init() command (0x062E).

Prerequisites for LoRa Basics™ Modem:

• No additional requirements

Prerequisites for LoRa Basics™ Modem-E:

• No additional requirements

Step-by-Step Procedure¶

1. Make sure the stream interface has been initialized. See the Reliable Octet Stream Encoding (ROSE) documentation for details.

2. Complete the precursor steps associated with performing an assisted GNSS scan. See the GNSS Assisted Scan scenario for details.

3. If the first byte of the NAV message is 0x00, the GNSS scan failed. The rest of the payload will indicate the status. For more information, see the LoRa Basics Modem-E Reference Manual.

4. If the first byte of the NAV message is 0x01, the scan succeeded.

5. Use the modem_send_stream_data() command to send the rest of the payload (that is, the NAV message without the first byte) to the modem.

6. The modem should return the code OK and then start the streaming process to the application server.

7. The application server receives the uplink and forwards it to the LoRa Cloud™ Modem & Geolocation Services.

8. The LoRa Cloud™ Modem & Geolocation Services take the streaming packets and return the complete NAV message when the stream record is reassembled.

9. The application server is responsible for recognizing this data as a GNSS scan, and for passing it back to the LoRa Cloud™ Modem & Geolocation Services for computation of the GNSS position.

10. The LoRa Cloud™ Modem & Geolocation Services will return a location (if one can be computed). It may also return a downlink, such as the assistance position update.

Used By¶

MCU, LR111x/LoRa Edge™ chip, LoRaWAN® network server, application server, Modem & Geolocation API

Troubleshooting¶

None at this time.

References¶

• LoRa Cloud™ Modem & Geolocation Services Documentation

• LoRa Basics™ Modem-E API Reference Manual

• LR1110 Transceiver User Manual