The document discusses the basic mathematics behind MIMO (Multiple Input Multiple Output) technology used in wireless communications. It contains the following key points: 1) MIMO systems use multiple antennas at both the transmitter and receiver to enhance performance. This allows for transmitting and receiving multiple data streams simultaneously. 2) There are two main MIMO modes - spatial multiplexing provides throughput/capacity gains by transmitting different data symbols from each transmitter, while space-time block coding provides diversity gains through redundant transmission to improve reliability. 3) The MIMO system can be modeled by a channel matrix relating the transmitted and received signals, where each element represents fading between an antenna pair. Techniques like zero-forcing equalization are used