my project is about rail track fault detection and interstation distance is around 10-12kms. Sensor data need to be send to nearby stations and is it possible to do this with ZigBee module?
\$\begingroup\$
\$\endgroup\$
8
-
\$\begingroup\$ With a directional antenna properly matched to a powerful enough transmitter, probably. Might run into some legal trouble though. \$\endgroup\$– MastCommented Jan 30, 2017 at 6:52
-
\$\begingroup\$ @Mast what are the most common communication methods? For a project I want to make use of IR . But it simply doesn't pass through walls and the like. I need to communicate over 10m long. Can you suggest a more reliable way of doing that? \$\endgroup\$– dirac16Commented Jan 30, 2017 at 7:23
-
1\$\begingroup\$ @dirac16 My bad. In that case, I'd stick to Wi-Fi or Bluetooth, depending on the rest of your requirements. Bluetooth at 10m will likely fail if the walls are made out of concrete or similar though, you might want to get yourself a development kit with both technologies (a recent version of Bluetooth and Wi-Fi) on it to test (plenty of such boards available nowadays). \$\endgroup\$– MastCommented Jan 30, 2017 at 7:40
-
5\$\begingroup\$ @Dirac - you should start your own question rather than asking in the comments of this one. \$\endgroup\$– JRECommented Jan 30, 2017 at 7:45
-
3\$\begingroup\$ Do not use the rails to send signals, they are already used für Train Protections Systems, at least in some countries. If you hit the right frequencies, you can stop all trains in the vicinity. \$\endgroup\$– ChristianCommented Jan 30, 2017 at 8:26
|
Show 3 more comments
3 Answers
\$\begingroup\$
\$\endgroup\$
The trouble with Zigbee (XBee and Xbee pro) is that devices like this are intended for fairly high data rates and this limits the receiver sensitivity. This means you have to transmit more power to get a certain distance compared to a naturally low-speed data rate system whose receiver has much more band limiting and therefore can cut out more noise. A general rule of thumb for the power needed by a receiver is this: -
Power required in dBm is -154dBm + 10\$log_{10}\$(data rate) dBm
So, if the data rate is 1000 bits per second, the receiver power needed at the antenna is -124 dBm. Zigbee has a receiver sensitivity of about -100 dBm and this implies data rates of about 250 kbps i.e. a lot faster but speed isn't needed for this application.
How much further can the extra 24 dB get you?
The generally accepted formula for link loss is this: -
Link Loss (dB) = 32.4 + 20\$log_{10}\$(F) + 20\$log_{10}\$(d)
where F is MHz and d is distance between the two antennas (kilometres).
At 1 GHz and 1000 metres, link loss is 92.4 dB. At 10 km, link loss is 112.4 dB so clearly an extra 24 dB in receiver sensitivity is going to yield a working distance that is over 10 times greater.
Having said all that I would seriously look at sharing the existing telephony facilities that exists between rail stations. It's not a great big problem to modulate the data up to 100 kHz and superimpose this on the cables used for telephony. It's rather like how broadband hi-jacks the telephone copper but simpler. You get the added bonus of a system that cannot be easily hacked or interfered with.
answered Jan 30, 2017 at 11:33
\$\begingroup\$
\$\endgroup\$
The wikipedia page, citing the ZigBee specficiation claims:
Outdoors with line-of-sight, range may be up to 1500 m depending on power output and environmental characteristics. The output power of the radios is generally 0-20 dBm (1-100 mW).
It's likely your range could improve with further amplifation on transmitter and receiver side, but at that point you may be exceeding the legal limits for transmission power in that unlicensed frequency band.
That's point-to-point, however. If you could guarantee you had a node fairly regularly then the mesh capability of ZigBee could potentially pass your data much further.
\$\begingroup\$
\$\endgroup\$
I think if you build your network as mix network using x bee and Lo Ra you can gain good range for your project.
