The evolution to denser radio-access networks with small cells in cluttered urban environments has introduced new challenges for microwave backhaul. A direct line of sight does not always exist between nodes, and this creates a need for near- and non-line-of-sight microwave backhaul. Using non-line-of-sight (NLOS) propagation is a proven approach when it comes to building RANs However, deploying high-performance microwave backhaul in places where there is no direct line of sight brings new challenges for network architects. The traditional belief in the telecom industry is that sub-6GHz bands are required to ensure performance for such environments. This article puts that belief to the test, providing general principles, key system parameters and simple engineering guidelines for deploying microwave backhaul using frequency bands above 20GHz. Trials demonstrate that such high-frequency systems can outperform those using sub-6GHz bands - even in locations with no direct line of sight.
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