To deal with the explosive increase of mobile data traffic, the fifth generation (5G) communications system has come at the forefront of wireless communications theoretical research . Two main approaches in 5G are massive antennas and dense deployments of access points, which lead to the massive multiple‐input multiple‐output (MIMO) and small cell techniques .
Massive MIMO employs hundreds of antenna elements at the base station (BS) to serve tens of users simultaneously at the same time‐frequency resource block (RB) [3–5]. The large size of transmit antenna array not only significantly increases the capacity with excessive spatial dimensions [6–9] but also averages out the effect of fast channel fading and provides extremely sharp beamforming concentrated into small areas [ 3,4]. Aside from these, the huge degrees‐of‐freedom offered by massive MIMO can also reduce the transmit power .
On the other track, a small cell improves the system capacity by densely deploying low‐power access points into traditional high‐power macrocells [ 2,11]. In this fashion, the distance between the transmitter and receiver can be significantly ...