Features of nRF91 Series

The nRF91 Series SiPs integrate an application MCU, a full LTE modem, an RF front end, and power management capabilities. These SiPs are designed to support a wide range of cellular IoT applications and DECT NR+ applications.

Development Kits and Evaluation Kits

nRF9160 DK - A development kit for designing and developing application firmware on the nRF9160 System in Package (SiP), supporting LTE Cat-M1 and Cat-NB1 and GNSS with 3GPP 13 support.
nRF9161 DK - A development kit for designing and developing application firmware on the nRF9161 SiP, supporting LTE Cat-M1 and Cat-NB1 and GNSS with 3GPP 14 support and DECT NR+.
nRF9151 DK - A development kit for designing and developing application firmware on the nRF9151 SiP, supporting LTE Cat-M1 and Cat-NB1 and GNSS with 3GPP 14 support and DECT NR+.
nRF9131 EK - A single-board evaluation kit for the nRF9131 SiP, designed for DECT NR+ applications.

Prototyping Platforms

Nordic Thingy:91 - A battery-operated prototyping platform for cellular IoT systems, suitable for prototyping asset tracking, environmental monitoring and more. Thingy:91 integrates an nRF9160 SiP that supports LTE-M, NB-IoT, and Global Navigation Satellite System (GNSS) and an nRF52840 SoC that supports Bluetooth® Low Energy, Near Field Communication (NFC) and USB.
Nordic Thingy:91 X - An advanced version of the Thingy:91. Thingy:91 X integrates the following components:
- An nRF9151 SiP with LTE-M, NB-IoT, and Global Navigation Satellite System (GNSS) support.
- The nRF7002 companion IC that adds support for low power Wi-Fi®.
- An nRF5340 SoC that supports Bluetooth Low Energy, 802.15.4 protocols, and USB.

With built-in GNSS support, these devices are a great choice for asset tracking applications.

The following figure illustrates the conceptual layout when targeting an nRF91 Series Cortex-M33 application MCU with TrustZone:

Overview of nRF91 application architecture

Application MCU 

The application core is a full-featured Arm Cortex-M33 processor including DSP instructions and FPU. Use this core for tasks that require high performance and for application-level logic.

The M33 TrustZone, one of Cortex-M Security Extensions (CMSE), divides the application MCU into Secure Processing Environment (SPE) and Non-Secure Processing Environment (NSPE). When the MCU boots, it always starts executing from the secure area. The secure bootloader chain starts the Trusted Firmware-M (TF-M), which configures a part of memory and peripherals to be non-secure, and then jumps to the user application located in the non-secure area.

For information about CMSE and the difference between the two environments, see Processing environments.

Secure bootloader chain 

A secure bootloader chain protects your application against running unauthorized code, and it enables you to do device firmware updates (DFU). See Secure bootloader chain for more information.

A bootloader chain is optional. Not all of the nRF91 Series samples include a secure bootloader chain, but the ones that do use the nRF Secure Immutable Bootloader sample and MCUboot.

Trusted Firmware-M (TF-M)

Trusted Firmware-M provides a configurable set of software components to create a Trusted Execution Environment. It has replaced Secure Partition Manager as the solution used by nRF Connect SDK applications and samples. This means that when you build your application for board targets with the */ns variant, TF-M is automatically included in the build. TF-M is a framework for functions and use cases beyond the scope of Secure Partition Manager.

For more information about the TF-M, see Running applications with Trusted Firmware-M. See also TF-M Hello World for a sample that demonstrates how to add TF-M to an application.

Application 

The user application runs in NSPE. Therefore, it must be built for the nrf9151dk/nrf9151/ns, nrf9161dk/nrf9161/ns, nrf9160dk/nrf9160/ns, or thingy91/nrf9160/ns board target, depending on the DK that you are using.

The application image might require other images to be present. Some samples include the nRF Secure Immutable Bootloader sample (CONFIG_SECURE_BOOT) and Introduction to MCUboot (CONFIG_BOOTLOADER_MCUBOOT). Depending on the configuration, all these images can be built at the same time in a multi-image build.

LTE modem 

The LTE modem handles LTE communication. It is controlled through AT commands. The AT commands are documented in the nRF91x1 AT Commands Reference Guide and nRF9160 AT Commands Reference Guide.

The firmware for the modem is available as a precompiled binary. You can download the firmware from the nRF9151 product website (compatible downloads), nRF9161 product website (compatible downloads), or nRF9160 product website (compatible downloads), depending on the SiP you are using. The zip file contains the release notes, and both the full firmware and patches to update from one version to another. A delta patch can only update the modem firmware from one specific version to another version (for example, v1.2.1 to v1.2.2). If you need to perform a major version update (for example, v1.2.x to v1.3.x), you need an external flash with a minimum size of 4 MB.

Different versions of the LTE modem firmware are available, and these versions are certified for the mobile network operators having their own certification programs. For more information, see the following documents, depending on the SiP you are using:

Note

Most operators do not require certifications other than GCF or PTCRB. For the current status of GCF and PTCRB certifications, see nRF9151 certifications, nRF9161 certifications, or nRF9160 certifications, depending on the SiP you are using.

Modem firmware update 

There are two ways to update the modem firmware:

Full update

You can use either a wired or a wireless connection to do a full update of the modem firmware:

When using a wired connection, you can use either the nRF Connect Programmer, which is part of nRF Connect for Desktop, or the nRF pynrfjprog Python package. Both methods use the Simple Management Protocol (SMP) to provide an interface over UART, which enables the device to perform the update.

You can use the nRF Connect Programmer to perform the update, regardless of the images that are part of the existing firmware of the device. For example, you can update the modem on an nRF9160 DK using the instructions described in the Updating the modem firmware section.

You can also use the nRF pynrfjprog Python package to perform the update, as long as a custom application image integrating the lib_fmfu_mgmt subsystem is included in the existing firmware of the device. See the Cellular: Full modem firmware update using SMP Server sample for an example on how to integrate the subsystem in your custom application.

When using a wireless connection, the update is applied over-the-air (OTA). See FOTA updates for more information.

See Modem bootloader for more information on the full firmware updates of modem using Modem library.

Delta patches

Delta patches are updates that contain only the difference from the last version. See Delta firmware updates for more information on delta firmware updates of modem using Modem library. When applying a delta patch, you must therefore ensure that this patch works with the current firmware version on your device. Delta patches are applied as firmware over-the-air (FOTA) updates. See FOTA updates for more information.

Band lock 

The modem can operate on a number of LTE bands. To check which bands are supported by a particular modem firmware version, see the release notes for that version.

You can use band lock to restrict modem operation to a subset of the supported bands, which might improve the performance of your application. To check which bands are certified in your region, visit nRF9151 certifications, nRF9161 certifications, or nRF9160 certifications, depending on the SiP you are using.

To set the LTE band lock, enable the LTE link control library by setting the Kconfig option CONFIG_LTE_LINK_CONTROL to y in your prj.conf project configuration file.

Then, enable the LTE band lock feature and the band lock mask in the project configuration file, as follows:

CONFIG_LTE_LOCK_BANDS=y
CONFIG_LTE_LOCK_BAND_MASK="10000001000000001100"

The band lock mask allows you to set the bands on which you want the modem to operate. Each bit in the CONFIG_LTE_LOCK_BAND_MASK option represents one band. The maximum length of the string is 88 characters (bit string, 88 bits).

For Thingy:91, you can configure the modem to use specific LTE bands by using the band lock AT command. The preprogrammed firmware configures the modem to use the bands currently certified on the Thingy:91 hardware. When building the firmware, you can configure which bands must be enabled.

For more detailed information, see the band lock section in the nRF9160 AT Commands Reference Guide or the band lock section in the nRF91x1 AT Commands Reference Guide, depending on the SiP you are using.

System mode 

The system mode configuration of the modem is used to select which of the supported systems, LTE-M, NB-IoT and GNSS, are enabled.

When using the LTE link control library, all supported systems are enabled by default and the modem selects the used LTE system based on the LTE system mode preference. You can change the enabled systems using the CONFIG_LTE_NETWORK_MODE Kconfig option and the LTE system mode preference using the CONFIG_LTE_MODE_PREFERENCE Kconfig option.

When the LTE link control library is not used, the modem starts in LTE-M mode. You can change the system mode and the LTE system mode preference using the AT%XSYSTEMMODE AT command.

For more detailed information, see the system mode section in the nRF9160 AT Commands Reference Guide or the system mode section in the nRF91x1 AT Commands Reference Guide, depending on the SiP you are using.

LTE-M / NB-IoT switching

Thingy:91 has a multimode modem, which enables it to support automatic switching between LTE-M and NB-IoT. A built-in parameter in the Thingy:91 firmware determines whether the modem first attempts to connect in LTE-M or NB-IoT mode. If the modem fails to connect using this preferred mode within the default timeout period (10 minutes), the modem switches to the other mode.

Modem library 

The nRF Connect SDK applications for the nRF91 Series devices that communicate with the nRF91 Series modem firmware must include the Modem library. The Modem library is released as an OS-independent binary library in the nrfxlib repository and it is integrated into nRF Connect SDK through an integration layer, nrf_modem_lib.

The Modem library integration layer fulfills the integration requirements of the Modem library in nRF Connect SDK. For more information on the integration, see Modem library integration layer.

Modem trace 

The modem traces of the nRF91 Series modem can be captured using the Cellular Monitor. For more information on how to collect traces using Cellular Monitor, see the Cellular Monitor documentation. To enable the modem traces in the modem and to forward them to the Modem trace module over UART, include the nrf91-modem-trace-uart snippet while building your application as described in nRF91 modem tracing with UART backend using snippets.

Note

For the Serial LTE modem application and the Cellular: AT Client sample, you must also run AT%XMODEMTRACE=1,2 to manually activate the predefined trace set.

You can set the trace level using the AT command AT%XMODEMTRACE. For more information, see the modem trace activation %XMODEMTRACE section in the nRF9160 AT Commands Reference Guide or the same section in the nRF91x1 AT Commands Reference Guide, depending on the SiP you are using.

See Modem trace module for other backend options. If the existing trace backends are not sufficient, it is possible to implement custom trace backends. For more information on the implementation of a custom trace backend, see Adding custom trace backends.

Remote observability using Memfault 

The nRF Connect SDK bundles support for remotely monitoring and debugging device fleets. This support enables quicker identification and triage of issues in the field, and optimizes connection quality and battery life for global deployments. The collection system has been optimized to work in intermittent connectivity environments and has extremely low overhead.

The cellular stack consists of out-of-the-box collection of the following key connectivity health vitals:

Total bytes sent and received
The network operator
Frequency band
Signal quality measurements

For debugging, any system crashes and modem traces can be remotely collected for further analysis.

See the Memfault integration page for more information on how to enable Memfault in your nRF Connect SDK project on an nRF91 Series SiP to visualize the data across the fleet and by device.

GNSS 

An nRF91 Series device is a highly versatile device that integrates both cellular and GNSS functionality. Note that GNSS functionality is only available on the SICA variant and not on the SIAA or SIBA variants. For more information, see the following documents, depending on the SiP you are using:

There are many GNSS constellations (GPS, BeiDou, Galileo, GLONASS) available but GPS is the most mature technology. An nRF91 Series device supports both GPS L1 C/A (Coarse/Acquisition) and QZSS L1C/A at 1575.42 MHz. This frequency band is ideal for penetrating through layers of the atmosphere (troposphere and ionosphere) and suitable for various weather conditions. GNSS is designed to be used with a line of sight to the sky. Therefore, the performance is not ideal when there are obstructions overhead or if the receiver is indoors.

Customers who are developing their own hardware with the nRF9160 are strongly recommended to use the nRF9160 Antenna and RF Interface Guidelines as a reference. See GPS interface and antenna for more details on GNSS interface and antenna.

Thingy:91 has a GNSS receiver, which allows the device to be located globally using GNSS signals if it is activated. In Asset Tracker v2, the GNSS receiver is activated by default.

Note

Starting from nRF Connect SDK v1.6.0 (Modem library v1.2.0), the GNSS socket is deprecated and replaced with the GNSS interface.

Obtaining a fix 

GNSS provides lots of useful information including 3D location (latitude, longitude, altitude), time, and velocity.

The time to obtain a fix (also referred to as Time to First Fix (TTFF)) will depend on the time when the GNSS receiver was last turned on and used.

Following are the various GNSS start modes:

Cold start - GNSS starts after being powered off for a long time with zero knowledge of the time, current location, or the satellite orbits.
Warm start - GNSS has some coarse knowledge of the time, location, or satellite orbits from a previous fix that is more than around 37 minutes old.
Hot start - GNSS fix is requested within an interval of around 37 minutes from the last successful fix.

Each satellite transmits its own ephemeris data and common almanac data:

Ephemeris data - Provides information about the orbit of the satellite transmitting it. This data is valid for four hours and becomes inaccurate after that.
Almanac data - Provides coarse orbit and status information for each satellite in the constellation. Each satellite broadcasts almanac data for all satellites.

The data transmission occurs at a slow data rate of 50 bps. The orbital data can be received faster using A-GNSS.

Due to the clock bias on the receiver, there are four unknowns when looking for a GNSS fix - latitude, longitude, altitude, and clock bias. This results in solving an equation system with four unknowns, and therefore a minimum of four satellites must be tracked to acquire a fix.

Concurrent GNSS and LTE 

The GNSS operation in an nRF91 Series device is time-multiplexed with the LTE modem. Therefore, the LTE modem must either be completely deactivated or in RRC idle mode or Power Saving Mode (PSM) when using the GNSS receiver. For more information, see the nRF9151 GPS receiver Specification, nRF9161 GPS receiver Specification, or the nRF9160 GPS receiver Specification, depending on the SiP you are using.

Enhancements to GNSS 

When GNSS has not been in use for a while or if the device is in relatively weak signaling conditions, it might take longer to acquire a fix. To improve this, Nordic Semiconductor has implemented the following methods for acquiring a fix in a shorter time:

A-GNSS or P-GPS or a combination of both
Low accuracy mode

Assisted GNSS (A-GNSS)

A-GNSS is commonly used to improve the Time to first fix (TTFF) by using a connection (for example, over cellular) to the Internet to retrieve the almanac and ephemeris data. A connection to an Internet server that has the almanac and ephemeris data is several times quicker than using the slow 50 bps data link to the GNSS satellites. There are many options to retrieve this A-GNSS data. Two such options are using nRF Cloud and SUPL. nRF Connect SDK provides example implementations for both these options. The A-GNSS solution available through nRF Cloud has been optimized for embedded devices to reduce protocol overhead and data usage. This, in turn, results in the download of reduced amount of data, thereby reducing data transfer time, power consumption, and data costs. Starting from modem firmware v2.0.0, GNSS supports assistance data also for QZSS satellites. nRF Cloud can provide assistance data for both GPS and QZSS. See A-GNSS data for more information about the retrieval of A-GNSS data.

Predicted GPS (P-GPS)

P-GPS is a form of assistance, where the device can download up to two weeks of predicted satellite ephemerides data. Normally, devices connect to the cellular network approximately every two hours for up-to-date satellite ephemeris information or they download the ephemeris data from the acquired satellites. P-GPS enables devices to determine the exact orbital location of the satellite without connecting to the network every two hours with a trade-off of reduced accuracy of the calculated position over time. Note that P-GPS requires more memory compared to regular A-GNSS.

Also, note that due to satellite clock inaccuracies, not all functional satellites will have ephemerides data valid for two weeks in the downloaded P-GPS package. This means that the number of satellites having valid predicted ephemerides reduces in number roughly after ten days. Hence, the GNSS module needs to download the ephemeris data from the satellite broadcast if no predicted ephemeris is found for that satellite to be able to use the satellite.

Note

For more information on the various trade-offs of using A-GNSS compared to using P-GPS, see the nRF Cloud Location Services documentation.

nRF Cloud compared with SUPL library

The nRF Cloud A-GNSS library is more efficient to use when compared to the SUPL library, and the latter takes a bit more memory on the device.
With nRF Cloud, the data is encrypted, whereas SUPL uses plain socket.
nRF Cloud also supports assistance for QZSS satellites, while SUPL is limited to GPS.
No licenses are required from external vendors to use nRF Cloud, whereas for commercial use of SUPL, you must obtain a license.
The nRF Cloud A-GNSS library is highly integrated into Nordic Semiconductor’s IoT cloud platform.

Low Accuracy Mode

Low accuracy mode allows the GNSS receiver to accept a looser criterion for a fix with four or more satellites or by using a reference altitude to allow for a fix using only three satellites. This has a tradeoff of reduced accuracy. This reference altitude can be from a recent valid normal fix or it can be artificially injected. See Low accuracy mode for more information about low accuracy mode and its usage.

Samples using GNSS in nRF Connect SDK 

There are many examples in nRF Connect SDK that use GNSS. Following is a list of the samples and applications with some information about the GNSS usage:

The Asset Tracker v2 application uses nRF Cloud for A-GNSS, P-GPS, or a combination of both. The application obtains GNSS fixes and transmits them to nRF Cloud along with sensor data.
The Serial LTE modem application uses AT commands to start and stop GNSS and supports nRF Cloud A-GNSS and P-GPS. The application displays tracking and GNSS fix information in the serial console.
The Cellular: GNSS sample does not use assistance by default but can be configured to use nRF Cloud A-GNSS, P-GPS, or a combination of both. The sample displays tracking and fix information as well as NMEA strings in the serial console.

Operating modes 

nRF91 Series devices can display multiple LED patterns that indicate the operating state of the device as described in the LED indication section of the User Interface module of the Asset Tracker v2 documentation.