Range of RSSI Value

jieyang · **Joined:** Wed Aug 31, 2011 11:56 am **Posts:** 41

Hi,

I use ZigBee Pro and I have questions about RSSI value.

What range of value is good? What range of value is bad and have potential to lose communication?

In my project, RSSI value around 75 is the worst one which I can get. Is it the worst value for communication?

libelium-dev · **Joined:** Mon Sep 28, 2009 1:06 pm **Posts:** 7818

Dear jieyang,

Let us quote from a Digi datasheet, the description of the command used to get RSSI.

Quote:

DB (Received Signal Strength) Command
<Diagnostics> DB parameter is used to read the
received signal strength (in dBm) of the last RF
packet received. Reported values are accurate
between -40 dBm and the RF module's receiver
sensitivity.
AT Command: ATDB
Parameter Range [read-only]: 
0x17-0x5C (XBee), 0x24-0x64 (XBee-PRO)
Absolute values are reported. For example: 0x58 = -88 dBm (decimal). If no packets have been
received (since last reset, power cycle or sleep event), “0” will be reported.

Check the specific datasheet for your module to get exact values.

We can tell you that usually goes from -40dBm (good) to -90dBm (poor).

Kind regards.

jieyang · **Joined:** Wed Aug 31, 2011 11:56 am **Posts:** 41

Thank you very much.

In my project, some nodes with RSSI value around 70 lose connection frequently. Could you tell me some potential reasons? Because according to your saying, 70 should be not such bad.

Regards

ghorbel · **Joined:** Mon Dec 12, 2011 1:20 pm **Posts:** 27

Hi
Can you post your code to discuss it...

Best Regard
Ghorbel

jieyang · **Joined:** Wed Aug 31, 2011 11:56 am **Posts:** 41

ghorbel wrote:

Can you post your code to discuss it...

Sorry for the delay, because I was in holiday. I think the problem is not in the code, because when I use AT command ND on XBee directly (bypass my code), I can not find the nodes with 70 RSSI value for all of time. Therefore, I think this should be the problem with hardware or communication interference. However, this is just my hypothesis, how do you think?

Regards,
Jie

libelium-dev · **Joined:** Mon Sep 28, 2009 1:06 pm **Posts:** 7818

Dear jieyang,

When a hw problem occurs, it happens in one of the items (or few of them). If you are experiencing the same effect in all the nodes, it is not probable it is a hw problem; it is just the normal behaviour.

We do not believe it is a hardware problem. RSSI is not a static value, it varies much. We mean you probably got the motes around -75 dBm, but they have poorer RSSI sometimes, below the receiver's sensibility so the link cannot be set.

Anyway, Xbee's RSSI value is not very exact, it is just an aid the user has. The correct way to measure RSSI would be with accurate laboratory intruments.

One of the best thing of WSN is that you can place intermediate nodes when there is too much distance. This can be the solution for you.

Best regards

jieyang · **Joined:** Wed Aug 31, 2011 11:56 am **Posts:** 41

libelium-dev wrote:

We do not believe it is a hardware problem. RSSI is not a static value

Dear,

Thank you very much for your help, and it makes sense to me.