On the outage performance of line-of-sight massive MIMO with a fixed-length uniform linear sparse array

Increasing the inter-element spacing of a uniform linear sparse array results in reducing the mutual coupling and simplifying the heat dissipation control of the array. However, increasing the inter-element spacing may result in the appearance of grating lobes in the field-of-view (FoV). In this paper, 0.05-outage capacity is used as the performance metric to optimize the inter-element spacing for a given array size in line-of-sight scenarios. For the case of two users, we propose to increase the inter-element spacing as long as the 0.05-outage capacity does not reduce more than 1% compared to the capacity achieved when the two users have orthogonal channel vectors. Radiated power at the base station is adjusted to have the same effective isotropic radiated power for different arrays. Simulation results for an array size of 40λ show that for FoVs of 60° to 120°, the inter-element spacing can be increased from 0.5λ to more than 1.14λ.