Modal analysis of MIMO capacity in a hallway

Systems with multiple element transmitter and receiver arrays have been shown to achieve very high spectral efficiencies. This is especially important in wireless applications that are power, bandwidth and complexity limited. The achievable capacity depends on the channel between the transmitters and the receivers, and a common assumption is that of a rich scattering environment. However an environment such as a hallway is more closely approximated as a waveguide, and we look into the limitations this poses on the achievable rates. We first show that the number of allowable propagation modes in a lossless waveguide limits the number of equivalent spatial sub-channels. We then apply a similar analysis to a lossy waveguide, where the losses are due to imperfectly conducting boundaries and imperfections in the dielectric. For demonstration purposes we show these effects for a waveguide of small dimensions. A hallway, which is a more practical environment for wireless applications, can be treated as an overmoded waveguide. In a hallway the losses are higher because the boundaries are dielectric materials that allow high power leakage. We again demonstrate the above effects, taking into account the losses off the walls