Exploiting multiple antennas in maritime radio channels

Reliable maritime communication systems are essential for both safety-critical operations and emerging applications such as autonomous shipping, remote pilotage, and drone-assisted search and rescue. These scenarios demand ultra-reliable, low-latency wireless connectivity, where communication outages are unacceptable. Equally important is the need for dependable positioning systems. In situations where GNSS (Global Navigation Satellite System) signals are unreliable, a robust backup positioning solution is essential. Recent wireless technology trends, such as massive multiple-input multiple-output (MIMO) in fifth-generation (5G) and distributed MIMO in future sixth-generation (6G) networks, involve the deployment of large-scale antenna arrays to enhance reliability and capacity. Inspired by these developments, this thesis investigates the use of multiple antennas in maritime radio channels to improve both communication reliability and positioning capability. The investigation focuses on sea surface fading mitigation and ranging, supported by both theoretical analysis and real-world measurements. A high-performance wideband distributed massive MIMO channel sounder operating in the 5 GHz band was developed to support this research. The sounder is also well-suited for broader 6G research, including distributed MIMO and joint communication and sensing. The thesis demonstrates that deploying multiple antennas, particularly in vertical configu-rations, yields significant advantages for maritime wireless systems. Through a combination of analytical modeling and empirical measurements, it shows that vertical antenna arrays can effectively mitigate deep fading caused by sea surface reflections. Closed-form expressions based on the two-ray model are derived to identify optimal antenna spacing and array configurations and to provide practical design insights. Experimental validation in open-sea environments confirms that even arrays of only three elements can enhance link reliability by up to 15 dB. Furthermore, the two-ray model is extended to enable GNSS-independent ranging between vessels and base stations on land without requiring time synchronization, achieving sub-10-meter accuracy with eight vertically distributed antennas, offering a viable independent positioning method.