CC2431-RTR1 datasheet(8/15 Pages) TI

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CC2431

SWRS034

Page 8 of 14

n index

1.000 16

3.375

1.250 17

3.500

1.500 18

3.625

1.750 19

3.750

1.875 20

3.875

2.000 21

4.000

2.125 22

4.125

2.250 23

4.250

2.375 24

4.375

2.500 25

4.500

2.625 26

4.625

2.750 27

5.000

2.875 28

5.500

3.000 29

6.000

3.125 30

7.000

3.250 31

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.

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