RIS Aided Cell-Free Massive MIMO System with Wireless Fronthaul

Cell-free (CF) massive multiple input multiple output (MIMO) system exhibits great potential in terms of achievable rate and coverage, however, the high infrastructure construction cost of CF system makes it difficult to deploy on wireless communication devices. To this end, the wireless fronthaul based CF system is considered. Motivated by the benefit of overcoming “multiplicative fading” and low hardware cost, an active reconfigurable intelligent surface (ARIS) aided CF massive MIMO system with wireless fronthaul is proposed, in which part of access point (AP) is replaced by ARIS and each AP works in dual-band to guarantee high data rate of fronthaul. The feasibility of replacing AP with ARIS is demonstrated. Then, a problem of maximizing the minimum (max-min) user achievable rate is formulated and a joint precoding and discrete ARIS phase design algorithm with low computation complexity is provided. Finally, simulation results verify that the proposed ARIS-aided CF system can enhance the minimum user achievable rate with more flexible wireless fronthaul.