Coexistence of short-range radio and other radios

This guide describes how to add short-range radio and other radio coexistence support to your application in nRF Connect SDK.

Short-range RF technologies (here referred to as SR), such as Bluetooth LE or 802.15.4, use a different radio than other technologies like Wi-Fi or LTE (here referred to as the other radios). However, if both SR and the other radio attempt to transmit simultaneously, the radio frequency (RF) waves interfere with each other, causing decreased performance and higher power consumption. Also, in cases like receiving an acknowledgment (ACK), radios should not transmit to ensure correct reception.

These issues are defined as coexistence issues. To mitigate these issues and to improve performance, a Packet Traffic Arbiter (PTA) is used. When both SR and the other radio request access to RF, the Packet Traffic Arbiter grants or denies that access.

Integration considerations 

The nRF Connect SDK provides the coexistence feature by providing SR protocol drivers that can call the coexistence API and its implementations. The coexistence feature is provided in following ways:

Coexistence based on MPSL CX API

MPSL provided Bluetooth-only coexistence

Coexistence based on MPSL CX API 

This coexistence feature is based on Short-Range Protocols External Radio Coexistence provided by the Multiprotocol Service Layer (MPSL) library. It is recommended for new designs.

The following SR protocols are compatible with the coexistence based on MPSL CX API:

Bluetooth LE, if the implementation used is the SoftDevice Controller.

Protocols based on nRF 802.15.4 Radio Driver, such as Thread and Zigbee.

This way of providing coexistence applies to the following implementations:

nRF70 Series Wi-Fi coexistence

Generic three wire coexistence

Custom coexistence implementations

The nRF Connect SDK provides a wrapper that configures Wi-Fi Coexistence based on devicetree source (DTS) and Kconfig information.

The following are the common requirements to use coexistence based on the MPSL CX API:

The Kconfig option CONFIG_MPSL must be enabled. Some protocol drivers, like SoftDevice Controller, enable this option by default.
The Kconfig option CONFIG_MPSL_CX must be enabled.
The requirements specific to the selected coexistence implementation must be met. These include at least selecting one of supported values of the CONFIG_MPSL_CX_CHOICE choice. For details on the requirements specific to the selected coexistence implementation, consult its documentation.
Ensure that the configuration of the nrf_radio_coex node appropriate for the selected implementation is present in the devicetree. When using one of the supported implementations, you must use the nrf_radio_coex name for the node. However, if you add a custom user implementation, you can also use a different name. Some boards supported by the nRF Connect SDK (like nrf7002dk) provide this node by default. You can provide the node using either the devicetree source file of the target board or an overlay file. See Devicetree Guide for more information about the DTS data structure, and Devicetree versus Kconfig for information about differences between DTS and Kconfig.
On the nRF5340 SoC, the GPIO pins required for the communication with the PTA must be handed over to the network core. You can use the nrf-gpio-forwarder node in application’s core devicetree for that.
You can add a new device binding and use it as the compatible property for the node, if the provided hardware interfaces are unsuitable.

Note

When using the nRF5340, apply steps 1 and 2 only to the network core. See Multi-image builds.

MPSL provided Bluetooth-only coexistence 

The MPSL-provided Bluetooth-only coexistence can be used only with the Bluetooth-only 1-wire coexistence implementation.

It is based on Bluetooth-Only External Radio Coexistence provided by the Multiprotocol Service Layer (MPSL) library.

Supported implementations 

The following are the implementations supported by the MPSL-provided Bluetooth-only coexistence.

Note

Do not enable Wi-Fi coexistence on the nRF5340 SoC in conjunction with Coded Phy and FEM, as this can lead to undefined behavior.

nRF70 Series Wi-Fi coexistence 

Refer to Coexistence based on MPSL CX API for the general requirements of this implementation.

Hardware description

The nRF70 Series device interface consists of the signals listed in the table below. The Pin is the pin name of the nRF70 Series device. The Direction is from the point of view of the SoC running the SR protocol. The DT property is the name of the devicetree node property that configures the connection between the SoC running the SR protocol and the nRF70 Series device.

nRF70 Series device coexistence protocol pins
Pin	Direction	Description	DT property
COEX_REQ	Out	Request signal	req-gpios
COEX_STATUS0	Out	SR transaction direction TX or RX	status0-gpios
COEX_GRANT	In	Grant	grant-gpios

Enabling nRF70 Series Wi-Fi coexistence

To enable Wi-Fi coexistence on the nRF70 Series device, complete the following steps:

Add the following node to the devicetree source file:

/ {
      nrf_radio_coex: nrf7002-coex {
         status = "okay";
         compatible = "nordic,nrf700x-coex";
         req-gpios =     <&gpio0 24 (GPIO_ACTIVE_HIGH)>;
         status0-gpios = <&gpio0 14 (GPIO_ACTIVE_HIGH)>;
         grant-gpios =   <&gpio0 25 (GPIO_ACTIVE_HIGH | GPIO_PULL_UP)>;
   };
};

Optionally, replace the node name nrf7002-coex with a custom one.
Replace the pin numbers provided for each of the required properties:
- req-gpios - GPIO characteristic of the device that controls the COEX_REQ signal of the nRF70 Series device.
- status0-gpios - GPIO characteristic of the device that controls the COEX_STATUS0 signal of the nRF70 Series device.
- grant-gpios - GPIO characteristic of the device that controls the COEX_GRANT signal of the nRF70 Series device.
Note

GPIO_PULL_UP is added to avoid a floating input pin and is required on some boards only. If the target board is designed to avoid this signal being left floating, you can remove GPIO_PULL_UP to save power.

The phandle-array type is used, as it is commonly used in Zephyr’s devicetree to describe GPIO signals. The first element &gpio0 indicates the GPIO port (port 0 has been selected in the example shown). The second element is the pin number on that port.
On the nRF5340, apply the same devicetree node mentioned in Step 1 to the network core. Apply the overlay to the correct network-core child image by creating an overlay file named child_image/*childImageName*.overlay in your application directory, for example child_image/multiprotocol_rpmsg.overlay.

The *childImageName* string must assume one of the following values:
- multiprotocol_rpmsg for multiprotocol applications having support for both 802.15.4 and Bluetooth.
- 802154_rpmsg for applications having support for 802.15.4, but not for Bluetooth.
- hci_ipc for application having support for Bluetooth, but not for 802.15.4.
Enable the following Kconfig options:
- CONFIG_MPSL_CX
- CONFIG_MPSL_CX_NRF700X
Note

If a nordic,nrf700x-coex compatible node is present in the devicetree and CONFIG_MPSL_CX is set to y, MPSL_CX_NRF700X will be selected by default.

Generic three wire coexistence 

Refer to Coexistence based on MPSL CX API for the general requirements of this implementation.

Hardware description

The generic three wire interface consists of the signals listed in the table below. The Pin is a generic pin name of a PTA, identified rather by its function. The Direction is from the point of view of the SoC running the SR protocol. The DT property is the name of the devicetree node property that configures the connection between the SoC running SR protocol and the nRF70 Series device.

Generic three wire coexistence protocol pins
Pin	Direction	Description	DT property
REQUEST	Out	Request signal	req-gpios
PRIORITY	Out	SR transaction direction TX or RX	pri-dir-gpios
GRANT	In	Grant signal	grant-gpios

Enabling generic three-wire coexistence

To enable the generic three-wire coexistence, do the following:

Add the following node to the devicetree source file:

/ {
      nrf_radio_coex: radio_coex_three_wire {
         status = "okay";
         compatible = "generic-radio-coex-three-wire";
         req-gpios =     <&gpio0 24 (GPIO_ACTIVE_HIGH)>;
         pri-dir-gpios = <&gpio0 14 (GPIO_ACTIVE_HIGH)>;
         grant-gpios =   <&gpio0 25 (GPIO_ACTIVE_HIGH | GPIO_PULL_UP)>;
   };
};

Optionally, replace the node name radio_coex_three_wire with a custom one.
Replace the pin numbers provided for each of the required properties:
- req-gpios - GPIO characteristic of the device that controls the REQUEST signal of the PTA.
- pri-dir-gpios - GPIO characteristic of the device that controls the PRIORITY signal of the PTA.
- grant-gpios - GPIO characteristic of the device that controls the GRANT signal of the PTA (RF medium access granted).
  
  Note
  
  GPIO_PULL_UP is added to avoid a floating input pin and is required on some boards only. If the target board is designed to avoid this signal being left floating, you can remove GPIO_PULL_UP to save power.
The phandle-array type is used, as it is commonly used in Zephyr’s devicetree to describe GPIO signals. The first element &gpio0 indicates the GPIO port (port 0 has been selected in the example shown). The second element is the pin number on that port.
On the nRF5340, apply the same devicetree node mentioned in Step 1 to the network core. Apply the overlay to the correct network-core child image by creating an overlay file named child_image/*childImageName*.overlay in your application directory, for example child_image/multiprotocol_rpmsg.overlay.

The *childImageName* string must assume one of the following values:
- multiprotocol_rpmsg for multiprotocol applications having support for both 802.15.4 and Bluetooth.
- 802154_rpmsg for applications having support for 802.15.4, but not for Bluetooth.
- hci_ipc for application having support for Bluetooth, but not for 802.15.4.
Enable the following Kconfig options:
- CONFIG_MPSL_CX
- CONFIG_MPSL_CX_THREAD

Custom coexistence implementations 

Refer to Coexistence based on MPSL CX API for the general requirements that must be fulfilled by the implementation.

To add a custom coexistence implementation based on the MPSL CX API, complete following steps:

Determine the hardware interface of your PTA. If your PTA uses an interface different from the ones already provided by the nRF Connect SDK, you need to provide a devicetree binding file. See nrf/dts/bindings/radio_coex/generic-radio-coex-three-wire.yaml file for an example.
Extend the Kconfig choice CONFIG_MPSL_CX_CHOICE with a Kconfig option allowing to select the new coex implementation.
Write the implementation for your PTA. See the nrf/subsys/mpsl/cx/thread/mpsl_cx_thread.c file for an example. Add the C source file(s) with the implementation, which must contain the following parts:
- The implementation of the functions required by the interface structure mpsl_cx_interface_t. Refer to MPSL CX API for details.
- The initialization code initializing the required hardware resources, based on devicetree information.
- A call to the function mpsl_cx_interface_set() during the system initialization.
Add the necessary CMakeLists.txt entries to get your code compiled when the new Kconfig choice option you added is selected.

Bluetooth-only 1-wire coexistence 

Refer to MPSL provided Bluetooth-only coexistence for the general requirements of this implementation.

The Bluetooth-only 1-wire coexistence feature allows the SoftDevice Controller to coexist alongside an LTE device on a separate chip. It is specifically designed for the coex interface of the nRF91 Series SiP. The implementation is based on 1-Wire coexistence protocol, which is provided into the Multiprotocol Service Layer (MPSL) library.

Enabling Bluetooth-only 1-wire coexistence

Enable the following Kconfig options:

CONFIG_MPSL_CX

CONFIG_MPSL_CX_BT_1WIRE

The configuration is set using devicetree (DTS). For more information about devicetree overlays, see Use devicetree overlays. See samples/bluetooth/radio_coex_1wire/boards/nrf52840dk_nrf52840.overlay for an example of a devicetree overlay. The elements are described in the bindings: dts/bindings/radio_coex/sdc-radio-coex-one-wire.yaml. See samples/bluetooth/radio_coex_1wire for a sample application using 1-wire coexistence.