Inquiry regarding LBT support for MM6108

Software
1

Hi all,

I would like to know whether MM6108 supports LBT (listen-before-talk).

In order to properly use Wi-Fi HaLow in South Korea, it must not interfere with the transmission of other devices (e.g. wireless microphones) that use the same frequency band.

First of all, is it technically possible?

If possible, I would like to ask which layer is handling that part and how I can tune it.

Thank you.

Best regards,

Jongsoo

2

Hi @jsjeong

Wi-Fi uses CSMA/CA to share the medium - and Wi-Fi HaLow is no different! The CA (collision avoidance) is the listen before talk you are looking for!

The timing between frame transmissions is defined by the short interframe space (160us for Wi-Fi HaLow - not configurable) and the arbitration interframe spacing which is defined by the access point (see hostap parameters), though this is typically used for traffic prioritisation.

I will confirm with our team who are currently looking at Korean regulatory details for any other specific details!

EDIT:
Just an additional note, prior to starting transmission we wait DIFS (Distributed Interframe Space) + random backoff. At the end of backoff timer, it transmits. If medium is found to be busy during random backoff countdown, the counter stops until medium is free.
DIFS is SIFS + 2 slot times (160 + 52*2 us for HaLow)

3

Hi @ajudge

Thank you for your reply.

In Korea, to avoid interference with wireless microphones, Wi-Fi HaLow devices must detect signal strength before transmitting and transmit only when the strength is -85 dBm or lower.

However, according to 802.11-2020, section 23.3.18.5.3 CCA sensitivity for operating classes requiring CCA-ED, the CCA-ED threshold is defined as -75 dBm (primary 1 MHz) and -72 dBm (primary and secondary 2 MHz).

I wonder if there’s a way to adjust the signal strength parameters related to this.

While searching for information, I came across a document called “Wi-Fi HaLow™ Availability Global Spectrum Report June 2023 Version 2.1” published by Morse Micro. (For some reason, I couldn’t find it in the Customer Portal.) And within that material, I found the following well-organized section on Korean regulations for 925~931 MHz band:

Bandwidth: 1 MHz or 2 MHz

LBT required

  • Listen: 264 us
  • RX signal strength: <= -85 dBm
  • TX time: <= 220 ms
  • Pause after TX: >= 264 us (except control or ack signal)

Spurious emissions limit: see regulatory document

No duty cycle limit

TX power limit is 10 mW/200 kHz EIRP

  • ~17 dBm EIRP in 1 MHz
  • 20 dBm EIRP in 2 MHz

Effective date: Oct. 8, 2021

I hope this helps you a little.

Best regards,

Jongsoo

4

Hi @ajudge ,

As previously mentioned, South Korea’s regulatory restrictions require HaLow devices to detect lower energies than those specified in IEEE 802.11-2020’s CCA-ED standard.

Could you confirm whether there are any technical issues with this, please?