DALI+ Over OpenThread performance near a 2.4 GHz Wi‑Fi access point

Summary

DALI+ Over OpenThread devices operate in the 2.4 GHz band and can be affected by nearby Wi‑Fi access points. This is most likely when the DALI+ Over OpenThread channel is close to, or within the sideband energy of, a Wi‑Fi channel.

A Wi‑Fi access point can transmit at much higher power than a DALI+ Over OpenThread device. If the DALI+ Over OpenThread device is physically close to the access point, especially inside a strong antenna lobe, the Wi‑Fi energy can drown out the lower-power DALI+ Over OpenThread signal.

This can happen even when the two systems are not configured on exactly the same channel.

Applies to

• DALI+ Over OpenThread devices
• DALI+ Over OpenThread border routers
• 2.4 GHz Wi‑Fi networks
• Sites where DALI+ Over OpenThread devices are installed close to Wi‑Fi access points
• Sites using overlapping or adjacent 2.4 GHz channels

Symptoms

A site may experience one or more of the following issues:

• DALI+ Over OpenThread devices intermittently drop offline
• Slow or unreliable DALI+ Over OpenThread communication
• Increased retries or delayed responses
• Devices working correctly when moved away from a Wi‑Fi access point
• Devices becoming unreliable when installed close to a high-power Wi‑Fi access point
• Better performance when the DALI+ Over OpenThread channel or Wi‑Fi channel is changed

Cause

DALI+ Over OpenThread and Wi‑Fi can both use the 2.4 GHz band, but they do not use the same radio format.

Wi‑Fi access points use wider channels and generally transmit at higher power. DALI+ Over OpenThread devices use narrower, low-power IEEE 802.15.4 radio channels.

A Wi‑Fi access point does not transmit energy only inside a perfect channel boundary. In real RF systems, some transmitted energy extends beyond the main Wi‑Fi channel. This can appear as sideband energy, adjacent-channel energy or spectral sidelobes.

If the DALI+ Over OpenThread channel sits near this Wi‑Fi sideband energy, the DALI+ Over OpenThread receiver may detect the Wi‑Fi access point as noise or interference. The closer the DALI+ Over OpenThread device is to the access point, the stronger this interference may be.

Why distance from the access point matters

A Wi‑Fi access point is usually a much stronger transmitter than a DALI+ Over OpenThread device.

When a DALI+ Over OpenThread device is close to the access point, the Wi‑Fi signal and its sideband energy can be very strong at the DALI+ Over OpenThread receiver. If the device is also positioned in a strong antenna lobe from the access point, the interference can be even greater.

As the DALI+ Over OpenThread device is moved further away from the access point, the received Wi‑Fi energy usually reduces. This improves the chance that the DALI+ Over OpenThread signal can be received correctly.

Practical placement factors include:

• Distance between the Wi‑Fi access point and the DALI+ Over OpenThread device
• Distance between the Wi‑Fi access point and the DALI+ Over OpenThread border router
• Antenna direction and mounting orientation
• Reflections from walls, ceilings, metal surfaces, racks or enclosures
• Access point transmit power
• Wi‑Fi channel width
• DALI+ Over OpenThread channel selection

Why the Wi‑Fi access point does not avoid the DALI+ Over OpenThread packet

The Wi‑Fi access point does not decode DALI+ Over OpenThread packets. DALI+ Over OpenThread traffic is not Wi‑Fi traffic, so the access point does not treat it as another Wi‑Fi client or Wi‑Fi packet.

If the DALI+ Over OpenThread channel is only adjacent to the Wi‑Fi channel, or sitting in the Wi‑Fi sideband, the access point may not detect the DALI+ Over OpenThread transmission as something it needs to avoid.

This is different from two Wi‑Fi devices using the same Wi‑Fi channel. In that case, Wi‑Fi devices can use carrier sensing and collision avoidance to help share the channel.

If DALI+ Over OpenThread and Wi‑Fi are placed directly on the same channel area, collision avoidance may become more likely because the radios may detect more energy on the channel. However, this does not mean co-channel operation is preferred. A high-power or high-usage Wi‑Fi network on the same frequency can still prevent reliable low-power DALI+ Over OpenThread communication.

For this reason, channel separation is usually preferred.

Sideband interference example

The example below shows how a nearby Wi‑Fi access point can drown out a lower-power DALI+ Over OpenThread device.

In this example, the Wi‑Fi sideband energy remains the same. The DALI+ Over OpenThread signal improves as the DALI+ Over OpenThread transmit power is increased.

This improves the signal-to-noise or signal-to-interference margin. In simple terms, the DALI+ Over OpenThread packet becomes stronger compared with the Wi‑Fi noise.

Important limitation of increasing transmit power

Increasing the DALI+ Over OpenThread transmit power can improve communication from that device to other devices.

However, it is not a complete fix.

Higher transmit power may help the DALI+ Over OpenThread device be heard by the network, but it does not necessarily help the device receive incoming messages while the nearby Wi‑Fi access point is transmitting.

Transmit power must also remain within:

• Product limits
• Regulatory limits
• Site design requirements
• Battery-life requirements, where applicable

Increasing transmit power should be treated as one possible mitigation, not the primary solution.

Recommended actions

1. Increase physical separation

Avoid installing DALI+ Over OpenThread devices directly beside, above, below or behind a Wi‑Fi access point.

Where possible, increase the distance between:

• The Wi‑Fi access point and the DALI+ Over OpenThread device
• The Wi‑Fi access point and the DALI+ Over OpenThread border router
• High-power 2.4 GHz transmitters and low-power DALI+ Over OpenThread devices

Even a small change in position can improve performance in some environments.

2. Review antenna placement and orientation

Access points do not radiate evenly in every direction. Antenna lobes can create areas of stronger RF energy.

If a DALI+ Over OpenThread device is installed inside a strong Wi‑Fi antenna lobe, it may experience higher interference.

Where possible:

• Avoid placing DALI+ Over OpenThread devices in the strongest coverage area immediately around the access point
• Avoid mounting devices directly in line with high-gain access point antennas
• Test different mounting positions where performance is unreliable

3. Use better channel separation

Select Wi‑Fi and DALI+ Over OpenThread channels that are separated as much as practical.

Avoid placing the DALI+ Over OpenThread channel close to the edge of a high-power Wi‑Fi channel where sideband energy may be present.

Where possible:

• Keep 2.4 GHz Wi‑Fi on a known fixed channel
• Avoid automatic Wi‑Fi channel changes where they may move Wi‑Fi closer to the DALI+ Over OpenThread channel
• Select a DALI+ Over OpenThread channel with the lowest measured interference
• Re-test after changing Wi‑Fi channel plans

4. Use 20 MHz Wi‑Fi channels in 2.4 GHz

Avoid using 40 MHz Wi‑Fi channels in the 2.4 GHz band where DALI+ Over OpenThread devices are installed.

Wider Wi‑Fi channels occupy more of the 2.4 GHz band and leave fewer clean areas for DALI+ Over OpenThread operation.

5. Reduce Wi‑Fi transmit power where possible

A high-power Wi‑Fi access point can raise the local RF noise floor for nearby low-power devices.

Where Wi‑Fi coverage allows, reducing the 2.4 GHz transmit power may improve DALI+ Over OpenThread reliability.

This should be done carefully so that Wi‑Fi coverage is not degraded below site requirements.

6. Increase DALI+ Over OpenThread transmit power where supported

If the DALI+ Over OpenThread device supports configurable transmit power, increasing transmit power may improve the outgoing signal margin.

This can help where the DALI+ Over OpenThread signal is being drowned out by Wi‑Fi sideband energy.

Do not rely on transmit power alone. It should be used with good channel planning and physical separation.

Resolution checklist

Use the following checklist when diagnosing this issue:

• Check whether the DALI+ Over OpenThread device is close to a 2.4 GHz Wi‑Fi access point
• Check whether the device is close to the access point antenna or directly in a strong antenna lobe
• Confirm the active 2.4 GHz Wi‑Fi channel
• Confirm the active DALI+ Over OpenThread channel
• Check whether the DALI+ Over OpenThread channel is adjacent to, or inside the sideband area of, the Wi‑Fi channel
• Confirm whether the Wi‑Fi access point is using 20 MHz or 40 MHz channel width
• Test the DALI+ Over OpenThread device further away from the access point
• Test a different DALI+ Over OpenThread channel, where supported
• Test a different 2.4 GHz Wi‑Fi channel, where supported
• Reduce 2.4 GHz Wi‑Fi transmit power, where site coverage allows
• Increase DALI+ Over OpenThread transmit power, where supported and permitted

Key takeaway

A nearby high-power Wi‑Fi access point can interfere with DALI+ Over OpenThread even when the DALI+ Over OpenThread channel is not exactly the same as the Wi‑Fi channel.

If the DALI+ Over OpenThread channel sits in the sideband of the Wi‑Fi channel, the access point may not detect or avoid the DALI+ Over OpenThread transmission. The access point is not decoding the DALI+ Over OpenThread packet; it is simply transmitting Wi‑Fi energy that can drown out the lower-power DALI+ Over OpenThread signal.

Increasing DALI+ Over OpenThread transmit power can improve the signal margin, but the preferred solution is to use better channel separation, increase physical separation, reduce unnecessary Wi‑Fi transmit power and avoid placing DALI+ Over OpenThread devices close to high-power access points.