On the Effects of Channel Aging in D2D Two-Way Relaying with Space-Constrained Massive MIMO

This paper studies the spectral efficiency (SE) of a space-constrained multi-pair two-way massive multiple-input multiple-output (MIMO) decode-and-forward (DF) relay system with channel aging for device-to-device (D2D) communications in the Internet of Things (IoT) environments. Maximum ratio combining-Maximum ratio transmission (MRC/MRT) processing is employed at the relay and imperfect channel estimation is assumed. With the consideration of the spatial correlation due to insufficiently spaced antennas, and the time correlation due to channel aging, we study the closed-form large-scale approximations of the SE performance. Our analytical studies and performance results demonstrate that a degree of both spatial correlation due to antenna proximity, and time correlation due to channel aging can be tolerated in the massive MIMO regime without significant performance degradation.