80
8168C-MCU Wireless-02/10
AT86RF212
6.4 Received Signal Strength Indicator (RSSI)
The Received Signal Strength Indicator is characterized by:
a dynamic range of 87 dB
a resolution of about 3 dB
6.4.1 Overview
The RSSI value indicates the received signal power in the selected channel. No attempt
is made to distinguish IEEE 802.15.4 signals from others; only the received signal
strength is evaluated. The RSSI provides the basis for an ED measurement, see
6.4.2 Reading RSSI
In Basic Operating Modes, the RSSI value is valid in any receive state and is updated
at time intervals according to
Table 6-24. The current RSSI value can be accessed by
reading register bits RSSI of register 0x06 (PHY_RSSI).
Table 6-24. RSSI Update Interval
PHY Mode
Update Interval [s]
BPSK-20
32
BPSK-40
24
O-QPSK
8
It is not recommended reading the RSSI value when using the Extended Operating
Modes. Instead, the automatically generated ED value should be used, see section
6.5.
6.4.3 Data Interpretation
The RSSI value is a 5-bit value in a range of 0 to 28, indicating the receiver input power
in steps of about 3 dB.
A RSSI value of 0 indicates a receiver input power less than or equal to
RSSI_BASE_VAL [dBm], a value of 28 an input power equal to or larger than
(RSSI_BASE_VAL + 87) [dBm]. The value RSSI_BASE_VAL itself depends on the PHY
mode, refer to section
7.1. For typical conditions, it is shown in
Table 6-25.
Table 6-25. RSSI_BASE_VAL
PHY Mode
RSSI_BASE_VAL [dBm]
BPSK with 300 kchip/s
-100
BPSK with 600 kchip/s
-100
O-QPSK with 400 kchip/s
-98
O-QPSK with 1000 kchip/s, sine shaping (SIN)
-98
O-QPSK with 1000 kchip/s, raised cosine shaping (RC-0.8)
-97
The receiver input power can be calculated as follows:
PRF [dBm] = RSSI_BASE_VAL + 3.1 RSSI