MU-MIMO: What It Is and Do You Need It?

In the field of high-end routers in the past two years, MU-MIMO has been one of the key focuses that manufacturers have highlighted in their promotion. With the halo of new technologies such as 802.11ac Wave2, MU-MIMO and WiFi6, routers are getting more and more expensive. In most cases, due to limited conditions, users do not quantitatively test the actual effects of these technologies. Whether the routers that support MU-MIMO technology purchased at a high price are worth the money has become a question in the minds of some users.

To understand MU-MIMO, one must first understand MIMO. To explain the concept of MIMO, let's first understand what SISO is.

• SISO

• SISO stands for Single Input and Single Output, which is quite easy to understand. In the field of wireless routers, it can be simply explained as using one antenna for both transmission and reception. Based on SISO, SIMO and MISO technologies have been developed, representing single input multiple output and multiple input single output respectively.

• MIMO

• MIMO stands for Multiple Input Multiple Output, referring to the situation where a message is transmitted by multiple antennas at the transmitting end and received by multiple antennas at the receiving side. It utilizes multiple antennas at the transmitting end to independently send signals, and simultaneously uses multiple antennas at the receiving end to receive and restore the original information, thus achieving a higher transmission rate at a lower cost.

• MIMO technology can be traced back to 1908, when the renowned Italian radio engineer Marconi proposed using it to combat fading. In the 1970s, the idea of applying multiple-input multiple-output technology to communication systems was proposed. However, the foundational work that greatly promoted multiple-input multiple-output technology in wireless mobile communication systems was completed by scholars at Bell LABS in the 1990s.

• SU-MIMO

• In the field of wireless routers, MIMO is not a new thing. Ten years ago, in 802.11n, traditional MIMO technology was already a standard configuration. Conventional MIMO can be called SU-MIMO, where SU stands for Single User, that is, "Single user multiple input multiple output". Although it can enhance the network communication rate between the router and the client device through simultaneous multi-link transmission, within the same time and frequency band, the router can only communicate with one client device. Therefore, even if the client device cannot fully occupy the wireless bandwidth of the router, the router cannot allocate the remaining bandwidth to other devices for use.

• MU-MIMO

• MU-MIMO technology is based on conventional MIMO and adds a multi-user simultaneous communication mechanism. Therefore, MU-MIMO can utilize all wireless bandwidth. In the case of multi-user access, the network latency conditions of each device will be significantly improved.
  

MU-MIMO implementation requirements

• To apply MU-MIMO technology, not only must the router support the MU-MIMO function, but all terminal connected devices must also support it. If any device in the network environment does not support MU-MIMO, the router will be in the ordinary MIMO mode of queuing up in turn. However, in the real environment, the popularity rate of MU-MIMO devices is not high. The iPhone XS only supports 2x2 MIMO from this generation.

• In addition, to achieve good results, the number of transmission channels (antennas) of the MU-MIMO router must be greater than the sum of the terminal transmission channels. However, the current wireless routers generally have a maximum of 4x4 MU-MIMO, and after WiFi6, they need to reach 8x8 MU-MIMO to have a wider range of application scenarios. But many conditions still need to be met to benefit.
  

Finally, the MU-MIMO technology is mainly developed by Qualcomm. Other brands, including Mediatek and Broadcom, are relatively lagging behind, and the compatibility among these brands is not good. This leads to the situation in some scenarios where the MU-MIMO technology, which claims to enhance network speed, actually reduces the actual network speed.