<div>Fig 1. General hardware structure of the PLB system</div><div>The ultra-low-power standby circuit
is used to control the system power up or down. When the system in the
state of ultra-low power standby, once the system touches the water or
launch button pressed, the system power up. When the system is in the
state of working, once the cancel button pressed, the system returns to
ultra-low power standby. The battery is used to power the system. The
DC-DC converter is used to convert the battery voltage to the system’s
operating voltage. The RDSS module and RDSS antenna are used to realize
transmitting distress information to the Beidou satellite and receiving
information from the rescue center. The COSPAS-SARSAT transmitter and
406MHz antenna are used to transmit rescue information to COSPAS-SARSAT
rescue center. Vital signs monitoring sensors are temperature sensors
that monitor the ear temperature of persons in distress. LEDs are used
to show the status of the transmitter, when the red light is on
indicates that the system is working, when the green light flashes
indicates that it is transmitting distress information, when the green
light is on for a long time indicates that the information from the
rescue centre is received. SD card module is used to store the
information of people in distress. The cancel button controls the system
to cancel the transmit. The GNSS receiver and the GNSS receiver antenna
are for positioning; The STM32 controller is used to control these
modules.</div><div>Its logical sequence proposed is as flows. First, when the PLB is in
standby mode, the battery only provides power to the ultra-low-power
circuit. Second, when the person is in marine accident that falls into
the sea or presses the manual start switch, the reset circuit will
generate a reset signal. Then the switch circuit controlled by the reset
signal, the switch circuit will be opened which result in the battery
voltage is allowed to supply to the system. And then, the STM32F413
controller is powered on and control to output a high voltage to remain
the switch circuit opens, and the battery continues to supply to the
system. At this moment, the STM32F413 controller controls the GNSS
receiver receive the location information, the SD card store the
location information, the LEDs flash, the life detect sensor collect the
human life information, the BeiDou transmitter and COSPAS-SARSAT
transmitter transmit the SOS information to the BeiDou Rescue centre or
the global search and rescue organization through the medium of
electromagnetic waves. When the BeiDou Rescue centre or the global
search and rescue organization received the SOS information , it feeds
back the PLB a feedback information through the BeiDou receiver. When
the BeiDou receiver of the PLB receives the feedback electromagnetic
wave signal, it decodes it, converts it into feedback information, and
transmits it to the STM32 controller
through the serial port, then stop sending SOS message to rescue centre
and the BeiDou receiver will still works. When the receiver receives the
message for asking for location, it will send the location information
to the related organizations. Last, when the cancel button is pressed,
the STM32 controller controls the switch circuit disconnected and the
system will powered off.</div><div>In our system, the power consumption mainly comes from the COSPAS
transmitter, the BeiDou transmitter and Beidou receiver. We can let the
receiver work to realize the interaction with the rescue center. When it
is determined that the rescue centre received the distress signal to
stop transmitting distress information to save power, thus extending the
working time of the PLB.</div><div>The program flowchart for our PL is shown in Fig2.</div>