2 reading rssi, 3 data interpretation, 4 energy detection (ed) – Rainbow Electronics ATmega128RFA1 User Manual
Page 68: 1 overview, Reading, Atmega128rfa1
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8266A-MCU Wireless-12/09
ATmega128RFA1
received signal strength is evaluated. The RSSI provides the basis for an ED
measurement. See section
for details.
9.5.3.2 Reading RSSI
In Basic Operating Mode the RSSI value is valid in any receive state, and is updated
every t
TR25
= 2 µs to register PHY_RSSI.
It is not recommended to read the RSSI value when using the Extended Operating
Mode. The automatically generated ED value should then be used (see section
).
9.5.3.3 Data Interpretation
The RSSI value is a 5-bit value indicating the receive power in steps of 3 dB and with a
range of 0- 28.
An RSSI value of 0 indicates a receiver RF input power of P
RF
< -90 dBm. For an RSSI
value in the range of 1 to 28, the RF input power can be calculated as follows:
P
RF
= RSSI_BASE_VAL + 3 • (RSSI - 1) [dBm]
Figure 9-17. Mapping between RSSI Value and Received Input Power
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
RSSI
R
e
c
e
iv
e
r
In
p
u
t
P
o
w
e
r
P
R
F
[
d
B
m
]
Measured
Ideal
9.5.4 Energy Detection (ED)
The Energy Detection (ED) module is characterized by:
•
85 unique energy levels defined;
•
1 dB resolution.
9.5.4.1 Overview
The receiver ED measurement is used by the network layer as part of a channel
selection algorithm. It is an estimation of the received signal power within the bandwidth
of an IEEE 802.15.4 channel. No attempt is made to identify or decode signals on the
channel. The ED value is calculated by averaging RSSI values over eight symbols
(128 µs).