Enabling Cell-Free Massive MIMO Systems with Wireless mmWave Fronthaul

IEEE Transactions on Wireless Communications, 2022

Umut Demirhan and Ahmed Alkhateeb

Wireless Intelligence Lab, ASU

Can we realize the cell-free massive MIMO gains with wireless fronthaul?

Proposed Architecture: A mmWave CPU provides fronthaul to the different sets of user-centric AP groups via different beamforming vectors. The wireless APs jointly serve their users through a cell-free massive MIMO access channel at sub-6GHz.


Cell-free massive MIMO systems have promising data rate and uniform coverage gains. These systems, however, typically rely on optical fiber based fronthaul for the communication between the central processing unit (CPU) and the distributed access points (APs), which increases the infrastructure cost, leads to high installation time, and limits the deployment flexibility and adaptability. To address these challenges, this paper proposes two architectures for cell-free massive MIMO systems based on wireless fronthaul that is operating at a \textit{higher-band} compared to the access links: (i) A wireless-only fronthaul architecture where the CPU has a wireless fronthaul link to each AP, and (ii) a mixed-fronthaul architecture where the CPU has a wireless link to each cluster of APs that are connected together via optical fibers. These dual-band architectures ensure high-data rate fronthaul and provide high capability to synchronize the distributed APs. Further, the wireless fronthaul reduces the infrastructure cost and installation time, and enhances the flexibility, adaptability, and scalability of the network deployment. To investigate the achievable data rates with the proposed architectures, we formulate the end-to-end data rate optimization problem accounting for the various practical aspects of the fronthaul and access links. Then, we develop a low-complexity yet efficient joint beamforming and resource allocation solution for the proposed architectures based on user-centric AP grouping. With this solution, we show that the proposed architectures can achieve comparable data rates to those obtained with optical fiber-based fronthaul under realistic assumptions on the fronthaul bandwidth, hardware constraints, and deployment scenarios. This highlights a promising path for realizing the cell-free massive MIMO gains in practice while reducing the infrastructure and deployment overhead.


If you want to use the scripts in this page, please cite the following paper:

U. Demirhan and A. Alkhateeb, “Enabling Cell-Free Massive MIMO Systems With Wireless Millimeter Wave Fronthaul,” in IEEE Transactions on Wireless Communications, vol. 21, no. 11, pp. 9482-9496, Nov. 2022, doi: 10.1109/TWC.2022.3177186.

author={Demirhan, Umut and Alkhateeb, Ahmed},
journal={IEEE Transactions on Wireless Communications},
title={Enabling Cell-Free Massive {MIMO} Systems with Wireless Millimeter Wave Fronthaul},