Wireless networks - Lecture 8: Evolution of wireless networks (Part 1)

Wireless Networks

Lecture 8
Evolution of Wireless Networks
Dr. Ghalib A. Shah

1


 Review of previous lecture #7
 1G wireless cellular networks
► NMT
► AMPS
► TACS

 2G cellular systems
►
►
►
►

GSM
IS-136
PDC
IS-95

 Summary of today’s lecture
2


Last Lecture Review

 CSMA
► Versions of CSMA
► CSMA/CA
► Example

 Spread Spectrum
► Frequency Hoping
► Direct Sequence

3


Evolution of Wireless Systems
 The worldwide success of cellular telephone
has lead to the development of newer wireless
systems and standards for other types of
communications besides mobile voice.
 For example
► Cellular networks to facilitate high speed data traffic
► Replace fiber optics and copper lines between fixed
points several kms apart.
► Replacement of wires within homes, offices etc
(evolution of Bluetooth)
4


First-Generation Cellular Networks
 Analog systems
 Standards
► NMT (Nordic Mobile Telephone)

•

used in Nordic countries, Switzerland, Netherlands,
Eastern Europe and Russia.

► AMPS (Advanced Mobile Phone System)
•

used in the United States,

► TACS (Total Access Communications System)
•

Used in the United Kingdom,

► C-450
•

in West Germany, Portugal and South Africa,

► Radiocom 2000 in France
► RTMI in Italy.
► In J apan there were multiple systems. Three standards, TZ801, TZ-802, and TZ-803
5


Evolution Tree of Wireless Systems

6

NMT
 First fully-automatic cellular phone system
► Started in 1970, in service 1981

 Two standards NMT-450 and NMT-900
► Corresponds to frequency and the later has higher
bands.

 Cell size range from 2 km to 30 km.
► Use smaller size in urban areas for better quality and
larger in less-populated areas.

 Handsets 1 watt and Car phone uses 6-15 watt
 Automatic switching (dialing) and handover.
7


NMT Contd.
 No spec. for voice traffic encryption
► Buy a scanner, tune to the desired channel and intercept.

 NMT also supported a s im p le  d ata trans fe r m o d e
called DMS (Data and Messaging Service) or NMTText
 Using DMS, also text messaging was possible between
two NMT handsets before SMS service started in GSM
 but this feature was never commercially available
except in Russian and Polish NMT networks.
 NMT Suspended
► In Finland TeliaSonera's NMT on December 31, 2002.

► Norway's last NMT network on December 31, 2004.
► Sweden's TeliaSonera NMT on December 31, 2007.
8


AMPS
 1G cellular phone used in US, which uses FDMA
 Operates in 800 MHz band
► Total of 832 channels;
•
•
•

416 in 824–849 MHz for transmissions from mobile to the base
416 in 869–894 MHz for transmissions from base to the mobile.
Each channel is 30 KHz wide

 Require large bandwidth for large base population.
 No protection against eavesdropper
► ESN (Electronic Serial Number) was cloned in 1990s to make
free calls from different cells.

 Replaced with D-AMPS, GSM and CDMA for better
security and capacity
9


TACS
 A variant of AMPS developed by Motorola.
 It has been used in some European countries

(including the UK & Ireland), as well as J apan
and Hong Kong.
 ETACS was an extended version of TACS with
more channels.
 The last ETACS service operated by Vodafone
was discontinued on 31 May 2001

10


Second-Generation Cellular Networks
 Digital system i.e. voice is digitized
 Unlike 1G that relies on FDMA/FDD, 2G use digital
modulation formats and TDMA/FDD, CDMA/FDD
multiple access techniques
 Can be divided into two standards; TDMA and CDMA
 The main 2G standards are
► GSM (TDMA-based), originally from Europe but used
worldwide
► IS-136 aka D-AMPS, TDMA-based, used in the Americas
► IS-95 aka cdmaOne, CDMA-based, used in the Americas and
parts of Asia
► PDC (TDMA-based), used exclusively in J apan
11


2G Contd.
 Using digital signals between the handsets and
the towers increases system capacity in two
key ways:

► Digital voice data can be compressed and
multiplexed much more effectively than analog voice
encodings through the use of various CODECs,
allowing more calls to be packed into the same
amount of radio bandwidth.
► The digital systems were designed to emit less radio
power from the handsets. This meant that cells could
be smaller, so more cells could be placed in the
same amount of space. This was also made
possible by cell towers and related equipment
getting less expensive.
12


2G Advantages
 The lower powered radio signals require less
battery power, so phones last much longer
between charges, and batteries can be smaller.
 The digital voice encoding allowed digital
error checking which could increase sound
quality by reducing dynamic and lowering the
noise floor.
 Going all-digital allowed for the introduction of
digital data services, such as SMS and email.
 Better security, harder to be scanned
13


GSM
 2.27 billion subscribers across more than 212

countries, 81% of the global mobile market
 Its ubiquity provides international roaming very
common
 8-slots TDMA with 200 KHz radio channel, with frame
duration of 4.615 ms
 The channel data rate is 270.833 kbit/s
 Operates in four different bands
►
►
►
►

Mostly 900 MHz or 1800 MHz
US and Canada use 850 MHz and 1900 MHz
25 MHz bandwidth of each subdivided into 124 channels
E.g. in 900 MHz, uplink 890-915 MHz, downlink 935-960 MHz
14


Others Systems
 IS-136 or D-AMPS
► 3-Slot TDMA, used in North and South America, Australia
► Channel bandwidth is 30 KHz.
► Frequency bands (824-849MHz and 869-894 MHz)

 Pacific Digital Cellular (PDC)
►
►
►
►

J apanese standard similar to IS-136
25 KHz channel
11.2 kbps at 3-slot and 5.6 kbps at 6-slot
Operates in 800 MHz downlink 810-888 MHz, uplink 893-958
MHz)
► In 1.5 GHz (downlink 1477-1501 MHz, uplink 1429-1453 MHz)

15


Other Systems Contd..
 IS-95 or cdmaOne
► Supports up to 64 users that are orthogonally coded
► Channel bandwidth is 1.25 MHz
► Widely deployed in N. America, Korea, J apan,
China, S. America, Australia
► Channel data rate is 1.2288 Mchips/s (Me g a Chips )

16


17


18


Subscriber base as a function of Cellular technology
2500

Subscribers (millions)

2000

1500

1000

500

0
Analog

GSM

WCDMA CDMA

CDMA
1X

CDMA
1X EVDO

TDMA

PDC

iDEN

19


Summary of today’s lecture
 1G analog systems
►
►
►
►

NMT
AMPS
TACS
C-450

 2G digital cellular systems
► GSM
► IS-136
► IS-95

 Ne xt Le c ture
► 3G and 4G 
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