Spherical Wave Channel and Analysis for Large Linear Array in LoS Conditions

Massive MIMO is considered a key technology for the future wireless communication systems. The promising properties in terms of higher spectral and transmit-energy efficiency are brought by the large number of antennas at the base station(BS). As the number of antennas increases, the aperture of the BS antenna array may become much larger, as compared to today´s antenna arrays. In this case, mobile stations (MSs) and significant scatterers can locate inside the Rayleigh distance of large arrays, and spherical wavefronts rather than planar wavefronts are experienced over the arrays. In this paper, we propose an analytical spherical-wave channel model for large linear arrays, which is also compatible with conventional planewave models. Based on the spherical- wave model, we investigate how MSs can be spatially separated in simple line-of-sight (LoS) scenarios. The results theoretically explain the observation in experiments that spherical wavefronts help decorrelate the MS channels more effectively than planar wavefronts.