5 measurement time, 6 link quality indication (lqi), 1 overview – Rainbow Electronics ATmega128RFA1 User Manual
Page 72: Atmega128rfa1
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8266A-MCU Wireless-12/09
ATmega128RFA1
9.5.5.5 Measurement Time
The response time for a manually initiated CCA measurement depends on the receiver
state.
In RX_ON state the CCA measurement is done over eight symbol periods and the
result is accessible 140 µs after the request (see section
page 71).
In BUSY_RX state the CCA measurement duration depends on the CCA Mode and the
CCA request relative to the reception of an SHR. The end of the CCA measurement is
indicated by a TRX24_CCA_ED_DONE interrupt. The variation of a CCA measurement
period in BUSY_RX state is described in
.
Table 9-22. CCA Measurement Period and Access in BUSY_RX state
CCA Mode
Request within ED measurement
(1)
Request after ED measurement
Energy above threshold
.
1
CCA result is available after finishing
automated ED measurement period.
CCA result is immediately available
after request.
Carrier sense only
.
2
CCA result is immediately available after request.
Carrier sense with Energy above threshold (AND)
.
3
CCA result is available after finishing
automated ED measurement period.
CCA result is immediately available
after request.
Carrier sense with Energy above threshold (OR)
.
0
CCA result is available after finishing
automated ED measurement period.
CCA result is immediately available
after request.
Note:
1. After receiving the SHR an automated ED measurement is started with a length of
8 symbol periods (PSDU rate 250 kb/s), refer to section
page 68. This automated ED measurement must be finished to provide a result
for the CCA measurement. Only one automated ED measurement per frame is
performed.
It is recommended to perform CCA measurements in RX_ON state only. To avoid
accidental switching to BUSY_RX state the SHR detection can be disabled by setting
bit RX_PDT_DIS of register RX_SYN. Refer to section
for
details. The receiver remains in RX_ON state to perform a CCA measurement until the
register bit RX_PDT_DIS is set back to continue the frame reception. In this case the
CCA measurement duration is 8 symbol periods.
9.5.6 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 signal-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.
9.5.6.1 Overview
The LQI measurement of the radio transceiver is implemented as a measure of the link
quality which can be described with the packet error rate (PER) of this link. A LQI value