MIMO channel measurements for urban military applications

This paper presents results from a measurement campaign that was conducted to characterize the multiple input multiple output (MIMO) channel characteristics in a low-rise urban environment in the military UHF frequency band. Data were collected in Baltimore, Maryland using a 2times3 MIMO testbed in June 2007. Testing consisted of transmitting orthogonal channel probes from a stationary transmit test van and using a mobile receive van that collected data while traveling through predetermined routes in the city. Data were collected on both straight line-of-sight (LOS) paths and on L-shaped routes that involved turning onto a perpendicular street that was not within LOS of the transmitter. Statistics of the fading were characterized and found to exhibit Ricean behavior in LOS regions and Rayleigh statistics in non-LOS regions. The channel transfer matrix was computed based on measured data and used to infer the MIMO communications channel capacity as a function of distance from the transmitter and antenna spacing. The measured capacity was compared to the theoretical capacity of a 2times3 reference system with a stationary channel. These comparisons show that MIMO processing is capable of increasing the capacity by a factor of 1.3 to 1.8 relative to the reference system. Results are also presented that show capacity is insensitive to antenna spacing down to a minimum spacing of 0.25lambda for the conditions encountered in this study.