Design Considerations for Over-Water Microwave Radio Links - A Case Study

Arabian Gulf region with its hot, humid and prolonged summer is known to be one of the most challenging environments for radio-wave propagation. Over-the-sea microwave radio links here face degradation and unpredictability in performance due to anomalous propagation, ducting and reflective effects of large water bodies. This paper presents microwave radio link design challenges in an offshore environment and the methods implemented to overcome these challenges in the context of specific project experience in offshore field areas. A baseline design for the links was established initially which was optimized during the course of the project and during on-site implementation. Several design changes to achieve the desired performance were evaluated and implemented in the field. Required microwave link availability and performance objectives were achieved as a result of collaborative efforts between the operating company, contractor and radio manufacturer over a multi-year period. Use of quadruple diversity, optimal selection of frequencies, judicious use of ATPC (Automatic Transmit Power Control) and use of optimal signal polarisation were some of the methods used to achieve the desired link availability and performance. While these are well-known methods in radio engineering, the particular combination(s) employed to realize the desired performance objectives are identified in the paper as a lessons-learnt exercise which can be of wider application in the petroleum industry in the Gulf region. Over-water wideband microwave links are generally considered unreliable in terms of performance for utilization in process control applications involving remote shutdown and other critical operations. However, the links referred to in this paper continue to serve the field control system applications till date.