Presented by: Anuj Srivastava

1
Presented byAnuj Srivastava
Authors Matthew J. Miller Cigdem Sengul
Indranil Gupta ICDCS 2005
2
Exploring Energy-Latency Tradeoffs for Sensor
Network Broadcasts

• Authors
• Matthew J. Miller
• Cigdem Sengul
• Indranil Gupta
• ICDCS 2005

3
Matthew J. Miller

• PhD candidate Dept. of Computer Science,
  University of Illinois at Urbana Champaign
• Interests
• Cross layer designs for energy efficient ad-hoc
  and sensor networks
• Sensor network security

4
Cigdem Sengul

• PhD student Dept. of Computer Science,
  University of Illinois at Urbana Champaign
• Interests
• Ad hoc and Sensor networks
• Routing and energy conservation in ad-hoc networks

5
Indranil Gupta

• PhD Cornell University
• Assistant Professor, Dept. of Computer Science at
  University of Illinois at Urbana Champaign
• Interests
• Distributed systems and protocols
• Fault tolerant distributed systems,
• scalable process group communications,
• peer-to-peer systems
• Real-time systems and
• Ad-hoc networks

6
Key Contributions

• Probabilistic protocol for broadcasting
• Any sleep scheduling protocol
• Analysis of energy-latency trade-off for
  different levels of reliability

7
MAC Layer approaches

• Additional wake-up radio
• Additional hardware
• Active -sleep cycle
• Latency
• Redundant packets

8
Sensor Application 1

• Code Update Application
• E.g., Trickle Levis et al., NDSI 2004
• Updates Generated Once Every Few Weeks
• Reducing energy consumption is important
• Latency is not a major concern

Here is Patch 27
9
Sensor Application 2

• Short-Term Event Detection
• E.g., Directed Diffusion Intanagonwiwat et al.,
  MobiCom 2000
• Intruder Alert for Temporary, Overnight Camp
• Latency is critical
• With adequate power supplies, energy usage is not
  a concern

Look For An Event With These Attributes
10
Energy-Latency Options
Energy
Latency
11
Sleep Scheduling Protocols

• Nodes have two states active and sleep
• At any given time, some nodes are active to
  communicate data while others sleep to conserve
  energy
• Examples
• IEEE 802.11 Power Save Mode (PSM)
• Most complete and supports broadcast
• Not necessarily directly applicable to sensors
• S-MAC/T-MAC
• STEM

12
IEEE 802.11 PSM Example With Broadcasts
N1
N2
N3
ATIM Pkt
Data Pkt
13
IEEE 802.11 PSM

• Nodes are assumed to be synchronized
• Every beacon interval (BI), all nodes wake up for
  an ATIM (Adhoc Trfc Ind Msg) window (AW)
• During the AW, nodes advertise any traffic that
  they have queued
• After the AW, nodes remain active if they expect
  to send or receive data based on advertisements
  otherwise nodes return to sleep until the next BI

14
Protocol Extreme 1
N1
N2
N3
ATIM Pkt
Data Pkt
15
Protocol Extreme 2
N1
N2
N3
ATIM Pkt
Data Pkt
16
Probability-Based Broadcast Forwarding (PBBF)

• Introduce two parameters to sleep scheduling
  protocols p and q
• When a node is scheduled to sleep, it will remain
  active with probability q
• When a node receives a broadcast, it sends it
  immediately with probability p
• With probability (1-p), the node will wait and
  advertise the packet during the next AW before
  rebroadcasting the packet

17
PBBF Comments

• p0, q0 equivalent to the original sleep
  scheduling protocol
• p1, q1 approximates the always on protocol
• Still have the ATIM window overhead
• Effects of p and q on metrics

18
Percolation

• Bond (edge) percolation theory
• Determines the connectivity of a random graph
• Different from Haas Gossip-Based Routing which
  used site (vertex) percolation theory
• A phase transition occurs when the probability of
  an edge between two vertices is greater than the
  critical value
• In this phase, the probability that an infinitely
  large cluster exists in a graph is close to one
• A phase transition occurs when the probability of
  an edge is less than the critical value
• In this phase, the probability that an infinitely
  large cluster exists in the graph is close to zero

19
Analysis Reliability

• In PBBF, the probability that a broadcast is
  received on a link is
• pq (1-p)
• Thus, if pq (1-p) is greater than a critical
  value, then every broadcast reaches most of the
  nodes in the network
• Tested PBBF on grid topology with ideal MAC and
  physical layers

20
Analysis Reliability

• Phase transition when
• pq (1-p) 0.8-0.85
• Larger than bond percolation threshold
• Still shows phase transition

p0.25
p0.37
Fraction of Broadcasts Received by 99 of Nodes
p0.5
p0.75
q
21
Analysis Energy
1 q (BI - AW)/AW
No Power Save
PBBF
Joules/Broadcast
802.11 PSM
q
22
Analysis Latency
p0.75
p0.37
Average 60-Hop Flooding Hop Count
Increasing Reliability
q
23
Analysis Latency
1. Reliability Increasing
2. Phase Transition
3. p Increasing
1
Average Per-Hop Broadcast Latency (s)
p0.05
2
p0.37
3
p0.75
q
24
Analysis Energy-Latency Tradeoff
Achievable region for reliability 99
Joules/Broadcast
Average Per-Hop Broadcast Latency (s)
25
Application Results

• Simulated code distribution application in ns-2,
  where a base station periodically sends patches
  for sensors to apply
• 50 nodes
• Average One-Hop Neighborhood Size 10
• Uniformly random node placement in square area
• Topology connected
• Full MAC layer

26
Application Reliability

• Different reliability metric
• Average fraction of broadcasts received per node
• Better fit for application

p0.5
Average Fraction of Broadcasts Received
q
27
Work In Progress

• Dynamically adjusting p and q to converge to
  user-specified QoS metrics
• E.g., Energy and latency are specified
• Subject to those constraints, p and q are
  adjusted to achieve the highest reliability
  possible

1.0
q
0.5
p
0.0
Time
28
Conclusion
Achievable Region
Energy
Latency
29
Questions???

• Matthew J. Miller
• https//netfiles.uiuc.edu/mjmille2/www
• Cigdem Sengul
• https//netfiles.uiuc.edu/sengul/www
• Indranil Gupta
• http//www-faculty.cs.uiuc.edu/indy

30
Some more ...

• P 0.5 q 0.5
• Power levels for transmit/recv/idle/sleep?
• Assume No collisions cost of retransmit
• 802.15.4

31
802.15.4 For more Information visit
www.IEEE802.org
Following slides, courtsey José A.
Gutierrez Principal Engineer e-mail
JoseGutierrez_at_eaton.com
RF/Communications Group Innovation Center -
Eaton Corp. 4201 North 27th Street Milwaukee, WI.
53216
32
802.15.4 General Characteristics

• Data rates of 250 kb/s, 40 kb/s and 20 kb/s.
• Star or Peer-to-Peer operation.
• Support for low latency devices.
• CSMA-CA channel access.
• Dynamic device addressing.
• Fully handshaked protocol for transfer
  reliability.
• Low power consumption.
• Frequency Bands of Operation
• 16 channels in the 2.4GHz ISM band
• 10 channels in the 915MHz ISM band
• 1 channel in the European 868MHz band.

33
IEEE 802.15.4 MAC Overview Typical Network
Topologies
34
IEEE 802.15.4 MAC Overview Device Classes

• Full function device (FFD)
• Any topology
• Network coordinator capable
• Talks to any other device
• Reduced function device (RFD)
• Limited to star topology
• Cannot become a network coordinator
• Talks only to a network coordinator
• Very simple implementation

35
IEEE 802.15.4 MAC Overview Star Topology
PAN Coordinator
Master/slave
Communications flow
Full function device
Reduced function device
36
IEEE 802.15.4 MAC Overview Peer-Peer Topology
Cluster tree
Point to point
Full function device
Communications flow
37
IEEE 802.15.4 MAC Overview Combined Topology
Clustered stars - for example, cluster nodes
exist between rooms of a hotel and each room has
a star network for control.
Communications flow
Full function device
Reduced function device
38
IEEE 802.15.4 MAC Overview Addressing

• All devices have IEEE addresses
• Short addresses can be allocated
• Addressing modes
• Network device identifier (star)
• Source/destination identifier (peer-peer)

39
IEEE 802.15.4 MAC Overview General Frame Structure

• 4 Types of MAC Frames
• Data Frame
• Beacon Frame
• Acknowledgment Frame
• MAC Command Frame

40
IEEE 802.15.4 MAC Overview Optional Superframe
Structure
GTS 2
GTS 1
Contention Access Period
Contention Free Period
15ms 2n where 0 ? n ? 14
Transmitted by network coordinator. Contains
network information, frame structure and
notification of pending node messages.
Network beacon
Beacon extension period
Space reserved for beacon growth due to pending
node messages
Contention period
Access by any node using CSMA-CA
Guaranteed Time Slot
Reserved for nodes requiring guaranteed bandwidth
n 0.
41
Thanks!