Multi-antenna systems can provide improvements in wireless systems increasing spectral efficiency, reliability, range, and system capacity. Herein we show how some of the potentials of MIMO systems can be realized on a simple radio hardware platform by utilizing advanced real-time signal processing and coding. We present a real-time implementation of a 2 by 2 MIMO system employing spatial multiplexing to achieve high spectral efficiency in an indoor non-line-of-sight environment operating in the 1800 MHz range. Well-known processing and coding techniques are employed and our contributions lie in: discussing implementational aspects and solutions often overlooked but critical for high-performance operation; demonstrating the degree to which the simple baseband AWGN model can be used to accurately model/predict the MIMO system on the current hardware; and demonstrating the feasibility of real-time spatial multiplexing achieving up to 15 bps/Hz on a 2 by 2 system in a realistic indoor environment with off-the-shelf radio hardware.