Passive Passing
Typical Values
-40dBm for a very close by Transponder
-80dBm for a barely detected Transponder
Active TrackPing
Typical Values
-40dBm or better, for a transponder very close by
-90dBm for a barely detected transponder
Data Reduction Algorithm
To reduce the amount of data, the TrackBox does the following with each TrackPing it receives:
- If transponder unknown, create a new entry in internal short term list with minRSSI=peakRSSI both set to the first RSSI received
- If transponder known and new RSSI < minRSSI -> overwrite minRSSI and minDiffTime
- If transponder known and new RSSI >= peakRSSI -> overwrite peakRSSI (+ update all other Data like flags, index and location)
Every second the short term list is searched for entries where (neither minRSSI, nor peakRSSI have been updated within the last 10s) OR (which have been recorded for 30s or more). Those entries are taken off the short term list and stored in the internal buffer for further transmission to server.
Goal: Detect and report every minimum and every maximum while not transmitting more data than necessary.
Typical Data of a slow passing resulting in 3 calls (with each a min an max value, giving us 6 values in total):
TrackPing RSSI vs Distance
Important: RSSI is a very very rough measure for distance. Local effects around the transponder let it vary significantly. A weaker RSSI does NOT AUTOMATICALLY MEAN, that the transponder is far away.
But: A strong RSSI does mean, that the transponder must be close by. A very rough calulation for maximum distance based on RSSI can be done with this graph:
Example. If a RSSI of -57dBm is reported, it is very likely that the transponder is within 10m or closer.