CC2431 Texas Advanced Optoelectronic Solutions, CC2431 Datasheet - Page 7

• Manufacturer Part Number: CC2431
• Description: System-on-Chip for 2.4 GHz ZigBee/ IEEE 802.15.4 with Location Engine
• Manufacturer: Texas Advanced Optoelectronic Solutions

2.1.1
The Location Engine requires a set of between
three and 16 reference coordinates [x0, y0, x1,
y1, …, x15, y15] to be input. The reference
coordinates express each reference nodes
position in meters, as unsigned values in the
interval [0, 63.75] meters. The finest possible
readout resolution is 0.25 meter. The format
used is fixed-point data with the two LSBs
representing the fractional part and the
remaining six bits representing the integer
part, thus e.g. 63.75 is represented as 0xFF.
Reference coordinates are loaded into the RF
register
REFCOORD
bit
2.1.2
After the reference coordinates have been
written, a set of measured parameters must be
input
parameters consist of two radio parameters:
Four search boundary coordinates and 16
2.1.2.1 Parameter Definitions
The measured parameters are described in
this section together with how these should be
estimated.
2.1.2.1.1
The radio parameter A is defined as the
absolute value of the average power in dBm
received at a close-in reference distance of
one meter from the transmitter, assuming an
omni-directional
example, if the mean received power at one
meter is -40 dBm, the parameter A is specified
as 40.
2.1.2.1.2
The radio parameter n is defined as the path
loss exponent that describes the rate at which
the signal power decays with increasing
distance from the transmitter. This decay is
proportional to d
between transmitter and receiver.
The actual parameter n value written to the
Location Engine is an integer index value
selected from a lookup table shown in Table 2.
LOCENG.REFLD
to
Reference Coordinates
Measured Parameters
REFCOORD
Parameter n
Parameter A
, a 1 must be written to the register
the
-n
Location
radiation
where d is the distance
to indicate that a set of
.
Before
Engine.
pattern.
CC2431 Data Sheet (Rev. 2.01) SWRS034B
writing
These
For
to
reference coordinates are being written. Once
the coordinate load process commences
(
must always be written. However, it is possible
for the Location Engine to use less than 16
reference coordinates, by marking certain
reference coordinates as unused. Zeros shall
be used to fill the unused reference coordinate
slots, and they will be interpreted as unused
when 0.0 is loaded as the RSSI value for
those reference coordinates.
The reference coordinates are written in the
order [x0, y0, x1, y1, …, x15, y15] to the
register
been written, a 0 is written to the register bit
LOCENG.REFLD
RSSI values. The radio parameters are the
values A and n. These radio parameters are
used in the Engine’s algorithm used to find the
estimated location. The parameters A and n
can be adjusted to describe the propagation
environment in which a network of devices will
operate.
The Engine expects the parameter A to be in
the range [30.0, 50.0] with precision 0.5. The
parameter A is given as an unsigned fixed-
point value where the LSB bit is the fractional
bit and the remaining bits are the integer part.
A typical value for A is 40.0.
As an example, in the case when the value
n=2.98 is found from measurements, the
closest available value of n in the lookup table
is 3.00, corresponding to index 13. Therefore,
the integer value 13 is used for the parameter
n written to the Location Engine.
Refer to section 2.1.2.1.3 in order to find the
value for n to be used.
LOCENG.REFLD
REFCOORD
.
. After all coordinates have
=1), 16 coordinate pairs
CC2431
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