Wireless device queues
Typically, wireless devices have four queues for the different access categories, and additionally buffer somewhere for aggregation in HT mode.
Note that the software queues exist for each virtual interface, and the aggregation queue there exists for each aggregation session. This picture reflects iwlwifi – the aggregation queues might be in the driver (software) instead (ath9k).
The FIFOs are typically shallow and only used to buffer DMA latencies. In any case, they typically can't be changed anyway.