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Mobile Computing COE 446 Introduction. Tarek Sheltami KFUPM CCSE COE http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm. Principles of Wireless Networks K. Pahlavan and P. Krishnamurth. Background: # wireless (mobile) phone subscribers now exceeds # wired phone subscribers! - PowerPoint PPT Presentation
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April 21, 2023 1
Mobile Computing COE 446
IntroductionTarek Sheltami
KFUPMCCSECOE
http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm
Principles of Wireless Networks
K. Pahlavan and P. Krishnamurth
April 21, 2023 2
Background: # wireless (mobile) phone subscribers
now exceeds # wired phone subscribers!
computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access
two important (but different) challenges communication over wireless link handling mobile user who changes point of
attachment to network
Introduction
April 21, 2023 3
Cellular Subscribers
April 21, 2023 4
Cellular Subscribers..
April 21, 2023 5
Characteristics of selected wireless link standards
384 Kbps384 Kbps
56 Kbps56 Kbps
54 Mbps54 Mbps
5-11 Mbps5-11 Mbps
1 Mbps1 Mbps
802.15
802.11b
802.11{a,g}
IS-95 CDMA, GSM
UMTS/WCDMA, CDMA2000
.11 p-to-p link
2G
3G
Indoor
10 – 30m
Outdoor
50 – 200m
Mid rangeoutdoor
200m – 4Km
Long rangeoutdoor
5Km – 20Km
April 21, 2023 6
Introduction- Conventional Wireless Communications
April 21, 2023 7
Mobile Switching
Center
Public telephonenetwork, andInternet
Mobile Switching
Center
Components of cellular network architecture
connects cells to wide area net manages call setup (more later!) handles mobility (more later!)
MSC
covers geographical region base station (BS) analogous to 802.11 AP mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS
cell
wired network
April 21, 2023 8
Cellular networks: the first hop
Two techniques for sharing mobile-to-BS radio spectrum
combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots
CDMA: code division multiple access
frequencybands
time slots
April 21, 2023 9
Cellular standards: brief survey
2G systems: voice channels IS-136 TDMA: combined FDMA/TDMA
(north america) GSM (global system for mobile
communications): combined FDMA/TDMA most widely deployed
IS-95 CDMA: code division multiple access
April 21, 2023 10
Cellular standards: brief survey
2.5 G systems: voice and data channels for those who can’t wait for 3G service: 2G extensions general packet radio service (GPRS)
evolved from GSM data sent on multiple channels (if available)
enhanced data rates for global evolution (EDGE) also evolved from GSM, using enhanced modulation Date rates up to 384K
CDMA-2000 (phase 1) data rates up to 144K evolved from IS-95
April 21, 2023 11
Cellular standards: brief survey
3G systems: voice/data Universal Mobile Telecommunications
Service (UMTS) GSM next step, but using CDMA
CDMA-2000
April 21, 2023 12
Cellular standards: brief survey
3G+ systems: voice/data High Speed Downlink Packet Access
Hybrid Automatic Repeat Request
Fast cell site selection
Adaptive Modulation and Coding
Why HSDPA?
Comparison Between 3G & 3.5G. Data Rate ( 2Mbps -----> 10 Mbps)
Modulation ( QPSK -----> QPSK&16QAM)
Transmission Time Interval (TTI) ( 10ms ---->
2ms )
HSDPA EVOLUTION
April 21, 2023 15
Public switched telephonenetwork
mobileuser
homeMobile
Switching Center
HLR home network
visitednetwork
correspondent
Mobile Switching
Center
VLR
GSM: indirect routing to mobile
1 call routed to home network
2
home MSC consults HLR,gets roaming number ofmobile in visited network
3
home MSC sets up 2nd leg of callto MSC in visited network
4
MSC in visited network completescall through base station to mobile
April 21, 2023 16
Mobile Switching
Center
VLR
old BSSnew BSS
old routing
newrouting
GSM: handoff with common MSC Handoff goal: route call via
new base station (without interruption)
handoff initiated by old BSS
April 21, 2023 17
home network
Home MSC
PSTN
correspondent
MSC
anchor MSC
MSCMSC
(a) before handoff
GSM: handoff between MSCs anchor MSC: first MSC
visited during call call remains routed
through anchor MSC new MSCs add on to
end of MSC chain as mobile moves to new MSC
IS-41 allows optional path minimization step to shorten multi-MSC chain
April 21, 2023 18
home network
Home MSC
PSTN
correspondent
MSC
anchor MSC
MSCMSC
(b) after handoff
GSM: handoff between MSCs anchor MSC: first MSC
visited during cal call remains routed
through anchor MSC new MSCs add on to
end of MSC chain as mobile moves to new MSC
IS-41 allows optional path minimization step to shorten multi-MSC chain
19
Segmenting the Telecom Market
Cordless
WiMAX
WiFi
DSL / Cable
3G
Mobile
Local
Fixed
Narrowband Broadband
Dialup
Cellular
POTS
The Evolution from Audio to Video
20
WiMAX: A new paradigmWIMAX
Any Operator
VoIP, Data, Video
100 Mbps
Consumer Products
Internet IEEE
Intel & Others
$20 - $40 / month
3G+
Incumbent Operator
Voice and Data
30 Mbps
$200 Handsets
Telecom ITU
Qualcomm
$50 - $70 / month
April 21, 2023 21
Potential of networking: move bits everywhere, cheaply, and with desired performance characteristics
Break the space barrier for information
Network provides “connectivity”
Networks
April 21, 2023 22
What is “Connectivity” ?
Direct or indirect access to every other node in the network
Connectivity is the media needed to communicate if you do not have a direct pt-pt physical link. Tradeoff: Performance
characteristics worse than true physical link!
April 21, 2023 23
Connectivity.
Building Blocks links: coax cable, optical fiber... nodes: general-purpose workstations...
Direct connectivity: point-to-point
multiple access
April 21, 2023 24
Connectivity..
Indirect Connectivity switched networks
=> switches
inter-networks => routers
April 21, 2023 25
Connectivity …
Internet: Best-effort (no performance
guarantees) Packet-by-packet
A pt-pt physical link: Always-connected Fixed bandwidth Fixed delay Zero-jitter
April 21, 2023 26
Wired and Wireless Multiple Access Most multiple access were originally
developed for wired networks Requirements for wired & wireless networks
are different The main difference between wired and
wireless channels are availability of BW and reliability of transmission
The wired medium is moving toward optical media with enormous BW and very reliable transmission
BW of wireless systems always limited because of the air medium
April 21, 2023 27
Wired and Wireless Multiple Access..
Wireless medium always suffers from multi-path and fading, which causes serious threat to reliable data transmission over the communication link
Wireless have evolved around voice and data application
Wireless Networks
Voice Oriented
Data Oriented
April 21, 2023 28
Wired and Wireless Multiple Access.. Voice oriented networks are designed
for relatively long telephone conversation as the main application, therefore exchange of several Mbytes of information in both directions
Data oriented networks are designed for bursts of data (packet switching)
Wireless networks assigns a time slot, a portion of frequency, or a code to user preferably for the entire length of the conversation.
April 21, 2023 29
ALOHA-Based Wireless Random Access Techniques (Pure ALOHA)
MT transmits an information packets when the packet arrives from the upper layers of the protocol stack
MTs say “hello” to the air interface as the packet arrives
Each packet is encoded with an error-detection code
The BS checks the parity of the received packet, if it is OK, it sends a short ACK packet
If no ACK received the packet is assumed lost in a collision and it is transmitted again with randomly selected delay to avoid repeated collisions
April 21, 2023 30
ALOHA-Based Wireless Random Access Techniques (Pure ALOHA) ..
Advantages Simple No synchronization between MTs
Disadvantage Low throughput under heavy load
conditions Max throughput for pure ALOHA 18%
What is the max throughput of pure ALOHA network with large number of users and transmission range of 1 Mbps?
Max Throughput = 1 Mbps X 18% = 180 Kbps
April 21, 2023 31
ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA) ..
Transmission time is divided into time slots BS transmits beacon signal for time and all MTs
is divided into time slots to this beacon signal When MT generates a packet, it is buffered and
transmitted at the start of the next time slot Assuming equal length packet, either we have a
complete collision or no collision Throughput of slotted ALOHA = 36%, which is
still low
April 21, 2023 32
ALOHA-Based Wireless Random Access Techniques (R-ALOHA) ..
Time slots are divided into contention periods and contention free periods
During contention interval, an MT uses very short packets to contend for the upcoming contention free intervals that will be used for transmission of the long information packets
April 21, 2023 33
ALOHA-Based Wireless Random Access Techniques..
Disadvantages of ALOHA-based Random Access: The main drawback of ALOHA based
contention is the lack of efficiency caused by collision and retransmission
Users don’t take into account what other users are doing when they attempt to transmit data packets
There is no mechanisms to avoid collision
April 21, 2023 34
ALOHA-Based Wireless Random Access Techniques (Pure ALOHA) ..
April 21, 2023 35
ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA) ..
April 21, 2023 36
ALOHA-Based Wireless Random Access Techniques (R-ALOHA) ..