Blokkadebestendige mmWave Communicatiesystemen via ISAC en Multipuntconnectiviteit

The increasing demand for high data rates and low-latency communication is driving the growth of millimeter-wave (mmWave) communication, which offers a vast bandwidth that supports applications like high-definition video streaming, augmented/virtual reality (AR/VR), telemedicine, and autonomous driving. Despite this advantage, mmWave communication faces significant challenges due to higher propagation losses compared to legacy sub-6 GHz bands. To compensate for these losses, directive beamforming is required. Unfortunately, the reliance on directive beams makes the system susceptible to blockage. Human activities, such as walking or standing in the vicinity of mmWave link, can cause significant signal attenuation and prolonged shadowing, leading to degraded received signal levels and communication interruptions. This thesis aims to improve the robustness of mmWave communication against human blockage through two following approaches: Blockage prediction via integrated sensing and communication (ISAC) and Link redundancy via mmWave multi-point connectivity networks. The first approach corresponds to the proactive approach to detect the potential human blockage, such that the system can take a measure to mitigate the blockage before affecting the communication link. The latter approach relies on the link redundancy employing multiple serving access points to deal with the blockage, avoiding the single-link failure. In the context of blockage prediction via ISAC, our main focus is on expanding sensing coverage to enable early blockage detection, addressing the challenge posed by the limited illumination of directive mmWave communication beams. This method jointly utilises communication-centric waveforms and phased-arrays, configured in both bistatic and monostatic sensing modes, to enable simultaneous communication and sensing. To this end, we propose a novel concept termed guard beam(s), which are additional beams steered alongside the main communication beam. These beams expand the sensing field of view, focusing towards the surroundings of mmWave communication link to it against the obstruction caused by approaching blockers. The use of RSS-based guard beams in a bistatic sensing scenario demonstrates its effectiveness in extending the receiver's field of view beyond the coverage of the directive communication beam. Measurement results further confirm that this method enables the early detection of an approaching blocker before it obstructs the communication beam. In a monostatic sensing scenario, ISAC-based guard beams expands the sensing coverage beyond the directive communication beam's range without the need for full environmental scanning. Additionally, the optimised design of guard beams successfully maintains the communication performance by balancing array resource allocation between communication and sensing. In the context of link redundancy to alleviate the blockage impact, we investigate the effectiveness of mmWave multi-point connectivity networks. Our experimental findings demonstrate that one or more beam pairs often remain unaffected by blockages, highlighting the link redundancy advantages of this approach. Furthermore, we analysed the spectral efficiency losses caused by blockages, providing insights into the number of access points required in a service cluster to achieve significant spectral efficiency benefits, even in blockage scenarios. In addition to blockage resilience, this thesis explores other critical aspects of multi-point connectivity, including user association and beam misalignment caused by user movement. An effective beam training method is proposed to significantly reduce the overhead and energy consumption during user association, particularly in densely deployed mmWave cell-free networks. Furthermore, the robustness of multi-point connectivity is assessed under dynamic conditions through the use case of a mmWave VR application, characterised by frequent and rapid user movements. Our proposed dual-beam reception for the mmWave head-mounted display (HMD) proves effective in reducing outage rates caused by misalignments during head movements. The experimental study further demonstrated the benefits of increased access point separation and a locally distributed subarray on the HMD in improving angular coverage during head rotations. Finally, to ensure seamless beam transitions during misalignments, a predictive beam transition method is proposed, enabling accurate prediction of future beams and preventing signal degradation caused by delayed transitions.