Plane wave against spherical wave assumption for non-uniform linear massive MIMO array structures in LOS condition

The massive capacity and connectivity requirements of the fifth generation (5G) wireless communication systems, have motivated the application of hundreds of antenna elements at the base station (BS). This kind of system known as massive multiple-input multiple-output (MIMO), offers a huge spectral and energy efficiency against traditional wireless communication techniques. As the number of antennas increases significantly in massive MIMO systems, the previous MIMO channel models will not be valid longer. One of the main issues is that the planar wavefront assumption cannot be considered over the massive MIMO arrays while spherical wavefronts are experienced. In this paper, the channel matrix of a multi-user (MU) massive MIMO system is derived for both the plane wave and spherical wave assumptions in the line-of-sight (LOS) condition, where the base station (BS) is equipped with a large non-uniform linear array of antennas. This non-uniformity causes to increase the orthogonality between sub-channels and the rank of the channel matrix. The obtained channel capacities are investigated by some simulation results.