MIMO

MIMO, or multiple-input multiple-output, is a wireless technology that uses multiple antennas at the transmitter and receiver to improve communication performance. By exploiting multipath propagation, MIMO can increase data throughput, reliability, or both, without requiring additional bandwidth or transmit power in ideal conditions. The wireless channel is represented as a matrix that mixes signals across spatial paths, and the system can exploit this for spatial multiplexing or diversity.

In spatial multiplexing, independent data streams are transmitted simultaneously from multiple antennas and separated at the receiver, increasing spectral efficiency. The achievable rate depends on the channel condition and the number of parallel streams. Diversity techniques transmit redundant information across different antennas or time slots to reduce the probability of error due to fading, improving link robustness.

Common techniques include space-time coding (e.g., Alamouti) for simple diversity, and more generally precoding and beamforming when channel state information is available. OFDM is often used with MIMO to handle frequency-selective channels, as in MIMO-OFDM. Massive MIMO extends the idea to very large antenna arrays, using favorable propagation and advanced signal processing to serve many users simultaneously, particularly in cellular networks. MIMO is also employed in Wi‑Fi and 5G networks to raise capacity and reliability.

Key considerations include channel state information at the transmitter and receiver, antenna placement and correlation, and practical limits such as hardware complexity and pilot overhead. MIMO remains a foundational technology in modern wireless communications.