Rainbow Electronics AT86RF231 - Manual (Page 99)

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8111A–AVR–05/08
AT86RF231
8.6 Link Quality Indication (LQI)
According to IEEE 802.15.4, the LQI measurement is a characterization of the strength and/or
quality of a received packet. The measurement may be implemented using receiver ED, a sig-
nal-to-noise ratio estimation, or a combination of these methods. The use of the LQI result by the
network or application layers is not specified in this standard. LQI values shall be an integer
ranging from 0x00 to 0xFF. The minimum and maximum LQI values (0x00 and 0xFF) should be
associated with the lowest and highest quality compliant signals, respectively, and LQI values in
between should be uniformly distributed between these two limits.
8.6.1 Overview
The LQI measurement of the AT86RF231 is implemented as a measure of the link quality which
can be described with the packet error rate (PER) for this link. An LQI value can be associated
with an expected packet error rate. The PER is the ratio of erroneous received frames to the
total number of received frames. A PER of zero indicates no frame error, whereas at a PER of
one no frame was received correctly.
The radio transceiver uses correlation results of multiple symbols within a frame to determine
the LQI value. This is done for each received frame. The minimum frame length for a valid LQI
value is two octets PSDU. LQI values are integers ranging from 0 to 255.
As an example, Figure 8-6 on page 99 shows the conditional packet error when receiving a cer-
tain LQI value.
Figure 8-6. Conditional Packet Error Rate versus LQI
The values are taken from received frames of PSDU length of 20 octets on transmission chan-
nels with reasonable low multipath delay spreads. If the transmission channel characteristic has
higher multipath delay spread than assumed in the example, the PER is slightly higher for a cer-
0
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0 50 100 150 200 250
PER
LQI