CC2431 Datasheet, PDF (5/15 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, such as mobile neighbor nodes
with the same Location Engine, or fixed
infrastructure 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:
• Three to eight reference nodes
can be used for the location
estimation algorithm
• Location estimate with resolution
of 0.5 meters
• Time to estimate node location
less than 40 µs
• Location range 64 x 64 meters
• Location error can be less than 3
meters, depending on factors
described below
• 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.
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 eight 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 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.
SWRS034
Page 5 of 14