[Imported] Video Stream on 900 MHz vs 2.4 GHz license-free radio

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>>Message imported from previous forum - Category:Trio Data Radios<<
User: joelw, originally posted: 2018-10-17 23:00:46 Id:125
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.

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**_Rjshull56:
I'm hoping Joel or someone with some knowledge and experience can explain this to me. I've searched high and low for a clear explanation..._**

**_1) I understand that 2.4GHz has a higher bandwidth than 900MHz, more oscillations at a higher frequency. But the J 2.4GHz only has a data rate of up to 256kbps and the Trio J 900 has 512kbps. (Ignore distance and losses and all that for now). Does that technically mean that the 900MHz can do more data faster than a 2.4GHz radio? It would seem that bps wise the 900 is faster but if the 2.4 has a higher frequency should the data rate not be higher? How is that possible? How exactly does this work? Why is 2.4 recommended for video streams etc.
2) How does this translate to Ethernet? Speeds of Ethernet are up in Gigs now but even if I plug it into a 10Meg connection how does that equate to baud rate? Does the Video stream transmit only as quickly as the Trio radio port can pick it up? Does it just lower the quality to match the 256kps again would the quality not be higher at 500kbps?
Any explanation, literature, links, phone calls, anything to help me clarify this would be greatly appreciated!
Thanks for your time,_**

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jweder:
Hi Robert,

Feel free to call our Sales Support or Tech Support team any time to get more immediate clarification of any issue. (or me if you can catch me in the office) Their number is 1-888-226-6876.

The 2.4 GHz version of the Trio J Series radio in fact does NOT have a higher bandwidth than the 900 MHz version. Both radios have a 382 kHz channel bandwidth. The 2.4 GHz version simply has more channels to play with, as that band is wider than the 900 MHz band. The frequency a signal is sent on does not itself relate to the maximum data rate. That is more directly related to the channel bandwidth. Some competitor products have far wider bandwidth eg 600 kHz or even several MHz in some cases.

However it was found by our engineers that the 2.4 GHz version cannot operate at the higher 512 kbps radio data rate without suffering a much higher degredation in receiver sensitivity than the 900 MHz version. (internal circuitry issues) As a result they disabled the 512 kbps speed in that version of the radio. A bit disappointing yes, but I'm sure in the next generation of the radio they'll work out some improvement.

Neither Schneider nor Trio recommends our 2.4 GHz radio for video as far as I know. Some companies may do so because they sell a product (with wider bandwidth than J Series) that can talk faster on that band. The 900 band has 26 MHz to play with, while the 2.4 band has about 85 MHz of room. So theoretically you can have channel bandwidths that are much wider, to push more data through.

Only problem with the wider channel bandwidth that some companies provide is that it means a lower resistance to interference, and that the available power is spread over a wider range of frequencies. This combination means the maximum range (distance) is going to be significantly less than J Series. We don't aim J Series at the video market, but rather at the SCADA / Telemetry market, which benefits from the ability to go farther (or push thru more obstacles) reliably.

If a high bit rate application such as a video stream (eg at 1 Mbps) is connected to a Trio J Series radio configured for eg 256 kbps, there will be trouble. The radio can only transmit at a certain speed, so its internal transmit buffer memory will quickly overflow and the ethernet connection will suffer. There will be gridlock on the channel as a result. It is thus critical to manage the channel by providing no more data than the radio can handle.

It is worth noting that none of our direct competitors are capable of handling a high bit rate video stream any better than J Series. To do this you need typically a direct sequence type spread spectrum radio rather than frequency hopping. Eg a WiFi or WiMax type device. (typically fairly short range) We do work with a Partner company called Redline Communications that can provide industrial grade (better than WiMax) products for very high data rate applications. Feel free to give them a call.

The attached informal document summarizes some testing I did a few years ago with J Series radios and a security camera.

Attached file: (editor/zj/0s843nh9u9g4.pdf), Network Camera Over J Series.pdf File size: 279309

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>>Responses imported from previous forum

Reply From User: joelw, posted: 2018-10-17 23:02:07
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.

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**_Robzilla56:
I wrote this original post and I'm back for more questions. We did end up using a 900 Trio J with a camera successfully at 256kbps. No problems,
Now my question becomes technical. Several engineers we work for are trying to push for radios with high data rates and more channels etc. I understand that we get more distance out of the Trios because they are designed that way.
The part I can't explain to them or myself is what "factor" or "value" can be used to demonstrate that yes your getting high data rates but you can't achieve the distance we need.
Specifically if I were to put two radios into Pathloss there has to be something to demonstrate that the advertised data rates are not the best solution over long distances.
For example someone recently handed me a spec with a GE MDS Orbit advertising 1250kbps with 80 channels bandwidth 1320kHz with a sesitivity 1x10-6 of -95db. How can I say thats only effective over this distance due to this. And what "factor" or value in pathloss would show this loss or degradation over a long distance.
I know I'm not a radio expert but I think you will understand what I'm asking. Thanks!_**

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jweder:
There are several parameters that combine to make a radio suitable for long-distance use. We take all of these into account when testing a link for reliability using our Pathloss software.

1) Frequency - Lower frequencies lose less signal over a given distance than higher frequencies. For example a radio operating at 455 MHz will lose 6 dB less than a radio operating at 910 MHz. (double the frequency) This 6 dB reduction cuts the maximum range of a system by 50%, unless higher gain antennas are used or taller towers (to eliminate obstacles) or both.

2) Transmit Power Limit - Luckily in the USA, the FCC allows the same EIRP (effective isotropic radiated power) in both the 900 MHz and 2.4 GHz bands. In much of the world the 2.4 GHz band is far more limited. (and 900 is not available at all in many of these places) More power is always good! (but this does NOT mean you should install an amplifier! Such things can often do more harm than good)

3) Channel Bandwidth - A wider channel (required by radios running at higher data rates) is inevitably going to allow more noise & interference through to the receiver, in addition to the desired signal. In noisy environments this can require the engineered receive signal levels to be much higher than in quiet locations.

4) Receiver Sensitivity - Radios with higher bandwidth typically require more complex modulation types. These normally have lower sensitivity than narrower-bandwidth modulation types. A 6 dB reduction in sensitivity will cut the maximum distance in half. A 12 dB reduction cuts it to 1/4!

If you want to talk far at moderate data rates, then a radio like a Trio is a good solution. If you want to talk a short distance at very high data rates, maybe you'll be looking at WiFi or similar. If you need to transmit a high bandwidth signal a long distance that can be done, but it must be managed carefully. We find the MDS Orbit and similar radios tend to "fall apart" under situations with more than a little interference or on longer paths.

It is very important to understand the data rate that you REALLY need. Eg do you need to send live high resolution video? Or can you reduce the frame rate and resolution, and add some compression, to bring the bandwidth requirement down?

One other thing that can often be done in modern cameras is to run a first-in-first-out buffer that lasts maybe a minute. Set the camera up to trigger an alarm (sent over the SCADA system) if a problem is detected. That alarm triggers the camera to save a file which can be downloaded later.

If the requirement, after all analysis, truly does require high bandwidth, long distance and reliability I suggest you contact Redline Communications. They are a partner of Schneider, and can provide high quality solutions at up to 80 Mbps.