WiFi · Networking
MIMO
Also known as: Multiple Input Multiple Output
Uses multiple antennas on both transmitter and receiver to send multiple data streams simultaneously over the same frequency, multiplying throughput without additional spectrum.
MIMO exploits a phenomenon called multipath propagation. In a real RF environment, signals bounce off walls, furniture, and people, arriving at the receiver via multiple paths with different delays. In traditional single-antenna systems, this causes interference. MIMO's multiple antennas distinguish these paths and use them to carry separate data streams simultaneously.
A 4x4 MIMO link has 4 transmit and 4 receive antennas, capable of 4 simultaneous spatial streams. Each stream operates independently — a 4x4:4 MIMO AP running at 600Mbps per stream delivers 2.4Gbps aggregate to a single client with a matching 4-stream NIC.
MIMO notation: the first number is transmit antennas, the second is receive antennas, and the third (if shown) is the maximum spatial streams. A 4x4:3 radio has 4 transmit and 4 receive antennas but a maximum of 3 spatial streams.
In practice, most client devices have 2 or fewer spatial streams (laptops with 2x2 MIMO, phones often with 1x1 or 2x2). The AP can have 4 or 8 transmit/receive chains, but the client is often the bottleneck on spatial stream count.
MIMO is the foundation for MU-MIMO: once an AP can handle multiple spatial streams, it can direct different streams to different clients simultaneously.