noting that the gateway average current can be further reduced
by using the hardware SPI port to interface with the radio de-
vices and by programming the latter to autonomously scan for
incoming packets instead of the software-controlled LPL over a
software SPI port emulation used currently.
The gateways perform field data aggregation in a buffer
(up to about 400 messages in the microcontroller internal data
memory) to save energy and connect to the server either period-
ically (time-driven behavior), or when the buffer becomes full
or as soon and as long alert messages are received from field
(event-driven behavior). Since the sensor nodes transmit mostly
heartbeat messages that update their state on the gateway, the
message buffer fills gradually unless the gateway is configured
to collect variable field data (such as temperature readings) that
the sensor nodes piggyback on the heartbeat messages.
The repeater node uses the gateway design with unused hard-
ware and software components removed.
C. Field Deployment Device Implementation
The deployment device is made by a gateway device con-
nected through a serial port to an Openmoko smartphone
platform1 that runs a Linux operating system (see Fig. 9).
The gateway interfaces with the field nodes, while the field
data processing and the user interface (UI) are handled by an
application running on Openmoko Linux OS.
The Openmoko GPS can be used to assist field orientation of
the operator and node localization during deployment.