This section describes how Multiuser (MU) MIMO allows an AP to transmit and receive traffic with multiple connected devices simultaneously.
The technology started in the 802.11ac/Wi-Fi5 standard for MU “Downlink” traffic operations and extended in 802.11ax to support also MU “Uplink”. MU-MIMO lets the AP manage the Multiuser traffic in separate simultaneous ‘lanes’, where each lane is dedicated to a connected device at given time, not logically separated to traffic timing and sizes.
Unlike OFDMA, the MU-MIMO does not ‘split’ the given channel into independent-subcarriers of the spectrum in which each does not contend with others, thus able to ‘fill’ unused vacancies in the spectrum. Instead, MU-MIMO is very effective in scenarios where multiple Users/Devices all need to receive and transmit full-buffers of traffic with all connected devices without any time gaps in between, such as during high-throughput applications by all the participating users.
The MU-MIMO’s gain and effectiveness during high-throughput of Multiuser traffic, compared to without MU-MIMO, largely depends on the following factors:
The Width of the channel. The wider the width, the faster the ongoing full buffers can be crammed into each of the given number of connected devices.
The AP execution of the Multiuser connections. This is a combination of APs hardware dependencies, such as MIMO capabilities (2x2, 4x4, 8x8), and the APs concurrency of the connections over the MIMO. It is expected that as long as the AP can manage the full-buffers for a number of devices of less than or equal to the physical MIMO capabilities, then the relative gain of the MU-MIMO speed for all of those devices is the highest. Whereas if larger number of devices participate in full-buffers scenario, the AP needs to multiplex its MIMO operations and that can reduce the relative gain.
MU-MIMO in an ecosystem of 6GHz connections greatly benefits from the default channel widths of 80MHz, in the sense that the 80MHz is efficient for both the MU-MIMO type of applications as well as traffic and OFDMA type of applications. Thus, the connection of 6GHz serves all the application types mostly automatically, compared to ecosystems of 2.4GHz band which typically is 20MHz only for all applications, and 5GHz band which typically is 20MHz if it needs to support latency-sensitive applications.
The following chart depicts six test results of Multiuser aggregated downlink speed in Mbps unit, for each given number of participating devices. The six tests are performed in combinations of MU-MIMO Enabled vs Disabled for each of the three AP channel widths settings: 20MHz, 40MHz, and 80MHz.
Aggregated Throughput Results of MU-MIMO Enabled vs. Disabled
The chart illustrates the following points:
The wider the channel, the higher the result is of the Multiuser aggregated speed.
Within the context of each width (20, 40, or 80MHz), the speed gain of the MU-MIMO in all three is relatively high in up to four to six participating devices, averaging ~50% relative gain, whereas once the number of participating devices is higher, the relative gain in all widths is diminishing to average of 20%. This test example of diminishing to a 20% gain in the larger amount of devices is subjected to specific AP's model. This can vary greatly to higher or lower gains, depending on the AP model and its number of antennas.
