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Extension to question: Zigbee communication outdoors at long distance ( around 1 - 1.5 km)

I was wanting to set up communication between controllers around the school campus, originally I plan to go for Zigbee, however, due to it's limit in transmission distance, I was not able to imply it to my project (My project requires a transmission distance of 1-1.5km).

However, recently I came across an article, which shows that XBee communication can go up to 10km ! And according to here(3), XBee is actually based on ZigBee. So question 1: is it true that XBee can go up to 10km transmission distance? would it be practical to use on ground? (altitude depended?)

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  • \$\begingroup\$ [3]: sparkfun.com/pages/xbee_guide [4]: sparkfun.com/products/retired/10918 \$\endgroup\$ – MW_hk Apr 11 '14 at 3:24
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    \$\begingroup\$ You write as if ZigBee and XBee are two different technologies. Isn't ZigBee just a protocol specification and XBee an actual radio module using the ZigBee protocol? I haven't head of XBee going over 1-2km (which is already XBee Pro with increased transmission power if I remember correctly). We are using that in a project for communication between stations on a camp ground, but only with several hundred meters between each module. \$\endgroup\$ – Rev1.0 Apr 11 '14 at 7:35
  • \$\begingroup\$ Like any RF communications system, "range" is chiefly dependent on signal-to-noise ratio. A directional antenna, low interference, and good line of sight can get up to 10km on ZigBee, but whether or not you'll be able to do this in your actual application will require math. \$\endgroup\$ – Peter Apr 11 '14 at 8:41
  • \$\begingroup\$ Can't you just set up a mesh network and throw a few routers in between? zigbee.org/Specifications/ZigBee/NetworkTopology.aspx \$\endgroup\$ – Black-Pixel Apr 11 '14 at 10:50
  • \$\begingroup\$ How about the power? then I'll need power for every router. Maintenance would be a hard job.... ( provided the amount of controller would increase......) \$\endgroup\$ – MW_hk Apr 11 '14 at 14:48
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All the clues are in the answer linked to in your question. Here's a recap: -

  • Using minimum data rate (20kbps) you need a theoretical power at the receiver of -111dBm
  • Free space link loss at 10km is 120dB (use the formula - I've used 10km and 2.45GHz)
  • If output power from transmitter is +10 dBm, receiver power is -110dBm

That's almost a perfect match and remember this is almost equivalent to a free space set-up because the plane is high. Also, the ground antenna used has a gain of 14dB, so now the set-up is 15 dB better than free-space theoretical.

Also, I believe zigbees can be used at lower frequencies than 2.45GHz, something around 1GHz and if so, this adds another 8dB improvement so now we have a theoretical margin of about 23 dB. There isn't enough info in the article about the plane to determine this.

On the ground, this is not reliably possible (as explained in my linked answer), but as a one-off experiment where the transmitter (plane) never went out of site of the receiver this was clearly possible.

EDIT

If you look at the specification of Xbee Pro (the one used by the guy flying the plane), it's operating frequency was 900MHz and if you check on page 7 it can transmit at +24dBm and use a bit rate of 10kbps.

All these little things, when thrown into the pot can make a difference between a usable system and a system that will never work. It's a fight (for sure) and you need to use every scrap of advantage you can grab when making a reliable radio link.

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  • \$\begingroup\$ Thanks. Yes, I'd guess that plane example was close to "clear space".... How about power line carrier? any info/ experience on that? \$\endgroup\$ – MW_hk Apr 11 '14 at 14:49
  • \$\begingroup\$ Powerline transmission - I doubt if it could go from building to building because of the way power can be distributed on 3-phase systems. However, there may be some research that can show it does. However, getting a km is very unlikely due to the nature of AC wiring systems. \$\endgroup\$ – Andy aka Apr 11 '14 at 15:26

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