Does a Large Array Aperture Pay Off in Line-Of-Sight Massive MIMO?

Massive multiple-input multiple-output (MIMO) is considered a promising PHY scheme for future mobile communications systems. As it aims to serve many users simultaneously via spatial multiplexing, a high number of antennas at the base station is required. Since this leads to implementation issues in terms of hardware and signal processing complexity, efforts to increase the system performance for a given number of antennas are worthwhile. In this contribution, we investigate the gain in achievable downlink sum spectral efficiency (SE) of a massive MIMO system due to increased array apertures. We compare different antenna array configurations and precoder normalization strategies for maximum ratio transmission precoding and regularized zero forcing precoding. By quantifying the increase in achievable SE that is obtained when increasing the inter-antenna spacing of a linear array, we show that it hardly pays off to increase the array aperture.