Atmel AVR2016 Manual de usuario descargar pdf (Pagina 2)

design. Our PMM handles energy management and does

not require an additional charge controller. Moreover, to the

best of our knowledge, the N4C design does not implement

a sleep mode and has no second radio for discovery.

The remainder of this paper is structured as follows. In

Section 2 the application scenarios that motivated the devel-

opment of the PMM are introduced. Section 3 ﬁrst gives an

overview of the system design and then continues with a de-

tailed description of the hardware and software components.

In Section 4 we present the evaluation of the solar charge

management, discovery range and energy consumption. Fi-

nally, we conclude the paper.

2. APPLICATION SCENARIOS

Statinary DTN-nodes are useful in various scenarios. The

main application area of solar-powered nodes are remote

locations without mains infrastructure, but also in other

cases, even in urban settings, such a self-contained DTN-

node can be useful due to its simplicity and fast installation.

Usually (but not necessarily) these nodes are stationary and

located at elevated positions for better radio coverage. The

following exemplary application scenarios are common for

such systems:

2.1 Bundle Relay for Message Ferries

In this scenario the solar-powered DTN node’s task is

mainly to store and forward messages from and to ferries.

This means that the node is positioned at the path of regularly

passing ferries, and spends much time idly waiting for a

contact. Here the PMM comes into play and wakes the

node shortly before a contact. For deterministic contacts the

PMM can use a schedule (time triggered wakeup) and does

not require the low power radio, but for non-deterministic

contacts, a low power 802.15.4 radio on the ferry sends

beacons to the PMM (selective discovery triggered wakeup).

Upgrading an existing ferry node with such a radio should

be unproblematic, since there are several inexpensive and

energy-eﬃcient 802.15.4 transceivers available (e.g. ’USB-

dongles’). Of course, we recommend using a PMM for new

designs of ferry nodes.

2.2 DTN Access for Mobile Users

In this scenario, the solar-powered DTN node provides

DTN access to mobile users who only sporadically use the

network, e.g. for sending and receiving text or voice messages.

Again, the solar-powered node is mainly idle. If a user needs

service a wakeup signal is sent from the user’s mobile device

to the PMM. Currently almost all smartphones are equipped

with Bluetooth, and the PMMs modular hardware also allows

to use Bluetooth for discovery. However, we strongly favor

802.15.4 for its better energy-eﬃciency, range and security,

and we expect that future smartphones will include 802.15.4

radios. Moreover, laptops are easily upgraded with such

interfaces. As a last resort there is a port pin on the PMM

to externally trigger a wakeup, e.g., by a motion sensor or

simply a push button.

2.3 Delay-tolerant on Demand Backbone

In this scenario, several solar-powered, ﬁxed DTN nodes

operate as backbone between remote locations. Diﬀerently

from the usual DTN assumption, there is a stable wireless

link between the nodes. However, we assume that there

are energy constraints so that there is only an intermittent

power supply available. This is a very reasonable assumption

for solar-powered nodes, because even with highly oversized

(and therefore very expensive) solar panels and batteries it

is hardy possible to guarantee continuous operation in all

weather conditions and all seasons.

All backbone nodes are equipped with a PMM, which is

used to wake up the next hop node. In this scenario there

are several battery capacity thresholds. First, if the battery

is almost full and the sun is shining a node is always on,

to ensure a low latency and because there is no reason to

switch the node oﬀ while the solar cells harvest enough energy.

Second, if the battery is neither almost full nor almost empty,

the node is powered oﬀ if there are no bundles to route;

and selectively powered on via the PMM if there is work

to do. It can be expected that nodes spend most of their

time in this ”on demand” mode. Third, if the batteries of the

nodes are below the emergency energy budget, the nodes stay

powered oﬀ unless high priority bundles are transmitted. To

distinguish between the diﬀerent levels of urgency of bundles,

the two bit priority ﬁeld according to RFC5050 can be used.

3. SYSTEM DESIGN

The block diagram in ﬁgure 1 shows two possible DTN node

conﬁgurations. On the left is a DTN node equipped with an

PMM, which is capable to switch on/oﬀ the embedded system

running Linux and a DTN daemon. The PMM triggers a

wakeup event if it receives a wakeup message on its integrated

IEEE 802.15.4 radio. This beacon is either transmitted from

another PMM, or by another DTN node without a PMM. In

this case the node requires an 802.15.4 interface, as shown

on the right.

This paper focuses on the power management module

(PMM), but a realistic evaluation of the PMM is only possible

with a solar-powered DTN node. For this reason we also

present our node in section 3.2.

Node without PMM

IEEE

802.15.4

IEEE

802.11

Embedded

Linux-

System

PMM

Node with PMM

IEEE

802.15.4

(Embedded)

Linux-

System

IEEE

802.11

Figure 1: Possible DTN node conﬁgurations

3.1 Power Management Module

The PMM’s architecture shown in ﬁgure 2 is based on an

Atmega644P MCU, which connects via an FT232RL serial-

to-USB chip with the DTN node. Moreover, the PMM has

a socket for low power radios, which is currently populated

with an XBee-Pro[5] 802.15.4 radio, as shown in ﬁgure 4.

However, there are several other low power radios available

with diﬀerent PHY/MAC technologies but with the same

footprint and pin-out. This makes our design very versatile,

and allows compliance with (and exploitation of) diﬀerent

national radio spectrum regulations. As an additional feature

the PMM can enable a virtual serial port (see right side in

ﬁgure 2) that allows the DTN-node direct access to the low

power radio, to use it as if it were its own wireless interface.

1 2 3 4 5 6

Comentarios a estos manuales

Sin comentarios

Atmel AVR2016 Manual de usuario Pagina 2

Comentarios a estos manuales

Relacionado con productos y manuales para No Atmel AVR2016