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 wasintroduced in the IEEE 802.11n standard, which marked the beginning of high-throughput (HT) Wi-Fi.
According toRUCKUS One Online Helpand theRUCKUS Analytics 3.5 User Guide, MIMO enables spatial multiplexing,diversity gain, andbeamforming, 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 requiressupport on both the AP and clientfor full functionality; otherwise, the connection falls back to single-stream operation. It is used in bothuplink and downlinkdirections (especially in Wi-Fi 6 and later).
Thus, optionB-introduced in 802.11n-is correct, while options A, C, and D are incorrect.
References:
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