Common sources of WiFi interference

The biggest source of WiFi interference in most buildings is other WiFi: your own access points on the same channels and the networks of your neighbours. Non-WiFi devices such as microwave ovens and wireless cameras, and building features that block or reflect signals, cause the rest. Finding the real source takes measurement, because the symptoms all look alike.

How interference shows up

Users rarely say "interference". They report slow connections at certain times, video calls that freeze, scanners that drop in one area, or WiFi that works fine until lunch. Behind those symptoms, devices are waiting for a clear channel, retrying failed transmissions or falling back to slower data rates. Each of those uses more airtime and slows everyone else down.

Interference from WiFi

Co-channel interference from your own network

WiFi devices on the same channel take turns to transmit. When too many access points on one channel can hear each other, they all share the same airtime, so adding access points can actually reduce capacity. This is the most common cause of a network that shows strong signal everywhere and still feels slow. It usually comes from too many access points, transmit power set too high, wide channels in a crowded band, or a poor channel plan. WiFi channel planning covers how to avoid it.

Adjacent-channel interference

Channels that partly overlap, or access points mounted very close together on neighbouring channels, can bleed into each other. In the 2.4 GHz band, using anything other than the standard non-overlapping channels is a common cause.

Neighbouring networks

Tenants in multi-tenant buildings, adjacent businesses and residential units all run their own WiFi, often at full power with automatic channel selection. You cannot control them, but a survey shows how much they affect you and which channels are least crowded.

Personal hotspots and rogue access points

Phones used as hotspots, personal routers plugged in at desks, and printers, TVs or other devices broadcasting their own networks all add to the congestion.

Non-WiFi interference

These sources transmit on the same frequencies as WiFi but do not follow WiFi's rules for sharing the channel. Ordinary WiFi tools cannot identify them; a spectrum analyzer can.

• Microwave ovens, which leak energy in the 2.4 GHz band while running, often in break rooms near work areas.
• Bluetooth devices, also in 2.4 GHz. One headset is minor; many in a busy office add up.
• Wireless video transmitters, such as some older security cameras and video senders, which can transmit continuously.
• Other 2.4 GHz devices such as some wireless keyboards, baby monitors, and proprietary industrial or medical telemetry.
• Radar near airports and weather stations, which WiFi equipment must avoid on certain 5 GHz channels, causing access points to change channel suddenly.
• Faulty electrical equipment, such as failing lighting ballasts or motors, which can raise background noise.

Building materials and contents

These do not create interference in the strict sense, but they weaken and distort signals in ways that look similar to users:

• Concrete, brick, masonry block and stone walls and floors.
• Metal: studs, wire lath plaster, foil-backed insulation, ductwork, elevator shafts, shelving and warehouse racking.
• Low-emissivity coated and mirrored glass.
• Water: in pipes, tanks, stock such as beverages, and in people. A full room absorbs more signal than an empty one.

Metal surfaces also reflect signals, creating multipath, where copies of the signal arrive at slightly different times. Modern WiFi uses multipath to its advantage in many cases, but heavy reflection in metal-rich industrial spaces can still cause problems. WiFi for warehouses and industrial sites covers this in more detail.

Finding the source

1. Record when and where the problems happen, and which devices are affected.
2. Run a passive survey to map channel use, overlap and neighbouring networks.
3. Use spectrum analysis to look for non-WiFi sources, especially where the noise floor is high.
4. Review access point power and channel settings, and check for rogue access points.
5. Change one thing at a time and measure again.

How ehZee can help

Our surveys measure the radio environment, including neighbouring networks, channel overlap, noise and SNR, as part of our standard checklist. Our WiFi surveys service identifies what is interfering with your network and recommends changes to channels, power, placement or equipment.

Common questions