MRF24J40_08 Datasheet, PDF (95/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

3.7 Link Quality Indication (LQI)
Link Quality Indication (LQI) is a characterization of
strength or quality of a received packet. Several
metrics, for example, RSSI, Signal to Noise Ratio
(SNR), RSSI combined with SNR, etc., can be used for
measuring link quality. Using RSSI or SNR alone may
not be the best way to estimate the quality of a link. The
received RSSI value will be a very high value if a packet
is received with greater signal strength or even if an
interferer is present in the channel. Hence, for better
approximation of link quality, the MRF24J40 reports the
correlation degree between spreading sequences and
the incoming chips during the reception of a packet.
This correlation value is directly mapped to a range of
0-255 (256 values), where an LQI value of 0 indicates
that the quality of the link is very low, and an LQI value
of 255 indicates the quality of the link is very high. The
correlation degree between spreading sequences and
incoming chips is computed over a period of 3 symbol
periods during the reception of the preamble of a
packet.
The LQI is reported along with each received packet in
the RX FIFO as shown in Figure 3-2.
MRF24J40
3.8 Beacon-Enabled and
Nonbeacon-Enabled Networks
The IEEE 802.15.4 Standard defines two modes of
operation:
• Beacon-enabled network
• Nonbeacon-enabled network
3.8.1 BEACON-ENABLED NETWORK
In a beacon-enabled network, beacons will be transmit-
ted periodically by the PAN coordinator. These
beacons are mainly used to provide synchronization
services between all the devices in the PAN and also to
support other extended features, like Guaranteed Time
Slots (GTS), a Quality of Service (QoS) mechanism for
the IEEE 802.15.4 Standard. The PAN coordinator
defines the structure of the superframe using beacons.
© 2008 Microchip Technology Inc.
Preliminary
DS39776B-page 93