MRF24J40-ISLASHT datasheet(97/156 Pages) MICROCHIP

97 / 156 page

Preliminary

DS39776C-page 97

MRF24J40

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.

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.

MRF24J40-I/T Datasheet(PDF) 97 Page - Microchip Technology

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