Andong Zhou’s research while affiliated with University of Arkansas at Fayetteville and other places

Employing massively distributed antennas brings radio access points (RAPs) closer to users, enabling aggressive spectrum reuse that can bridge gaps between the scarce spectrum resource and extremely high connection densities in future wireless systems. Examples include the cloud radio access network (C-RAN), ultradense network (UDN), and cell-free massive multiple-input, multiple-output (CF-mMIMO) systems. These systems are usually designed in the form of fiber wireless communications (FWC), where distributed antennas or RAPs are connected to a central unit (CU) through optical fronthauls. A large number of densely deployed antennas or RAPs require an extensive infrastructure of optical fronthauls. Consequently, the cost, complexity, and power consumption of the network of optical fronthauls may dominate the performance of the entire system. This article provides an overview and outlook on the architecture, modeling, design, and performance of massively distributed antenna systems (DAS) with nonideal optical fronthauls. Complex interactions between optical fronthauls and wireless access links require optimum designs across the optical and wireless domains by jointly exploiting their unique characteristics. It is demonstrated that systems with analog radio-frequency-overfiber (RFoF) links outperform their baseband-overfiber (BBoF) or intermediate-frequency-overfiber (IFoF) counterparts for systems with shorte fiber length and more RAPs, which are all desired properties for future wireless communication systems.

Employing massively distributed antennas brings radio access points (RAPs) closer to users, thus enables aggressive spectrum reuse that can bridge gaps between the scarce spectrum resource and extremely high connection densities in future wireless systems. Examples include cloud radio access network (C-RAN), ultra-dense network (UDN), and cell-free massive multiple-input multiple-output (MIMO) systems. These systems are usually designed in the form of fiber-wireless communications (FWC), where distributed antennas or RAPs are connected to a central unit (CU) through optical front-hauls. A large number of densely deployed antennas or RAPs requires an extensive infrastructure of optical front-hauls. Consequently, the cost, complexity, and power consumption of the network of optical front-hauls may dominate the performance of the entire system. This article provides an overview and outlook on the architecture, modeling, design, and performance of massively distributed antenna systems with non-ideal optical front-hauls. Complex interactions between optical front-hauls and wireless access links require optimum designs across the optical and wireless domains by jointly exploiting their unique characteristics. It is demonstrated that systems with analog radio-frequency-over-fiber (RFoF) links outperform their baseband-over-fiber (BBoF) or intermediate-frequency-over-fiber (IFoF) counterparts for systems with shorter fiber length and more RAPs, which are all desired properties for future wireless communication systems.

This letter develops an optimum beamforming method for downlink transmissions in cell-free massive multiple-input multiple-output (MIMO) systems, which employ a massive number of distributed access points to provide concurrent services to multiple users. The optimum design is formulated as a max-min problem that maximizes the minimum signal-to-interference-plus-noise ratio of all users. It is shown analytically that the problem is quasi-concave, and the optimum solution is obtained with the second-order cone programming. The proposed method identifies the best achievable beamforming performance in cell-free massive MIMO systems. The results can be used as benchmarks for the design of practical low complexity beamformers.

This letter develops an optimum beamforming method for downlink transmissions in cell-free massive multipleinput multiple-output (MIMO) systems, which employ a massive number of distributed access points to provide concurrent services to multiple users. The optimum design is formulated as a max-min problem that maximizes the minimum signal-tointerference- plus-noise ratio of all users. It is shown analytically that the problem is quasi-concave, and the optimum solution is obtained with the second-order cone programming. The proposed method identifies the best achievable beamforming performance in cell-free massive MIMO systems. The results can be used as benchmarks for the design of practical low complexity beamformers.