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CC2431_07 Datasheet, PDF (8/14 Pages) Texas Instruments – System-on-Chip for 2.4 GHz ZigBee/ IEEE 802.15.4 with Location Engine
CC2431
n index
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
n
1.000
1.250
1.500
1.750
1.875
2.000
2.125
2.250
2.375
2.500
2.625
2.750
2.875
3.000
3.125
3.250
n index
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
n
3.375
3.500
3.625
3.750
3.875
4.000
4.125
4.250
4.375
4.500
4.625
5.000
5.500
6.000
7.000
8.000
Table 2: n parameter lookup table
The parameter n is written to the Location
Engine as an integer index in the range [0,
31] as the index is given as an integer
value with no fractional bits, e.g. the value
n = 7 is loaded as 00000111. A typical
value for n is 13.
2.1.2.1.3 Parameter Estimation
The parameters A and n can be estimated
empirically by collecting RSSI data (and
therefore path loss data) for which the
distances between the transmitting and
receiving devices are known. Figure 2 is a
scatter plot of abs(RSSI) data versus log
distance in meters. A least-squares best-fit
line is used to glean the specific values of
A and n for the environment in which the
data were measured:
• A is the y-intercept of the line, and
• n is the slope of the line
The data in Figure 2 give A=42.4 and
n=2.98 for that environment. Note that the
plot in this example does not show the
actual y-intercept i.e. the point on the line
where x=0.
The value of A loaded into the engine in
this case would by 42.5. The value of n
loaded into the engine, is seen to be 13
from Table 2.
CC2431 PRELIMINARY Datasheet (Rev. 1.01) SWRS034A
Page 8 of 13