User Manual

PLUS System Manual System Installation 49
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Figure 2-45: Tag Statistics
Pull down the Select Tag box to select the ID of the Tag you wish to monitor. Click the Reset
button, and allow statistics to accumulate. The received statistics for each Reader in the system can
then be observed.
For a Tag in a given location, the nearest Readers are most significant in calculating a position. The close-by
Readers should show good statistics. Tag statistics observed on Readers that are far away will show low signal
strength and throughput.
Click on the RX% to sort RX% high to low, or low to high. Click on the Reader column to sort the Readers by
name.
For the Readers that are closest to the Tag being observed, check that the Received Signal Strength
Indicator (RSSI) is adequate. RSSI values of 100 or higher are best for calculating a good position.
The Received and Dropped columns show the number of Tag packets that were received or dropped
by a given Reader. The percentage of packets that were received correctly is shown in the RX%
column. Higher confidence locations will result when the RX% is 80% or higher.
2.6.3 Time Difference of Arrival (TDOA) Statistics
When a Reader receives a Tag transmission, it calculates an accurate timestamp to mark the time at
which the packet arrives. A single timestamp is called the Time of Arrival (TOA) for that packet.
When two timestamps generated by two different Readers are compared, the difference in the two
values is called the Time Difference (or Delay) of Arrival (TDOA). Each TDOA value describes a
line on a 2D map. The intersection of two or more of these lines is used to determine the position of a
Tag.