In a few years, some U.S. broadband markets could be much more competitive than they are today.

A slew of tech and telecom giants are keen on using high-frequency spectrum bands to drive the rollout of fixed wireless broadband services, via 5G and other radio technologies. The group includes Facebook (FB) , which just announced it's working with Qualcomm (QCOM)  to commercialize its Terragraph fixed-wireless system for urban areas. It also includes Verizon (VZ) , T-Mobile US (TMUS) and Alphabet's (GOOGL) Google Fiber unit.

Fixed wireless still faces major questions related to technical issues such as range, in-building signal strength and potential congestion in high-density urban zones. And even if these issues are addressed, major network rollouts will still likely take a few years and often require using the fiber infrastructures of existing ISPs.

But advances in silicon and radio technologies make fixed wireless far more intriguing as a broadband alternative than it was a decade ago. Factor in the size and resources of its backers, and there are good reasons for investors in cable ISPs such as Comcast (CMCSA) and Charter (CHTR)  to closely monitor its rise. Even if there's no need to panic at this point.

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