Mechanism of Interference at PHY and MAC Layers

Interference from non-Wi-Fi devices (like wireless audio transmitters) operates at two main levels:

• Physical (PHY) Layer: IEEE 802.11 devices use the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) algorithm to check if a channel is busy. When a wireless audio transmitter operates continuously on the 2.4 GHz band, Wi-Fi stations detect this radiofrequency energy as “noise” or a “busy medium” at the PHY layer
• MAC Layer: If the medium is sensed as busy, the Wi-Fi device must “back off” and wait for a random period before re-checking. If a collision occurs due to sporadic interference, the data frame is corrupted, leading to NO ACK (no acknowledgment) and forcing continuous retransmissions, which drastically reduces useful throughput

Impact of Channel Occupancy on Throughput

The relationship between channel occupancy (utilization) and throughput is mathematically defined in the sources. For Single-Link Operation (SLO), the average throughput ($Th_{SLO}$) can be approximated as:

$$\begin{aligned} Th_{SLO} &= \frac{(1 - \alpha)L}{T} \end{aligned}$$

Where:

• $\alpha$ is the occupancy (utilization) of the primary link
• $L$ is the packet size
• $T$ is the total transmission time

As occupancy ($\alpha$) increases toward 1.0 (100%), the “free airtime” ($1− \alpha$) approaches zero, causing throughput to plummet