Low-Power Wireless Bus Federico Ferrari 1, Marco Zimmerling 1, Luca Mottola 2, Lothar Thiele 1 1...
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Transcript of Low-Power Wireless Bus Federico Ferrari 1, Marco Zimmerling 1, Luca Mottola 2, Lothar Thiele 1 1...
Low-Power Wireless Bus
Federico Ferrari1, Marco Zimmerling1, Luca Mottola2, Lothar Thiele1
1 Computer Engineering and Networks Laboratory, ETH Zurich, Switzerland2 Politecnico di Milano, Italy and Swedish Institute of Computer Science (SICS)
SenSys '12, November 7, 2012Toronto, ON, Canada
Low-Power Wireless Bus 2
Low-Power Wireless Applications
November 7, 2012
Have diverse communication requirements…
Environmental monitoring:
Long-term data collectionat a single sink
PermaSense [Beutel et al., IPSN 2009]
Low-Power Wireless Bus 3
Clinical monitoring:
Mobile nodes immersed in static infrastructure
[Chipara et al., SenSys 2010]
Have diverse communication requirements…
Low-Power Wireless Applications
November 7, 2012
Low-Power Wireless Bus 4
Have diverse communication requirements…
Low-Power Wireless Applications
November 7, 2012
Closed-loop control:
Collection at multiple sinks and dissemination
TRITon [Ceriotti et al., IPSN 2011]
Low-Power Wireless Bus 5
Have diverse communication requirements…
Low-Power Wireless Applications
November 7, 2012
Employ increasingly complex protocol ensembles
• Which protocol(s) for future applications?– Distributed control loops– Highly mobile scenarios
DRAP + CTP+ custom MAC
Custom collection/ dissemination + LPL
Dozer
Low-Power Wireless Bus 6
Low-Power Wireless Bus (LWB)
• Shared bus for low-power wireless networks,where all nodes receive all packets– Multiple communication patterns– Node mobility without performance loss– Resilience to topology changes– High reliability and efficiency
November 7, 2012
Low-Power Wireless Bus
Low-Power Wireless Bus 7
LWB Design Principles
• Use only network floods– Multi-hop wireless network Shared bus
• Synchronized, time-triggered operation– Collision-free and efficient bus accesses
• Centralized scheduling– A controller node orchestrates all communication
November 7, 2012
controller
Low-Power Wireless Bus
Low-Power Wireless Bus 8
Network Flooding: Glossy
• Fast and reliable– A few ms to flood > 100 nodes– Reliability > 99.99 % in most scenarios
• Accurate global time synchronization (< 1 ms)– Enables time-triggered operation
• No topology-dependent state– Enables support for mobility
November 7, 2012
[Ferrari et al., IPSN 2011]
Low-Power Wireless Bus 9
Time-Triggered Operation
• LWB operation is confined to rounds
• A round consists of non-overlapping slots
• Each slot correspondsto a distinct flood
November 7, 2012
Round period T t
n1 n2 n3n1
n1
n2
n3
Low-Power Wireless Bus 10
Time-Triggered Operation
• LWB operation is confined to rounds
• A round consists of non-overlapping slots
• Each slot correspondsto a distinct flood
November 7, 2012
Round period T t
n1 n2 n3n2
n1
n2
n3
Low-Power Wireless Bus 11
Time-Triggered Operation
• LWB operation is confined to rounds
• A round consists of non-overlapping slots
• Each slot correspondsto a distinct flood
November 7, 2012
Round period T t
n1 n2 n3n3
n1
n2
n3
Low-Power Wireless Bus 12
• Add and remove periodic streams of datastream_id add_stream(period, start_time)void remove_stream(stream_id)
• Send and receive application datavoid send_data(&data)void data_received(&data)
Low-Power Wireless Bus
Application Interface
November 7, 2012
controllerApplication
add_stream()
remove_stream()
send_data()
data_received()LWB
Low-Power Wireless Bus 13
Centralized Scheduling
• Scheduler: active at the controller– Receives stream requests– Computes communication schedule
• Round period T• Allocation of slots to streams
• Example scheduling policy– Minimize energy while providing enough bandwidth– Ensure fair allocation of slots to streams
November 7, 2012
T tn1 n2 n3
Low-Power Wireless Bus 14
LWB Activity during a Round
• Schedule: sent by the controller, also for time-sync• Data: transmitted by allocated sources• Contention: competed by sources for stream requests
November 7, 2012
T t
controller
Schedule
(not allocated)
Contention
n1
Data
n2
Data
n3
Data
…controllercomputes
new schedule
Low-Power Wireless Bus 15
0
Example LWB Execution
November 7, 2012
n2n1
c
t = 0Schedule Contention
n1 generates packets at t = 0, 3, 6, …, 60, …
add stream
Receivefrom n1
Computenew schedule
T = 1{Ø}
add stream
n2 generates packets at t = 0, 5, 10, …, 60, …
add stream
Receivefrom n1
Computenew schedule
T = 1{Ø}
add stream
t
c
n1
n2
c is aware of n1’s data stream
Low-Power Wireless Bus 16
1
Example LWB Execution
November 7, 2012
n2n1
c
t = 1
Computenew schedule
T = 1{n1}
data 0
add stream
Schedule ContentionData
Computenew schedule
T = 1{n1}
data 0
add stream
0 t
c
n1
n2
c is aware of n1’s and n2’s data streams
n1 generates packets at t = 0, 3, 6, …, 60, …n2 generates packets at t = 0, 5, 10, …, 60, …
Low-Power Wireless Bus 17
20
Example LWB Execution
November 7, 2012
n2n1
c
t = 2Schedule ContentionData
Computenew schedule
T = 1{n2}
data 0
Computenew schedule
T = 1{n2}
data 0
1 t
c
n1
n2
Allocate slots for packets ready to be transmitted
n1 generates packets at t = 0, 3, 6, …, 60, …n2 generates packets at t = 0, 5, 10, …, 60, …
Low-Power Wireless Bus 18
…
60210
Example LWB Execution
November 7, 2012
n2n1
c
t = 60
t
c
n1
n2
Computenew schedule
T = 30{n1,n2}
data 60
data 60
Schedule ContentionData Data
Traffic is stable: Increase T
n1 generates packets at t = 0, 3, 6, …, 60, …n2 generates packets at t = 0, 5, 10, …, 60, …
Low-Power Wireless Bus 19
120……
60210
Example LWB Execution
November 7, 2012
n2n1
c
t = 90
t
c
n1
n2
Computenew schedule
T = 30{n1,n2}
S C
Computenew schedule
Data
…
63 66 69 72 75 78 81 84 87 90
65 70 75 80 85 90
90
n1 generates packets at t = 0, 3, 6, …, 60, …n2 generates packets at t = 0, 5, 10, …, 60, …
Low-Power Wireless Bus 20
LWB Run-Time Challenges
• Node failures– Remain operational after controller failures– Stop allocating slots to failed sources
• Communication failures– Nodes communicate only if synchronized
• Promptly adapt to traffic changes– Decrease T after a received stream request
November 7, 2012
Low-Power Wireless Bus 21
Evaluation Methodology
• LWB prototype
– On top of Contiki, targeting Tmote Sky nodes
• Metrics
– Data yield: fraction of packets received at sink(s)
– Radio duty cycle: fraction of time with radio on
November 7, 2012
Low-Power Wireless Bus 22
Evaluation Methodology
• Four testbeds
• Seven combinations of routing+MAC protocols
November 7, 2012
Testbed TWIST KANSEI CONETIT LOCAL
Location TU Berlin Ohio State Univ. Univ. of Seville ETH ZurichNodes 90 260 26 (5 mobile) 55Diameter 3 hops 4 hops 3 hops 5 hops
Scenario ProtocolsMany-to-one CTP+{CSMA, LPL, A-MAC}, DozerMany-to-many Muster+{CSMA, LPL}Mobile sink/sources BCP+CSMA, CTP+CSMA
Low-Power Wireless Bus 23
Key Evaluation Findings(256 runs, 838 hours)
The same LWB prototype:
• Is efficient under a wide range of traffic loads
• Supports mobile nodes with no performance loss
• Outperforms many-to-many state of the art
• Is minimally affected by interference or failures
November 7, 2012
The same LWB prototype:
• Is efficient under a wide range of traffic loads
• Supports mobile nodes with no performance loss
• Outperforms many-to-many state of the art
• Is minimally affected by interference or failures
Low-Power Wireless Bus 24
sink
LOCAL (5 hops):1 sink, 54 sourcesgeneration period: 2 min
• High data yield (99.98 %)
• Low, even radioduty cycle (0.43 %)
• Average performancecomparable to Dozer
• Outperforms contention-based protocols
November 7, 2012
Many-to-One: Light Traffic
Low-Power Wireless Bus 25
sink
LOCAL (5 hops):1 sink, 54 sources14 with varying generation period
• LWB promptly adaptsto varying traffic load– Round period T– Slot allocation
• Additional complexityto make Dozer andLPL adaptable
November 7, 2012
Many-to-One: Fluctuating Traffic
Low-Power Wireless Bus 26
(1 m/s)sink
CONETIT (3 hops):1 sink, 25 sourcesgeneration period: {4, 2, 1} s
• LWB performs as instatic scenarios(no topology-dependentstate to update)
• Performance losswith BCP
Static vs. Mobile Sink
November 7, 2012
Low-Power Wireless Bus 27
Limitations
• Scalability– Linear with total amount of traffic– Outperforms state of the art at 52 pkt/s
• Impact of network diameter– Efficiency decreases in long networks– 14 hops: up to 300 streams with a period of 5 s
November 7, 2012
Low-Power Wireless Bus 28
Conclusion: Simplicity = Efficiency
• LWB: Unified solution for diverse applications
– Flooding for all communication
– Time-triggered and centralized operation
– Highly reliable and energy-efficient
– Same performance with mobility
November 7, 2012
Self Managing Situated ComputingERC advanced grant
Low-Power Wireless Bus 29
Questions?
November 7, 2012