Transcript Wireless Sensor Networks

Department of Computer and IT Engineering
University of Kurdistan
Computer Networks II
Wireless Networks
By: Dr. Alireza Abdollahpouri
Outline
 Basic Concepts of Wireless Networks
 Applications of Wireless Networks
 Overview of Research Topics
2
Outline
 Basic Concepts of Wireless Networks
 Applications of Wireless Networks
 Overview of Research Topics
3
Wireless Communications
 There is no physical link in wireless networks. Signals are
transmitted on a certain frequency, propagate in the space
and are captured by the receiver tuned to the same
frequency.
 Wireless communication is normally broadcast
communication, i.e., all nodes within the transmission range
of a particular node can receive the transmitted packets.
 Transmissions in a common neighborhood will interfere
with each other. If the Signal-to-Interference-Noise-Ratio
(SINR) in the receiver is large enough, a packet can be
correctly decoded.
4
Wireless Communications
5
Electromagnetic wave
6
ELECTROMAGNETIC SPECTRUM
7
Wireless Attracts Many Users
I’ve Upgraded
To Wireless
8
Elements of a Wireless Network
wireless hosts
 laptop, PDA, IP phone
 run applications
 may be stationary (nonmobile) or mobile
network
infrastructure

wireless does not
always mean
mobility
9
Elements of a Wireless Network
network
infrastructure
base station
 typically connected
to wired network
 relay - responsible
for sending packets
between wired
network and wireless
host(s) in its “area”
 e.g., cell towers,
802.11 access
points
10
Elements of a Wireless Network
network
infrastructure
wireless link
 typically used to
connect mobile(s) to
base station
 also used as
backbone link
 multiple access
protocol coordinates
link access
 various data rates,
transmission
distance
11
Mobility vs. Throughput
12
Wireless Propagation Channel(s)
Outdoor

indoor
Multipath propagation: signals reach the receiver via multiple paths.
13
Shadowing
D
C
B
A
A
B
C
D
14
‫‪Radio Propagation‬‬
‫اثربازتابي ‪(Reflection effect) :‬‬
‫اين اثر نيزبه خاطر وجود موانع بزرگ (درمقايسه با طول موج سيگنال تابش شده) است‪ .‬دراين حالت سيگنال تابش شده پس از برخورد به مانع‬
‫بزرگ منعكس مي گردد‪ .‬اما سيگنال منعكس شده داراي توان كمتري نسبت به سيگنال اصلي است‪.‬‬
‫اثرپخش ي ‪(Scattering effect) :‬‬
‫اگراندازه مانع درحدود طول موج يا كمترازطول موج سيگنال تابيده شده باشد‪ ،‬مانع مي تواند باعث پخش شدن موج تابيده شده شود‪ .‬بنابراين موج‬
‫تابيده شده به چند موج ضعيف ترشكسته مي شود‪.‬‬
‫اثرشکست ‪(Refraction effect) :‬‬
‫اين اثر به دلیل ورود سیگنال ازیک محیط به محیط دیگر به وجود می آید‪.‬‬
‫‪15‬‬
Distance Sensitivity in Wireless Networks
SNR
25
20
15
10
64QAM
16QAM
5
0
-5
QPSK
Distance
16
Throughput
Robustness
Adaptive Modulation and Coding
AMC
To provide a tradeoff
between throughput and
robustness
17
Antennas
18
Limitations of the Wireless Environment

Limitations of the Wireless Network
 limited communication bandwidth
 frequent disconnections
 heterogeneity of fragmented networks

Limitations Imposed by Mobility
 route breakages
 lack of mobility awareness by system/applications

Limitations of the Mobile Device
 short battery lifetime
 limited capacities
19
Wireless Networks
 Single-hop wireless networks: cellular network,
wireless LAN.
 Multi-hop wireless networks: mobile ad hoc
network, wireless mesh network, wireless
sensor network.
20
Wireless Mesh Networks (WMN)
Mesh nodes
21
Wireless Mesh Networks (WMN)
22
Wireless Sensor Networks (WSN)
Sensor nodes
23
Wireless Sensor Networks (WSN)
24
Wireless Multi-hop (Mesh vs. Sensor)
Wireless Sensor Networks Wireless Mesh Networks
 Bandwidth is limited
(tens of kbps)
 In most applications,
fixed nodes
 Energy efficiency is an
issue
 Resource constrained
 Most traffic is user-togateway
 Bandwidth is generous
(>1Mbps)
 Some nodes mobile,
some fixed
 Normally not energy
limited
 Resources are not an
issue
 Most traffic is user-togateway
25
Relaying
Relaying for (a) Throughput enhancement,
and (b) Coverage extension
26
Outline
 Basic Concepts of Wireless Networks
 Applications of Wireless Networks
 Overview of Research Topics
27
Applications
Broadband home
networking.
Community networking.
28
Applications - Biomedical
29
Habitat Monitoring on Great Duck Island

http://www.greatduckisland.net/

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
30
Applications - Habitat monitoring
31
FireBug





Wildfire Instrumentation System Using Networked Sensors
Allows predictive analysis of evolving fire behavior
Firebugs: GPS-enabled, wireless thermal sensor motes based on TinyOS that
self-organize into networks for collecting real time data in wild fire
environments
Software architecture: Several interacting layers (Sensors, Processing of
sensor data, Command center)
A project by University of California, Berkeley CA.
32
Applications
Metropolitan
area networks
Transportation systems
33
Applications
Emergency Response
Source: www.meshdynamics.com
34
Many Other Applications
 Remote monitoring
and control
 Public transportation
Internet access
 Multimedia home
networking
Source: www.meshnetworks.com
(now www.motorola.com).
35
Outline
 Basic Concepts of Wireless Networks
 Applications of Wireless Networks
 Overview of Research Topics
36
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
37
Advanced Physical Layer Techniques
 Combination of different modulation and
coding rates
 Using OFDM and UWB for high speed
transmission
 Using Multi-antenna systems like: MIMO,
Smart antenna
Multiple-antenna systems
 Software Antenna: Programmable RF
bands, Channel access modes and
channel modulation
38
PHY - Modulation
 Existing modulations work well (OFDM, DSSS,
FSK, etc.).
 UWB may be an interesting alternative for short
distances (480 Mbps up to 1.6 Gbps at
distances up to a few meters)
 Spread spectrum solutions are preferred as
they tend to have better reliability in the face of
 Fading (very important for mobile applications)
 Interference (more of a factor than in any other
wireless system)
39
PHY – Smart Antennas
 Background
 Implemented as an array of
omnidirectional antennas
 By changing the phase,
beamforming can be
achieved
 The result is a software
steered directional antenna
Omnidirectional
antenna
Variable
delay
Signal to
transmit
Direction
changed by
the delays
Radiation Pattern
40
PHY-Smart Antennas Advantages
 Low power transmissions
 Battery not a big
concern in many
applications
 Enables better spatial
reuse and, hence,
increased network
capacity
41
PHY-Smart Antennas Advantages (cont.)
 Punch-through links
 Better delays
 Less packet loss
 Better data rates
 Less power
42
PHY-Smart Antennas Advantages (cont.)
 Better SNR
 Better data rates
 Better delays
 Better error rates
43
PHY-Smart Antennas Disadvantages
 Specialized hardware
 Specialized MAC (difficult
to design)
 Difficult to track mobile
users
44
PHY – Transmission Power Control
GW
GW
Too low
Too high
GW
Just right
Transmission power can control network
topology
45
PHY – Transmission Power Control
(cont.)
 Optimization Criteria
Network capacity
Delay
Error rates
Power consumption
 The ideal solution will depend on
Network topology
Traffic load
46
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
47
MAC: A Simple Classification
Wireless
MAC
Centralized
Distributed
On Demand MACs, Polling
Guaranteed
or
controlled
access
Random
access
Aloha, CSMA/CA
SDMA, FDMA, TDMA
48
MAC – Multichannel
What?
c
f
 Channels can be
implemented by:
c
t
f
 TDMA (difficult due to lack
of synchronization)
 FDMA
 CDMA (code assignment is
an issue)
 SDMA (with directional
antennas)
 Combinations of the above
t
c
c
f
t
c
t
s1
f
s2
t
f
c
t
s3
f
c
f
t
49
MAC – Multichannel
Why?
 Increases network capacity
1
2
Ch-1
1
Ch-1
2
3
2
3
4
Ch-1
3
4
1
Ch-2
User bandwidth = B/2
User bandwidth = B
Chain bandwidth = B
B = bandwidth of a channel
50
Multi-Hop Networks with Single Radio
Source
Mesh Router
Destination
With a single radio, a node can not transmit and
receive simultaneously.
51
Multi-Hop Networks with Multiple Radios
Source
Mesh Router
Destination
With two radios tuned to non-interfering
channels, a node can transmit and receive
simultaneously.
52
MAC – Research challenges
 The scalability issue in multi-hop ad hoc networks
has not been fully solved yet.
 A MAC protocol for WNs must consider both
scalability and heterogeneity between different network
nodes.
 Advanced bridging functions must be developed in
the MAC layer
 Development of MAC protocols with multiple QoS
metrics such as delay, packet loss ratios and jitter
 MAC/Physical Cross-layer design
53
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
54
Routing
 Finds and maintains
routes for data flows
 The entire
performance of the
WN depends on the
routing protocol
55
Routing
An optimal routing protocol must capture the
following features:
 Multiple performance metrics
 Scalability
 Robustness (to link failure and congestion)
56
Routing – different routing protocols
 Routing protocols with various performance metrics
example : LQSR
 Multi-radio routing (using WCETT)
example: MR-LQSR
 Multi-path routing for load balancing and fault
tolerance
 Hierarchical routing
 Geographic routing
57
Existing Routing Protocols
 Internet routing
protocols (e.g., OSPF,
BGP, RIPv2)
 Ad-hoc routing
protocols (e.g., DSR,
AODV, OLSR, TBRPF)
 Well known and trusted
 Designed on the
assumption of seldom
link changes
 Without significant
modifications are
unsuitable for WNs in
particular or for ad hoc
networks in general.
 Newcomers by
comparison with the
Internet protocols
 Designed for high rates
of link changes; hence
perform well on WNs
 May be further
optimized to account for
WNs’ particularities
58
Routing Protocols
 Proactive protocols (OLSR , TBRPF)
 Determine routes independent of traffic pattern
 Traditional link-state and distance-vector routing
protocols are proactive
 Reactive protocols (DSR , AODV)
 Maintain routes only if needed
 Hybrid protocols
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Power-Aware Routing
Define optimization criteria as a function of
energy consumption.
 Minimize energy consumed per packet
 Maximize duration before a node fails due
to energy depletion
Example: LEACH Algorithm
60
Routing – Hierarchical Routing
 Organizes the mobile
nodes into clusters
 Each cluster is
governed by a clusterhead
 Only heads send
messages to a BS
 Suitable for data fusion
 Self-organizing
61
Routing – Geographic Routing
 It is assumed that every node knows it own and its
network neighbors positions.
 Compared to topology-based routing schemes,
geographic routing schemes forward packets by only
using the position information of nodes in the vicinity and
the destination node.
 Topology change has less impact on the geographic
routing than other routing protocols.
62
Routing – metrics
Existing Routing Metrics are Inadequate
2 Mbps
18 Mbps
18 Mbps
Destination
Mesh Router
Source
11 Mbps
11 Mbps
Shortest path: 2 Mbps
Path with fastest links: 9 Mbps
Best path: 11 Mbps
63
Link Metric: Expected Transmission
Time (ETT)
 Link loss rate = p
 Expected number of transmissions
ETX 
1
1- p
 Packet size = S, Link bandwidth = B
 Each transmission lasts for S/B
S
ETT    * ETX
B 
 Lower ETT implies better link
64
ETT: Illustration
11 Mbps
5% loss
Source
18 Mbps
10% loss
50%
Destination
1000 Byte Packet
ETT : 0.77 ms
ETT
ETT :: 0.89
0.40ms
ms
65
Combining Link Metric into Path Metric
 Add ETTs of all links on the path
 Use the sum as path metric
SETT = Sum of ETTs of links on path
(Lower SETT implies better path)
Pro: Favors short paths
Con: Does not favor channel diversity
66
SETT does not favor channel diversity
6 Mbps
No Loss
6 Mbps
No Loss
1.33ms
1.33ms
Mesh Router
Source
Destination
1.33ms
1.33ms
6 Mbps
No Loss
6 Mbps
No Loss
Path
Throughput
SETT
Red-Blue
6 Mbps
2.66 ms
Red-Red
3 Mbps
2.66 ms
67
Impact of Interference
 Interference reduces throughput
 Throughput of a path is lower if many links are
on the same channel
 Path metric should be worse for non-diverse paths
 Assumption: All links that are on the same
channel interfere with one another
 Pessimistic for long paths
68
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
69
Impact of Transmission Errors
 TCP can’t distinguish between packet losses
due to congestion and transmission errors
 Unnecessarily reduces congestion window
 Throughput suffers
70
TCP Problems
 Causes for missing ACKs or loss packets in Wireless
Networks:
 Wireless transmission error
 Broken routes due to mobility (both users and wireless
routers)
 Delays due to MAC contention
71
Impact of Multi-Hop Wireless Paths
[Holland99]
Connections over
multiple hops are at
a disadvantage
compared to shorter
connections,
because they have to
contend for wireless
access at each hop
1600
1400
1200
1000
800
600
400
200
0
TCP
Throughtput
(Kbps)
1 2 3 4 5 6 7 8 9 10
Number of hops
TCP Throughput using 2 Mbps 802.11 MAC
72
TCP
Efficiency Solutions
 Focus on eliminating the
confusion between
congestion loss and all other
reasons
 Many approaches developed
for single-hop wireless
systems
 Snoop
 I-TCP
 M-TCP
 End to end
 SACK
 Explicit error notification
 Explicit congestion notification
(e.g. RED)
 Several solutions for multi-hop
 A-TCP
 Freeze-TCP
73
Split Connection Approach
 Connection between wireless host MH and
fixed host FH goes through base station BS
FH-MH = FH-BS
FH
Fixed Host
BS
Base Station
+
BS-MH
MH
Mobile Host
74
Split Connection Approach
 Split connection results in independent flow
control for the two parts
 Flow/error control protocols, packet size, timeouts, may be different for each part
Examples : I-TCP and M-TCP
75
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
76
Application Layer
 Improve existing Internet applications in order
to work under the architecture of WNs.
 Propose new application-layer protocols for
distributed information sharing.
 Develop Innovative applications for WNs.
77
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
78
Security
 Authentication
 Prevent theft of service
 Prevent intrusion by
malicious users
 Reliability – protect:




Routing data
Management data
Monitoring data
Prevent denials of service
 Privacy - user data is at
risk while on transit in
the WN due to:
 Wireless medium
 Multi-hop
79
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
80
Network Management
 Monitor the “health” of
the network
 Determine when is time
to upgrade
 Either hardware
 New gateway
 Detect problems
 Equipment failures (often
hidden by the self-repair
feature of the network)
 Intruders
Source: www.meshdynamics.com
 Manage the system
81
Overview of Research Topics
 Physical Layer
 Security
 MAC Layer
 Network Management
 Network Layer
 Cross-layer design
 Transport Layer
 Application Layer
82
Cross-layer Design
In order to provide
satisfactory performance of a
wireless network, MAC,
routing, and transport
protocols have to work
together with the physical
layer.
83
Cross-layer Design
Cross-layer design can be performed in two ways:
1 - To improve the performance of a protocol layer by considering
parameters in other protocol layers.
Example1: the packet loss rate in the MAC layer can be reported to
the transport layer so that a TCP protocol is able to differentiate
congestion from packet loss.
Example2: the physical layer can report the link quality to a routing
protocol as an additional performance metric for the routing
algorithms.
2- To merge several protocols into one component.
Example: in ad hoc networks, MAC and routing protocols can be
combined into one protocol in order to closely consider their
interactions.
84
Questions!