MIMO Explained

Multiple Input Multiple Output, or MIMO for short, seems to make it into every wireless radio technology today from Wifi to WiMAX, HSPA+ and LTE. Yes, we know that it requires multiple antennas at the transmitter and the receiver and offers to multiply throughput by sending an individual data stream over each antenna in the same frequency band. But just how can the receivers at the other end separate the two data streams again as they have combined in the air to something completely incomprehensible!? National Instruments has a great introduction to MIMO on their web page which describes this in simple terms with just the right amount of maths that it is still understandable for someone out of college for a decade or more and who hasn't touched maths since  :-)