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Fixed Wireless Equipment

Bridging the Wide-Open Spaces

More and more, WISPs are circumventing wire-line backhaul—either because it's not available, or because it's easier or cheaper to do it with RF. New equipment is helping make this a reality.

[July 29, 2003]

On ISP-Wireless last March, LC mused about a challenging long-hop installation he was contemplating:

"Is a link over 60 miles and four hops between NOC and CPE sustainable?

I am trying to expand my wireless coverage into an area about 60 miles away from our present NOC. One of the four links that will make up the backhaul is a point-to-point (PtP) 36 mile link between two 300 foot towers on small mountains.

I have researched using convertered 2.4GHz transmitting over the air between two 38dBi 4-foot 5.8GHz dishes using Karlnet Turbocell. Fresnel zone and System Operating Margin calculations look okay. If the SNR on the PtP links are 17-22dB can I expect a useable, stable link? With two long (20-mile-plus) hops and two short hops between the central office and the CPE is this something that is do-able?"

[MV (a representative of Redline Communications) advised] "When distances get long, and multiple hops are required, you need too look at more than just link budget.

For a 36-mile hop at 5.8 GHz you need to add a serious amount of fade margin to allow for such effects as refraction.

For multiple hops the impact of latency will become critical.

I can tell you that Redline's AN-50 is being used in many multi-hop long-range backhaul applications. It can handle four hops, and 36-mile hops. The latency will likely still be under 10 ms even with four hops. It uses dynamic modulation so that it will give you the best available speed at any time, but ramp up to more robust modulation when link conditions deteriorate."

[KD expanded on this] "Both Redline and Alvarion provide excellent equipment probably capable of doing the job for you. Without knowing more specifics about your situation it is difficult to comment.

Another possibility might be using Lonnie [Nunweiler]'s Star-OS equipment. I don't think he supports 5 GHz but I understand his equipment can reliably provide wireless links at those ranges using 2.4 GHz band.

[BD responded with a testimonial] "We will have several Redline links put in this summer of 20-plus miles or more.

The only improvement that Redline could make in performance, IMO, is to make the control box fit in a smaller cabinet. Especially for a remote repeater site, this is a must. Oh, and an "N" connector on the ODU would be good too.

Other than that, it does wonderful things!"

[MV responded to this aside] "For those who requested the upgrade to an N connector, you will be happy to know that effective immediately we are shipping a new ODU revision with an N connector instead of the SMA connector.

[BD enthused] That is cool. It is so hard to turn an SMA connector on anything when it is cold out and you are hanging on a tower with the wind slamming you. Did I mention cold?

[MS, joining the main thread, priced out the job] "Should be fine. PtP links of 20 miles should be a walk in the park.

Or if you've got a bit of a budget you could easily drop in several megs in one hop if you could get the antennas high enough. For two 30-mile shots we should be able to deliver 30 megs for less than $50,000 including equipment install on towers."

[CC jumped all over this proposal] "$50k for two 30-mile 30 Mbps links? I will happily do two 36 Mbps links, install and everything, for half that."

[MS cheerfully responded] "Sure, if there is only a need for 36 Mbps delivered, towers to work from, etc.

I'd rather start too high and be able to come down than to lowball everything than sneak extra fees in all the time.

But we really don't have all the info needed to price this out correctly. Your numbers are probably pretty realistic—if there are existing structures to work from that aren't already flooded with 5 Ghz equipment."

[SS added one final data point] "It's going to be a hard one to field, depending on what speeds you'd like. I have done a 74-mile Redline with 2-foot panels but it was on a reduced modulation and it was very mountain top, minimal if not any fresnel from a hill along the path. That was not a normal thing, or one that I have seen used often. Just the other day we did a "pool shot" or reflective trajectory shot and gained over 24 Mbps without tweaking the antennas.

Redline calls that "normal" though ;-)"

—End