This slides about Wireless sensor network MAC protocol, There are bunch of MAC protocol in research field. It classify the MAC protocol and summarize the feature of typical sensor network MAC protcol

1. Wireless Sensor Network:
MAC protocol
김대우
1

2. 2

3. INTRODUCTION TO WSN01
3

4. Introduction to WSN
Definition:
• A sensor network is composed of a large
number of sensor nodes that are densely
deployed inside or very close to the
phenomenon
– Multi-hop, self-organize
– Wireless communication
– Cooperative sensing, collection, process
– Send to observe.
4

5. Introduction to WSN
WSN communication Architecture
5
Wireless Communication
link
Sensor field
Inaccessible
Environment
Sink
or
Base station (BS)
To External
network
Sensors

6. • Intel Research Laboratory at Berkeley initiated a
collaboration with the College of the Atlantic in Bar
Harbor and the University of California at Berkeley
to deploy wireless sensor networks on Great Duck
Island, Maine (in 2002)
• Monitor the microclimates in and around nesting
burrows used by the Leach's Storm Petrel
• Goal : habitat monitoring kit for researchers
worldwide
Habitat Monitoring on Great Duck Island
Introduction to WSN

7. Introduction to WSN
• Wildfire Instrumentation System Using
Networked Sensors
• A project by University of California, Berkeley
CA.
FireBug

8. Introduction to WSN
Application
8

9. Introduction to WSN
• Differences between WSN and ad-hoc
network
– Battery powered nodes  Energy efficiency
– Large quantity of densely deployed nodes
– This dense deployment brings high degree of
interactions
– Resources constraint
– Auto configuration and auto organization
9

10. Design Considerations
• Level 1 issues
– Energy efficiency
• Often difficult recharge batteries or replace them
• Prolonging the life-time is important
– Collision avoidance - a basic task of MAC protocols
– Good scalability
– Hardware Constraints
• Clock drift
• Memory Constraints
• Level 2 issues
– Latency, fairness, throughput, bandwidth
10

11. The sensor network protocol stack
11
• Power management
• Mobility management
- Sensor node의 움직임
• Localization
- Sensor node의 위치
• Synchronization

12. MEDIUM ACCESS CONTROL02
12

13. MAC
• Link
– 통신 경로상의 인접한 노드들을 연결하는 통신 채널을 링
크라고 한다.
• Link의 종류
– Point-to-point link
– Broadcast link
• multiple access problem
13

14. Challenges for MAC
• Energy Consumption
– Idle listening
– Collisions
– Protocol overhead
– Overhearing
– Transmit vs. receive power
• Event-based Networking
• Correlation
14

15. WSN에서 MAC
• 3 Types of MAC techniques
– Contention Based
– Reservation Based
– Hybrid solution
• CSMA, TDMA가 사용된다.
– FDMA : BW의 한계 때문에 사용하기 힘들다
• Narrow band
– OFDMA, CDMA의 경우 cost constraints
15

16. CONTENTION-BASED MAC02-1
16

17. Carrier Sense Multiple Access(CSMA)
• Listen before transmitting
• Stations sense the channel before transmitting
data packets.
17
S R H
X Collision at R
Hidden Terminal Problem

18. CSMA with Collision Avoidance
• Stations carry out a handshake to determine
which one can send a data packet
18
S R H
RTS
CTS
Data
ACK Backoff due to CTS

19. Contention-Based Medium Access
• 장점
– Flexible
– Robustness
– Scalability
– With out Message exchanges, infrastructure
• 단점
– Density 높아지면 collision probability 높아진다
19

20. Contention-Based Medium Access
• CSMA/CA
– Energy efficiency가 낮다
• Idle listening
• Sleeping mode
20

21. AsynchronousSynchronous
Contention-Based Medium Access
21
Contention-
based MAC
S-MAC B-MAC CC-MAC

22. Synchronous MAC
• Nodes define common active/sleep periods
Active period
– Used for communication
Sleep period
– Saving energy
• Nodes maintain a certain level of
synchronization
22

23. S-MAC
• Design
– Goal
• Reduce energy consumption
• Support good scalability and collision avoidance
– Solutions to energy inefficiency issues
• Collision avoidance - using RTS and CTS
• Overhearing avoidance - switching the radio off when the
transmission is not meant for that node
• Control overhead - Message Passing
• Idle listening - Periodic listen and sleep
23

24. S-MAC (Sleep MAC)
• Goal: Reduce idle listening -> power save
• Trade off : throughput, latency
– Virtual Cluster 구성
24

25. Network Assumption
• Composed of many small nodes
– Short-range, multi-hop communication
• Most communication will be between nodes
as peers, rather than to a single base station
• In-network processing is critical to network life
time
25

26. • Periodic listen and Sleep
– Duty Cycle
– MAC scheme
Periodic Listen and Sleep
26

27. Choosing Schedule (Virtual cluster)
27
Listen first
Set its own
schedule
(Synchronizer)
Broadcast SYNC
Listen SYNC
w/o neighbor
discard schedule
Follow the
schedule
(Follower)
Announce its
schedule
Both schedules
(Border Node)
No signal SYNC

28. Border Node
• Not all neighboring nodes can synchronize
together
• Border node follow both schedule
28
Schedule 2
Schedule 1

29. Maintaining Schedule
• Synchronization error
– Clock Drift
• Solution
– Relative timestamp
– Listen period is significantly longer than clock drift
rates
29

30. Collision Avoidance
• Problem: Multiple senders want to talk
• Solution: Following IEEE 802.11 ad hoc
procedures
– Carrier sense
– Randomized backoff time
– RTS/CTS for hidden terminal problem
– RTS/CTS/DATA/ACK sequence
30

31. Overhearing Avoidance
• Problem: Receive packets destined to others
• Solution: Letting other nodes sleep after they
hear an RTS or CTS packet
– Which nodes should sleep?
• All neighbors except sender and receiver
– How long?
• The duration field in each packet informs other nodes the
sleep interval
• Sleep until the NAV becomes zero
31

32. Adaptive Listening
• Problem : There is potential Delay on each hop
• Solution : Transmit two hop in one duty cycle
– RTS, CTS -> both the neighbors of the sender and
receiver will learn about transmission
32

33. Message passing
• Problem: Sensor net in-network processing
requires entire message
• Solution: Don’t interleave different messages
– Advantages
• Reduces latency of the message
• Reduces control overhead
– Disadvantage
• Node-to-node fairness is reduced, as nodes with small
packets to send has to wait till the message burst is
transmitted
33

34. S-MAC 평가
• 장점
– 기존 CSMA/CA에 비해 Energy를 적게 사용
– Lightly loaded networks에 강하다
– Cluster-based protocol에 적용하기 쉽다
• 단점
– Heavy loaded에선 Energy 이득이 적다
– High-density, Heavy loaded의 경우
Short listen interval 동안의 contention으로 충돌 가능
성이 높아질 수 있다.
– Sync를 위한 Energy 소비
34

35. T-MAC
• Static schedules is the waste of energy
• When traffic is low, reduce the Listen Interval
– 𝑇𝐴 > 𝐶 𝑐𝑜𝑛𝑡𝑒𝑛𝑡𝑖𝑜𝑛𝑎𝑙 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 + 𝑅(𝑅𝑇𝑆) + 𝐶(𝐶𝑇𝑆)
35

36. Asynchronous MAC
• B-MAC
– Adaptive preamble sampling scheme
• CC-MAC
– Using spatial correlation information
36

37. B-MAC
• Design goal
– Low power operation
– Effective collision
– Simple implementation, small code & RAM size
– Flexible Interface
– Efficient channel utilization at low & high data rates
– Reconfigurable by network protocols
– Tolerant to changing RF/Networking conditions
– Scalable to large numbers of nodes

38. B-MAC Design
• Simple
– Low power listening via Preamble
– CSMA via CCA (Clear Channel Assessment) & back-
off
– Acknowledgment
• Export control to higher services to support
wide variety of WSN workloads
– WSNs are supposed to support various applications
39

39. B-MAC: motivation
• Drawback of Synchronous Operation
1. Periodic messages; SYNC packet
2. All nodes are active during the listen period
3. S-MAC의 경우 virtual cluster 구성해야 한다.
40

40. B-MAC: motivation
• S-MAC is not only a link protocol, but also
network and organization protocol
• Application must rely on S-MAC’s internal
policies
• B-MAC
– Particular lower policy
– Easy to use
41

41. • Sender Sends a preamble before each packet
to wake up the intended receiver
Preamble period = 𝑇𝑝
• Sender node broadcast Preamble
– Intended node : Start listening
– Other node : Sleeping mode
B-MAC: Low power Listening
42

42. B-MAC: Low power Listening
• Sleep and wake schedule w/o synchronization
• Each node determines its own schedule
• Only Transmitter and receiver synchronize each
other
• Longer Preamble
• Length of Check Interval configurable by
higher layers
43

43. B-MAC: Clear Channel Assessment
• Ambient noise change by environment
• Sensing the activity channel 중요
• Failure of detecting Preamble
– Detection failure
– Collision
• CCA
– Noise floor estimation
– Signal detection
44

44. Noise floor estimation
• Each node calculate noise floor
• Signal strength samples are taken while
channel is idle
– Right after transmission packet
– No valid data is received
• Weighted moving average with decay
𝐴 𝑡 = 𝑎𝑆𝑡 + 1 − 𝑎 𝑆𝑡−1
45

45. Signal Detection
• Traditional approach: threshold approach
• Detecting failure
– Channel noise depends on the environment
– Fluctuation
• Outlier detection
– Valid packet could never have an outlier
significantly below the noise floor
– If outlier exists, channel is clear
– If 5 samples are taken and no outlier is found, the
channel is busy
46

46. Signal Detection
• Outlier detection
47

47. B-MAC: 평가
• 장점
– Efficiency carrier sensing(CCA)
– Noise floor estimation -> 주위 환경 변화에 강하다
– Simple light weight -> memory 적게 사용
– Can be controlled by higher layer easily
• High layer가 turn on/off 가능 -> 다양한 적용 가능
• 단점
– Simple CSMA – hidden terminal problem 해결X
• High traffic 에서 나쁘다
– LPL mechanism
• High-traffic 에서 preamble 계속 쏴줘야 함 비효율적
48

48. STEM
B-MAC의 단점
• Sender가 Preamble를 긴 시간 동안 보낸다.
• 목적 노드를 발견해도 Preamble 주기가 끝난 후
data 전송 시작한다.
– Energy 낭비
– Latency 증가
49

49. STEM
• Preamble 보내는 중간에 목적노드 발견하면 바로
data 전송 시작
• 각 노드에서는 listen interval 이 조금 늘어나는 단
점
50

50. Wise MAC
• Sender node에서 목적 노드의 sleep schedule를
알고 있다면?
– Preamble을 많이 줄일 수 있다.
51

51. Wise MAC
• ACK에서 자신의 schedule을 알려준다
– 그 schedule에 맞춰서 preamble을 broadcast한다.
• 단점
– Memory 사용
– Clock drift 오차 생각해서 preamble 시간 정해줘야함
52

52. CC-MAC
53

53. CC-MAC
• Spatial Correlation-Based Collaborative MAC
• Spatially dense sensor deployment
• Sensor records may be spatially correlated
subject to an event
• Iterative Node Selection
– At Sink Node
• CC-MAC protocol
– E-MAC
– N-MAC
• At Sensor Nodes
54

54. Architecture & Spatial Correlation Model
55
• Correlation model and architecture

55. Spatial Correlation Model
• Distortion
𝐷 𝐸 = 𝐸 𝑑 𝐸 𝑆, 𝑆
• Observations of each sensor node can be
modeled as joint Gaussian random variables
𝐸 𝑆𝑖 = 0, 𝑖 = 1, … , 𝑁
𝑣𝑎𝑟 𝑆𝑖 = 𝜎𝑆
2
, 𝑖 = 1, … , 𝑁
𝑐𝑜𝑣 𝑆𝑖 = 𝜎𝑆
2
𝑐𝑜𝑟𝑟 𝑆𝑖, 𝑆𝑗
𝑐𝑜𝑟𝑟 𝑆𝑖, 𝑆𝑗 = 𝜌𝑖,𝑗 = 𝐾 𝜗 𝑑𝑖,𝑗 =
𝐸[𝑆𝑖, 𝑆𝑗]
𝜎𝑆
2
56

56. Spatial Correlation Model
𝑋𝑖 = 𝑆𝑖+ 𝑁𝑖
𝑌𝑖 =
𝑃 𝐸
𝜎 𝑆
2+𝜎 𝑁
2 𝑋𝑖 , (𝑃𝐸:encoding power constraint)
𝑍𝑖 =
𝐸[𝑆𝑖 𝑌𝑖]
𝐸[𝑌𝑖
2
]
𝑌𝑖
𝑆 𝑀 =
1
𝑀
𝑖=1
𝑀
𝑍𝑖
𝐷 𝑀 = 𝐸 𝑆 − 𝑆 𝑀
2
= 𝜎𝑆
2
−
𝜎𝑆
4
𝑀 𝜎𝑆
2
+ 𝜎 𝑁
2 2
𝑖=1
𝑀
𝜌 𝑠,𝑖 − 1 +
𝜎𝑆
6
𝑀2 𝜎𝑆
2
+ 𝜎 𝑁
2 2
𝑖=1
𝑀
𝑖≠𝑗
𝑀
𝜌 𝑖,𝑗
57

57. Spatial Correlation Model 결론
• Located close to the event source S
• Located as far apart from each other as possible
58

58. Iterative Node Selection Algorithm
• Goal
– Find the ideal locations of representative nodes
such that the required distortion can be maintained
at the sink
• Input
– Statistical properties of the node distribution
• Output
– Correlation radius value for distributed operation
Assumption
• Statistical properties of the WSN topology is known by the
INS algorithm; density and node distribution
59

59. Iterative Node Selection Algorithm
Vector Quantization method in coding theory
• Form a sample topology
• Start with selecting all the nodes in the event
region as representative node
• Iteratively, decreases the number of
representative nodes until the distortion
constraint 𝐷 𝑚𝑎𝑥 is met
60

60. Iterative Node Selection Algorithm
• 결과
– Correlation Radius
– Correlation Neighbor
• correlation radius,
𝑟𝑐𝑜𝑟𝑟,is informed to the
individual nodes
61

61. CC-MAC Protocol at node
• 𝑟𝑐𝑜𝑟𝑟 is broadcast to each
sensor node during the
network setup
• E-MAC
– To prevent the transmission of
redundant information
• N-MAC
– To prioritize the forwarding of
filtered data to sink
62

62. Packet Structure
63
• First Hop(FH)
–Differentiate the type of
packet
• Newly generated packet
• Route-thru packet
–처음에는 set 한번 거치는 순간
clear

63. Event MAC
• Forming correlation regions based on the
correlation radius
• In each correlation region, single
representative sensor node transmits data for
a specific duration
• All other node stop transmission attempts
64

64. Event MAC
• First Contention phase(FCP)
– All node with event contend for the medium
– Each node sets FH field of RTS and tries to capture
the medium
– Some of sensor nodes access the channel:
Representative Sensor Node
• 𝑛𝑗 listen to RTS packet of 𝑛𝑖 with set FH
𝒅(𝒊,𝒋) < 𝒓 𝒄𝒐𝒐𝒓
– Stop its transmission
𝒅(𝒊,𝒋) > 𝒓 𝒄𝒐𝒐𝒓
– Contend for the medium if it has a packet to send
65

65. Network MAC
• Route-thru packet must be given priority
– correlation has already been filtered out
using E-MAC
66

66. RESERVATION-BASED MAC
67
02-2

67. Reservation-Based Medium Access
• Collision-free communication
• TDMA가 사용된다.
– FDMA : BW의 한계 때문에 사용하기 힘들다
• Narrow band
– OFDMA, CDMA의 경우 cost constraints
68

68. TRAMA
• Traffic-adaptive Medium Access Protocol
• Energy Efficiency
– No collision
– Sleeping node
• Based on time-slot structure
• Distributed election scheme
– No central entity
– Using priority information, allocate transmission slot
69

69. TRAMA
4 Main Phase
• Neighborhood discovery
• Traffic information exchange
• Schedule establishment
• Data transmission
70

70. TRAMA
3 Mechanism
• Neighbor Protocol
• Schedule Exchange Protocol
• Adaptive Election Algorithm
71

71. Neighbor Protocol
• Main Function:
– Gather two-hop neighborhood information by
using signaling packets.
• TRAMA start in random access mode
• Random access period
– Periodically operates
– New node join the network
– Time synchronization
– Send out their neighborhood updates and receive
update from neighbors
– Collision 발생 가능
• 충분한 시간 할당
72

72. Neighbor Protocol
• Signal packet 교환
– Neighborhood update
– “Keep alive” beacon when no update
73
• Because a node knows the one-hop neighbors
of its one-hop neighbors, eventually consistent
two-hop neighborhood information makes its
way across the network

73. 74
Schedule Exchange Protocol (SEP)
• Schedule consists of list of intended receivers
for future transmission slots.
• Schedules are established based on the
current traffic information at the node.
• Propagated to the neighbors periodically.
• SEP maintains consistent schedules for the
one-hop neighbors.

74. 76
Adaptive Election Algorithm (AEA)
• Decides the node state as either Transmit,
Receive or Sleep.
• Uses the schedule information obtained
by SEP.
• Nodes without any data to send are
removed from the election process,
thereby improving the channel utilization.

75. Adaptive Election Algorithm (AEA)
• Adaptive election algorithm
– Priority정보를 이용하여 time slot을 할당
– Globally known hash function
𝑝 𝑢, 𝑡 = ℎ 𝑢 + 𝑡
– After each node determines the slot to
transmit, informs its intended receivers
77

76. TRAMA: 평가
• 장점
– Energy efficiency: increasing sleeping
– Decrease the collision rate
• 단점
– Delay
– Frequent message exchange
– High density network -> overhead
78

77. PMAC (Pattern MAC)
Pattern 교환을 통해 서로의 스케쥴 정한다.
• Each node makes own patern
• A sleep-wakeup pattern is a stream of bits
• Pattern is tentative plan, it can change
• The schedule for a node is derived from its
own pattern
• The schedules are decided based on a node’s
own traffic and neighbors
79

78. PMAC (Pattern MAC)
Pattern Generation
• 𝑃 𝑗
: binary string representing the pattern of
node j
• 𝑃 𝑗 is restricted a pattern to be 0 𝑚1
(𝑤ℎ𝑒𝑟𝑒 𝑚 = 0,1, … , 𝑁 − 1)
• Example
1, 01, 001, 0001, … , 0 𝑁−1
1
– Bit 1: the node intends to stay awake
– Bit 0: the node intends to sleep
80

79. PMAC (Pattern MAC)
Pattern Exchange
• Pattern repeat time frame
– Each node repeats its current pattern
• Pattern exchange time frame
– New patterns are exchanged between neighbors
81

80. PMAC (Pattern MAC)
• Schedule Generation
82
Pattern bit at
node j
Packet to send
Pattern bit at
receiving node
Schedule at
node j
1 1 1 1
1 1 0 1-
1 0 * 1-
0 1 1 1
0 1 0 0
0 0 * 0

81. HYBRID MAC
84
02-3

82. Hybrid Medium Access
장점 단점
Contention-
based
Overhead 낮다
Low contention
High traffic
Reservation-
based
Schedule
-> collision 낮다
Capacity
Energy efficiency
85
• Combine best of both
• Eliminate worst of both

83. Z-MAC (Zebra-MAC)
• Use a base TDMA schedule
– Rely on time slot
• Each slot can be stolen
– Provided owners are not transmitting
– Stealing done through competition (CSMA)
• CSMA in low contention
• TDMA in high contention
86

84. Z-MAC
• 4 main components
– Neighbor discovery
• 2-hop의 정보를 알고 있음
– Local frame exchange
• Neighbor 수에 따라서 Frame 크기 조절
– Transmit control
• Steal time slot
– Time synchronization
87

85. Z-MAC: Local frame exchange
Time Frame Rule (TF Rule)
• Let node i be assigned to slot 𝑆𝑖, and let
number of nodes within two hop
neighborhood be 𝐹𝑖
• then node i's time frame is set to be 2 𝑎, where
positive integer a is chosen to satisfy condition
2 𝑎−1 ≤ 𝐹𝑖 < 2 𝑎 − 1
88

86. Z-MAC: Transmission Control
89
Time
Slots
A(0)
B(1)
0 021
Ready to Send, Start Random(To) Backoff
Ready to Send, Start To + Random(Tno) Backoff
After Backoff, CCA Idle
After Backoff, CCA Busy
Non-Owner Backoffs
Owner Backoffs

87. Z-MAC: Time synchronization
• Local clock synchronization among senders
• Each data sender transmits a synchronization
message containing its current clock value
periodically
• Update clock value by taking a weighted
moving average
90

88. 결론
• Energy efficiency
• Purpose of Application
91

89. 92

90. 93

91. WSN communication Architecture
95

92. 96
Physical Layer
• Use available Wireless Protocols:
• Radio Frequency : ISM Band 433MHz to 2.4GHz
• Modulation : Phase-Shift Keying
• BPSK or MPSK
• Data Rate : 0.25 Mbps to 54 Mbps
Source [2]

93. 97
Data Link Layer
Medium Access Control (MAC) Protocols:
- Sensor-MAC (SMAC):
- periodic listen & sleep
- collision avoidance
- Timeout-MAC (TMAC):
- enhance the energy savings in SMAC
Source [1]

94. 98
Network Layer
Two Types of Routing Algorithms:
1) Hirarchical Routing Protocols:
Low-Energy Adaptive Clustering Hierarchy (LEACH)
2) Location-Based Routing Protocols:
Geographical Adaptive Fidelity (GAF)
Source [2]

95. CSMA protocol
99

96. CSMA/CA
100

97. NAV mechanism in IEEE 802.11.
• Network Allocation Vector(NAV)
101