nRF9160: A-GPS¶
The A-GPS sample demonstrates how the nRF Connect for Cloud Assisted GPS (A-GPS) feature or an external SUPL client can be used to implement A-GPS in your application.
The sample uses the generic A-GPS library, which allows the selection of different A-GPS sources via the CONFIG_AGPS_SRC_SUPL configurable option.
By default, nRF Connect for Cloud is used for A-GPS and cloud communication.
Requirements¶
The sample supports the following development kits:
Hardware platforms |
PCA |
Board name |
Build target |
|---|---|---|---|
PCA20035 |
thingy91_nrf9160 |
|
|
PCA10090 |
|
The sample also requires an nRF Connect for Cloud account.
The sample is configured to compile and run as a non-secure application on nRF91’s Cortex-M33. Therefore, it automatically includes the Secure Partition Manager that prepares the required peripherals to be available for the application.
You can also configure it to use TF-M instead of Secure Partition Manager.
Note
This sample does not support the modem firmware v1.1.x (or earlier).
Overview¶
The use of A-GPS speeds up the time to first GPS position fix (commonly known as TTFF or Time to first fix), as the required satellite information is downloaded from the A-GPS source instead of direct download of the data from the satellites.
The Assistance GPS data includes the following information:
UTC time
Integrity data
Approximate location
GPS system clock
Ionospheric correction parameters for Klobuchar Ionospheric Model
TTFF is expected to be less when compared to that in the scenario of GPS without assistance data, performing a cold or a warm start. The TTFF is expected to be comparable to that of a GPS hot start and is usually in the range of 5 to 20 seconds in good satellite signaling conditions. Good satellite signaling conditions in this context means that the device is positioned in a way to have a direct line of sight to a large portion of the sky.
Note that the radio component on the nRF9160-based device is shared between LTE and GPS and hence only one of these can be active at any moment of time. LTE has priority over the radio resources, and GPS operates in the time interval between LTE required operations as per LTE specification. Consequently, GPS is blocked from searching as long as the modem is in RRC connected mode.
The modem is in RRC connected mode when sending and receiving data over the LTE network. After data transmission is complete, the modem stays in RRC connected mode for a period of network-specific inactivity time, before entering RRC idle mode. The inactivity time varies between networks. It is typically in the range of 5 to 70 seconds for a specific network. In RRC idle mode, the GPS is usually able to operate.
It is recommended to use LTE Power Saving Mode (PSM) and extended Discontinuous Reception (eDRX) mode to increase the allowed time of operation for GPS.
During the defined intervals of PSM and eDRX, LTE communication does not occur, and the GPS has full access to the radio resources.
In this sample, both PSM and eDRX are enabled by default.
You can enable or disable these features by using the CONFIG_LTE_POWER_SAVING_MODE and CONFIG_LTE_EDRX_REQ configuration options.
Note
For nRF9160 DK v0.15.0 and later, set the CONFIG_NRF9160_GPS_ANTENNA_EXTERNAL option to y when building the application to achieve the best external antenna performance.
User interface¶
You can send a predefined message to nRF Connect for Cloud by pressing button 1.
The message can be changed by setting the CONFIG_CLOUD_MESSAGE to a new message.
To ease outdoors and remote testing of A-GPS feature, two methods for resetting the kit are provided, if the default A-GPS source is used. Both are equivalent to pressing the reset button on the nRF9160 DK, or power-cycling the nRF9160 DK or Thingy:91.
- Button 1:
Press the button to send a predefined message to nRF Connect for Cloud (the default A-GPS source). Press the button for a minimum of 3 seconds to reset the nRF9160-based device.
- nRF Connect for Cloud:
Use the terminal pane in the device view for a particular device in nRF Connect for Cloud and send the
"{"reboot":true}"command to reset the nRF9160-based device.
Configuration¶
See Configuring your application for information about how to permanently or temporarily change the configuration.
Configuration options¶
Check and configure the following configuration options for the sample:
-
CONFIG_LTE_POWER_SAVING_MODE- LTE Power Saving Mode¶
This configuration option enables or disables the LTE Power Saving Mode.
Additional configuration¶
Check and configure the following library options that are used by the sample:
Building and running¶
This sample can be found under samples/nrf9160/agps in the nRF Connect SDK folder structure.
The sample is built as a non-secure firmware image for the nrf9160dk_nrf9160ns build target. Because of this, it automatically includes the Secure Partition Manager. You can also configure it to use TF-M instead of SPM.
See Building and programming a sample application for information about how to build and program the application.
The configuration file for this sample is located in samples/nrf9160/agps.
See Configuring your application for information on how to configure the parameters.
Testing¶
After programming the sample to your development kit, test it by performing the following steps:
Place the nRF9160-based device in a location with direct line of sight to a large portion of the sky. This is to achieve sufficient satellite coverage to get a position fix.
Optionally, connect the nRF9160-based device to a PC with a USB cable. The kit is assigned a COM port (Windows) or ttyACM device (Linux), which is visible in the Device Manager.
Optionally, connect to the kit with a terminal emulator (for example, PuTTY) to see log output. See How to connect with PuTTY for the required settings. You can also use the Bluetooth LE service of Thingy:91 to see log output on a mobile device.
Log into your nRF Connect for Cloud account and select your device.
Power on the nRF9160-based device.
Note
The sample outputs shown in the subsequent steps correspond to the scenario when nRF Connect for Cloud is used as the A-GPS source.
The device connects to the LTE network and nRF Connect for Cloud as shown below:
------------------------- I: A-GPS sample has started I: Connecting to LTE network. This may take minutes. I: PSM mode requested +CEREG: 2,"7725","0138E000",7,0,0,"11100000","11100000" +CSCON: 1 +CEREG: 1,"7725","0138E000",7,,,"00000010","00000110" I: Network registration status: Connected - home network
Note
If the credentials on the device are used to connect to nRF Connect for Cloud for the first time, the device will be disconnected, and a
CLOUD_EVT_DISCONNECTEDevent will be logged on the terminal. This happens due to the configuring of the device on the cloud by AWS IoT Just-in-time-provisioning and the subsequent termination of the connection. In general, the devices reconnect automatically. However, for the simplicity of the sample, reconnection is not implemented. Hence you must reset the device manually.Make sure that GPS has started by confirming that the device requests GPS assistance data and receives a response. You can do this by checking the logs.
D: GPS socket created, fd: 1232491587 I: CLOUD_EVT_CONNECTED I: CLOUD_EVT_DATA_RECEIVED I: CLOUD_EVT_PAIR_DONE I: CLOUD_EVT_READY I: CLOUD_EVT_DATA_RECEIVED D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 3 D: Sent A-GPS data to modem, type: 7 D: Sent A-GPS data to modem, type: 8 D: Sent A-GPS data to modem, type: 1 D: Sent A-GPS data to modem, type: 4 D: Sent A-GPS data to modem, type: 9 I: A-GPS data successfully processed I: GPS will start in 3 seconds I: CLOUD_EVT_DATA_RECEIVED D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 D: Sent A-GPS data to modem, type: 2 I: A-GPS data successfully processed I: GPS will start in 3 seconds D: GPS mode is enabled D: GPS operational
Observe that the GPS starts to track the position based on the satellite data received as shown below:
I: Periodic GPS search started with interval 240 s, timeout 120 s D: A-GPS data update needed D: Waiting for time window to operate +CSCON: 0 D: GPS has time window to operate D: Tracking: 0 Using: 0 Unhealthy: 0 D: Seconds since last fix 23 I: Tracking: 29 D: Tracking SV 29: not used, healthy D: Tracking: 1 Using: 0 Unhealthy: 0 D: Seconds since last fix 24 I: Tracking: 5 29 D: Tracking SV 29: not used, healthy D: Tracking SV 5: not used, healthy D: Tracking: 2 Using: 0 Unhealthy: 0 D: Seconds since last fix 25 I: Tracking: 5 9 21 26 29 D: Tracking SV 29: not used, healthy D: Tracking SV 5: not used, healthy D: Tracking SV 9: not used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: not used, healthy D: Tracking: 5 Using: 0 Unhealthy: 0 D: Seconds since last fix 26 D: Tracking SV 29: not used, healthy D: Tracking SV 5: not used, healthy D: Tracking SV 9: not used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: not used, healthy D: Tracking: 5 Using: 0 Unhealthy: 0 D: Seconds since last fix 27 D: Tracking SV 29: not used, healthy D: Tracking SV 5: not used, healthy D: Tracking SV 9: not used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: not used, healthy D: Tracking: 5 Using: 0 Unhealthy: 0 D: Seconds since last fix 28 D: Tracking SV 29: not used, healthy D: Tracking SV 5: not used, healthy D: Tracking SV 9: not used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: not used, healthy D: Tracking: 5 Using: 0 Unhealthy: 0 D: Seconds since last fix 29 D: Tracking SV 29: used, healthy D: Tracking SV 5: used, healthy D: Tracking SV 9: used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: used, healthy D: Tracking: 5 Using: 4 Unhealthy: 0 D: Seconds since last fix 30 D: Tracking SV 29: used, healthy D: Tracking SV 5: used, healthy D: Tracking SV 9: used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: used, healthy D: Tracking: 5 Using: 4 Unhealthy: 0 D: Seconds since last fix 31 D: Tracking SV 29: used, healthy D: Tracking SV 5: used, healthy D: Tracking SV 9: used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: used, healthy D: Tracking: 5 Using: 4 Unhealthy: 0 D: Seconds since last fix 32 D: Tracking SV 29: used, healthy D: Tracking SV 5: used, healthy D: Tracking SV 9: used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: used, healthy D: Tracking: 5 Using: 4 Unhealthy: 0 D: Seconds since last fix 33 D: PVT: Position fix D: Stopping GPS
Observe that the current position of the device shows up on the GPS position map in nRF Connect for Cloud, after acquiring the GPS position fix. The position details are also displayed on the terminal as shown below:
I: --------- FIX --------- I: Time to fix: 20 seconds I: Longitude: 5.399481 Latitude: 61.362466 Altitude: 10.276114 Speed: 0.118597 Heading: 0.000000 Date: 2020-09-07 Time (UTC): 08:52:29 I: ----------------------------------- D: Tracking SV 29: used, healthy D: Tracking SV 5: used, healthy D: Tracking SV 9: used, healthy D: Tracking SV 21: not used, healthy D: Tracking SV 26: used, healthy D: Tracking: 5 Using: 4 Unhealthy: 0 D: Seconds since last fix 0 D: NMEA: Position fix I: GPS position sent to cloud
Optionally, press Button 1 and observe that the predefined message is sent from the device to nRF Connect for Cloud. Note that this interrupts the GPS search for a period of time since LTE requires the use of the radio resources of the device.
Known issues and limitations¶
Approximate location assistance data is based on LTE cell location. Since all cell locations are not always available, the location data is sometimes absent in the A-GPS response.