WiFi6 - MU-MIMO and OFDMA

OFDMA
OFDMA divides a radio channel into multiple sub-channels (subcharriers) to form frequency resource blocks. User data is carried on the resource blocks, instead of occupying the entire channel, so that multiple users can transmit data concurrently in the same time period.
Metaphorically speaking, in the orthogonal frequency division multiplexing (OFDM) scheme of Wi-Fi 5, goods are delivered by order, and one vehicle is dispatched for one order, even if the order just specifies one single piece of small item. In this case, the vehicle's compartment is often empty, leading to low efficiency and wasted resources. Comparatively, in the OFDMA scheme of Wi-Fi 6, a truck is not dispatched until it is fully loaded with goods of merged orders, so that much higher transmission efficiency is achieved.


MU-MIMO

MU-MIMO allows one router to communicate with multiple devices simultaneously.
Specifically, MU-MIMO of Wi-Fi 5 allows one router to communicate with four devices at a time and supports only downlink MU-MIMO. With better performance, MU-MIMO of Wi-Fi 6 allows one router to communicate with up to eight devices in the meantime and supports both uplink and downlink MU-MIMO.
In the preceding metaphorical example, such a difference means that four lanes on the road are increased to eight lanes, and vehicles (devices) no longer queue at and move through the same exit, but can simultaneously and efficiently move in or out on different lanes.


OFDMA vs. MU-MIMO
These two technologies are different though they have something in common: both enable multi-user uplink and downlink transmission and increase wireless access density. OFDMA and MU-MIMO are parallel transmission solutions and are complementary to each other. They comply with different technical theories and are applicable to different scenarios, and should be used based on service application types.