Transcript WN1 92-93-2 Introductionx

‫دانشکده مهندس ی کامپیوتر‬
‫شبکه‌های‌بی‌سیم‌(‪)40-873‬‬
‫مقدمه‬
‫ّ‬
‫نیمسال دوم ‪92-93‬‬
‫افشین ّ‬
‫همتیار‬
References
 A. Kumar, D. Manjunath, and J. Kuri,
Wireless Networking,
Morgan Kaufmann Publishers, 2008.
 C.M. Cordeiro and D.P. Agrawal,
Ad Hoc and Sensor Networks: Theory and
Applications, 2nd Ed,
World Scientific, 2011.
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Contents
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Background
Wireless communication: concepts, techniques,
and models
Application models and performance issues
Cellular FDM-TDMA
Cellular CDMA
Random Access and Wireless LANs (WLANs)
Mobile Ad-hoc Networks (MANETs)
Wireless Mesh Networks (WMNs)
Wireless Sensor Networks ( WSNs)
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Wired Vs. Wireless Communications
Wired
Wireless
Each cable is a different channel
One media shared by all
Low signal attenuation
High signal attenuation
No interference
High interference
noise; co-channel interference; adjacent
channel interference
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Why Wireless?

Advantages
• Sometimes it is impractical to lay cables
• User mobility
• Cost

Limitations
•
•
•
•
Bandwidth
Fidelity
Power
Security
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Propagation Principle
electric
field
propagation direction
magnetic
field
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Electromagnetic Spectrum
ISM band
902 – 928 Mhz
2.4 – 2.4835 Ghz
5.725 – 5.785 Ghz
LF
30kHz
10km
MF
300kHz
1km
VHF
HF
3MHz
30MHz
100m
10m
UHF
300MHz
1m
SHF
3GHz
EHF
30GHz
300GHz
1cm
100mm
10cm


X rays

infrared visible UV
1 kHz
1 MHz
1 GHz
1 THz
1 PHz
Gamma rays
1 EHz
Propagation characteristics are different in each frequency band.
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Unlicensed Radio Spectrum
(ISM: Industrial, Science, Medicine)

33cm
26 Mhz
902 Mhz
12cm
83.5 Mhz
2.4 Ghz
928 Mhz
cordless phones
baby monitors
WaveLan
2.4835 Ghz
802.11b
Bluetooth
Microwave oven
5cm
125 Mhz
5.725 Ghz
5.850 Ghz
802.11a
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Propagation Mechanisms
Line-of-Sight
S
D
Non Line-of-Sight
Reflection
Diffraction
Scattering
λ << D
λ  D
λ >> D
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Propagation in the “Real World”
a wave
can
be absorbed
penetrate
reflect
bend
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Path-loss Models

Path-Loss Exponent Depends on environment:
n
L(d) = L(d0)(d/d0)
Free space
Urban area cellular
Shadowed urban cell
In building LOS
Obstructed in building
Obstructed in factories
n
n
n
n
n
n
=
=
=
=
=
=
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2.7 to 3.5
3 to 5
1.6 to 1.8
4 to 6
2 to 3
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Networking as Resource Allocation
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Resource Allocation

Wireline
o Static bit-carrier infrastructure
o High quality digital transmission over copper or optical
media
o Bit pipes with a certain bit rate and very small bit error
rate
o Dynamically reconfigured based on traffic demands
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Wireless
o Point-to-point Line-of-sight
(same as wireline or higher bit rate)
o Time-varying channel impairments
o Adaptable PHY layer
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Wireless Networking

Our view:
All the mechanisms, procedures, or
algorithms for efficient sharing of a
portion of the radio spectrum so
that all instances of communication
between the various devices obtain
their desired Quality of Service
(QoS).
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Wireless Networks
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Fixed Networks
Point to point
 Long distance transmission
 High gain antennas
 Tall masts
 Higher bit rate and also higher bit error
rate than wireline

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Mobile and Ad-hoc Networks
Access Networks
Mesh Network
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Mobile Networks: Circuit Multiplexing

GSM
(2G)
o Narrowband
o FDM-TDMA
o High SINR
o Careful frequency planning to avoid cochannel interference
o Call admission control
 GSM-GPRS
 GSM-EDGE
(2.5G) Combining TDM Time slots
(2.75G) Combining TDM Time slots
and higher order modulation schemes
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Mobile Networks:
Centralized Statistical Multiplexing (1)

CDMA
o
o
o
o
o
o
(IS-95)
Wideband
CDMA (Spread spectrum)
Correlation receivers
No frequency planning
Interference limited
Call admission control
 WCDMA
(CDMA-2000)
o Most widely adapted standard for 3G
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Mobile Networks:
Centralized Statistical Multiplexing (2)

WiMAX
o
o
o
o
(IEEE 802.16 series)
Wireless access to Internet
Fixed subscriber stations
OFDMA
TDD (uplink & downlink)
o Specifications now have been extended
to include broadband access to mobile
users.
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Mobile Networks:
Distributed Statistical Multiplexing

WLAN
(IEEE 802.11 series)
Wireless access to Internet
Limited mobility
Statistical TDMA
Few Mbps (over 100s of meter)
up to 100Mbps (over a few meters)
o MIMO-OFDM (enhancement)
o
o
o
o
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Ad hoc Networks:
Internet Access and Sensor Networks

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No infra-structure
Multi-hop communication
Point-to-point store and forward
traffic
Miniature devices for nodes
Low power, low bit rate digital
radio transceiver, and small battery
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Technical Elements
General:
 Transport of the user’s bits over the
shared radio spectrum
 Neighbor discovery, association and
topology formation, routing
 Transmission scheduling (cross layer)
Only in ad hoc sensor networks:
 Location determination
 Distributed computation
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