CC2431 Datasheet, PDF (5/16 Pages) Texas Instruments – System-on-Chip for 2.4 GHz ZigBee-TM / IEEE 802.15.4 with Location Engine

CC2431
2 Location Engine
The Location Engine is used to estimate the
position of nodes in an ad-hoc wireless
network. Reference nodes exist with known
coordinates, typically because they are part of
an installed infrastructure. Other nodes are
blind nodes, whose coordinates need to be
estimated. These blind nodes are often mobile
and attached to assets that need to be
tracked.
The Location Engine implements a distributed
computation algorithm that uses received
signal strength indicator (RSSI) values from
known reference nodes. Performing location
calculations at the node level reduces network
traffic and communication delays otherwise
present in a centralized computation
approach.
The Location Engine has the following main
features:
2.1 Location Engine Operation
This section describes the basic steps
required to obtain location estimates from the
Location Engine.
The Location Engine requires a set of three to
16 reference coordinates to be input together
with a set of measured parameters. The output
from the Location Engine consists of a pair of
estimated location coordinates.
Before any input data is written, the Location
Engine must be enabled by writing a 1 to the
enable bit, LOCENG.EN. When the Location
• 3 to 16 reference nodes can be used for
the location estimation algorithm
• Location estimate with readout resolution
of 0.25 meters (note: The accuracy of the
location estimate will depend on several
factors described below).
• Time to estimate node location is 50 µs to
13 ms
• Location range 64 x 64 meters
• Runs location estimation with minimum
CPU usage
To achieve the best possible accuracy one
should use antennas that have near-isotropic
radiation characteristics. The location error
depends on signal environment, deployment
pattern of reference nodes and the density of
reference nodes in a given area. In general,
having more reference nodes available
improves the accuracy of the location
estimation.
Engine is not in use, writing a 0 to
LOCENG.EN will reduce the power
consumption of the CC2431 by gating off the
Engine’s clock signal.
Figure 1 shows the basic operation of the
Location Engine.
CC2431 Data Sheet (Rev. 2.01) SWRS034B
Page 5 of 15