Location module

The location module controls the GNSS, cellular and Wi-Fi positioning functionality. It can be used to retrieve the location of the device in the form of events containing a position, velocity and time (PVT) structure.

Features

This section documents the various features implemented by the module.

Location control

The module uses the Location library to communicate with the nRF91 Series modem and control its GNSS and LTE neighbor cell measurement functionalities as well as with the nRF7002 Wi-Fi positioning functionality. A location request starts when the module receives an APP_EVT_DATA_GET event and the APP_DATA_LOCATION type is listed in the event’s data_list member containing the data types that shall be sampled.

The default configuration for the location request is set as follows:

  • GNSS, Wi-Fi and cellular positioning are set in priority order of the location methods. Wi-Fi is omitted if it is not built into the application. If GNSS fails, both Wi-Fi and cellular positioning are tried. The priority order of the methods can be changed through Location library Kconfig options. Methods that should not be used can be configured by adding them into No Data List. See Real-time configurations for more information.

  • Timeout, which can be configured as part of Real-time configurations with Location timeout.

The location module receives configuration updates as payload in the following two events:

  • DATA_EVT_CONFIG_INIT - The event contains the value configured at build time or received from cloud and stored to flash. The event is distributed from the data module as part of the application initialization.

  • DATA_EVT_CONFIG_READY - The event is received when the data module has processed an incoming message from cloud with a configuration update.

The module sends the following events based on the outcome of the location request:

  • LOCATION_MODULE_EVT_GNSS_DATA_READY: GNSS position has been acquired

  • LOCATION_MODULE_EVT_CLOUD_LOCATION_DATA_READY: Neighbor cell measurements or Wi-Fi access points (or both) have been obtained

  • LOCATION_MODULE_EVT_DATA_NOT_READY: Location request failed

  • LOCATION_MODULE_EVT_TIMEOUT: Timeout occurred

  • LOCATION_MODULE_EVT_AGNSS_NEEDED: A-GNSS request should be sent to cloud

  • LOCATION_MODULE_EVT_PGPS_NEEDED: P-GPS request should be sent to cloud

GNSS LNA configuration

Different devices have different GNSS antenna and LNA setups depending on the antenna type (onboard or external). The application uses the Modem antenna library for configuring the LNA. The library has Kconfig options to control the LNA using either the COEX0 or MAGPIO interface of the nRF91 Series device. See the library documentation for more details on how to configure the antenna and LNA.

GPS assistance data

The location module receives requests for GPS assistance data from the Location library. When the module receives an A-GNSS request, it distributes it to the other modules as a LOCATION_MODULE_EVT_AGNSS_NEEDED event that contains information about the type of assistance data needed. Providing the requested A-GNSS data typically reduces significantly the time it takes to acquire a GNSS fix.

Wi-Fi positioning

Wi-Fi positioning is supported with an nRF7002 EK on the nRF91 Series DK. To enable Wi-Fi positioning and especially nRF7002 functionality, use the -DSHIELD=nrf7002ek and -DEXTRA_CONF_FILE=overlay-nrf7002ek-wifi-scan-only.conf options. The following is an example of the CLI command:

 west build -p -b board_target -- -DSHIELD=nrf7002ek -DEXTRA_CONF_FILE=overlay-nrf7002ek-wifi-scan-only.conf

Replace the board_target with the board target of the DK you are using (see Requirements).

Wi-Fi positioning has the following limitations:

  • Only nRF Cloud is supported.

  • The UI module must be disabled. Functionalities related to LEDs and buttons have conflicts with the nRF7002 EK.

Note

The Wi-Fi configuration uses both flash and SRAM extensively. You can configure the number of scan results with the CONFIG_LOCATION_METHOD_WIFI_SCANNING_RESULTS_MAX_CNT Kconfig option to reduce SRAM consumption. Align the CONFIG_NRF_WIFI_SCAN_MAX_BSS_CNT Kconfig option with CONFIG_LOCATION_METHOD_WIFI_SCANNING_RESULTS_MAX_CNT. You can also change the value of the CONFIG_HEAP_MEM_POOL_SIZE Kconfig option.

Module internals

The location module is a threadless module in terms of message processing. In this sense, it differs from many other modules.

All incoming events from other modules are handled in the context of the Application Event Manager callback, because they all complete fast enough to not require a separate thread.

The Location library handles cellular and Wi-Fi positioning together when the location request method list has them next to each other. This means that LTE neighbor cell measurements and Wi-Fi scanning results are combined into the same LOCATION_EVT_CLOUD_LOCATION_EXT_REQUEST event.

The location module sends the cellular and Wi-Fi positioning request forward with LOCATION_MODULE_EVT_CLOUD_LOCATION_DATA_READY event, and waits for an event from the cloud module on the result of the positioning. This result is forwarded to the Location library. Depending on the cloud integration, positioning result from the cloud service might be requested or not. The result must be indicated with one of the following events:

  • CLOUD_EVT_CLOUD_LOCATION_RECEIVED: Location has been resolved successfully. The Location library does not continue to use other positioning methods and the location request completes quickly.

  • CLOUD_EVT_CLOUD_LOCATION_ERROR: Location resolution failed. The Location library performs a fallback to the next positioning method in the priority list.

  • CLOUD_EVT_CLOUD_LOCATION_UNKNOWN: Location resolution result is unknown, that is, cloud integration is not capable of or configured to resolve it. The Location library performs a fallback to the next positioning method.

Configuration options

CONFIG_LOCATION_MODULE

Enables the location module.

Module states

The location module has an internal state machine with the following states:

  • STATE_INIT - The initial state of the module in which it awaits the modem to be initialized and receive the location related configuration.

  • STATE_RUNNING - The module has performed all required initialization and can respond to requests to start a location request. The running state has two sub-states:

    • SUB_STATE_SEARCH - A location request is ongoing.

    • SUB_STATE_IDLE - The module is idling and can respond to a request to start a location request.

  • STATE_SHUTDOWN - The module has been shut down after receiving a request from the utility module.

State transitions take place based on input from other modules, such as the application module, data module, utility module and modem module.

Module events

The asset_tracker_v2/src/events/location_module_event.h header file contains a list of events sent by the location module with associated payload.

Dependencies

The module uses the following nRF Connect SDK libraries:

API documentation

Header file: asset_tracker_v2/src/events/location_module_event.h
Source files: asset_tracker_v2/src/events/location_module_event.c
Location module event