Atmel AVR2016 Bedienungsanleitung PDF herunterladen (Seite 4)

wakeup events and energy thresholds to the PMMs non-

volatile memory. Furthermore, the daemon is able to provide

a virtual serial port that allows direct access to the serial

port of the low power radio module. This feature is useful for

our future low power radio convergence layer, which allows

the DTN node to send small bundles more energy eﬃcient.

3.1.3 Wakeup Strategies

In our current version there are three strategies imple-

mented to wake up the DTN node.

By Request

Another station can send a request including

start, duration, and priority to the PMM, to wake up

the DTN node via the 802.15.4-connection. With help

of the transmitted priority, the module can decide if

there is suﬃcient energy stored in the battery or if

enough energy can be harvested by the PV-panel. If

the amount is to small at the beginning of the requested

time span, the event will not be discarded, but the DTN

board will not be powered on either. This provides

an opportunity to boot the node later, if the energy

collected by the node in the meantime exceeds the limit

needed for the requested priority.

By Contact

The DTN node can conﬁgure the PMM to

trigger a wakeup if the PMM receives a beacon from a

speciﬁc node. Then the node issues a shutdown request

to the PMM and sleeps until the speciﬁc node is within

range or another wakeup event occurs.

Opportunistic

For a system that should be able to work

reliable all over the year, the components to collect and

store electrical energy will probably be - depending on

the region - oversized for summer seasons. Since the

battery can store only a limited amount of energy, it

will likely come to a point at which it can happen that

the battery is fully charged but there is still energy

provided by the solar panel. To use it, the DTN node

will be powered up even if it was not requested.

3.2 Solar-Powered DTN node

The solar-powered DTN node was developed in the Op-

tracom project

. For this reason the DTN node hardware

is based on the Optracom node design. A Ubiquiti Router-

Station (an embedded router platform) runs the OpenWRT

embedded Linux distribution. It provides several miniPCI

sockets and USB ports for extension. An UB5 802.11a inter-

face card is installed and connected to an external antenna

with 10dbi gain. The node runs the IBR-DTN[6] bundle pro-

tocol agent. Figure 5 shows the basic setup. Both the solar

panel and the battery connect to the PMM, which manages

charging and also switches the RouterStations power. The

RouterStation connects via USB to the PMM.

The photo in ﬁgure 6 shows the internals of the node’s case.

The battery is at the botton, the PMM on the upper left,

besides the RouterStation. Also note the vertical, internal

PMM antenna. The complete system with external antenna

and solar panel is shown in ﬁgure 10.

3.3 Mobile Nodes

As stated earlier, solar-powered nodes are commonly sta-

tionary. However, several use cases require mobile nodes

(mainly mobile users and ferries) to send wakeup-requests

http://www.optracom.de/

Solar-

panel

PMM,

XBee Radio

RouterStation

Battery

switched by PMM

USB

Figure 5: Simpliﬁed block diagram of the system

PMM

internal

802.15.4

antenna

Router-

Station

Battery

Connector

for external

802.11a

antenna

To solar panel

Figure 6: The complete system with opened case

to the PMM by an 802.15.4 interface. 802.15.4. is widely

used in wireless sensor networks and industrial controls, but

not yet integrated into regular smartphones. For evaluation

purposes we used an USB-stick[7], shown in ﬁgure 7. Figure 8

shows a mobile node for vehicles operating as message ferries.

It is equipped with several dual- and tri-band antennas and

will be used in a future evaluation of diﬀerent low power

radios.

4. EVALUATION

In this section we present our preliminary evaluation re-

sults. The evaluation setup is shown in ﬁgure 10. The graph

in ﬁgure 9 shows the line of sight range of the 802.15.4 and

the 802.11a radios. Note that 802.15.4 operates with a trans-

mit power of 18dBm on an internal vertical 3dbi gain antenna

while 802.11a operates with 23dBm on an external 10dbi

antenna. However, the 802.15.4 range still achieves a higher

range. Therefore, a wakeup can be requested by a mobile

node before it is within 802.11a range. This is important to

maximize contact time, because the DTN node needs some

seconds to boot up.

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