Abstract
For mobile communication networks, radio spectrum resources have always been a scarce commodity. With the cultivation of millimeter Wave (mmWave) wavelengths, a vast amount of spectrum at frequencies above 24.25 GHz has become available to serve the demands of enhanced mobile broadband services and applications of fifthgeneration of mobile communications (5G). However, the higher carrier frequencies compared with the heretofore allotted spectrum comes with novel challenges for the operation of a cellular network: The more significant propagation losses require directional/ beam antennas and their directivity needs to be adjusted permanently and individually per user. In addition, the poor obstacle penetration necessitates a careful beam alignment based on Line-Of-Sight (LOS) conditions. In case of obstructions, signal reflection paths need to be leveraged, which may be volatile and time-consuming to discover. By means of signal quality measurements, a self-contained beam tracking may maintain the LOS or virtual LOS via reflections to mobile devices. As a further feature, the directional knowledge of the base station antenna beams can even be exploited for a bearing-like localization approach allowing for an enhanced network positioning service compared with cell-level approaches. The sophisticated Software- Defined Radio (SDR)-based mmWave platform allows for the experimental evaluation of the mentioned features. The results prove the potential of mmWave communications for various vehicular and logistics use cases. The lessons learned will go into future research directions such as smart radio environments. The novel technology of Reconfigurable Intelligent Surface (RIS) is a promising strategy for improving the capabilities of the general environment to supply better radio conditions to a wireless channel in non-LOS conditions. For example, a RIS can purposefully redirect the base station’s mmWave pencil beam to reach a device in an obstructed area and thus extend the network coverage. Future integrated, radar-like sensing capabilities of communication networks are expected to operate at mmWave frequencies due to large bandwidth, high directionality, and low multipath features promising high-quality measurements. We show that the channel information of current mmWave systems, beam orientation in particular, already enables novel sensing applications.
