RF Spectrum Sharing: Wi-Fi, Bluetooth, and IEEE 802.15.4 in the 2.4 GHz Band

Wi‑Fi, Bluetooth (BLE), and IEEE 802.15.4 all commonly operate in the 2.4 GHz ISM band, which is why they can interfere with each other if not managed properly.

Most IoT devices use:

2.4 GHz Wi-Fi 2400 ~ 2483.5 MHz

Channels:

CH1 ~ CH13 (US: 1~11)

Bandwidth:

20 MHz 40 MHz

A single Wi‑Fi channel occupies a relatively large portion of the spectrum.

Example:

CH1 ≈ 2412 MHz CH6 ≈ 2437 MHz CH11 ≈ 2462 MHz

Also uses:

2400 ~ 2483.5 MHz

But divides it into many narrow channels.

Classic Bluetooth:

79 channels 1 MHz each

BLE:

40 channels 2 MHz each

Bluetooth employsfrequency hopping:

2402 2404 2406 ... 2480 MHz

jumping channels many times per second.

The 2.4 GHz version uses:

2405 ~ 2480 MHz

Channels:

CH11 ~ CH26

Example:

CH11 = 2405 MHz CH15 = 2425 MHz CH20 = 2450 MHz CH25 = 2475 MHz

Used by:

Thread Matter over Thread Zigbee

2400 MHz 2483.5 MHz |----------------------------------------------| Wi-Fi CH1 [====================] Wi-Fi CH6 [====================] Wi-Fi CH11 [====================] 802.15.4 CH11 CH12 CH13 ... CH24 CH25 CH26 | | | | | | BLE +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ hops everywhere across the band

ESP32-S31 contains:

Wi-Fi Bluetooth LE 802.15.4

sharing the same 2.4 GHz radio subsystem.

The chip doesnottransmit all three simultaneously on the same frequency.

Instead it uses:

RF coexistence (Time Division)

Example:

Wi-Fi TX ↓ BLE TX ↓ Thread TX ↓ Wi-Fi RX

The scheduler allocates RF time slots.

Because Wi‑Fi uses:

20 MHz 40 MHz

wide channels with much higher transmit power.

Whereas:

802.15.4 = 2 MHz wide BLE = 2 MHz wide

Therefore a nearby Wi‑Fi AP can significantly reduce Zigbee/Thread performance.

If your router uses:

Wi-Fi CH1 Center: 2412 MHz

it overlaps heavily with:

802.15.4 CH11 802.15.4 CH12 802.15.4 CH13

So Zigbee/Thread installers often choose:

CH20 CH25

to avoid common Wi‑Fi channels.

Common recommendations:

802.15.4 CH15 802.15.4 CH20 802.15.4 CH25

because they tend to have less overlap with Wi‑Fi CH1/6/11.

This is important:

Can use:

2.4 GHz 5 GHz 6 GHz (Wi‑Fi 6E / Wi‑Fi 7)

Mostly:

2.4 GHz only

Can use:

868 MHz (Europe) 915 MHz (US) 2.4 GHz (Worldwide)

However, in almost all modern consumer smart-home products:

Wi‑Fi → 2.4 GHz BLE → 2.4 GHz Thread → 2.4 GHz Zigbee → 2.4 GHz Matter/Thread → 2.4 GHz

So when evaluating anESP32-S31design, you can generally assume thatWi‑Fi, BLE, and 802.15.4 are sharing the same 2.4 GHz RF spectrum, and RF coexistence and antenna design become important considerations.