Power levels?


I understand what different power levels mean. At least to the point where if its to high its not good and vise versa.

My question for the community is, whats the technical reasoning behind the power level? In other words, whats it really mean? :slight_smile:

I am just starting out at an ISP and have been given the task of over seeing our WWAN network. Well at least over seeing troubleshooting connection issues which I’m finding very interesting if there is nothing wrong with the hardware…

On top of power levels any other information or advise would be great. Although I am learning alot on these forums.


Couple things-

Noise floor: this is the power level of the noise around you in your spectrum. Near or below this point the radio will have trouble differentiating between a signal and noise.

Fade margin: amount of “breathing” room between your noise floor and your signal level. Canopy technically needs only 3db of fade to maintain a link, however most of us try to maintain at least 10db of fade margin.

Let’s say you’re running a 900MHz system. Your noise floor is around -80db. What this means is in order to maintain a stable link to Canopy spec your signal would at least need to be -77db. If your noise floor is around -70db (getting pretty noisy) you’d need a signal of -67db.

Wireless signals will fluctuate throughout the day, month and year depending on environment and weather conditions. The more fade margin you give yourself, the more it will take to cause the link to drop which ultimately means more uptime.

Whenever you’re checking signal levels, always check both the SM and the AP. You can check the SM power level (RSSI) through the web interface. To check the signal level for the SM on the AP, log into the AP’s web interface and go to the Sessions page. The power level (again RSSI) will be listed in the entry for the SM.

My personal advice is familiarize yourself with the Canopy software as best you can using the user guide and/or Canopy training. Also, this forum has been invaluable for me as a lot of great advice is always available. We’re always here to help. :smiley:

The manual is your best resource for gaining a fundamental understanding of Canopy. I highly recommend it.

Thanks for the info wifiguy, really appreciate it.

Btw I’m going to have a ton of questions now regarding your reply, sorry if I seem so uninformed.

First thing I need to know I suppose is how do I determine our Noise Floor?

Do we just make up a number and go with it or is there a tool on the AP/SM that will help determine this?

Also am I getting this straight, the higher the number the better?
so -72 would be worse then -77?

Thanks again and sorry for the neophyte questions.


I will definitly get to craken on the manual, thanks :slight_smile:

You determine the noise floor by doing a spectrum analysis of your broadcast site. Canopy equipment includes a built in spectrum analyzer. What you would do is bring your access point up to where you would likely broadcast from, switch it to an SM through through the web interface and use the spectrum analyzer tool to get a basic baseline for what you’re working with. The shorter the lines in the spectrum analyzer, the better.

As for the signal levels, if your noise floor was -80, a -72 signal on the SM would be better than a -77 signal. Reason being you have more fade margin. 80 minus 72 is 8, whereas 80 minus 77 is 3. You have some wiggle room with the 8db fade margin where the 3db fade margin has no wiggle room before it loses connectivity. So in general, the lower the number the better (ignoring the minus sign).

Keep in mind you can also have signal levels that are too high. a -45 for instance is pretty hot for any wireless link.

You’ll want to do some searching through the forum on RF level balancing on your access points to get some more insight on why this is.

OK, I believe i’m understanding it better now.

Correct me if iI’m wrong.

If we find that an AP has a Noise Floor of -80dbm, then any SM connecting to that should have a power level of -77dbm (-3dbm rule of thumb) or less or it will become a very unstable connection… If that SM lets say runs alot higher, like -82dbm then it would definitly need to be reaimed/repositioned or all together tell the customer it isn’t going to work out. Would that be a true statement?

Initially you mentioned power level (RSSI). Does this mean that on the SM the RSSI is in direct relation to the power level?

As in, compared to my noise floor at the AP (lets say -70dbm) I have a really good power level at the SM (like-58dbm) that would equal a good RSSI reading no matter what?

ok, enough questions I need to find a manual and start reading :slight_smile:

http://motorola.motowi4solutions.com/so ... 736a196890

Just to make sure you understand, we’re dealing in negative numbers here. In other words, -80 is LESS than -77. -70 is 10 dB MORE than -80. It can be confusing to get used to, but you’ll adapt quickly.

Absolutely read the manual, it’s big, but well written and you’ll find new things every time you read it.

Also, once you’ve got an understanding of power levels, here’s how to put that knowledge to good use.

Jerry, you ought to get a royalty every time one of us links to this post!

PayPal to jrichardson-at-aircloud-dot-com :slight_smile: