Optimized Uplink Transmission for C-RAN with Hybrid Analog-digital Beamforming and Resolution-adaptive ADCs

Abstract

In this paper, we consider the uplink in a cloud radio access network, where analog-beamforming and resolution- adaptive ADCs are adopted at each the network remote radio heads (RRH) with large number of antennas. To maximize the minimum uplink signal-to-interference-plus-noise ratio over all users, the transmit power at the users, the analog beamforming and the quantization bit allocation at each RRH, and the digital beamforming at the baseband processing unit are jointly optimized. Specifically, we consider a limited fronthaul capacity and per-user power constraint as well as the modulus constraint on the analog beamforming elements. The analog combiner for an RF chain is designed to maximize the effective channel gain of the selected user while reducing the inter-user interference in a distributed manner at each RRH. For a given analog combiner, the user power, quantization bit allocation at each RRH, and the digital beamforming are jointly designed via an alternating optimization technique. Numerical results show the resulting significant performance advantage of the proposed scheme.