UAVs‐Assisted Low‐Bit Quantized CF‐mMIMO Systems With MmWave Communications Under MRC Detection

ABSTRACT The cell‐free massive multiple input multiple output (CF‐mMIMO) approach, due to its high coverage and the ability to attenuate the large‐scale fading impacts in wireless communications, has drawn a lot of attention. Additionally, because of their movement ability, low power, and low‐cost employed infrastructures, unmanned aerial vehicles (UAVs) are considered a promising technology to provide service on demand in various applications, deployed as either base stations (BSs) or user equipment (UEs). This paper considers a UAV‐equipped CF‐mMIMO wireless network, assuming millimetre‐wave (mmWave) connections between UAV‐BSs and ground users. Leveraging the additive quantisation noise model (AQNM), closed‐form expressions for the uplink data rate and energy efficiency (EE) under maximum ratio combining (MRC) detection are obtained. The impacts of effective parameters, including the UAV's altitude, the number of antennas, and the resolution of analogue‐to‐digital converters (ADCs), on system performance are investigated. Simulation results demonstrate that EE can be optimised for these factors to achieve the maximum value. In addition, the optimal number of quantisation bits to maximise EE is based on the number of antennas and the height of the UAVs. Comparing analytical results with accurate ones shows the accuracy of our approximations due to the same trend of variations.