Sensor Networks

1
Sensor Networks
2
Outline

• Introduction and Issues
• Architecture and Applications
• Localization
• Routing and Intercommunication
• MAC Layer Issues
• Security Issues

3
What are Sensor Networks?

• A group of wireless nodes or embedded devices
• Collectively the nodes sense, collect, and
  analyze data
• The sensor nodes are small, low power,
  inexpensive, and have high SNR.
• The network usually consists of a large number of
  dense nodes distributed at random
• They can be deployed in any kind of terrain with
  hostile environment places where traditional
  wired network cannot be deployed

4
Sensor Network Architecture
SINK
Internet/ Satellite
TASK MANAGER
5
Sensor Node Architecture

• Sensor nodes include a combination of
• Microelectromechanical systems (MEMS) such as
  sensing devices, actuators, RF components, and
  CMOS building blocks
• Low power computing and wireless networking
  support

6
Architecture of a Sensor Node
Software
Processor
Trans- ceiver
Sensing Unit
A/D
Memory
Battery Power
7
Applications of Sensor Networks

• Surveillance and security
• Environmental monitoring
• Transport monitoring
• Precision agriculture
• Smart spaces
• Manufacturing and inventory control
• Other specialized tasks

8
Different from cellular networks and MANETS?

• Cellular networks and MANETs are designed to
  provide good throughput/delay characteristics
• Cellular networks and MANETs are supposed to
  facilitate high-bandwidth QoS-sensitive
  applications
• Mobility management is a big concern in cellular
  networks and MANETs.
• Nodes can be identified by their assigning IP
  addresses.

9
Differences - continued

• Sensor networks consists of thousands of nodes
  designed for unattended operations
• Traffic in sensor networks in statistical in
  nature requires low data rate
• Addressing may be attribute based
• The flow of data in sensor networks is
  predominantly unidirectional
• Prolonging the battery life is a prime goal the
  batteries are usually not rechargeable

10
Operational Challenges

• Ad hoc deployment should be able to discover the
  topology and self-configure for
  intercommunication
• Dynamically adapt to changes in topology due to
  node failures and environmental conditions
• Automatic configuration/reconfiguration
• Untethered for energy and communication

11
Localization Issues

• What is Localization?
• Why is it important?
• Categorization
• Some Localization Mechanisms
• GPS
• Beacon based ranging
• Range free methods

12
What is Localization?

• A mechanism for discovering spatial relationships
  between objects

13
Why is Localization Important?

• Sensor Network Data is typically interpreted
  based on a sensors location
• report event origins
• giving raw sensor readings a physical context
• Temperature readings ? temperature map
• objects tracking
• Enables data-centric network design
• assist with routing
• evaluate network coverage

14
Categorization Bulusu00

• Coarse-grained Localization
• Proximity to a given reference point
• E.g., Active Badge
• Fine-grained Localization
• Coordinates estimation
• E.g., Distance to a given reference point

15
Fine-Grained Localization

• Ranging based methods
• Timing
• Signal Strength
• Directionality Based
• Ranging free methods
• E.g. Centroid based, DV-hop, APIT

16
Ranging (Distance Measuring) Techniques

• Time based methods
• Time of Arrival (ToA), TDoA
• Used with radio, IR, acoustic, ultrasound
• Signal Strength
• Uses received signal strength indicator (RSSI)
  readings and wireless propagation model
• Directionality based
• Angle of Arrival (AoA) measured with directional
  antennas or arrays

17
Timing

• Time of flight of communication signal
• Signal Pattern
• Global Positioning System
• Local Positioning System
• Pinpoints 3D-iD
• Different modalities of communication
• Active Bat

18
Signal Strength

• Attenuation of radio signal increases with
  increasing distance
• RADAR
• Wall Attenuation Factor based Signal Propagation
  Model
• RF mapping

19
Directionality Based Fine-Grained Localization

• Small Aperture Direction Finding
• Used in cellular networks
• Requires complex antenna array
• Disadvantages
• Costly
• Not a receiver based approach

20
Basic Concepts in Ranging

• Trilateration
• Triangulation
• Multi-lateration
• Considers all available beacons

Sines Rule
B
b
A
C
a
c
Cosines Rule
21
Localization Mechanisms

• GPS
• Beacon based ranging
• Range free methods

22
Global Positioning System (GPS) Getting93

• Started in 1973, built in 1993
• Wide-area radio positioning system
• Ranging-based method
• Using Timing of Arrival (ToA)

23
GPS System Architecture

• Constellation of 24 NAVSTAR satellites made by
  Rockwell
• Altitude 10,900 nautical miles
• Orbital Period 12 hours
• At least five satellites in view from every point
  in the Globe

24
How GPS Works

• The basis of GPS is trilateration" from
  satellites
• Distance measuring based on ToA
• accurate timing is important
• Along with distance, you need to know exactly
  where the satellites are in space
• High orbits and careful monitoring are the secret
• Finally you must correct for any delays the
  signal experiences as it travels through the
  atmosphere
• A Fourth satellite used for correction purpose

25
Differential GPS

• Ground-based Station with known location
  information can estimate the GPS measure errors
• These error estimations are made available to
  other GPS users in the area
• allow them to mitigate errors in their
  measurements
• such differential corrections are transmitted
  in real time over a FM radio link

26
GPS Not Always Applicable

• Many contexts you cannot have GPS on every node
• form factor
• energy
• cost
• obstructions

• Beacon based approaches for sensor networks
• Ranging based v.s. ranging free

27
Beacon Based Location Discovery Savvides01
28
Beacon Based Location Discovery

• No need of GPS
• No infrastructure support
• Ad hoc deployable
• Use RSSI for measuring node separation
• But how should the beacons be placed?
• Distributed Localization
• Iterative multilateration

29
Localization Approach

• Single hop beaconing
• Iterative multilateration
• Dynamic estimate the wireless channel parameters
• Can be done in conjunction with routing

30
Iterative Multilateration

• Start with a small number of beacons
• Number of beacons increases as more nodes
  estimate their positions

31
Advantages

• Data packets also act as beacon signals
• Location discovery is almost free
• Distributed
• relies on neighborhood information
• Fault tolerant

However, Ranging still requires expensive
circuits!
32
Range Free Methods

• Centroid approach Bulusu00
• Adaptive beacon placement Bulusu01
• Self-configuring localization Bulusu03
• DV-hop Niculescu01
• AoA approach Niculescu03
• APIT He03

33
Centroid Based Approach Bulusu00

• Multiple nodes serve as reference points
  (Beacons)
• Reference points transmit periodic beacon signals
  containing their positions
• Receiver node finds reference points in its range
  and localizes to the intersection of connectivity
  regions of these points

34
Model
35
Centroid Based Localization

• (Xest, Yest) (avg(Xi1Xik), avg(Yi1Yik))
• k No. of beacon nodes within connectivity range
• Xi1Xik Yi1Yik Beacon nodes locations

• Disadvantages
• Design using a idealized radio model with perfect
  spherical radio propagation
• Assume a regular grid of nodes with known
  location information to serve as Beacons

36
Impact of Beacon Placement
Beacons randomly placed LARGER mean granularity
37
Impact of Propagation Vagaries
38
Self-configuring Beacon Systems

• Idea
• Measure and adapt to unpredictable environment
• Exploit spatial diversity and density of
  sensor/actuator nodes
• Assuming large solution space, not seeking global
  optimal
• Questions
• What to measure?
• How to adapt?

39
Self-configuring Beacon Systems Bulusu02

• Three schemes
• GRID
• HEAP
• STROBE

40
GRID a Centralized Approach
41
HEAP a localized approach

• Given
• S set of all beacons reachable in grid
• E - An error estimation model
• Determine C - (x , y)
• Such that cumulative localization error in the
• grid is minimized by adding beacon at C

42
HEAP Illustration
43
STROBE Adaptive Density

• STROBE Selectively TuRning Off BEacons
• Goals
• Conserve energy to extend system lifetime without
  diminishing localization granularity
• Design Goals
• Localized algorithms
• Responsive but low adaptation overhead

44
STROBE Illustration
SLEEP state VOTING state DESIGNATED state
45
DV-Hop Niculescu01

• Standard DV propagation
• Never measures node distance
• Insensitive to signal strength errors
• Basic idea
• Range hop_count hop_size

46
DV-Hop How It Works

• Each node maintains a table Xi, Yi, hi by
  running classic DV
• Each Landmark Xi, Yi
• Compute a correction Ci and flood into the
  network
• Each node
• Use the correction from the closest landmark
• Multiply its hop distance by the correction

47
DV-Hop Example
48
DV-Hop Example (contd.)

• Landmarks compute corrections
• Assume A gets its correction from L2
• A estimates its ranges to the landmarks
• L1 316.42, L2 216.42, L3 316.42
• A performs trilateration with the above ranges

49
APIT He03

• Basic idea
• Point-In-Triangle Test (PIT)
• three anchors determine a triangle
• Repeat PIT tests with different anchor
  combination, until accuracy requirement is
  satisfied
• Calculate center of gravity (COG)

50
APIT Overview

• Area-based APIT narrow down the area

51
Localization Wrap up

• Localization is important in sensor networks
• GPS is useful, but not always applicable
• Beacons (aka, anchors, landmarks) can help
• Range based methods
• Range free methods

52
Routing in Sensor Networks

• Multihop Routing with the following constraints
  and features
• Power efficiency
• Attribute-based addressing
• Location awareness
• Data-centric (communication is for named data)

53
Routing Protocols

• Flooding
• Directed Diffusion
• SPIN
• Low Energy Adaptive Clustering Hierarchy (LEACH)
• Rumor Routing

54
Flooding

• Flooding is the simplest form of routing
• Each node broadcast the packets to all its
  neighbors and the process repeat until a maximum
  number of hops or the packet reaches its
  destination
• Problems
• Implosion (multiple copies of messages are sent
  to the same node)
• Overlap (Neighbor nodes receive duplicate
  messages because of overlap in observing region)
• Resource Blindness (Unaware of resources, energy)

55
Directed Diffusion Intanagonwiwat00

• Data-centric routing where sink broadcasts the
  request
• The sink sends out requirements in terms of
  attribute-value pairs called as interest
• This dissemination sets up gradients within the
  network designed to draw events
• Events start flowing towards the originators of
  interests along multiple paths
• The sensor network reinforces one or a small
  number of these paths.

56
Directed Diffusion
Event
Event
Event
Source
Source
Source
Sink
Sink
Sink
a) Interest Propagation
c)Data delivery
b) Gradients setup
57
SPIN Heinzelman99

• Sensor Protocols for Information via Negotiation
  (SPIN) uses negotiation and resource adaptation
  to address the deficiencies of flooding
• Propose a family of routing protocols
• Conserves energy by exchanging metadata during
  negotiation
• Nodes monitor and adapt to changes in their own
  energy resources to extend the operating lifetime
  of the system

58
SPIN Protocol
ADV
REQ
DATA
ADV
DATA
REQ
59
LEACH Heinzelman00

• LEACH is self-organizing, adaptive clustering
  protocol
• Randomly selects nodes as cluster-heads to
  distribute the energy load evenly
• High-energy dissipation in communicating with the
  base station is distributed among the sensor
  nodes.
• LEACH performs local data fusion to compress
  the amount of data being sent from the
  cluster-heads to the base station

60
Dynamic Clusters in LEACH
61
Rumor Routing Braginsky02

• A logical compromise between flooding queries and
  flooding event notifications
• Upon witnessing an event, a node
  probabilistically generates an agent, which
  travels the network, propagating information
  about local events to distant nodes.
• A query generated by a node traverses in a random
  direction until a TTL value or when it finds a
  node that has the path to the event
• A query can be retransmitted or flooding can be
  adopted as a last resort.

62
Medium Access Control

• Goals
• Establish communication links
• Fair and efficient sharing of communication links
• Should be energy efficient

63
MAC Layer Issues

• MAC protocols used for cellular networks or
  MANETs are not suitable
• Conventional Types
• Contention-based Channel Access
• Requires the radio transceivers to monitor the
  channels at all times expensive for low radio
  ranges
• Organized Channel Access
• Requires neighbor discovery and synchronization
  among the nodes expensive for sensor networks

64
MAC Protocols

• Self Organized MAC for Sensor Networks (SMACS)
  and Eavesdrop-And-Register (EAR)
• CSMA-based MAC
• Hybrid TDMA/FDMA
• S-MAC

65
SMACS Protocol Sohrabi00

• SMACS is a flat and distributed
  infrastructure-building protocol which enables
  nodes to discover neighbors and establish
  transmission/reception schedules for
  communication without any local or global master
  nodes.
• Neighbor discovery and channel assignment phases
  are combined
• Nonsynchronous slots in the network and randomly
  chosen frequencies are used for establishing the
  communication links.

66
EAR Algorithm

• EAR algorithm provides continuous service to
  mobile nodes
• Mobile nodes assume full control of the
  connection process
• The stationary nodes transmit a pilot signal
  periodically. Mobile nodes eavesdrop and records
  information about the connectivity
• EAR is transparent to SMACS

67
CSMA-based MAC Woo01

• The protocol should support highly correlated and
  dominantly periodic traffic
• Random delays for transmission and phase shifts
  in the backoffs help in robustness and energy
  conservation in sensor networks
• An adaptive transmission rate control (ARC) is
  adopted.
• Medium access fairness is achieved by balancing
  the rates of originating and route-thru traffic
• A progressive signaling scheme is used to adopt a
  linear increase and multiplicative decrease
  approach
• ARC is also extensible for multi-hop environments

68
Hybrid TDMA/FDMA Shih01

• Centrally controlled
• Pure TDMA dedicates full bandwidth to a single
  sensor node pure FDMA allocates minimum signal
  bandwidth per node
• The Hybrid TDMA/FDMA scheme optimizes the power
  consumption of the transmitter (TDMA) and the
  receivers (FDMA)
• The hybrid approach results in lowering the
  overall power consumption of the system

69
S-MAC Ye02

• Sensor-MAC Inspired by PAMAS, but uses in-band
  signaling
• Attempt to address all the following sources of
  power inefficiency
• Collision - due to follow-on transmissions on
  collisions
• Overhearing - node listens to packets meant for
  another destination
• Control packet overhead
• Idle listening - listening to receive possible
  traffic that is not sent (consumes 50- 100 of
  energy spent for receiving)

70
S-MAC overview

• Avoid collisions
• uses CSMA/CA (basic 802.11)
• Avoid overhearing
• puts a node to sleep when the neighboring nodes
  are transmitting
• Control overhead
• Applies message passing
• Avoid idle listening
• periodic listen and sleep (scheduled pattern)

71
Constraints (SmartDust Node link-1)

• Limited Computational Power
• 8 bit, 4 MHz
• Limited Memory
• 8 KB Instruction Flash (Tiny OS 3500 bytes)
• 512 bytes RAM, 512 bytes EEPROM
• Limited Bandwidth and Range
• 10 Kbps
• Hence, Public Key and Key Exchange protocols are
  not suitable

72
SPINS Perrig02

• Components
• SNEP Secure Network Encryption Protocol
• Data Confidentiality
• Two party data authentication
• Integrity
• Freshness
• µTESLA
• Authenticated broadcast

73
SPINS Architecture

• Base Stations (BS)
• Trusted
• Longer lifetime
• Larger memory
• Secret key between node and BS
• Single block cipher implements all cryptographic
  functions
• RC5 algorithm used
• Loose time synchronization

74
SNEP

• Endpoints(A,B) share a secret symmetric key ?AB
• Pseudo random function F used to generate
• Two keys for encryption (KAB and KBA)
• Two keys for message authentication (KAB and
  KBA)
• Counters used at both endpoints to ensure data
  freshness

75
SNEP Encryption

• Encryption done in counter mode
• M(K,ctr)

76
SNEP MAC

• MAC implemented using Cipher Block Chaining
• MAC(K,x)

77
µTESLA

• Authenticated broadcast by BS using MAC
• Loose time synchronization required
• Base station sends messages authenticated by key
  that is secret at that time
• All messages in a single time slot use same key
• Key revealed d time slots after use
• Node stores message until key is disclosed

78
µTESLA (contd.)

• One way key chain used by sender
• Last key Kn chose randomly
• Keys generated by Ki F(Ki1)
• F one way function
• Sender can authenticate key by verifiying Ki
  F(Ki1)

79
References

• Bharghavan94 V. Bharghavan, A. Demers, S.
  Shenker and L. Zhang, MACAW a media access
  protocol for wireless LANs, SIGCOMM94.
• Braginsky02 David Braginsky and Deborah Estrin.
  Rumor Routing Algorithm For Sensor Networks. In
  Proceedings of the First Workshop on Sensor
  Networks and Applications (WSNA), September 28
  2002, Atlanta, GA.
• Buchegger02 S. Buchegger and J. L. Boudec,
  Nodes Bearing Grudges Towards Routing Security,
  Fairness, and Robustness in Mobile Ad Hoc
  networks, Euromicro Workshop on Parallel,
  Distributed, and Network-Based Processing, 2002.
• Bulusu01 N. Bulusu, John Heidemann and Deborah
  Estrin. Adaptive Beacon Placement. In Proceedings
  of the Twenty First International Conference on
  Distributed Computing Systems (ICDCS-21), April,
  2001.
• Bulusu02 N. Bulusu. Self-Configuring
  Localization Systems, Ph.D Thesis, University of
  California at Los Angeles, October 2002.
• Bulusu00 N. Bulusu, John Heidemann and Deborah
  Estrin. GPS-less Low Cost Outdoor Localization
  for Very Small Devices. IEEE Personal
  Communications Magazine, Vol. 7, No. 5, pp.
  28-34. October, 2000.
• Bulusu03 N. Bulusu, J. Heidemann, D. Estrin,
  and T. Tran. Self-configuring Localization
  Systems Design and Experimental Evaluation. ACM
  Transactions on Embedded Computing Systems(TECS),
  Special Issue on Networked Embedded Computing,
  May 2003.
• Campbell01 A. Veres, A.T. Campbell, M. Barry,
  and L.H. Sun, Supporting service differentiation
  in wireless packet networks using distributed
  control, IEEE J. SAC, Oct, 2001.
• Chen99 S. Chen and K. Nahrstedt, "Distributed
  Quality-of-Service Routing in Ad-Hoc Networks,"
  IEEE Journal of Selected Areas on Communications,
  vol. 17, No. 8, August 1999.

80

• Chiang97 C.-C. Chiang, Routing in Clustered
  Multihop, Mobile Wireless Networks with Fading
  Channel, IEEE SICON (Singapore International
  Conference on Networks) , Apr, 1997
• Choudhury02 R. R. Choudhury, X. Yang, N.
  Vaidya, R. Ramanathan, Using directional
  antennas for medium access control in ad hoc
  networks, Mobicom, 2002.
• Dawkins76 R. Dawkins, The Selfish Gene, Oxford
  University Press, 1989 Edition, 1976.
• Getting93 I. A. Getting, "The Global
  Positioning Systems," IEEE Spectrum, pp. 36--47,
  December 1993.
• Haas97Z.J. Haas, "A New Routing Protocol for
  the Reconfigurable Wireless Networks", IEEE Intl.
  Conf. on Universal Personal Comm. (ICUPC'97), San
  Diego, Oct. 1997.
• He03 T. He, C. Huang, B. M. Blum, J. A.
  Stankovic,and T. F. Abdelzaher. Range-Free
  Localization Schemes in Large Scale Sensor
  Networks, the Ninth Annual International
  Conference on Mobile Computing and Networking
  (MobiCom 2003), San Diego, CA, September 2003.
• Heinzelman99 W. Heinzelman, J. Kulik, and H.
  Balakrishnan, Adaptive Protocols for
  Information Dissemination in Wireless Sensor
  Networks,'' Proc. 5th ACM/IEEE Mobicom Conference
  (MobiCom '99), Seattle, WA, August, 1999.
• Heinzelman00 Wendi Heinzelman, Anantha
  Chandrakasan, and Hari Balakrishnan,
  Energy-Efficient Communication Protocols for
  Wireless Microsensor Networks, Proc. Hawaaian
  Int'l Conf. on Systems Science, January 2000. 
•  Intanagonwiwat00 C. Intanagonwiwat, R.
  Govindan and D. Estrin. Directed Diffusion A
  Scalable and Robust Communication Paradigm for
  Sensor Networks. In Proceedings of MobiCOM 2000,
  August 2000, Boston, Massachusetts.
• Johnson96 D.B. Johnson, and D.A. Maltz,
  Dynamic Source Routing in Ad-Hoc Wireless
  Networks, Mobile Computing, T. Imielinkski and
  H. Korth, Eds., Kluwer, 1996, pp 153-181.

81

• Karn90 P. Karn, MACA a new channel access
  method for packet radio, Amateur Radio 9th
  Computer Networking Conference, 1990.
• Kleinrock75 L.Kleinrock and F.A.Tagobi,
  Packet switching in radio channels Part-II The
  hidden terminal problem in carrier sense
  multiple-access modes and the busy tone
  solution, IEEE Trans. Comm. Vol 23, no 12, 1975
• Ko00 Y.-B. Ko, V. Shankarkumar, N. Vaidya,
  Medium Access Control Protocols using
  Directional Antennas in Ad Hoc Networks, Infocom
  2000
• Ko98 Y. B. Ko and N. H. Vaidya,
  Location-Aided Routing (LAR) in Mobile Ad Hoc
  Networks, Mobicom, 1998.
• Lai02 B.C. Lai, S. Kim, I. Verbauwhede.
  Scalable session key construction protocol for
  wireless sensor networks. IEEE Workshop on Large
  Scale Real-Time and Embedded Systems (LARTES).
  December 2002
• Lee99S.J. Lee, M. Gerla, and C.C. Chiang,
  On-Demand Multicast Routing Protocol, IEEE
  WCNC, 1999.
• Lee98 S. Lee and A. T. Campbell "INSIGNIA
  In-band signaling support for QOS in mobile ad
  hoc networks", Proc of 5thInternational Workshop
  on Mobile Multimedia Communications (MoMuC,98) ,
  Berlin,Germany, October 1998.
• Li03 J. Li and P. Mohapatra, LAKER Location
  Aided Knowledge Extraction Routing for Mobile Ad
  Hoc Netwoks, WCNC 2003.
• Li03 Jian Li, and Prasant Mohapatra. "A Novel
  Mechanism for Flooding Based Route Discovery in
  Ad Hoc Networks," IEEE GlobeCom 2003 .
• Liao01 Wen-Hwa Liao, Yu-Chee Tseng, Shu-Ling
  Wang, Jang-Ping Sheu A Multi-path QoS Routing
  Protocol in a Wireless Mobile ad Hoc Network. ICN
  (2) 2001 158-167.

82

• Lin97 C.R. Lin, and M. Gerla, MACA/PR An
  Asynchronous Multimedia Multihop Wireless
  Network, IEEE INFOCOM, 1997
• Lin99 C. R. Lin and J. S. Liu, QoS routing in
  Ad hoc Wireless Networks", IEEE Journal on
  Selected Areas in Communications, August 1999.
• Liu01J. Liu, and S. Singh, ATCP TCP for
  mobile ad hoc networks, IEEE J-SAC, July, 2001
• Liu99M. Liu, R.R. Talpade, A. McAuley, and E.
  Bommaiah, AMRoute Adhoc Multicast Routing
  Protocol, Computer Science Dept. U. Maryland,
  TR-99-8
• Mohapatra03 P. Mohapatra, J. Li, and C. Gui,
  QoS in Mobile Ad Hoc Networks, IEEE Wireless
  Communications, June 2003.
• Murthy96 S. Murthy and J.J. Garcia-Luna-Aceves,
  An Efficient Routing Protocol for Wireless
  Networks, ACM MONET, Oct, 1996, pp 183-197
• Nasipuri00 A. S. Nasipuri, S. Ye, and R. E.
  Hiromoto, "A MAC Protocol for Mobile Ad Hoc
  Networks Using Directional Antennas", WCNC 2000
• Niculescu01 D. Niculescu and B. Nath, "Ad hoc
  Positioning System (APS)", GLOBECOM 2001, San
  Antonio, Nov 2001.
• Niculescu03 D. Niculescu and B. Nath, "Ad hoc
  Positioning System (APS) using AoA", INFOCOM 2003.

83

• Perkins94C. Perkins, Highly Dynamic
  Destination-Sequenced Distance-Vector Routing
  (DSDV) for Mobile Computers, ACM SIGCOMM, 1994
• Perkins99 C.E. Perkins, and E.M. Royer,
  Ad-hoc On-Demand Distance Vector Routing, IEEE
  Workshop on Mobile Computing Systems and
  Applications, Feb, 1999
• Perrig01 A. Perrig, R. Szewczyk, V. Wen, D.
  Culler, and J. Tygar. SPINS Security Protocols
  for Sensor Networks. In Seventh Annual ACM
  International Conference on Mobile Computing and
  Networks(Mobicom) 2001.
• Royer99E. Royer, and C.E. Perkins, Multicast
  operations of the ad-hoc on-demand distance
  vector routing protocol, ACM MOBICOM, 1999
• Sawide01 A. Savvides, C.C. Han and M. B.
  Srivastava, Dynamic Fine Grained Localization in
  Ad-Hoc Sensor Networks, Proceedings of the Fifth
  International Conference on Mobile Computing and
  Networking, Mobicom 2001, pp. 166-179, Rome,
  Italy, July 2001 
• Schurgers02C. Schurgers, V. Tsiatsis, S.
  Ganeriwal, and M. Srivastava, Optimizing Sensor
  Networks in the Energy-Latency-Density Design
  Space, IEEE Tran. Mobile Comp. Vol. 1, No. 1,
  Jan-Mar, 2002
• Shah01 Samarth H. Shah, Kai Chen, Klara
  Nahrstedt, Cross Layer Design for Data
  Accessibility in Mobile Ad Hoc Networks, in Proc.
  of 5th World Multiconference on Systemics,
  Cybernetics and Informatics (SCI 2001), Orlando,
  Florida, July, 2001.
• Shih01 Eugene Shih, Seong-Hwan Cho, Nathan
  Ickes, Rex Min, Amit Sinha, Alice Wang, and
  Anantha Chandrakasan. Physical Layer Driven
  Algorithm and Protocol Design for Energy-Ecient
  Wireless Sensor Networks. In Proceedings of
  MOBICOM 2001

84

• Singh98 S. Singh and C.S. Raghavendra, PAMAS
  power aware multi-access protocol with
  signaling for ad hoc networks, ACM SIGCOMM, 1998
• Sinha99a P. Sinha, R. Sivakumar, and V.
  Bharghavan, CEDAR A core extraction distributed
  ad hoc routing algorithm. In Proc. of IEEE
  Infocom, 1999.
• Sinha99bP. Sinha, R. Sivakumar and V.
  Bharghavan, MCEDAR Multicast extensions to
  Core-Extraction Distributed Ad hoc Routing
  algorithm'', IEEE WCNC, 1999
• SmartDust http//robotics.eecs.berkeley.edu/pis
  ter/SmartDust/
• Sobrinho99 J.L. Sobrinho, and A.S.
  Hrishnakumar, Quality-of-Service in Ad Hoc
  carrier sense multiple access wireless networks,
  IEEE J. SAC, Aug, 1999
• Sohrabi00 K. Sohrabi, J. Gao, V. Ailawadhi,
  and G.J. Pottie. Protocols for self-organization
  of a wireless sensornetwork. IEEE Personal
  Communications, 7(5)1627, October 2000.
• Tseng02Y.-C. Tseng, C.-S. Hsu, and T.-Y.
  Hsieh, Power-Saving Protocols for IEEE
  802.11-Based Multi-Hop Ad Hoc Networks, IEEE
  INFOCOM, 2002
• Woo01 A. Woo, D. Culler, A Transmission
  Control Scheme for Media Access in Sensor
  Networks, Mobicom 2001. 
• Ye02 W. Ye, J. Heidemann and D. Estrin. "An
  Energy-Efficient MAC Protocol for Wireless Sensor
  Networks," In Proceedings of the 21st
  International Annual Joint Conference of the IEEE
  Computer and Communications Societies (INFOCOM
  '02), New York, June 2002.
• Zheng03R. Zheng, J. Hou, and L. Sha,
  Asynchronous Wakeup for Power Management in Ad
  Hoc Networks, ACM MOBIHOC, 2003