Zigbit Distance

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Hi,

I am currently working on WSN (wireless sensor network) project.

The project will be used within building to link up temperature sensors.

My question is the distance, we are planing to use this within shopping complex (6-story),Sensor will be located in each floor and the final device, will be located in the basement which will receive all the sensor information and give it to SCADA to processes.

Using the amp-ed module, have anyone experience using this for same application.

I am not accepting the wireless to penetrate 6 floors, but at least 2-3 floor is accepted, (floor will have shops or car park)

Any advice will be appreciated.

Regards
M.Pathma

Last Edited: Fri. Oct 16, 2015 - 02:36 PM
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Are you using Zigbit 900 or 2400 ?

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Distance depends on frequency band, antenna design etc. In real life I would expect that everything will work through single concrete wall.

But if your sensors are mains powered then there is no problem. You can make them routers and link to the next one is enough.

NOTE: I no longer actively read this forum. Please ask your question on www.eevblog.com/forum if you want my answer.

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do the math
free space + wall/floor penetration losses versus hardware:

free space loss = 32.44+20log(MHz)+20log(meters)
wall/floor losses are frequency and materials-dependent.
See NIST report.
Example: allow about 2dB per layer of drywall at 2.4GHz, or 4dB per 2-layer wall. Floors vary widely: concrete, wood, etc. Can be 6-20dB. Outside, we have terrain and vegetation. For miles long lings, check Fresnel zone clearances.

Take this loss, then
transmitter power, say, 10dBm (10mW), receiver sensitivity, say, -85dBm, antenna gain if any at each end, less misc. losses. This is your prediction.

Lots of on-line calcualators for this stuff. Some have the math correctly coded.

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Concrete floors, especially parking garages, will have LOTS of rebar. That will really attenuate signals. The only way you will be able to tell is to test it for yourself with real hardware.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Another major consideration for in-building communications is multi-path fading. Can even be more of a problem than attenuation due to absorption. Direct sequence modems such as Zigbee are going to be more susceptable to this problem than frequency hopping modems... might be something to consider.

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802.15.4 (that's the MAC and PHY, not same as network layer=ZigBee) modems/radios/modules - are not vulnerable to indoor multipath. It's because the bandwidth is lower (2MHz) and the symbol period is long, as compared to what we see with 802.11.

The typical indoor multipath delay spread is 55nSec RMS (per ITU).
Also, '15.4 uses QPSK not QAM, so it is far more robust and works at lower SNRs than "broadband". This is all by intent.

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stevech wrote:
802.15.4 (that's the MAC and PHY, not same as network layer=ZigBee) modems/radios/modules - are not vulnerable to indoor multipath. It's because the bandwidth is lower (2MHz) and the symbol period is long, as compared to what we see with 802.11.

The typical indoor multipath delay spread is 55nSec RMS (per ITU).
Also, '15.4 uses QPSK not QAM, so it is far more robust and works at lower SNRs than "broadband". This is all by intent.

I think you might have meant to say that 802.15.4 is not as vulnerable to multipath fading as 802.11? Feel free to point me to a paper/study if I'm wrong here. While narrower channel bandwidth and a less complex modulation scheme are going to be affected less by fading (and have better sensitivity), the problem still exists. This is also a problem with frequency hopping systems. The difference is that a 50+ channel frequency hopper may be able to find usable channels when a direct sequence modem is not able to function any longer. A direct sequence modem pretty much works or it doesn't. In contrast, a frequency hopper's data throughput will start dropping with signal degradation before it stops working.

The reason I equated Zigbee = Direct sequence is because I wasn't aware of any other type. I'm really not that up on Zigbee. Are there FHSS Zigbee modems out there?

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Outdoors, yes, it is not *as* vulnerable. But what I said was
"are not vulnerable to indoor multipath".

Freq. hopping doesn't help mitigate multipath, in my opinion, because the frequency set used has all the freqs. very near one another. What does mitigate outdoor (long delay) multipath is combinational space/time diversity - as in 802.16e (not '16d), and is an OPTION in 802.11, or adaptive equalizers as in DOCSIS cable modems.

ZigBee is the name of one of the many network layer routing options used with 802.15.4 which defines the MAC and PHY but not the network layer.

One can DIY a FHSS with 802.15.4 - simple. But none of the network standards like ZigBee, ISA100.11a, 802.15.5 define and standardize hopping.

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stevech wrote:
Outdoors, yes, it is not *as* vulnerable. But what I said was
"are not vulnerable to indoor multipath".

Freq. hopping doesn't help mitigate multipath, in my opinion, because the frequency set used has all the freqs. very near one another. What does mitigate outdoor (long delay) multipath is combinational space/time diversity - as in 802.16e (not '16d), and is an OPTION in 802.11, or adaptive equalizers as in DOCSIS cable modems.

ZigBee is the name of one of the many network layer routing options used with 802.15.4 which defines the MAC and PHY but not the network layer.

One can DIY a FHSS with 802.15.4 - simple. But none of the network standards like ZigBee, ISA100.11a, 802.15.5 define and standardize hopping.

Hmm... I would certainly be interested to read any papers you might be aware of relating to indoor multipath fading *not* being an issue for 802.15.4 systems.. That certainly goes against everything I have heard/read/experienced. I will keep an open mind here and would be interested in reading any credible information about what you are stating in this regard.

Frequency hopping certainly does combat multipath fading and interference better than DSSS otherwise nobody would even bother with it. By using a narrow portion of the spectrum on any given channel and then spreading it over a wide range of frequencies and over time in a psuedo-random order (frequency and temporal diversity), FHSS is able to find usable portions of the spectrum where a DSSS would be rendered useless by interference/fading. A well designed FHSS system can support links up to 50+ miles from hilltop to hilltop with 1 Watt of conducted power and 6dBi omnis. This while being in close proximity to cell and paging systems.

Here is how I would characterize the advantages of DSSS over FHSS and likely the reasons why it is so prevalent.

DSSS pros:
Very fast sync time, near instantaneous
Higher data rates possible (no blanking time)
Much easier to implement the lower level firmware layers

Thats my take on it.

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To get extra distance i just add routers.

Thanks

Regards

DJ

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Wonder if you could build a router in 2 pieces and use a wire to get the network through the concrete floor.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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You could place a router on both sides, so one router pass data to another one.

I habe manged to get about 500+meters in open area, if i had more space i would have got more. So i presume it could go via a wall, but you can have dedicated routers for that.

DJ

Thanks

Regards

DJ

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Torby wrote:
Wonder if you could build a router in 2 pieces and use a wire to get the network through the concrete floor.

MeshBeans with PCB antenna are able to communicate via 2 walls in industrial building.

That should not be a problem to communicate over single wall.

NOTE: I no longer actively read this forum. Please ask your question on www.eevblog.com/forum if you want my answer.