CC2431
Path Loss vs. log-distance for source 0x85, Z=2.1082. A=42.4103, n=2.9773
95
90
85
80
Path Loss (dB)
75
70
65
60
55
50
45
2
4
6
8
10*log10(distance)
10
12
14
Figure 2: Path loss vs. log distance
2.1.2.1.4 Search Boundary Coordinates
It is possible to reduce error and estimation
time by setting search boundaries for the
estimated location X and Y coordinates. The
maximum area that can be considered is with
X and Y in the interval [0.0, 63.75] meters.
Assume that the Location Engine search is to
be limited to include only the rectangular area
bounded by the coordinates [x
min
, y
min
] and
[x
max
, y
max
].
Four search boundary parameters are entered
in the following order:
x
min
, x
delta
, y
min
, y
delta
2.1.2.1.5 RSSI Values
where:
x
delta
= x
max
- x
min
y
delta
= y
max
- y
min
Note that even when it is chosen to search in
the whole possible search space, these
coordinates must be entered as the
coordinates for the whole space, i.e. the
following values: 0.0, 63.75, 0.0, 63.75.
If some input parameters are omitted the
Location Engine will not estimate correctly.
The RSSI values are the RSSI measurements
corresponding to the set of reference
coordinates. The RSSI values are within the
interval [-40 dBm, -95 dBm] with precision 0.5
dBm. The negative sign is removed in the
value written. As an example, in the case
where the value RSSI = -50.35 dB, this would
be written into the location engine as 50.5.
2.1.2.2 Loading Parameters
All measured parameters described in the
previous sections are loaded into the RF
register
MEASPARM
. Before writing to
MEASPARM
, a 1 must be written to the register
Note that a value of 0.0 must be written as
RSSI value for unused reference coordinates,
if less than 16 reference nodes are used. The
engine will not function correctly if only some
of the parameters are loaded.
bit
LOCENG.PARLD
to indicate that a set of
measured parameters are being written. Once
the parameter load process commences
CC2431 Data Sheet (Rev. 2.01) SWRS034B
Page 9 of 15
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