bluetooth and sensor networks : a reality check
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Bluetooth and Sensor Networks : A Reality Check. Martin Leopold, Mads Dydensborg, Philippe Bonnet University of Copenhagen. A sensor net for sow monitoring Tracking in large pens Heat period alert Motion detectors Correlation between movement of sows (circles) and their heat period - PowerPoint PPT PresentationTRANSCRIPT
Bluetooth and Sensor Networks :A Reality Check
Martin Leopold, Mads Dydensborg, Philippe Bonnet
University of Copenhagen
Hogthrob• A sensor net for sow monitoring
– Tracking in large pens– Heat period alert
• Motion detectors• Correlation between movement of sows (circles) and
their heat period
• Sensor net– Interferences– Mobile nodes + Fixed infrastructure
• Sensor nodes– 2 years lifetime– Low cost– Packaged for tough conditions
Radio technology is key.Spread spectrum radios are natural candidates.Is Bluetooth a good option?
Bluetooth and Sensor Networks:Promises and Challenges
• Off-the-shelf radio– Representative of spread-spectrum
radios (frequency hopping)– Free 2.4 GHz band– Promise to be cheap
• The Bluetooth stack is complex– Stripped down version of
Bluetooth adapted to constraints of sensor nodes?
• A Bluetooth module embeds front-end radio, baseband and MAC layer
– Are standard Bluetooth physical layer and MAC layer adapted to the sensor network regime?
• Multihop capabilities – Scatternet support has been
announced for years but was not supported at the time of our study
– How to build multihop Bluetooth-based networks?
• Bluetooth is connection-based– How to define network self-
assembly based on Bluetooth device discovery. What is the impact on performance?
• Bluetooth implements Time Division Multiplexing (TDM) at the radio level
– Can applications leverage radio-driven TDM?
Our Approach
Pragmatic ApproachBTNodes from ETH Zurich
• Atmega 128 7.32 MHz
• 128 KiB flash
• Dual-radio – Ericsson’s Bluetooth
module ROK 101 007
• Port of TinyOS to BTNodes– Development of
TinyBluetooth
• Self-Assembly Procedure• Application using Radio-
level TDM– UC Berkeley’s TinyDB on
top of TinyBluetooth
• Performance Evaluation– Intrinsic properties– Prototype properties
Bluetooth Stack
RF
Baseband
HCI
L2Cap
Profiles
Applications
Physical Bus Hardware
TinyBluetooth Stack
RF
Baseband
HCI
Physical Bus Hardware
TinyBluetooth
TinyOS Application
TinyBluetooth Stack• Asynchronous Programming
Model– HCI mapped onto tinyOS events
and commands– UART events decoupled from
HCI events
• Buffer Trading– Buffers swapped between
modules– Generic Packet type casted into
specific packet depending on event/command
• Interesting information encapsulated inside Bluetooth module
Self-Assembly Procedure
• Each node is equipped with 2 radios
• For each node– To which node to connect?
– Connect as master or slave?• 3 node configurations:
– S-S
– M-M
– M-S, S-M
Self-Assembly Procedure• Building a connection tree as a
baseline (BlueTree [Petrioli, Basagni 2002])– Each node has a radio set up as a
master, the other as a slave– Recursive connection establishment
• First slave radio is turned on.• One node is chosen as the root of
the connection tree.• Master radio turned on once a
connection is established on slave radio.
– Rely on Bluetooth device discovery and connection establishment
M
M
M
M
M
M
M
M
M
S
S
S
S
S
S
S
S
S
UC Berkeley’s TinyDB
• Push declarative queries into sensor net– Impose a hierarchical routing tree onto the
network• Divide time into epochs• Every epoch, sensors evaluate query over (i) local
sensor data and (ii) data from children nodes– Aggregate local and children data– Each node transmits just once per epoch
• Rest of the time, sensors sleep (deep microcontroller sleep)
The TDM is driven by the application: How long should sensors sleep? What if interesting data needs to be transmitted while sensors sleep?
TinyDB on top of TinyBluetooth
• Connection tree supports hierarchical routing tree.
• Radio drives TDM– Bluetooth radio in Sniff mode:
Master and Slaves agree on synchronization points (ideally once per epoch). Rest of time sensor node sleeps or senses. Microcontroller waken up on radio signal.
– Pipelined aggregation along the routing tree.
• Separated Channels– No unplanned collisions
M M
MS
S
S
S
M
M
TinyDB on top of TinyBluetooth
• Problem # 1: The sniff period is not longer than 40 secs.
• Problem # 2: When a connection is in sniff mode, the microcontroller sleeps in idle mode (which is less efficient than the power save mode according to the Atmel specs).
M M
MS
S
S
S
M
M
Code Size Breakdown
Description code bss dataSupport & TinyOS core 1180UART 0 & Interrupts 346 4
UART1 & Interrupts 292 5
hciPacket0 604 155
hciPacket1 588 155
hciCore0 1624 159
hciCore1 1590 159
Assembly Component 4796 1021 16
Total 11020 1658 16
Throughput- Point-to-point throughput ishigh!- The performance weachieve is far from the
theoretical max– UART limit is 45
Kib/sec– Junk sent by
Bluetooth module- Slave-to-master andmaster-to-slave throughputare similar- Throughput degrades forMultipoint connections
73,2 59,73 90,4
0
5
10
15
20
25
30
35
40
45
50
DM1 DH1 DM3 DH3 DM5 DH5Bluetooth Encoding
Th
rou
gh
pu
t (k
b/s
ec
)
20 bytes payload
668 bytes payload (max)
Theoretical max
• DM and DH are two encoding schemes. DM offers a lower error rate.• 1, 3 and 5 corresponds to the number of consecutive slots during which slaves and masters communicate.
1 2 3
Aggregate 38.1 25.4 19.3
Per Slave 38.1 12.7 6.4
Energy Usage Breakdown
• 50mW when idle and 250 mW when communicating
• Berkeley’s mica motes: 10 mW when idle and 160 mW when communicating
Maintaining connections is very expensive
Different sleep modes!
Self Assembly
a. Node is turned on.b. Connection on slave radioc. 1st Connection on master
radiod. 2nd Connection on master
radioe. Master radio is
discoverablef. Data packets are
transmitttedg. Disconnections on master
radioh. Disconnection on slave
radio
Application Characteristics• Throughput is high
– Best suited for applications that transmit lots of data
• Energy consumption is high (in particular connections)– Life time of applicatoin must be short (days)
– Short periods of connections
• Suited for Asynchronous In-Network Processing with radio driven TDM.
Bluetooth-Based Sensor Network well suited for short lived deploymentsWith unplanned burst of data with high throughput (images, video).
Conclusion
• Code available in TinyOS contrib directory• More info on our project home page:
http://www.distlab.dk/manatee
• This study is a baseline for:– Intel motes– 802.15.4 radios– Tailored radios relying on Bluetooth front-end
(Pico Radio)