This is something at the protocol level, which allows multiple users to use a MIMO system at the same time. Generally speaking, routers have more antennas, and APs have fewer antennas, but more to less, the router's channel resources cannot be fully utilized. To this end, a mechanism is designed to allow multiple users to share router antenna resources. The user here refers to station. How to share it. Each user must be assigned a channel, so which channel does each user use?
In fact, a LUT is needed for management, and the AP needs to inform the station of the channel resources allocated by it in some form. And save a LUT table inside the AP, indicating the channel position of each station. For example, user1 occupies channels 1 and 2, and user2 occupies channels 3 and 4. Then, user1 uses channels 1 and 2 to send and receive, and user2 uses channels 3 and 4 to send and receive. For sta, it only needs to maintain such a table of the channel location where it is.
Carrier Sense monitors whether there are related radio waves at a certain channel (carrier) level. It does not affect simultaneous work on different channels.
So what about SU-MIMO? Under SU-MIMO, users do not need to maintain such a table.
MIMO technology:
Multiple inputs, multiple outputs. Take a user as an example. For example, if there are two antennas, then there are two channels. In fact, a user can use two channels for transmission. The bandwidth becomes larger and the speed becomes faster. At this time, the bandwidth of the signal itself has not changed, but the channel has changed from one to two. The throughput of the air interface is improved. For the MAC, it can send more data to the PHY in the same time without blocking the PHY.
Can a frame specify the channel used by each frame?
Beamforming：
This is used to improve the signal-to-noise ratio, not to increase the channel capacity, that is, multiple antennas transmit the same signal, and these multiple antennas are still the same channel. Therefore, beamforming is per-channel, and MIMO is channel-by-channel. Whether or not MAC needs beamforming, only one indicator bit is needed.
What is OFDMA technology?
This is actually a technique for matching signal bandwidth and channel bandwidth. That is, the signal bandwidth is, for example, del SBW, and the channel bandwidth is del CBW. Then the data can be divided into multiple slices, and each slice occupies a part of del CBW, that is, del SBW. In this case, multiple signals can be carried through the same antenna (channel).
Therefore, fragmentation, that is, according to the attributes of the data and the attributes of the channel, determines whether to use OFDMA technology.
Summary: OFDMA, subdivision within the channel, namely channel aggre, MU-MIMO, distribution between channels, MIMO has multiple channels, beamforming is spatial aggre.