Diversity and directivity tradeoff in indoor 60 GHz MIMO channels: A case study with dual-polarized hybrid planar antenna arrays

The channel capacity of indoor 60 GHz radio is studied in this work from the diversity and the directivity viewpoints of multiple input multiple output (MIMO) wireless systems. To characterize the diversity and directivity (DnD) tradeoff of using planar antenna arrays (PAA) in indoor 60 GHz channels, a hybrid architecture for dual-polarized PAA (DP-PAA) is employed to exploit the potential advantages between the two extremes of this DnD tradeoff. A DP-PAA under this hybrid architecture can either be configured to apply the spatial multiplexing (SM) gain of MIMO channel diversity, or to enhance the array gain with beamforming directivity. Furthermore, the polarization diversity of DP-PAA can provide the system with a minimum degree of SM gain and compensate the coverage hole of a single-polarized PAA. Through theoretical investigations and numerical simulations, we show that the indoor 60 GHz channel of using a hybrid DP-PAA pair at both the transmitter and the receiver can approximately be modeled as a Kronecker MIMO channel. In addition, using the directivity of DP-PAA can lead to a higher channel capacity than using its spatial diversity under FCC´s 40 dBm equivalent isotropically radiated power limit for indoor unlicensed 60 GHz links. This prevents the use of expensive high-dimensional MIMO to improve the channel capacity of indoor 60 GHz radio.