Max-Min Rate of Cell-Free Massive MIMO Uplink with Optimal Uniform Quantization

Manijeh Bashar (1) , Kanapathippillai Cumanan (1) , Alister Burr (1) , Hien Quoc Ngo (2) , Merouane Debbah (3) , Pei Xiao (4)

1 University of York [York, UK]
2 BESC - Belfast e-Science Centre [Belfast]
3 L2S - Laboratoire des signaux et systèmes
4 Institute for Communication Systems [University of Surrey]

Cell-free Massive multiple-input multiple-output (MIMO) is considered, where distributed access points (APs) multiply the received signal by the conjugate of the estimated channel, and send back a quantized version of this weighted signal to a central processing unit (CPU). For the first time, we present a performance comparison between the case of perfect fronthaul links, the case when the quantized version of the estimated channel and the quantized signal are available at the CPU, and the case when only the quantized weighted signal is available at the CPU. The Bussgang decomposition is used to model the effect of quantization. The max-min problem is studied, where the minimum rate is maximized with the power and fronthaul capacity constraints. To deal with the non-convex problem, the original problem is decomposed into two sub-problems (referred to as receiver filter design and power allocation). Geometric programming (GP) is exploited to solve the power allocation problem whereas a generalized eigenvalue problem is solved to design the receiver filter. An iterative scheme is developed and the optimality of the proposed algorithm is proved through uplink-downlink duality. A user assignment algorithm is proposed which significantly improves the performance. Numerical results demonstrate the superiority of the proposed schemes.

Keywords: Cell-free Massive MIMO; generalized eigenvalue; geometric programming; limited fronthaul

Domains: Signal and Image processing; Networking and Internet Architecture [cs.NI]

Manijeh Bashar, Kanapathippillai Cumanan, Alister Burr, Hien Quoc Ngo, Merouane Debbah, et al.. Max-Min Rate of Cell-Free Massive MIMO Uplink with Optimal Uniform Quantization. IEEE Transactions on Communications, 2019, 67 (10), pp.6796-6815. ⟨10.1109/TCOMM.2019.2926706⟩. ⟨hal-02904777⟩