[MC13213-Zigbee] LQI...how is calculated?

[CecchiSandrone]

Hi all,

I'm working on a project regarding relative distance estimation. What we want is a rough distance estimation in indoor places.
I'm reading the Zigbee 2006 standard and they talk about LQI (Link Quality Indicator) but they don't explain deeply how is calculated. Maybe is the value of this field relative to hardware vendor?

Did anyone get some good results using this value for distance estimation?
Can you advise me about articles or publications to consider?

[AmZig]

Hi ,

According to my little knowledge , you could get more info about LQI from IEEE 802.15.4 . And how its been calculated , if you are using MAC code base then look in file "Data.c ". As , i have used LQI in my project for assosciation between devices. I think from this Data.c file you could get very good idea abt LQI. Here is the code to calculate LQI on Freescale MC13213 boards

oid ConvertLinkQuality(void){
  uint8_t     linkQuality = gpPhyRxData->linkQuality;

  // Recalculate the link quality to conform with other link quality measures
  // Make dynamics of the energy level vary from 0x00-0xff
  if (linkQuality > 190) {
    linkQuality = 190; //190 = -95dBm as floor (translates to 0x00)
  }
  if (linkQuality < 33) {
    linkQuality = 33; //33 = -16.5 dBm as top (saturation)
  }
  linkQuality = 190 - linkQuality; 
  linkQuality = linkQuality + (linkQuality >> 1) + (linkQuality >> 3);
  gpPhyRxData->linkQuality = linkQuality;
}

Regards

Amzig

[CecchiSandrone]

Thanks AmZig, I've found this function. What I want to understand is the relationship between RSS and LQI. If I'm not wrong, ConvertLinkQuality converts RSS (in dBm) to LQi (a value between 00 and FF). In some publications I've found also RSSI (Received Signal Strenght Indicator), are LQI and RSSI the same?
Please clarify this AmZig...thanks!

[AmZig]

Hello Cecchi,

Good question Cecchi   , according to my assumtion , logically they are same . As, LQI is always calculated on the received packet or signal strength , for e.g LQI or MPDU lqi on received packet, and different LQI  of different coordinator in device POS.

[CecchiSandrone]

So they aren't calculated making statistical analysis. They are only numerical a "transformation" of the RSS.

[AmZig]

Hello Cecchi,

I didnt understand you clearly. But i would say that the RSS is a parameter for measuring the range or perfomance from one device to another.So , do the LQI when you are trying to do comparison of devices placed different ranges. This is what i have assumed after my project.

Regards

AmZig.

[bigmac]

Hello Cecchi,

The attached application note (non-Freescale) may be of interest to you.  It describes location detection issues in some detail.

Regards,

Mac

swra0951.pdf

Message Edited by t.dowe on 2009-10-27 12:25 PM

[CecchiSandrone]

I'm a little bit confused guys. I can't understand (if exists ) the difference between LQI contained in Zigbee packets (00 to FF) and RSS (expressed in dBm). Please explain this, thanks.