MIMO signal processing - the next frontier for capacity enhancement

Traditionally, enhancements to the capacity of single-user communication channels have been achieved by either increasing the baud rate (which leads to larger bandwidths) or by increasing the signal constellation size (which requires higher signal-to-noise ratios). Since bandwidth is a limited resource in both wireless and copper-wired communication systems, new signal processing techniques based on the MIMO (multiple-input multiple-output) principle are emerging that exploit the spatial dimension for increasing the channel capacity. In a MIMO system, information is sent synchronously on multiple transmitters and collected on multiple receivers, with the fundamental assumption that the multiple transmitted signals interfere linearly in the transmission medium. In this paper, we examine the application of MIMO techniques to three practical communication systems that are pushing the capacity envelope: (a) wireless LANs, (b) copper-wired LANs, and (c) ADSL in the local loop. For these applications, MIMO techniques offer the potential to scale data throughputs linearly, that would not be possible to achieve otherwise.