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Spring 2017 Lecture 14 Cellular Telephones · 2017-04-26 · Spring 2017 7 The First Mobile...
Transcript of Spring 2017 Lecture 14 Cellular Telephones · 2017-04-26 · Spring 2017 7 The First Mobile...
Department of Engineering Science
EE442 Analog & Digital Communication Systems Spring 2017
Lecture 14
Cellular Telephones
References
• http://en.wikipedia.org/wiki/Wireless_network
• Preston Gralla, “How Wireless Works,” 2nd ed., Que Publishing, Indianapolis, IN, 2005.
• Wikipedia: http://en.wikipedia.org/wiki/History_of_mobile_phones
• V. H. MacDonald, “The Cellular Concept,” Bell System Technical Journal, Vol. 58,
January 1979
http://www.cellularconcepts.com/Home.html
Spring 2017 2
Advantages:
1. Convenience – User access from nearly any convenient location
2. Mobility (Portability) – User can maintain connection as they move around
3. Connectivity – Can receive signal where cables can’t go
4. Productivity – User can be connected almost 24/7
5. Deployment and Expandability – Easy to setup (plug ‘n play) & upgrade
6. Cost – Wide adoption means lower cost for installation and operation
Disadvantages:
1. Security – Signals readily intercepted and special efforts needed to add security
2. Range – Range limited by antenna power and landscape (scattering)
3. Reliability – Signal receptions depends upon many conditions and can’t be
guaranteed under all circumstances at all times
4. Speed – Generally data rates are lower than for wireline networks and more
users typically slows down the overall systems data rate performance
Wireless Networks – Advantages & Disadvantages
Spring 2017 3
https://www.inarratoronhold.com/blog/2015/10/6/evolution-of-the-telephone-part-2
1876
Alexander Graham Bell’s First Telephone
Spring 2017 4
The Evolution of the Telephone
http://deeperwonderment.wordpress.com/category/uncategorized/
Wired Telephone –
Started in 1876 with
switchboards & operators
Automated switching began in
the 1920s, but
PSTN reached full automation
only in 1980s (digital)
Wireless Mobile Telephone –
Voice only mobile phones
in early 1980s
Voice + data mobile phones
in 1990s
Mobile smartphones with the
Internet mid-2000s
Now everything is mobile!
Spring 2017 5
Two Parts of Cellular Telephone System
1. It is a radio (handsets are both transmitters and receivers)
2. It is a computer-controlled data communication network
Spring 2017 6
AT&T Mobile Radio Experiment in 1924
This mobile, two-way, voice-based phone was actually
more like a walkie-talkie than a telephone.
Antenna
Spring 2017 7
The First Mobile “Radio Telephone” System (1945)
The first mobile radio telephone system (AT&T) was developed and
inaugurated in the United States in St. Louis, Missouri, in 1945.
It consisted of six channels and did not work well due to interference.
A better idea was needed – the cellular telephone concept emerged!
It used a single high-power
base station which all use
to communicate.
PSTN Telephone
System
Its
coverage area
was called a
“small zone system”
Base
Station
Spring 2017 8
Cellular networks were developed to provide mobile telephony
Goal: telephone access “anytime and anywhere.”
AT&T’s idea was a mobile phone system involving the division
of the coverage area into "cells." These "cells" were intended
to reduce bandwidth interference and expand number of users.
Core Principles:
1. Small cells “tessellated” over entire coverage area
2. Must have call handoff as cell phones moved from one cell to
another cell
3. Incorporate “frequency reuse” over the entire cellular network to
increase number of users in network
AT&T’s Breakthrough Cellular Network Concept
handoff
1
2
3
4
Spring 2017 9
An Array of Cells Forms a Cellular Network
www.ece.lehigh.edu/~skishore/research/lucid/lucid_2.ppt
BTS Base Station
Transceiver System
A tessellation of small functional cells over the entire coverage area.
Definition: Tessellation is the process of creating a
two-dimensional pattern using the repetition of a
geometric shape with no overlaps and no gaps.
Cellular
Network
Spring 2017 10
Each BTS (Base Station Transceiver System) cell serves those users within the cell itself. Users located beyond the edge of the cell receive weak signals and are best served by adjacent cells.
Benefits: (1) Smaller cell size means that a lower power is required for Base
Transceiver Station and also for each cell phone (2) Greater number of customers can be accommodated with
frequency reuse
Single Cell in the Cellular Telephone Network
www.ece.lehigh.edu/~skishore/research/lucid/lucid_2.ppt
Cell phone
Cell phone
hexagonal shaped cell
BTS
Spring 2017 11
Perspective of the Cellular Service Provider vs. Its Customers
Spring 2017 12
HLR
VLR
EIR
AuC
MSC
BSC
BTS BTS BTS
MS
Air Interface
PSTN
ISDN
PSDN
MS MS
MS = mobile stations
MSC = mobile switching
center
VLR = visitor location register
HLR = home location register
AuC = authentication center
EIR = equipment identity
register
BTS = base transceiver
station
BSC = base station
controller
Keeping Track of Individual Users Within Network
PSTN = public
switched telephone
network
ISDN = integrated
services digital
network
PSDN = packet-
switched digital
network
Spring 2017 13
GSM (Groupe Speciale Mobile) Now known as “Global System for Mobile communication)
• GSM supports voice and circuit-switched data services (digital)
• GSM supports data rates up to 14.4 kbps
• Uses a SIM card to enable users to personalize services
• GSM channel is actually 271 kHz wide, but channels are spaced
at 200 kHz apart
• Considered to be a 2G (second generation) cellular system
• Two types of channels – control channels & traffic channels
• Frequency bands for GSM are shown in table below
GSM Band Uplink Frequency Band
GSM850
GSM/PCS1900
GSM900
GSM/DCS1800
824.2 to 849.2 MHz
1850.2 to 1909.8 MHz
880 to 915 MHz
1710.2 to 1784.8 MHz
Downlink Frequency Band
869.2 to 894.2 MHz
1930.2 to 1989.8 MHz
925 to 960 MHz
1805.2 to 1879.8 MHz
Spring 2017 14
GSM PLMN Architecture (Public Land Mobile Network)
NSS = Network Switching Subsystem
BSS = Base Station System
MSC = Mobile Switching Center
GMSC = Gateway Mobile Switching Center
BSC
BTS
BTS
BTS
BTS
BSC
BTS
BTS
BTS
BTS
Register
VLR
MSC GMSC
MSC
VLR
HLR AUC
EIR
Base
Station
Subsystem
Base
Station
Subsystem
BSS
BSS
Gateway
PSTN
PSDN
ISDN
BSS
BSS
NSS
Spring 2017 15
Efficient Use of Radio Spectrum Achieved By
Frequency Reuse – Repeats the use of the same frequencies by physically separating cells from each other
Dynamic channel assignment – One cell can borrow channels from an adjacent cell if that cell is under-utilized
Cell splitting – In high population density areas, cells can be made smaller to accommodate the greater number of users
(Note: Setup of “microcells” and “picocells”)
Cell sectoring – Use directional radio signals (typically cells are divided into three sectors per cell)
Offload to Wi-Fi – Allows Wi-Fi enabled cell phones use Wi-Fi hotspots which are connected to the cellular network
Spring 2017 16
A “cluster of 7” has six neighbors which forms the “reuse pattern.” The cellular network repeats this reuse pattern over and over. Using the same frequencies again in each “cluster of 7” allows a service provider to support many more cell phone users in the area.
Frequency Reuse in a Cellular Network
1
2
3
4
5
“Cluster of 7”
BTS Cells
BTS = Base Station Transceiver System
Spring 2017 17
Cell Splitting
Expanding the capacity of a
cellular system can be achieved
by increasing the number of cell
sites covering the entire
geography. With cells covering
smaller areas the reuse of the
same frequencies can be
applied more often within the
whole geographic coverage
area. Smaller cell sizes also
allows lower power operation.
Parameter Macrocell Microcell Picocell
Cell Radius 1 to 10 km 0.1 to 1 km < 0.1 km
Transmission Power 1 to 20 W 0.1 to 1 W < 0.2 W
Maximum Bit Rate 0.3 Mbps 1 Mbps > 1 Mbps
http://ironbark.bendigo.latrobe.e
du.au/subjects/DC/lectures/22/
Region of higher
population density
Region of lower
population density
Macrocell
Microcell
Picocell
Spring 2017 18
Principle:
An increase in network capacity can be
achieved by reducing the number of
interfering co‐channel cells. If sectoring is
done so that all channels assigned to a
particular sector are always it the same
direction in the other cells, then the
interference is reduced which allows the
cluster size to be reduced – that increases
the network’s capacity.
Cell Sectoring (Smart Antennas)
3-sector base station antenna
3-sector base station antenna
pattern can be optimized by
directing signal beams
(dynamic sectoring shown)
http://en.wikipedia.org/wiki/History_of_mobile_phones
Spring 2017 19
Artificial trees are commonly used to mount cellular antennas and even
saguaro cactus are used in desert areas.
References: http://aphotoathought.blogspot.com/2012/01/stealth-cellphone-towers.html and
http://www.mindfully.org/Technology/2003/Cell-Stealth-Antennas14jan03.htm.
Stealth Cellular Telephone Antennas
Spring 2017 20
Cellular Telephone Generations
1980 1990 2000 2010 2020
1G
Ca
pa
city E
nh
an
ce
me
nts
by G
en
era
tio
n
2G
3G
Voice Telephony
Analog Cellular
Digital voice, Data
and Messaging
Wideband Digital,
Enhanced Data &
Multimedia Services
Digital Voice, Data
and Multimedia, &
Very High Data Rates
4G
LTE
2.5G
Much higher
Data Rates
LTE is “Long
Term Evolution”
Outdated & Retired Today
“G” means generation
Spring 2017 21
Cellular Telephone Generation Summary
Generation
Technology
Network
Service
Data rate
Coverage
1G
Analog
Circuit-
Switched
Voice
Telephony
No Data
Limited
Coverage
2G
Digital
Circuit-
Switched
Voice &
Limited Data
(Narrowband)
Slow Data
Trans-
national &
Limited
Global
Roaming
2.5G
Digital
Circuit &
Packet-
Switched
Voice +
Higher Data
Rates
Fast Data
Global
Coverage &
Global
Roaming
3G
Digital
Circuit &
Packet-
Switched
Voice +
Advanced
Data (MM)
Faster Data
Global
Coverage &
Global
Roaming
4G
Digital
All IP Packet-
Switched
Voice &
Advanced
Multimedia
Even Faster
Global
Coverage &
Global
Roaming
Transition
Phase 3.5G
Spring 2017 22
http://en.wikipedia.org/wiki/Motorola_DynaTAC
Martin Cooper (31 years ago) designed
the Motorola DynaTAC 8000X
First Commercial Cell Phone: Motorola DynaTAC
Introduced by Motorola, it was …First Generation* (1G) “analog voice-only phone”
First sale in March 1983
Battery – 30 minutes of talk time & 8 hours of standby
Weighed ~ 2 pounds and 13 inches high (tall)
Stored up to 30 phone numbers; 10 hours to recharge
Price started at $3,995
The
“Brick”
* Known as AMPS for “Advanced
Mobile Phone System”
AMPS*
1G used
800 MHz &
900 MHz
radio bands
Spring 2017 23
Second Generation (2G) Mobile Phones
http://en.wikipedia.org/wiki/Global_System_for_Mobile_Communications
Second Generation (2G) introduced in early 1990s to replace 1G
Digital (rather than analog) transmission of voice
Designed for circuit-switched networks (voice centric)
Uses 900 MHz and 1800 MHz frequency bands
Dominant 2G phone standard: GSM (Global System for Mobile)
Introduced SMS (aka “text messaging”)
GSM uses SIM card containing user ID (Subscriber Identity Module)
Began in Europe; rapidly expanded around the World
http://sharingmythoughts-
ben.blogspot.com/2010/09/histor
y-of-mobile-phone.html
Nokia 2G
Mobile
Phones
GSM is still
widest used
cell phone
standard
Worldwide!
Spring 2017 24
• A small smart card (Subscriber Identity Module)
• Encryption codes needed to identify the subscriber
• Subscriber IMSI number (International Mobile Subscriber Identity)
• Subscriber’s own information (telephone directory)
• Third party applications (banking etc.)
• Can also be used in other systems besides GSM, e.g., some WLAN
access points accept SIM based user authentication
http://microsim-shop.com/making-
your-own-microsim.html
http://www.ricksteves.com/tm
s/article.cfm?id=166
MS = ME + SIM
GSM Introduced the SIM Card
Spring 2017 25
Third Generation (3G) Mobile Phones
Third Generation (3G) introduced in early 2000 s to upgrade 2G
Wider range of advanced mobile services & better quality of service
(e.g., delivers multimedia with broadband access to Internet)
Digital transmission using data packets
Uses both circuit-switched & packet-switched networks
Uses 1800 MHz, 1900 MHz and 2100 MHz frequency bands
Faster data rates:
144 kbps – wide area vehicular (rapid motion) environment
384 kbps – pedestrian or urban environment
2,000 kbps (2 Mbps) – stationary (e.g., within buildings) environment
http://www.cheap3gphones
.net/samsung-3g-phones/
Spring 2017 26
Fourth Generation (4G) Mobile Phones
Fourth Generation (4G) introduction began in 2011
Known broadly as LTE (Long Term Evolution)
Provides for much faster data rates
It is an all IP – uses only packet-switched networks
Uses 700 MHz, 1,700 MHz, and 2,100 MHz frequency bands
Greater than 100 Mbps data rates possible (with max 20 MHz channel)
Will take some years to fully implement
http://www.droid-life.com/2011/01/10/chart-verizon-4g-lte-android-
phone-lineup/
Verizon 4G LTE Android phones Droid Bionic, HTC Thunderbolt, LG Revolution, Samsung SCH-I510
Spring 2017 27
WLAN
Cellular
Gen
era
tion
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GSM
IS-95
CDMA
GPRS
CDMA2000
1x-RTT
EDGE
2G 2.5G 3G 3.5G 3.75G 4G
WCDMA
(UMTS)
CDMA2000
1x-RTT
HPSA
(UMTS)
LTE Advanced
LTE
Cellular Generations
Most Important Evolution of Mainstream Cellular
Spring 2017 29
Multi-X: Radios, Bands & Applications
• Cellular (3GPP: GSM/EDGE/ W-
CDMA/HSDPA/HSUPA);
450/800/800/1700/1900/2100 MHz
Cellular Diversity
• Audio
15 Radios 41 Bands 2M Apps
• FM Stereo
• A-GPS • DAB
WLAN
Diversity • WLAN • 802.11a/b/g
• Bluetooth
• Infrared
From John Harmon (11/2013)
DAB = digital audio broadcast;
The modern smartphone has multiple capabilities!
Spring 2017 30
Multi-band
Cellular Radio
Transceivers +
WiFi
High-speed
Processor
Unit
Interface
Electronics
Flash
Memory
Micro-
phone
Display
Speaker
Keypad
Alarms
Battery
Power
Management
External
Charger
Wi-Fi
Bluetooth
Screen
(display)
Radios Antenna
Antenna
Camera (2)
Organization of a Modern Cell Phone
Spring 2017 31
Challenges to Cellular: Multi-Path Propagation
Base
Transceiver
System (BTS)
Mobile Station (MS)
multi-path
propagation
Path Delay
Po
we
r
path-2
path-2
path-3
path-3
path-1
path-1
Your cell phone must contend with multiple signals to properly operate.
path -2
path -1 Note delay of path -2
Spring 2017 32
Multi-Path Fading
In communication systems, fading refers to a specific kind of
attenuation which is highly frequency and time dependent.
Other types of attenuation such as loss on transmission lines, path
loss in radio transmission, etc. do not change rapidly with time or
frequency, at least not within the bandwidth of interest.
On the other hand, multi-path fading varies strongly with time and
frequency and can - unlike other sources of attenuation - result in a
very large frequency-dependent attenuation. This is a result of
multi-path propagation.
Spring 2017 33
Small-scale fading – Exhibits rapid fluctuations of the amplitude,
phase or multipath delays of a radio signal over a short travel
distance or short time interval.
Large-scale fading – Results from signal attenuation from signal
Propagation over large distances and diffraction around large
Objects in the propagation path.
Small-Scale & Large-Scale Fading
Spring 2017 34
Types of Small-Scale Fading
Small-scale Fading (Based upon multipath time delay spread)
Flat fading 1. BW of signal < channel BW
2. Delay spread < Symbol period
Frequency Selective fading 1. BW of signal > channel BW
2. Delay spread > Symbol period
Small-scale Fading (Based upon Doppler spread)
Fast fading 1. High Doppler spread
2. Coherence time < Symbol period
3. Channel variations faster than
baseband signal variations
Slow fading 1. Low Doppler spread
2. Coherence time > Symbol period
3. Channel variations slower than
baseband signal variations
Spring 2017 35
Challenges to Cellular: Signal Attenuation
http://en.wikipedia.org/wiki/Terrestrial_Trunked_Radio
Radio signal strength becomes weaker as energy spreads out.
Cell 1 Cell 2
RSS = received signal strength
distance
Spring 2017 36
Additional Slides
(including cell phone
radiation effects)
Spring 2017 37
Electromagnetic Radiation Hazards
Mobile phone hazard
As of 2009 there were ~ 2.5 billion mobile phone users worldwide.
Mobile phones use EM radiation in the radio spectrum. There is
controversy about such emissions being harmful to human health.
Dr. Keith L. Black, a preeminent brain surgeon and author of the
book, Brain Surgeon: A Doctor's Inspiring Encounters with
Mortality and Miracles, 2009, has said,
“While some studies showed no correlation between cell phone use and
brain tumors, other credible studies show brain tumor incidence that is
250% greater than non-cell phone users.”
He recommends using a Bluetooth ear piece with your cell phone
to reduce radiation intensity around your head as a precaution.
Some cell phones emit approximately one watt of transmit power.
http://en.wikipedia.org/wiki/Electromagnetic_radiation_and_health
Spring 2017 38
EM radiation distributions in head @ 1900 MHz.
(a) 11 % larger head size, (b) average head size, and (c) smaller head
size (such as in a child – note proportionally larger heating).
Gandhi & Kang, Phys. Med. Biol., 47, 1501-18, 2002.
Head Models for Electromagnetic Energy Absorption
SAM (is “standard anthropomorphic mannequin”)
DECT 6.0 1900 MHz cordless phones
Large
Adult Child
Spring 2017 39
Some simple steps you can take to substantially reduce
exposure to cell phone radiation:
1. Use a wired headset or wireless Bluetooth headset, or use
phone in speaker-phone mode. Better yet, send text messages.
2. Keep cellphones away from your body (particularly
pant/trouser or shirt pockets) or use a belt holster designed to
shield your body. When not in use, put in it in “stand-by mode.”
3. Avoid using in a moving car, train, bus, or in areas with weak
reception – results in an increase in EM power by the cell phone.
4. Use the cellphone like an answering machine. Keep it off until
you want to see who has called. Then return calls you want to.
5. Do not allow children under 18 to use cellphones except in
emergencies or very limited circumstances.
How to reduce EM exposure in using cell phones