  The evolution of the IEEE 802.11 standards marks a significant throughput
advancement in wireless access technologies, progressively increasing bandwidth
capacities from 20 MHz in the IEEE 802.11a to up to 320 MHz in the latest IEEE
802.11be (Wi-Fi 7). However, the increased bandwidth capacities may not be well
exploited due to inefficient bandwidth utilization on multiple channels. This
issue typically occurs when the primary channel is busy, secondary channels
(also known as non-primary channels) are prevented from being utilized even if
they are idle, thereby wasting the available bandwidth. This paper investigates
the fundamentals of the Non-Primary Channel Access (NPCA) protocol that was
defined in IEEE 802.11 Ultra-High Reliability (UHR) group to cope with the
above issue. We develop a novel analytical model to assess NPCA protocol
performance in terms of the average throughput and delay. Via simulation, we
verify that the NPCA network outperforms the legacy network by increasing at
least 50% average throughput while reducing at least 40% average delay.
