1. Mobile Computing COE 446 Introduction
Tarek Sheltami
KFUPM
CCSE
COE
Principles of Wireless Networks
K. Pahlavan and P. Krishnamurth
March 31, 2017

2. Introduction 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
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3. Cellular Subscribers
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4. Cellular Subscribers..
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5. Characteristics of selected wireless link standards
54 Mbps
802.11{a,g}
5-11 Mbps
.11 p-to-p link
802.11b
1 Mbps
802.15 3G
384 Kbps
UMTS/WCDMA, CDMA2000 2G
56 Kbps
IS-95 CDMA, GSM
Indoor
10 – 30m
Outdoor
50 – 200m
Mid range
outdoor
200m – 4Km
Long range
5Km – 20Km
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6. Introduction- Conventional Wireless Communications
In a conventional wireless network, the coverage area is divided into a number of cell sites. Each cell site is served by a single base station that provides wireless connectivity to the terminals in its vicinity. Base stations are interconnected in a fixed wired (or wireless) network. Thus, base stations act as central control units that carry out the MAC functions. An MTSO is in charge of keeping track of wireless subscribers and connects the wireless network to other wide-area networks, such as the PSTN or ISDN networks.
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7. 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 AP
mobile users attach to network through BS
air-interface: physical and link layer protocol between mobile and BS
cell
Mobile
Switching
Center
Public telephone
network, and
Internet
wired network
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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
frequency
bands
time slots
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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
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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
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11. Cellular standards: brief survey
3G systems: voice/data
Universal Mobile Telecommunications Service (UMTS)
GSM next step, but using CDMA
CDMA-2000
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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
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13. Why HSDPA? Comparison Between 3G & 3.5G.
Data Rate ( 2Mbps -----> 10 Mbps)
Modulation ( QPSK -----> QPSK&16QAM)
Transmission Time Interval (TTI) ( 10ms ----> 2ms )

14. HSDPA EVOLUTION

15. GSM: indirect routing to mobile
HLR
home
network
correspondent 2
home MSC consults HLR,
gets roaming number of
mobile in visited network
home
Mobile
Switching
Center 1
call routed
to home network 3
home MSC sets up 2nd leg of call
to MSC in visited network
Public switched
telephone
network
VLR
Mobile
Switching
Center 4
MSC in visited network completes
call through base station to mobile
mobile
user
visited
network
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16. GSM: handoff with common MSC
Handoff goal: route call via new base station (without interruption)
handoff initiated by old BSS
VLR
Mobile
Switching
Center
old
routing
new
routing
old BSS
new BSS
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17. 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
home network
Home MSC
correspondent
anchor MSC
PSTN
MSC
MSC
MSC
(a) before handoff
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18. 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
home network
Home MSC
correspondent
anchor MSC
PSTN
MSC
MSC
MSC
(b) after handoff
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19. Segmenting the Telecom Market
Nortel Corporate Presentation
Segmenting the Telecom Market
Narrowband
Mobile
Broadband
Cellular 3G
WiMAX
Local
Cordless
WiFi
Fixed
POTS
Dialup
DSL / Cable
The Evolution from Audio to Video
© 2004 Nortel

20. Nortel Corporate Presentation
WiMAX: A new paradigm
3G+
Incumbent Operator
Voice and Data
30 Mbps
$200 Handsets
Telecom ITU
Qualcomm
$50 - $70 / month
WIMAX
Any Operator
VoIP, Data, Video
100 Mbps
Consumer Products
Internet IEEE
Intel & Others
$20 - $40 / month
© 2004 Nortel

21. Networks Potential of networking:
move bits everywhere, cheaply, and with desired performance characteristics
Break the space barrier for information
Network provides “connectivity”
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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!
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23. Connectivity. Building Blocks links: coax cable, optical fiber...
nodes: general-purpose workstations...
Direct connectivity:
point-to-point
multiple access
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24. Connectivity.. Indirect Connectivity switched networks => switches
inter-networks
=> routers
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25. Connectivity … Internet: Best-effort (no performance guarantees)
Packet-by-packet
A pt-pt physical link:
Always-connected
Fixed bandwidth
Fixed delay
Zero-jitter
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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
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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
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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.
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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
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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
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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
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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
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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
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34. ALOHA-Based Wireless Random Access Techniques (Pure ALOHA)..
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35. ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA)..
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36. ALOHA-Based Wireless Random Access Techniques (R-ALOHA)..
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