MIMO technology is used for both WiFi and mobile network (Cellular) connections.
4x4 MIMO is now very popular on high-end segment phones like iPhone XS or XS Max. Galaxy S9 or S9 +, Google Pixel 3 or Pixel 3 XL also support this technology. They can support 4 data streams when supported mobile network connection.
But that's just a mobile network connection. iPhone XS and Pixel 3 both support 4x4 MIMO LTE networks but WiFi is only 2x2 MIMO. Even when connecting to the 4x4 MIMO router, you only get 2x2 MIMO speed because the mobile network and WiFi use separate antenna.
4x4 MU-MIMO stands for Multi User, Multi Input, Multi Output. Basically, many devices are connected to that router, all of which can simultaneously transmit four data streams. What are the readers who learn more about this technology at MU-MIMO article? Why should your next WiFi router have MU-MIMO?
If all parameters are equal, 4x4 MIMO is better than 2x2 MIMO. In other words, the more MIMO the better. Machines with multiple antennas will also be more expensive. High-end segment phones often have 4x4 MIMO.
Adding antennas is additional hardware, so the 4x4 MIMO will also consume more battery than 2x2 MIMO but probably not too big compared to many other battery-consuming tasks you perform on the device.
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