A New Point-to-Point Bridge, Some Impressive Numbers

Point-to-Point bridges are a fascinating part of wireless networking. As I’ve written about before, both in this blog and for Network Computing Magazine, I have designed and installed a number of links through the years. The rooftop work isn’t my primary gig, but I frequently design, align, troubleshoot, and occasionally install this incredibly enabling technology.

Even if you don’t work on wireless bridge links, it’ easy to appreciate the notion of making network where there is none, and pushing respectable bandwidth through the air thousands of feet, or dozens of miles.

I recently got wind of Cambium Networks, a company that specializes in the bridging side of wireless. Cambium is worth getting to know if you are looking around for bridging alternatives for point-to-point, point-to-multipoint, and other topologies.

Cambium has recently released their latest PTP model, the PTP 650. So what? New bridges get released fairly frequently from lots of companies, right? I found myself hooked by the range claims associated with the PTP 650.

From the release:

 PTP 650 shines in harsh environments: It is able to transmit up to 120 miles (193 kilometers) over water and desert and from ship to shore, and platform to ship. It is the most reliable NLOS (non-line-of-sight) wireless broadband solution on the market for well field automation.

There was quite a more to the PR, and it’s all impressive enough.  The PTP 650 works between 4.9 and 6 GHz, at a variety of channel widths and with different modulation types that can deliver up to 450 Mbps throughput for under $5K. That’s the condensed version. But if you know anything about bridging, anything that claims to go 120 miles wirelessly bares investigation. Lets look at that rate-versus-range thing.

Lot’s of wireless bridge makers provide “link calculators” which help designers know what to expect as they plan new installations. How far can you go with a given hardware set and still get the throughput you’re after? Here’s Cambium’s Link Planner. To cut to it- here’s what Cambium told me when I asked what the 650 could do at different lengths (without external antennas, using the built-ins)-

Example: Line of Sight; 5.8GHz spectrum; integrated 23dBi antenna; 45MHz channel bandwidth
 
Range (miles)
Maximum Aggregate Capacity
10
370 Mbps
25
220 Mbps
50
150 Mbps
100
45 Mbps

To me, this is impressive, as 45 Mbps is still a fairly beefy connection depending on what’s on the other end. At the same time, I can’t imagine trying to align a 100 mile link!

Having never used Cambium products or software, I’m not endorsing the PTP 650 here, but can appreciate what it’s out to solve (even a couple miles can be difficult at alignment time).

6 thoughts on “A New Point-to-Point Bridge, Some Impressive Numbers

  1. Veli-Pekka Ketonen

    Yes, that’s pretty impressive!

    An interesting follow up calculation is that what is the required tower height for line-of-sight over 193 km (120 miles) distance.

    This calculator below calculates that both antennas would have to be at 550m (1800 feet) elevation. This does not include additional Fresnel zone requirements (the required extra clearance for line-of-sight millimeter wave links).
    http://www.calculatoredge.com/electronics/lineofsight.htm

    Given these promises, 5-6 GHz frequencies still need to bend sufficiently due to layers in atmosphere to achieve this distance. These conditions also likely introduce quite a bit of fading that needs to be considered for reliable radio link hop, especially when trying to operate over this kind of distance. Most likely rain, heavy clouds, leaves in the trees (if not over the water), reflections from possible ice during winter and other similar conditions clearly impact on performance.

    Downloaded the calculator already. Did not yet calculate how tall radio towers are required for 120 miles link according to that. It’s would be interesting to compare this number to line-of-sight requirement.

    Would be nice to see how performance varies over time (from seconds to seasons) in practice.

    Reply
    1. wirednot Post author

      I was thinking the tower in this equation would have to be pretty ridiculous. Also, I do know that higher-gain antenna options are available, for what it’s worth. I can’t imagine what would be left of a sub- 6 GHz wavefront after this many miles, but Cambium must be delivering on their promises as they seem to be doing fairly well.

      Reply
  2. A

    You know it’s ex-Motorola’s Wireless Broadband division, right?
    This stuff is pretty good, many of it evolved from military development.
    Pity they failed to integrate it with WLAN offering, as promised initially.

    Reply
    1. wirednot Post author

      I did know that, and find it odd that they gave up Moto’s well-known handle for a new name nobody has heard of. I did not know there was a promised WLAN integration.

      Reply
  3. Pingback: Wireless Field Day 8 Takes “Wireless” Up a Notch | wirednot

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