An Analog Module for Hybrid Massive MIMO Testbeds Demonstrating Beam Alignment Algorithms

Hybrid analog-digital beamforming for massive MIMO is an important technology for millimeter-wave communication systems. Current experimentation of massive MIMO is based mainly on full digital solutions and in the sub-6 GHz frequency range. The technology for millimeter-wave massive MIMO systems is not yet available to the broad research community. Due to high path loss, sparsity of the channel, and restrictions of the hardware in the millimeter-wave band, new challenges in signal processing arise. One of these problems is the initial link acquisition also called beam alignment (BA). We present a hybrid analog-digital massive MIMO sub-6 GHz testbed with 64 antennas. This testbed enables the investigation of challenges connected to a hybrid analog-digital architecture like the BA problem. We demonstrate multiple BA algorithms to show their advantages and disadvantages. The testbed is based on a self-developed analog module with a high resolution of phase and amplitude settings. Our module can be connected to standard software defined radios (SDRs) and supports different types of hybrid architectures.