lecture_01_introduction to wireless networks.pdf

Wireless Embedded Internet group
http://sites.google.com/site/quanletrung/
Introduction
By Quan Le-Trung, Dr.techn.
Wireless Embedded Internet group
School of CSE, Intl University

Contents
 History and Background
 Evolution and Future Generation
 Current Wireless Systems

Is there a future for wireless?
Some history
 Radio invented in the 1880s by Marconi
 Many sophisticated military radio systems were
developed during and after WW2
 Cellular has enjoyed exponential growth since
1988, with almost 1 billion users worldwide today
 Triggered by the recent wireless revolution
 Fast growth rate
 3G (voice+data) supports many applications
 Many spectacular failures recently
 1G Wireless LANs/Iridium/Metricom
 Ancient Systems: Smoke Signals, Carrier Pigeons, …

Need of Wireless Networks
 Internet and laptop use exploding
 2G/3G wireless LANs growing rapidly
 Low rate data demand is high
 Military and security needs require wireless
 Emerging interdisciplinary applications

6: Wireless and Mobile Networks 6-5
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

Wireless Link Characteristics
Differences from wired link ….
 decreased signal strength: radio signal
attenuates as it propagates through matter
(path loss)
 interference from other sources: standardized
wireless network frequencies (e.g., 2.4 GHz)
shared by other devices (e.g., phone); devices
(motors) interfere as well
 multipath propagation: radio signal reflects off
objects ground, arriving ad destination at
slightly different times
…. make communication across (even a point to point)
wireless link much more “difficult”

Wireless network characteristics
Multiple wireless senders and receivers create
additional problems (beyond multiple access):
A
B
C
Hidden terminal problem
 B, A hear each other
 B, C hear each other
 A, C can not hear each other
means A, C unaware of their
interference at B
A B C
A’s signal
strength
space
C’s signal
strength
Signal fading:
 B, A hear each other
 B, C hear each other
 A, C can not hear each other
interferring at B

Elements of a wireless network
network
infrastructure
wireless hosts
 laptop, PDA, IP phone
 run applications
 may be stationary (non-
mobile) or mobile
 wireless does not
always mean
mobility

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

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

network
infrastructure
infrastructure mode
 base station connects
mobiles into wired
network
 handoff: mobile changes
base station providing
connection into wired
network

Ad hoc mode
 no base stations
 nodes can only transmit
to other nodes within link
coverage
 nodes organize
themselves into a
network: route among
themselves

Future Wireless Networks
Wireless Internet access
Nth generation Cellular
Wireless Ad Hoc Networks
Sensor Networks
Wireless Entertainment
Smart Homes/Spaces
Automated Highways
All this and more…
Ubiquitous Communication Among People and Devices
•Hard Delay Constraints
•Hard Energy Constraints

Design Challenges
 Wireless channels are a difficult and capacity-
limited broadcast communications medium
 Traffic patterns, user locations, and network
conditions are constantly changing
 Applications are heterogeneous with hard
constraints that must be met by the network
 Energy and delay constraints change design
principles across all layers of the protocol stack

Wireless Media
 Physical layers used in wireless networks
– have neither absolute nor readily observable
boundaries outside which stations are unable to
receive frames
– are unprotected from outside signals
– communicate over a medium significantly less reliable
than the cable of a wired network
– have dynamic topologies
– lack full connectivity and therefore the assumption
normally made that every station can hear every other
station in a LAN is invalid (i.e., STAs may be “hidden”
from each other)
– have time varying and asymmetric propagation
properties

Limitations of the mobile 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

Wireless v/s Wired networks
 Regulations of frequencies
– Limited availability, coordination is required
– useful frequencies are almost all occupied
 Bandwidth and delays
– Low transmission rates
• few Kbps to some Mbps.
– Higher delays
• several hundred milliseconds
– Higher loss rates
• susceptible to interference, e.g., engines, lightning
 Always shared medium
– Lower security, simpler active attacking
– radio interface accessible for everyone
– Fake base stations can attract calls from mobile phones
– secure access mechanisms important

Multimedia Requirements
Voice Video
Data
Delay
Packet Loss
BER
Data Rate
Traffic
<100ms - <100ms
<1% 0 <1%
10-3 10-6 10-6
8-32 Kbps 1-100 Mbps 1-20 Mbps
Continuous Bursty Continuous
One-size-fits-all protocols and design do not work well
Wired networks use this approach

Wireless Performance Gap
WIDE AREA CIRCUIT SWITCHING
User
Bit-Rate
(kbps)
14.4
digital
cellular
28.8 modem
ISDN
ATM
9.6 modem
2.4 modem
2.4 cellular
32 kbps
PCS
9.6 cellular
wired- wireless
bit-rate "gap"
1970 2000
1990
1980
YEAR
LOCAL AREA PACKET SWITCHING
User
Bit-Rate
(kbps)
Ethernet
FDDI
ATM
100 M
Ethernet
Polling
Packet
Radio
1st gen
WLAN
2nd gen
WLAN
wired- wireless
bit-rate "gap"
1970 2000
1990
1980
.01
.1
1
10
100
1000
10,000
100,000
YEAR
.01
.1
1
10
100
1000
10,000
100,000

Evolution of Current Systems
 Wireless systems today
 2/3-G Cellular: ~30-300 Kbps
 WLANs: ~10-100 Mbps
 Technology Enhancements
 Hardware: Better batteries. Better circuits/processors
 Link: Antennas, modulation, coding, adaptivity, DSP, BW
 Network: Dynamic resource allocation, Mobility support
 Application: Soft and adaptive QoS

ICPWC'02
384 Kbps
56 Kbps
54 Mbps
72 Mbps
5-11 Mbps
1-2 Mbps 802.11
Wireless Technology Landscape
Bluetooth
802.11b
802.11{a,g}
Turbo .11a
Indoor
10 – 30m
IS-95, GSM, CDMA
WCDMA, CDMA2000
Outdoor
50 – 200m
Mid range
outdoor
200m – 4Km
Long range
outdoor
5Km – 20Km
Long distance
com.
20m – 50Km
µwave p-to-p links
.11 p-to-p link
2G
3G

Future Generations
Rate
Mobility
2G
3G
4G
802.11b WLAN
2G Cellular
Other Tradeoffs:
Rate vs. Coverage
Rate vs. Delay
Rate vs. Cost
Rate vs. Energy
Fundamental Design Breakthroughs Needed

Crosslayer Design
 Hardware
 Link
 Access
 Network
 Application
Delay Constraints
Rate Constraints
Energy Constraints
Adapt across design layers
Reduce uncertainty through scheduling
Provide robustness via diversity

Current Wireless Systems
 Cellular Systems
 Wireless LANs
 Satellite Systems
 Paging Systems
 Bluetooth
 Self-Organized/Emerging Systems
 Mobile Ad-Hoc Networks (MANETs)
 Wireless Sensor Networks (WSNs)
 Internet of Things (IoT): RFID

Cellular Wireless
 Single hop wireless connectivity to the wired
world
– Space divided into cells, and hosts assigned to a cell
– A base station is responsible for communicating with
hosts/nodes in its cell
– Mobile hosts can change cells while communicating
– Hand-off occurs when a mobile host starts
communicating via a new base station

Cellular Systems:
Reuse channels to maximize capacity
 Geographic region divided into cells
 Frequencies/timeslots/codes reused at spatially-separated locations.
 Co-channel interference between same color cells.
 Base stations/MTSOs coordinate handoff and control functions
 Shrinking cell size increases capacity, as well as networking burden
BASE
STATION
MTSO
Mobile Telephone
Switching Office

Cellular Phone Networks
BS
BS
MTSO
PSTN
MTSO
BS
San Francisco
New York
Internet

Mobile
Switching
Center
Public telephone
network, and
Internet
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

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
GSM

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

3G systems: voice/data
 Universal Mobile Telecommunications Service (UMTS)
 GSM next step, but using CDMA
 CDMA-2000
….. more (and more interesting) cellular topics due to
mobility (stay tuned for details)

Evolution of cellular networks
 First-generation: Analog cellular systems (450-900 MHz)
– Frequency shift keying; FDMA for spectrum sharing
– NMT (Europe), AMPS (US)
 Second-generation: Digital cellular systems (900, 1800
MHz)
– TDMA/CDMA for spectrum sharing; Circuit switching
– GSM (Europe), IS-136 (US), PDC (Japan)
– <9.6kbps data rates
 2.5G: Packet switching extensions
– Digital: GSM to GPRS; Analog: AMPS to CDPD
– <115kbps data rates
 3G: Full-fledged data services
– High speed, data and Internet services
– IMT-2000, UMTS
– <2Mbps data rates

3G Cellular Design:
Voice and Data
 Data is bursty, whereas voice is continuous
 Typically require different access and routing strategies
 3G “widens the data pipe”:
 384 Kbps.
 Standard based on wideband CDMA
 Packet-based switching for both voice and data
 3G cellular struggling in Europe and Asia
 Evolution of existing systems (2.5G,2.6798G):
 GSM+EDGE
 IS-95(CDMA)+HDR
 100 Kbps may be enough
 What is beyond 3G? The trillion dollar question

 WLANs connect “local” computers (100m range)
 Breaks data into packets
 Channel access is shared (random access)
 Backbone Internet provides best-effort service
 Poor performance in some apps (e.g. video)
01011011
Internet
Access
Point
0101 1011
Wireless Local Area Networks
(WLANs)

Wireless LANs
 Infrared (IrDA) or radio links (Wavelan)
 Advantages
– very flexible within the reception area
– Ad-hoc networks possible
– (almost) no wiring difficulties
 Disadvantages
– low bandwidth compared to wired networks
– many proprietary solutions
• Bluetooth, HiperLAN and IEEE 802.11

Wireless LANs vs. Wired LANs
 Destination address does not equal destination
location
 The media impact the design
– wireless LANs intended to cover reasonable
geographic distances must be built from basic
coverage blocks
 Impact of handling mobile (and portable)
stations
– Propagation effects
– Mobility management
– Power management

Infrastructure vs. Ad hoc WLANs
infrastructure
network
ad-hoc network
AP
AP
AP
wired network
AP: Access Point

Wireless LAN Standards
 802.11b (Current Generation)
 Standard for 2.4GHz ISM band (80 MHz)
 Frequency hopped spread spectrum
 1.6-10 Mbps, 500 ft range
 802.11a (Emerging Generation)
 Standard for 5GHz NII band (300 MHz)
 OFDM with time division
 20-70 Mbps, variable range
 Similar to HiperLAN in Europe
 802.11g (New Standard)
 Standard in 2.4 GHz and 5 GHz bands
 OFDM
 Speeds up to 54 Mbps

802.11 LAN architecture
 wireless host communicates
with base station
 base station = access point
(AP)
 Basic Service Set (BSS) (aka
“cell”) in infrastructure mode
contains:
 wireless hosts
 access point (AP): base
station
 ad hoc mode: hosts only
BSS
1
BSS 2
Internet
hub, switch
or router
AP
AP

Satellite Systems
 Cover very large areas
 Different orbit heights
 GEOs (39000 Km) versus LEOs (2000 Km)
 Optimized for one-way transmission
 Radio (XM, DAB) and movie (SatTV) broadcasting
 Most two-way systems struggling or bankrupt
 Expensive alternative to terrestrial system
 A few ambitious systems on the horizon

Paging Systems
 Broad coverage for short messaging
 Message broadcast from all base stations
 Simple terminals
 Optimized for 1-way transmission
 Answer-back hard
 Overtaken by cellular

8C32810.61-Cimini-7/98
Bluetooth
 Cable replacement RF technology (low cost)
 Short range (10m, extendable to 100m)
 2.4 GHz band (crowded)
 1 Data (700 Kbps) and 3 voice channels
 Widely supported by telecommunications,
PC, and consumer electronics companies
 Few applications beyond cable replacement

Emerging Systems
 Ad hoc wireless networks
 Sensor networks
 Distributed control networks

Ad-Hoc Networks
 Peer-to-peer communications
 No backbone infrastructure
 Routing can be multihop
 Topology is dynamic
 Fully connected with different link SINRs

Multi-Hop Wireless
 May need to traverse multiple links to reach
destination
 Mobility causes route changes

Mobile Ad Hoc Networks (MANET)
 Do not need backbone infrastructure support
 Host movement frequent
 Topology change frequent
 Multi-hop wireless links
 Data must be routed via intermediate nodes
A
B A
B

Applications of MANETS
 Military - soldiers at Kargil, tanks, planes
 Disaster Management – Orissa, Gujarat
 Emergency operations – search-and-rescue, police and
firefighters
 Sensor networks
 Taxicabs and other closed communities
 airports, sports stadiums etc. where two or more people
meet and want to exchange documents
 Presently MANET applications use 802.11 hardware
 Personal area networks - Bluetooth

Design Issues
 Ad-hoc networks provide a flexible network
infrastructure for many emerging applications
 The capacity of such networks is generally
unknown
 Transmission, access, and routing strategies for
ad-hoc networks are generally ad-hoc
 Cross-layer design critical and very challenging
 Energy constraints impose interesting design
tradeoffs for communication and networking

Sensor Networks
Energy is the driving constraint
 Nodes powered by non-rechargeable batteries
 Data flows to centralized location
 Low per-node rates but up to 100,000 nodes
 Data highly correlated in time and space
 Nodes can cooperate in transmission, reception,
compression, and signal processing

Energy-Constrained Nodes
 Each node can only send a finite number of bits
 Transmit energy minimized by maximizing bit time
 Circuit energy consumption increases with bit time
 Introduces a delay versus energy tradeoff for each bit
 Short-range networks must consider transmit,
circuit, and processing energy
 Sophisticated techniques not necessarily energy-efficient
 Sleep modes save energy but complicate networking
 Changes everything about the network design:
 Bit allocation must be optimized across all protocols
 Delay vs. throughput vs. node/network lifetime tradeoffs
 Optimization of node cooperation

Distributed Control over
Wireless Links
 Packet loss and/or delays impacts controller performance
 Controller design should be robust to network faults
 Joint application and communication network design
Automated Vehicles
- Cars
- UAVs
- Insect flyers

Joint Design Challenges
 There is no methodology to incorporate random
delays or packet losses into control system designs
 The best rate/delay trade-off for a communication
system in distributed control cannot be determined
 Current autonomous vehicle platoon controllers are
not string stable with any communication delay
Can we make distributed control robust to the network?
Yes, by a radical redesign of the controller and the network

Spectrum Regulation
 Spectral Allocation in US controlled by FCC
(commercial) or OSM (defense)
 FCC auctions spectral blocks for set applications
 Some spectrum set aside for universal use
 Worldwide spectrum controlled by ITU-R
Regulation can stunt innovation, cause economic
disasters, and delay system rollout

Standards
 Interacting systems require standardization
 Companies want their systems adopted as standard
 Alternatively try for de-facto standards
 Standards determined by TIA/CTIA in US
 IEEE standards often adopted
 Worldwide standards determined by ITU-T
 In Europe, ETSI is equivalent of IEEE
Standards process fraught with
inefficiencies and conflicts of interest

Main Points
 The wireless vision encompasses many exciting
systems and applications
 Technical challenges transcend across all layers
of the system design
 Wireless systems today have limited
performance and interoperability
 Standards and spectral allocation heavily impact
the evolution of wireless technology

lecture_01_introduction to wireless networks.pdf

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