Dar es Salaam institute of Technology (DIT)
ETCT 06204
Digital Cellular Network
Ally, J
jumannea@gmail.com
DIT
Course Material
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Text: Wireless Communications: Principles and Practice by T.
Rappaport
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References
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From GSM to LTE by Martin Sauter
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Wireless Communications by Andrea Goldsmith
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Wireless Communications by Roy Blake
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Wireless & Mobile Networks Architecture by Yi Bing and
Imrich Chlamtac
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Wireless Communications and Networks by W. Stallings
DIT
Course Syllabus
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Introduction to Cellular Mobile Communication
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The Cellular Concept-System Design Fundamentals
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Multiple Access Techniques for Wireless Communication
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GSM/GPRS/EDGE Networks
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UMTS/HSPA/HSPA+ Networks
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LTE/LTE Advanced Networks
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5G Network
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Introduction to Cellular Mobile
Communications
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Wired Vs. Wireless Communication
Wired
Wireless
Each cable is a different channel
One media (cable) shared by all
Signal attenuation is low
High signal attenuation
No interference
High interference
noise; co-channel interference; adjacent
channel interference
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Why go Wireless?
Advantages
◼ Sometimes it is impractical to lay cables
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User mobility
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Cost
Limitations
◼ Restricted frequency range
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Standards are often restricted
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Security
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Objectives of Wireless Systems
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Large Capacity
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Efficient use of Resources (Spectrum)
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Adaptability to traffic density
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Quality of Service
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Affordability
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Mobile Radio Communication Systems
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Garage door openers
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Remote controllers
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Cordless phones
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Hand held walkie-talkie
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Pagers
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Cell telephones
These systems differ in cost, complexity, performance
and application.
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What is wireless communication?
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Any form of communication that does not require
the transmitter and receiver to be in physical
contact
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Electromagnetic wave propagated through freespace
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Radar, RF, Microwave, Optical (infrared, Laser).
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Classification of Mobile Radio Communication Systems
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Simplex Systems: Only one way communication
possible. Messages can be received but not
acknowledged. (paging systems)
Half-Duplex Systems: 2 way communication
possible but the same radio channel used for both
transmission and reception. At any given time a user
can only transmit or only receive information; “Push
to talk” and “release to listen” systems.
Full-Duplex Systems: Allow simultaneous
transmission and reception b/w subscriber and Base
Station
Simultaneous transmission and reception are
achieved by:
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Frequency Division Duplex (FDD)
Time Division Duplex (TDD)
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Frequency Division Duplex (FDD)
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It provides simultaneous radio transmission channels for
the subscriber and the base station, so that they both may
constantly transmit while simultaneously receiving signals
from one another.
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Uses a pair of frequency bands – one for Downlink
(Forward) Channel and another for Uplink (Reverse)
Channel.
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Downlink Channel (Forward Channel): used for
transmission of information from Base Station to Mobile.
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Uplink Channel (Reverse Channel): used for transmission
of information from Mobile to Base Station.
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Time Division Duplex (TDD)
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Shares a single radio channel in time
➢ a portion of the time is used to transmit from Base station to
mobile
➢ the remaining time is used to transmit from mobile to Base
Station
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TDD is only possible with digital transmission format
and digital modulation, and is very sensitive to timing.
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Used only for indoor or small area wireless application
where the physical coverage distance are much
smaller than the many kilometers used in conventional
cellular telephone systems.
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Paging Systems
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Broad coverage for short messaging
Message broadcast from all base stations
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Simple terminals
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Optimized for 1-way transmission
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Answer-back hard
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Overtaken by cellular
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Cordless Telephone Systems
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It is full duplex communication systems that use radio to connect a
portable handset and a dedicated Base Station, which is then
connected to a dedicated telephone line with a specific telephone
number on a Public Switched Telephone Network (PSTN).
First generation base station provides coverage to a few tens of
meters.
Second generation base station provides coverage to a few hundred
meters.
Wireless Link
PSTN
Fixed Port
(Base
Station)
Cordless
Handset
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Cellular Telephone Systems
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A cellular telephone system provides a wireless
connection to the PSTN for any user location
within the radio range of the system.
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Accommodate large number of users over a large
geographical area, within limited frequency
spectrum.
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Provide high quality service comparable to
landline telephone systems
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Examples of Mobile Radio Systems
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Mobile Communications Systems Definitions
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Base Station: a fixed station in a radio mobile system used for radio
communication with mobile stations.
Mobile Station: a station in the cellular radio service intended for use
while in motion at unspecified location.
Mobile Switching Centre (MSC): it connects the cellular base stations
and the mobiles to the (Public Switching Telephone Network (PSTN).
Control Channel: radio channels used for transmission of call setup,
call request, call initiation, and other beacons or control purposes.
Handover (Handoff): the process of transferring a mobile station from
one channel or base station to another.
Page: a brief message which is broadcast over the entire service area,
usually in simulcast fashion by many base stations at the same time.
Roamer: a mobile station which operates in a service area (market)
other than that which service has been subscribed.
Subscriber: a user who pays subscription charges for using a mobile
communication system.
Transceiver: a device capable of simultaneously transmitting and
receiving radio signals.
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Important First Generation Analog Systems
Type
AMPS
ETACS
NTT
Region
America
Europe
Japan
Multiple access
FDMA
FDMA
FDMA
Duplexing
FDD
FDD
FDD
Forward band
869 - 894 MHz
935 – 960 MHz
870 – 885 MHz
Reverse band
824 – 849 MHz
890 – 915 MHz
925 – 940 MHz
Channel spacing
30 KHz
25 KHz
25 KHz
No. of channels
831
1000
600
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Second Generation (2G) Cellular Networks
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Most of today’s ubiquitous cellular networks in use
2G technologies which conform to the second
generation cellular standards
It uses TDMA/FDD and CDMA/FDD multiple
access techniques
Most popular 2G standard are:
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Global System Mobile (GSM) – TDMA (Europe)
Interim Standard 136 (IS-136) – TDMA (North America)
Pacific Digital Cellular (PDC) – TDMA (Japan)
Interim Standard 95 Code Division Multiple Access (IS95 CDMA) – CDMA (North America)
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Important Second Generation Digital Systems
Type
IS-136
IS-95
GSM
PDC
Region
America
America
Europe
Japan
Multiple access
/Duplexing
TDMA/FDD
CDMA/FDD
TDMA/FDD
TDMA/FDD
Modulation
/4 DQPSK
QPSK/OQPSK
GMSK
/4 DQPSK
Forward Band
869 - 894 MHz
869 - 894 MHz
935 – 960 MHz
810 – 826 MHz
Reverse Band
824 – 849 MHz
824 – 849 MHz
890 – 915 MHz
940 – 956 MHz
Channel Spacing
30 KHz
1.25 MHz
200 KHz
25 KHz
Data/chip Rate
48.6 Kbps
1.2288 Mcps
270.833 Kbps
42 Kbps
Codec Rate Kbps
7.95
1.2/2.4/4.8/9.6
13.4
6.7
Users/channel
3
Up to 64
8
3
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3G Cellular Design: Voice and Data
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Data is bursty, whereas voice is
continuous
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Typically require different access and
routing strategies
3G “widens the data pipe”:
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384 Kbps (802.11n has 600 Mbps)
Standard based on wideband CDMA
Packet-based switching for both voice and
data
3G cellular popular in Asia and Europe
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4G/LTE/IMT Advanced
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Much higher peak data rates (100-1000
Mbps)
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Greater spectral efficiency (bits/s/Hz)
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Flexible use of up to 100 MHz of spectrum
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Low packet latency (<5ms).
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Increased system capacity
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Reduced cost-per-bit
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Support for multimedia
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Cellular Phones
Everything Wireless in One Device
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Challenges
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Network Challenges
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Scarce spectrum
Demanding/diverse applications
Reliability
Ubiquitous coverage
Seamless indoor/outdoor operation
Device Challenges
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Size, Power, Cost
Multiple Antennas in Silicon
Multiradio Integration
Coexistance
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Simplified picture of most important evolution paths
from 2G technologies (e.g., GSM) to 4G technologies
(e.g., LTE-Advanced)
DIT
DIT
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