Thursday, May 24, 2007
More on Moto..
After my recent comments on Motorola Canopy products interfering with other networks operating in unlicensed frequencies I have been asked by several people about more details on this. It seems to be a particular concern now that a number of operators in Ireland claim that they will be rolling out large-scale networks using Motorola Canopy hardware.
Rather that go into a lenghty explanation about the technicalities behind the interference I will just post some of the comments received from WISP's in the US that have experienced this problem in a real live environment:
I was running Trango gear in New Orleans when City Hall decided to start throwing up canopy gear. I tried to get them to work with me but could not. The more they threw up the worse it got. I had no choice but to change everything to canopy. At first I was able to change most of the trango gear to horizontal but then while I was doing that my two competitors were doing the same. Before the City did this all three of us worked together with no problems. The city was using the canopy omni's with no cmm's. They had absolutly no idea what they were doing. It was like putting a loaded gun in a 3 year olds hand. One large wisp that was here decided to call it quits.
Canopy will cause interference to networks that are deployed in the same spectrum, and the same polarity. However, it has to deal with the same environment as everything else. Canopy will not run in horizontal polarity (except for the 900mhz units), so use of H-pol helps a lot if you are in a Canopy environment. Use of non-802.11b equipment helps a lot too, especially 802.11a or g
running in 5 or 10mhz channels. I don't have personal experience with it, but I have heard several stories of Canopy systems taken offline by heavily loaded 802.11a based equipment, especially the Canopy (non-Orthogon) backhauls. It is speculation, but I would venture to say that a heavily populated 802.11a (or g) based system running in 5 or 10mhz channels would do just as much damage to a Canopy deployment as it would receive. I'd really like to see some testing to see what would happen in that situation. As with anything, as long as you keep your signal to noise ratio up,
there are ways to survive.
An example of when I would put my bets on 802.11a over canopy is if there's a high margin 802.11a PTP nearby a canopy PTMP system, but
that's not necessarily a fair stand-off. Nonetheless both system could be 'working' but niether of them would be working very well. Wouldn't it be better to just use the product that is designed for cellular WAN deployments(IE Canopy) and come to an agreement of sync scheduling with everyone else? IMO using dumb TDD equipment for cellular WAN deployment is a losing battle...
the trick is carrier to interfere....The Canopy radios are designed to work with a signal that is 3bB above the interference..i.e...if an 802.11xx signal is -75dBm and your Canopy link has a -71dBm signal..it should work...the 802.11xx radios C/I is 7 or 8dBm I think...6dB or more is significant....
I think this says enough. There is an issue here and it deserves to receive ComReg's attention. However as this equipment operates in an unlicensed spectrum there is no legislative solution to this problem...