Wi-Fi 6 specific improvements with FortiAPs
Wi-Fi 6 improvements over previous generations
Wi-Fi 6 changes includes higher data rates, spatial stream improvements and general enhancements to previous Wi-Fi generations. However, it also includes completely new techniques to improve high-density environments. As previously mentioned, when all clients were laptops, adding spatial-streams greatly increased capacity. Smart phones and tablets are more limited. More spatial streams require more antennas, and more antennas require not only more space in these smaller form factors, but more battery power. MU-MIMO is one way to improve the total networks capacity, but Wi-Fi 6 also introduces completely new technologies.
OFDMA
Wi-Fi is a spread spectrum technology. That means that a 20 MHz Wi-Fi channel is actually the sum of a number of smaller channels—about 48 per 20 MHz, depending on how you count. This is called OFDM (Othogonal Frequency Division Multiplexing). Channel bonding uses a bigger stretch of subcarriers, and so can carry more information. OFDMA (Orthogonal Frequency Division, Multiple Access) does the opposite, splitting the channel into smaller channels (called Resource Units) with fewer subcarriers, but it can use those smaller channels at the same time, from the same antenna.
With OFDMA a Wi-Fi channel can be divided up among multiple clients. Instead of using the entire channel for one client at a time, with OFDMA, subcarriers are divided into 'resource units' that can be directed at specific clients. This reduces contention and overhead resulting in more efficient use of the channel, especially for lower speed clients. Of course, the clients must be Wi-Fi 6 to support this.
8 stream MU-MIMO
MIMO (Multiple Input, Multiple Output) for single clients with multiple antennas was introduced in Wi-Fi 4 (802.11n). While OFDM and OFDMA are frequency multiplexing, MIMO is spatial-multiplexing, depending on multi-path (different paths) to the target antennas for each stream.
Wi-Fi 5 introduced MU-MIMO, or Multi-User MIMO, where each antenna stream could send data to antennas on different devices, allowing simultaneous downstream to multiple devices. The standard defined up to 8 streams, but no APs were deployed with more than 4.
Wi-Fi 6 extends MU-MIMO to 8 streams, and enables simultaneous uplink from multiple clients. MU-MIMO is supported on all Wi-Fi 6 FortiAPs, but the number of streams available depends on the number of antennas: 2 for an FAP-231F, 4 for an FAP-431F, and the FAP-831F has 8 antennas and supports 8 streams.
It is important to understand that MU-MIMO only works when the clients have enough 'spatial diversity.' If 2 smart phones are physically close together, it is unlikely that there is enough of a difference to mathematically resolve one antenna to one, one to another at the same time, while if the hypothetical smart phones are on opposite sides of the AP, a solution is much more likely. That's why the FAP-831F is considered a high-density AP. In an office environment with fewer devices, the 2 and 4 antenna APs are going to cover most of the possible MU-MIMO options. However, in a high-density deployment, like an auditorium with many client devices surrounding an FAP-831F, it is much more likely that MU-MIMO will provide a solid performance boost.
BSS coloring
As a reminder, there are two kinds of interference to be concerned with in a Wi-Fi network: Wi-Fi and non-Wi-Fi. Non-Wi-Fi interference is 'noise,' RF energy interfering with the medium. The classic example is a microwave oven disrupting a Wi-Fi connection. It is interference at layer 1 or the physical layer of the OSI model. However, Wi-Fi is no longer new. It is everywhere. Now the more important concern is other Wi-Fi signals on channel, including the local WLAN self-interfering.
If a signal is recognizable as Wi-Fi, then a Wi-Fi radio has to wait its turn (this function is called a CCA of Clear Channel Assessment). It interferes because of the way the protocol works; the medium is not clear and the radio has to wait its turn. It is fairly described as layer 2 interference because it is a media access issue. In a campus environment, your own APs on the same channel, or clients connected to them, may cause contention in other AP cells.
BSS coloring adds some header information, or a 6-bit 'color' tag. If a Wi-Fi packet is detected that has a different color, it is part of a different AP-client combination and the listening Wi-Fi radio can go ahead and transmit, treating the signal as if was background noise. Both signals can be transmitted simultaneously, network capacity goes up, and APs can be spaced closer together.
