MIMO (Multiple Input, Multiple Output) is a fundamental wireless technology that enhances Wi-Fi throughput and reliability by transmitting multiple data streams simultaneously using multiple antennas on both the transmitter and receiver. It was introduced in the IEEE 802.11n standard, which marked the beginning of high-throughput (HT) Wi-Fi.
According to RUCKUS One Online Help and the RUCKUS Analytics 3.5 User Guide, MIMO enables spatial multiplexing, diversity gain, and beamforming, allowing higher data rates and improved signal quality in multipath environments. Subsequent standards (802.11ac and 802.11ax) expanded this concept to MU-MIMO (Multi-User MIMO), allowing simultaneous communication with multiple clients.
MIMO requires support on both the AP and client for full functionality; otherwise, the connection falls back to single-stream operation. It is used in both uplink and downlink directions (especially in Wi-Fi 6 and later). Thus, option B-introduced in 802.11n-is correct, while options A, C, and D are incorrect.
Reference:
RUCKUS One Online Help - PHY Technologies and MIMO Concepts
RUCKUS Analytics 3.5 User Guide - Radio Metrics and Client PHY Data
RUCKUS AI Documentation - Wi-Fi 6 (802.11ax) MIMO and MU-MIMO Capabilities