CC2431 Datasheet, PDF (8/16 Pages) Texas Instruments – System-on-Chip for 2.4 GHz ZigBee-TM / IEEE 802.15.4 with Location Engine

CC2431
Table 2: n parameter lookup table
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
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
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:
as 00000111. The typical value for n depends
on the environment.
• 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 Data Sheet (Rev. 2.01) SWRS034B
Page 8 of 15