CC2430 Datasheet, PDF (168/212 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
Radio : MAC Security Operations (Encryption and Authentication)
14.21 MAC Security Operations (Encryption and Authentication)
CC2430 features hardware IEEE 802.15.4 MAC
security operations. Refer to section 13.12 on
page 136 for a description of the AES
encryption unit.
14.22 Linear IF and AGC Settings
C2430 is based on a linear IF chain where the
signal amplification is done in an analog VGA
(variable gain amplifier). The gain of the VGA
is digitally controlled.
The AGC (Automatic Gain Control) loop
ensures that the ADC operates inside its
dynamic range by using an analog/digital
feedback loop.
The AGC characteristics are set through the
AGCCTRLL:AGCCTRLH, registers. The reset
values should be used for all AGC control
registers.
14.23 RSSI / Energy Detection
CC2430 has a built-in RSSI (Received Signal
Strength Indicator) giving a digital value that
can be read from the 8 bit, signed 2’s
complement RSSIL.RSSI_VAL register bits.
The RSSI value is always averaged over 8
symbol periods (128 µs), in accordance with
[1].
The RSSI register value RSSI.RSSI_VAL can
be referred to the power P at the RF pins by
using the following equations:
P = RSSI_VAL + RSSI_OFFSET [dBm]
where the RSSI_OFFSET is found empirically
during system development from the front end
gain. RSSI_OFFSET is approximately –45.
E.g. if reading a value of –20 from the RSSI
register, the RF input power is approximately –
65 dBm.
A typical plot of the RSSI_VAL reading as
function of input power is shown in Figure 47.
It can be seen from the figure that the RSSI
reading from CC2430 is very linear and has a
dynamic range of about 100 dB.
-100
-80
-60
-40
RF Level [dBm]
60
40
20
0
-20
0
-20
-40
-60
Figure 47: Typical RSSI value vs. input power
14.24 Link Quality Indication
The link quality indication (LQI) measurement
is a characterization of the strength and/or
quality of a received packet, as defined by [1].
The RSSI value described in the previous
section may be used by the MAC software to
produce the LQI value. The LQI value is
required by [1] to be limited to the range 0
through 255, with at least eight unique values.
Software is responsible for generating the
appropriate scaling of the LQI value for the
given application.
Using the RSSI value directly to calculate the
LQI value has the disadvantage that e.g. a
narrowband interferer inside the channel
bandwidth will increase the LQI value although
it actually reduces the true link quality. CC2430
CC2430 Data Sheet (rev. 2.1) SWRS036F
Page 168 of 211