17-05-2012, 12:54 PM
Bluetooth and Sensor Networks: A Reality Check
[attachment=22235]
INTRODUCTION
It is now possible to develop software for sensor networks
and to conduct experiments using sensor nodes readily available
through research groups or commercial companies.
These sensor nodes, based on commercial off-the-shelf components,
guarantee a good trade-off between cost (of development
and production), reliability and performance. One
of the key differences between sensor nodes is their radio
component: it impacts not only energy consumption but
also software design (network self-assembly, multihop routing
and in-network processing).
BTNODES
The BTnodes were developed by ETH Zurich in the context
of the Smart-Its project [15]. They are based on the
Atmel ATmega128L microcontroller - an 8 bit microcontroller
(MCU) clocked at 7.4 MHz, with 4 KiB1 on chip
memory and an external memory chip of up to 64 KiB. The
MCU has digital and analog I/O ports that can be used to
connect external sensor devices through Molex plugs on the
edge of the board. The nodes are equipped with a Bluetooth
module (Ericsson ROK 101 007) together with an onboard
antenna. Two UARTs connect the MCU with the embedded
Bluetooth chip and one of the Molexpl ugs. Four leds can
be used for debugging purposes. The board also contains
a voltage regulator: the BTnode can be plugged to power
supplies ranging from 3.3 V to 12 V.
TINY BLUETOOTH STACK
In this section, we report on the design and implementation
of our Tiny Bluetooth stack. We compare it to the
ETH Bluetooth stack for the BTnodes and to existing communication
stacks developed for TinyOS.
Implementation
The HCI Core component is responsible for making the
HCI interface available in the TinyOS programming model.
This task is facilitated by the fact that both HCI and TinyOS
are based on an asynchronous programming model. TinyOS
commands are naturally mapped onto HCI commands. HCI
events need to be dispatched into TinyOS events.
Figure 3 illustrates how events are handled: The UART
component generates an event for each byte it receives. This
event is handled by HCI Packet in the UART interrupt context.
Once a packet is constructed with bytes from the
UART, the HCI Packet event handler posts a task that in
turn generates an event (this way this event will not be processed
in the UART interrupt context).
Related Work
Oliver Kasten [10] implemented a Bluetooth stack for the
BTnodes as part of the Smart-its software package. One of
their priorities was to make the BTnodes accessible from any
Bluetooth device. As a result, they implemented part of the
higher Bluetooth layers (link control, connection management
and profile). Our emphasis was different: we focused
on an efficient access to the Bluetooth radio for TinyOS applications
deployed on BTnodes. Minimal support for heterogeneity
could be added by implementing support for connectionless
l2cap packets in a component on top of the Tiny
Bluetooth stack.
[attachment=22235]
INTRODUCTION
It is now possible to develop software for sensor networks
and to conduct experiments using sensor nodes readily available
through research groups or commercial companies.
These sensor nodes, based on commercial off-the-shelf components,
guarantee a good trade-off between cost (of development
and production), reliability and performance. One
of the key differences between sensor nodes is their radio
component: it impacts not only energy consumption but
also software design (network self-assembly, multihop routing
and in-network processing).
BTNODES
The BTnodes were developed by ETH Zurich in the context
of the Smart-Its project [15]. They are based on the
Atmel ATmega128L microcontroller - an 8 bit microcontroller
(MCU) clocked at 7.4 MHz, with 4 KiB1 on chip
memory and an external memory chip of up to 64 KiB. The
MCU has digital and analog I/O ports that can be used to
connect external sensor devices through Molex plugs on the
edge of the board. The nodes are equipped with a Bluetooth
module (Ericsson ROK 101 007) together with an onboard
antenna. Two UARTs connect the MCU with the embedded
Bluetooth chip and one of the Molexpl ugs. Four leds can
be used for debugging purposes. The board also contains
a voltage regulator: the BTnode can be plugged to power
supplies ranging from 3.3 V to 12 V.
TINY BLUETOOTH STACK
In this section, we report on the design and implementation
of our Tiny Bluetooth stack. We compare it to the
ETH Bluetooth stack for the BTnodes and to existing communication
stacks developed for TinyOS.
Implementation
The HCI Core component is responsible for making the
HCI interface available in the TinyOS programming model.
This task is facilitated by the fact that both HCI and TinyOS
are based on an asynchronous programming model. TinyOS
commands are naturally mapped onto HCI commands. HCI
events need to be dispatched into TinyOS events.
Figure 3 illustrates how events are handled: The UART
component generates an event for each byte it receives. This
event is handled by HCI Packet in the UART interrupt context.
Once a packet is constructed with bytes from the
UART, the HCI Packet event handler posts a task that in
turn generates an event (this way this event will not be processed
in the UART interrupt context).
Related Work
Oliver Kasten [10] implemented a Bluetooth stack for the
BTnodes as part of the Smart-its software package. One of
their priorities was to make the BTnodes accessible from any
Bluetooth device. As a result, they implemented part of the
higher Bluetooth layers (link control, connection management
and profile). Our emphasis was different: we focused
on an efficient access to the Bluetooth radio for TinyOS applications
deployed on BTnodes. Minimal support for heterogeneity
could be added by implementing support for connectionless
l2cap packets in a component on top of the Tiny
Bluetooth stack.