Monday, September 26, 2011
In the last blog, I wrote something about how far the DECT signals typically go. There are two scenarios, where the base station cannot cover the area. The first one is in large buildings, for example hospitals or hotels where you need to install several base stations to cover it all, and potentially also a DECT handover if you don’t want to loose the call when walking down the stairs from one floor to another. The second scenario is where you need a “booster” that juts extends the reach of the signal, and in that case you would use a DECT repeater.
As the name suggests, what the repeater does is to repeat the signal. This is not “boosting” the signal, because the signal strength of the repeater is similar to the strength of the base station. It just repeats the signal, so that the traffic that occurs in one timeslot will be copied into another timeslot, so that the base can talk through the repeater to the handset. For example, if you have a long hallway, this is a simple and elegant solution to provide good signal strength everywhere. The repeater works from the handset point of view like a handover solution, because when the handset goes from one end of the hallway to the other, it will eventually perform a handover somewhere in the middle.
You can also add multiple repeaters to a base station. However, there are limits. First of all, because the number of timeslots is limited and they overlap to a certain extent, your timeslots will be eventually full and that’s it. The other problem is that once you have too many repeaters, you are increase the total jitter in the system, possibly to the degree that the whole system becomes instable and then calls drop like flies when you use that bug killer spray. I don’t know what exactly the limits are, but I would be conservative with the number of repeaters that you can safely add to the system. If you need 16 repeaters to cover your area, you probably need another solution and also you probably need more than the 4 concurrent calls that you can have with the m9.
The other problem is encryption. Because many vendors have come up with their own encryption protocols, you cannot connect any repeater to any base station. You have to either turn encryption off or you have to use a pair of base and repeater that use the same encryption protocol. For the snom m9, we have added a special version that deals with the problem (this will be called “snom m9r”, as the name suggest this has something to do with the repeater).
The ultimate goal is to have a system where you can handover from one base to another, without the need of repeaters. Right now, such systems are available; but with a hefty price tag. In many cases one or two properly set-up repeaters can solve the problem as well and the whole solution is cheaper and easier to install.