On Field Measurements and Modelling of 2x2 Microwave LOS-MIMO Systems

This paper presents channel measurements and preliminary analyses from three 2x2 microwave Line-of-Sight Multi-Input Multi-Output (LOS-MIMO) outdoor test links, operating on 8 GHz and 32 GHz. The main focus is to study channel conditions and the effects of rain and clear-air fading. First, we address the diverse performance measures used in the trials. In particular we introduce the MIMO phase difference as an additional channel metric to the received power. The MIMO phase difference is mainly determined by antenna positions, ground effects and atmospheric variations. The relation between antenna positions and channel conditions was addressed in a number of earlier works, while the atmospheric impact and the resulting link availability are rarely studied. Second, we present the preliminary results from the long-term measurement campaign. The long-term statistics of channel condition from the three links show stable performance. Analysis reveals that fluctuation of the phase difference and the channel condition number is likely due to abnormal atmospheric propagation which can be modelled using a two-ray reflection model. Meanwhile, rain attenuation is strongly correlated between MIMO sub-channels and its contribution to the long-term statistics of power loss is very close to the Single-Input Single-Output (SISO) case.