4G: Can't Stand the Rain

Time to tune into the Weather Channel: Meteorological and other natural conditions are likely to dampen the spirits of WiMax network engineers that plan to deploy microwave backhaul links.

That's because common weather conditions, such as rain, can affect the performance of the high-speed wireless connections.

Sprint Corp. (NYSE: S) and Clearwire LLC (Nasdaq: CLWR) have been vocal recently about the cost and bandwidth benefits of using high-speed microwave links as part of their planned mobile WiMax deployment. Backhaul vendor Proxim Wireless Corp. says the pair aren't the only operators interested in microwave. (See Clearwire's Backhaul Bet.)

"There's a huge amount of drive and interest in microwave," says Geoff Smith, VP of marketing and business development at Proxim. "Operators just need more bandwidth with the increased downloads over 3G networks -- it's only going to get worse with 4G."

Smith says Proxim's Tsunami "wireless Ethernet" GX bridges are designed to deliver up to 200 Mbit/s over a 20 mile range. "You can get them up to 30 miles if you get them up high," he adds.

Sprint is working with FiberTower Corp. to build its microwave links. Clearwire is said to be working with a variety of suppliers but will get access to Sprint's cell towers as the current deployment efforts get rolled into the "new" Clearwire venture by the end of 2008.

But like WiMax, Microwave backhaul has a couple of issues with which veteran wireless hands are very familiar, the most crucial being that microwave links have metro-area line-of-sight range constraints.

And those line-of-sight issues must be addressed at the network design stage. "For any microwave solution, if you're shooting it through the trees you need to design that with summer-time in mind so you allow for maximum leaf-coverage," comments Smith.

In addition, microwave links can also be adversely affected when it rains, a condition known in the industry as "rain fade." At higher frequencies, the radio signal can get progressively attenuated by fog, rain, ice, or snow in the air. Operators can get around this to a degree by automatically increasing system gain at the site.

That's an issue that hampered many of the free space optics "wireless laser" startups that emerged around the turn of the century: To an even greater extent than the microwave firms, they struggled with the issue of rain interfering with their wireless signals. (See The Infrared Solution.)

Nonetheless, microwave technology represents one of the only serious options for this new age of broadband wireless backhaul, unless operators invest in lots of fiber. As Clearwire CTO John Saw told Unstrung last week, "A couple of T1s just isn't good enough anymore."

— Dan Jones, Site Editor, Unstrung

dluechtefeld 12/5/2012 | 3:40:23 PM
re: 4G: Can't Stand the Rain I can assure readers that the CLWR's RF engineers are all familiar the basics of link budgeting, thankyouverymuch.
joset01 12/5/2012 | 3:40:22 PM
re: 4G: Can't Stand the Rain Surely

I'm not sure that everyone that reads this site is though, I thought it was a good time to reintroduce these topics.

lrmobile_ranavital 12/5/2012 | 3:40:16 PM
re: 4G: Can't Stand the Rain Please note there are new high capacity radios out there with 6-8 steps of ACM (Adaptive Coding & Modulation)that allow service provider to Flex the RF network planning constraints. Not only increasing the capacity on every given spectrum, but also improving availability, especially in rain conditions.
See Webinar http://www.lightreading.com/we...

lrmobile_kumaramitabh 12/5/2012 | 3:40:08 PM
re: 4G: Can't Stand the Rain While WiMAX itself is a robust technology and can stand atmospheric degradations quite well owing to its adaptive modulation featires, the same can not be said of its backhaul links, which are usually in much higher frequency bands such as 30/40 Ghz.

However it is not entirely true that the backhauls should get ruined by rain, particularly as they are usually designed to operate in a mest confuration and where possible in a multimodal configuration ( fiber+ Microwave).

A well designed backhaul network ought to keep working without difficulties in all weather conditions.

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