Timing issue?

Hello all,

Yesterday I went out on alimb after reading and reading. I change all our AP’s to the same DL% (80), MaxRange (7mi.), and control slots (4). Since then it looks like we have stabilized some of our larger loaded AP’s (it’s only been 24hrs).

Now the only reason of course I changed the control slot to 4 is because all of our higher pop AP’s need that, well actually only one. But according to some, if all our AP’s are able to hear one another then they all need to be the same, right?

We have 7 AP locations. 2 of those locations use CMM for timing and have 3 AP’s at each site. One of our sites (vertical polarity) have almost 80 customers, so I figured they would need 4 slots. So made the changes, now we have 3 smaller populated AP’s and the customers are dropping like flies unless they are hot and close to the AP.

Additionally all our sites generate sync except the 2 mentioned which use CMM’s.

Any obvious observations on problems would be helpful…


Tim Yarber
RTC Communications

Time all of your additional cell sites. It doesn’t do you any good to have part of your network sync’d and the rest generating its own sync. That would be my starting point. Willing to bet you see a nice improvement afterwards.

So definitely GPS syncing for all the other sites? I was kind of hoping someone would confirm this move. It’s not easy selling an idea to higher ups that really don’t understand it and there not documentation proving it needs to be done other than forums.

It helps to have technical backing when telling the money givers what needs to be done to improve the network.

Technically what’s GPS syncing do compared to generating your own sync that makes it that much more needed?

Thanks in advance!!

OK, we just ordered one Packetflux Parasictic for one of our sites to test. So hopefully we see a difference there after we re-channelize as well.

Basically what GPS sync (along with matching downlink%, control slots and max distance) ensures that all your APs are synced together. They listen for traffic at the same time and they transmit at the same time. This prevents them from stepping on one another when dealing with transmission, ie one AP won’t be transmitting a bunch of data to an SM while another AP close by is listening for data coming in from an SM.

It’s basically a way to almost completely eliminate or mostly mitigate the effects of self-interference (although channel planning still needs to come into play).

I was amazed at the performance difference I saw when I went from generating sync to GPS. We started small and all of our sites were omnis, so generating sync wasn’t such a big deal, but when we had to branch off one of our main POPs to 2 APs is when everything started to get nasty. It’s really worth the investment, especially since it is how the Canopy system was designed to operate.

You need to sync every tower site running @ 900MHz. Having 3 sites on GPS sync and 4 generating sync won’t change much. Having even one AP generating it’s own sync will create self interference within your network.

Once you get everything in sync, you should be able to reduce the number of control slots to 3 or even 2.

At one time our system was similar to yours, we actually linked in-band 900 from main site to slaves. We started out with one site and slowly add additional sites that generated sync.

With that said, there is a reason Motorola says not to do things this way and they are right (along with others whom have posted before me). Do yourself a big favor and buy a CMM Micro for each site. Once we used GPS sync at every site and linked using 5.7 BHs, there was a huge improvement system wide. This allows every component of the network to be sync’d off the same timing pulse.

mh is correct in that timing is needed, however a CMMmicro is overkill for a site with one AP. The syncpipes are fine and at 100 ea aren’t too hard on the budget.