Performance Evaluation of LoS MIMO Microwave Radio Systems Over Frequency Selective Multipath Fading Channels

Although spectrally efficient microwave LoS-MIMO (Line of Sight-Multiple Input Multiple Output) systems seem to be practically attractive mainly at higher frequency bands (above 15 GHz), also at lower frequency bands, where frequency selective multipath fading is the dominant impairment for the outage time, they could play a significant role. Under this perspective, the paper analyzes performance of LoS-MIMO systems affected by frequency selective fading, taking into account the necessary equalization for satisfying the outage objectives. For the purpose of the analysis, we adopted a frequency selective 2×2 LoS-MIMO channel model extrapolated from the 2-ray model historically used in SISO (Single Input Single Output) systems and, exploiting the full statistical behaviour of the propagation channel model, we described a methodology for the evaluation of frequency selective LoS-MIMO outage performance. Then the proposed methodology is used to investigate the effectiveness of equalization in the intersymbol and mutual interference reduction of two equalizer structures, linear MMSE and MMSE Partial Response, using as a practical reference the target outage probability predicted on the same link for a SISO system. Finally, it is discussed the opportunity of using the Condition Number of the LoS-MIMO channel matrix transfer function as an exhaustive indicator of the channel quality.