Mining Borer Wireless Connectivity

See this?

When I started working in mining, all of the mines I worked with were using Cisco APs mounted on the borer to facilitate a network connection to the less mobile equipment. The root of the link is usually the end of an extensible conveyor belt, and the PLCs controlling the belt communicate with the PLCs on the borer. There are things like safety interlocks which shut down the belt if the communication is interrupted. The extensible belt root AP is also uplinked to the rest of the mine network.

The Cisco bridges worked reasonably well at reasonable distances. On the bright side, EIRP was not a concern since we were far enough underground to prevent any sort of radiation into the open atmosphere, so very high gain antennas were standard operating procedure. I tried to find a pic, but just think parabolic dish.
But the borer moves away from the extensible as it does its work. We’re talking thousands of feet, and the cuts that the borer makes don’t stay level over the entire cut – so LoS is not maintained. On one hand, hard rock does an alright job bouncing signal along. On the other, throughput and data rate still faded quickly.

Can’t pull fiber and power in behind a borer – it will need to come back out the way it went in, and moving heavy machinery makes that idea asking for trouble. So ….

Yes, that IS two 1242 APs in a NEMA enclosure with back to back patch antennas, forming a repeater; AND I’m happy to see you!

It worked. No channel reuse (sorry Keith) because it was more important for unskilled miners to be able to move and install them with zero config. The entire set of root, repeaters and end bridge are hard coded to the same frequency.

Oh and if you could see to the ground in that picture, you’d find a car battery and some alligator clips. Fancy.

And yes that’s repeaters plural. The borer just got that far away. Sometimes it goes around a corner and then you need a repeater too.

So it’s not surprising to know that throughput was… not great. When VoIP was first brought out to the borers, we had a problem with the PLC interlock between the borer and the extensible belt dropping anytime someone picked up the phone. Neither the PLC interlock nor the VoIP call required much bandwidth, but there was enough latency or loss to starve the interlock, and VoIP tends to get prioritized by default. We had to do a little QoS reservation for the PLCs to keep them running at the expense of the calls.

So a year or two ago the instrumentation guys on site started playing with these:

This is a Ubiquiti PowerBridge M3. 3.5GHz licensed frequency? No problem – we’re thousands of meters underground! That’s a 20dBi integrated panel antenna, and a 2 SS radio.They use a root AP with a 26dBi antenna, and 12dBi repeaters, if necessary (sorry, I neglected to record the antenna specs on the Cisco gear when we installed them years back).

The results were rather stunning. At distances without repeaters, they can maintain near 100Mbps. With repeaters, they stay stable at distances of six to eight thousand feet without LoS due to elevation change. In the particular set I checked recently, the bridge was operating at the 32.5Mbps data rate (not throughput) over a 5Mhz wide channel, with 25dBm output power on the borer AP (100Mbps data rate was at 20MHz channel widths). The root has a 26dBi antenna, and the repeaters 12dBi. I didn’t have a chance to grab the models and power settings on those though.

Just for fun, here’s an idea of the perspective of the borer AP:


So these are significant (though unquantified) improvements from the 1242 and 1310 Cisco bridges. Had I thought to keep specs from then, perhaps I would have been able to provide more than just anecdotal commentary. But there are a few points that make it clear we’re not making an apples to apples comparison:

  • 3Ghz is not Wi-Fi At a rough level, it also goes farther with less loss.
  • 5Mhz wide channels are also not Wi-Fi. While there are some benefits to narrower channels being a little more robust against interference, interference generally isn’t a concern in this environment
  • Ubiquiti isn’t exactly known for playing by the rules in general. There are some proprietary enhancements at play – the data sheet for the M3 lists it as a MIMO TDMA protocol device

I’m no Ubiquiti fan. I know their gear is a lower quality hardware, and that they’ve caused some trouble in the unlicensed space. But that’s not the point.

This is a unique environment. Disposable hardware is favoured – service contracts are less useful here, so spares are kept on the shelf for quick deployment, which means low cost is a bonus. Performance is priority, and we’re not constrained by the rules of the surface world.

The engineers and technicians on site like a lot of things about the Ubiquiti bridges, including the simple (yet effective) GUI, and the physical signal strength indicators on the bridge, which simplify aiming.

In the end, I guess it comes back to designing for requirements. Each solution may shine or fail horribly in different scenarios.

I’m not the most experienced Wi-Fi engineer, but I’m learning, and I found this an interesting educational experience. I am curious to hear what the more experienced member of the Wi-Fi community think about Ubiquiti and their place in these less traditional deployments.


2 thoughts on “Mining Borer Wireless Connectivity

  1. Hey Brennan, this is a good and very interesting post. I just have a few points about the Ubiquiti gear.

    All their AirMax stuff, which includes the PowerBridges, is based on some sort of 802.11 chipset (I’m not sure which exactly, want to say Atheros). The 3.5 GHz and 3.65 GHz gear is downconverted from 5 GHz. They do use their own proprietary AirMax protocol, which indeed is TDMA. So in the beginning, it was Wi-Fi. You can even disable the AirMax protocol and run it as straight 802.11n gear. But really, you get better performance with TDMA, especially in such an isolated environment. It just isn’t as polite a protocol as 802.11 with CSMA/CA. I’m pretty sure anything in the AirFiber line is proprietary silicon.

    In a typical WISP setup, I usually say use only as much spectrum as you need to get the throughout you require, where your radio allows narrow channels. I like to call that spectrum politeness. That involves a properly designed link with good received signal level, appropriate fade margin and high modulation rate. In a mine with little to no concern for frequency reuse or spectrum politeness, I’d say blast away at 20 MHz, or more depending on the situation. You get higher throughput at lower signal levels, though I’m not sure if latency would be affected… I want to say it should be lower because increased throughput should equal more available airtime.

    I’m going to play devil’s advocate a little bit here and say that while Ubiquiti certainly didn’t lock down their firmware in the past, the onus should be on the system planner and/or installer to play by the rules put in place by the regulatory body for the region as far as channel selection and power levels go.

    I do agree with you that the Ubiquiti AirMax line is not, strictly speaking, Wi-Fi; but it is wireless networking, and has it’s place in certain projects. I believe a good WLAN pro should know what options are available to them and, as you said, design to the requirements.

    Thanks for the very interesting post, and for sharing your experience!


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