Re: [uracoli-devel] Question regarding LQI and ED values [Update]

[Axel Wachtler]

Hi Eric,

at first thanks for the positive feedback. But if there are things to 
improve, please let us also know about it.

On 28.08.2012 05:00, Eric Jennings wrote:

> One, my LQI is almost always at 255 but ED is at 0.  Once in a while
> LQI kicks down to 240, or 215, and once in a while to something like
> 116.  I figure this is just noise or whatever.  But why is ED always
> at 0?  I read the blogpost regarding LQI/ED relationships:
> (http://uracoli.blogspot.com/2010/05/playing-
> with-xmplradiorange.html), but I'm curious why I can't seem to get a
> positive number for the ED value?

This question is asked very many people. So ED=0 means that the frame
that you received was at a level at or below -90dBm
(see RSSI_BASE_VALUE in the data sheet). LQI=255 simply means that is
was perfectly correlated. Since the receiver can receive frames down to
a level of -100dBm, the pair ED=0 and LQI=255 is an often seen pair.

If you move the boards closer together, then you will definitely see
higher ED values (0 ... 0x53) (see also section 9.5.4 Energy Detection
(ED) of the ATmega128RFA1 data sheet.)

> Two, about one in 20 times or so, as I'm pinging the end node, I'll
> get an "ERR ping timeout".  Is this typical for the LQI/ED values I'm 
> seeing?

As you tell below, the boards are 40ft / 12m away in a building. I guess 
that there are people and things (e.g. doors) are moving during
the day. Probably WLAN/WiFi is also active. So this can may cause
temporary interruptions of the RF link.
this moving objects can cause fadings and

> In working through the random dropped pings, I was digging through the
> data sheet and came across the XTAL_MODE setting, to turn off the
> internal oscillator if using an external oscillator.  I gave it a shot,
> disabling the internal osc.

Did you change the value of XTAL_MODE from 0xf to 0x4?

> Now I get 100% ping response!
Could this result be time dependent and more correlated with
the presence of people and traffic in the rooms?

> Correlation, not sure it's causation yet, but I'm very happy.
> The two radio boards are about 40 feet away from each other, one
> in a room on the second story, and the other down in the basement
> surrounded by concrete.

> I'm quite pleased, despite the negative reviews I read about the Sparkfun dev 
> boards being of poor RF design.

Could it be, that sparkfun took the critics and did a rework of the board?

If you like, you can post the board abstractions that you have made and
we can add the sparkfun permanently to the source tree (I don't have one
here, to cross check it).

Best Regards, Axel