FIXED TELEPHONE, MOBILE TELEPHONE AND SATELLITE COMMUNICATION SYSTEMS

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TEL 213/05 Telecommunication Principle
Tutorial 4: FIXED TELEPHONE, MOBILE TELEPHONE
AND SATELLITE COMMUNICATION SYSTEMS
Semester January 2012

Introduction
• Students used to focus on either data communications or voice
communications.
• Today, the two fields are merging.
• Most voice systems are computer controlled and data
• networks support voice.
• Anyone studying the field of data communications and
• networks must learn some basic telecommunications too.
• Telecommunications used to be just “voice.”

Basic Telephone Systems
• POTS is the plain old telephone system that connects
most
• homes and small businesses.
• POTS lines were designed to transmit the human voice,
• which has a bandwidth less than 4000 Hz.
• A telephone conversation requires two channels, each
• occupying 4000 Hz.

Various telephone channels and
the assignment of frequencies

Limitations of
• A 4000 Hz analog signal can only carry about 33,600 bits per
• second of information while a 4000 Hz digital signal can
• carry about 56,000 bits per second.
• If you want to send information faster, you need a signal with
• a higher frequency.
• POTS cannot deliver faster signals.

Basic Telephone Systems -
Loops
• The local loop is the telephone line that runs from the
• telephone company’s central office to your home or business.
• The central office is the building that houses the telephone
company’s switching equipment and provides a local dial tone on your
telephone.
• If you place a long distance call, the central office passes
yourtelephone call off to a long distance provider.

Local Loops

Local Access Transport Areas
• The USA is divided into a few hundred local access transport
• areas (LATAs).
• If your call goes from one LATA to another, it is a long distance call
and is handled by a long distance telephone company.
• If your call stays within a LATA, it is a local distance call and is
handled by a local telephone company.

Trunk
• A trunk is a special telephone line that runs between central offices and
other telephone company switching centers.
• A trunk is usually digital, high speed, and carries multiple telephone circuits.
• A trunk is typically a 4-wire circuit, while a telephone line is a 2-wire circuit.
• Not associated with a single telephone number like a line is.
• A telephone number consists of an area code, an exchange, and a
subscriber extension.
• The area code and exchange must start with the digits 2-9 to separate them
from long distance and operator services.

•When the telephone company installs a line, it must not
proceed any further than 12 inches into the building. This
point is the demarcation point, or demarc.
•Modular connectors, such as the RJ-11, are commonly
used to interconnect telephone lines and the telephone
handset to the base.
•When the handset is lifted off the base (off-hook), an off-
hook signal is sent to the central office.

Services
• Foreign exchange service (FX) - customer calls a local
number which is then connected to a leased line to a
remote site.
• Wide area telecommunications services (WATS) –
discount volume calling to local and long distance sites.
• Off premises extensions (OPX) - dial tone at location B
comes from the PBX at location A.

PBX
• Private branch exchange (PBX) - a common internal
phone switching system for medium to large-sized
businesses.
• Provides advanced intelligent features to users, such as:
4-digit, special prefixes for WATS (wide area telephone
service), FX, etc (private dialing plans)
• PBX collects dialed digits and intelligently decides how to
route this call for lowest cost

PBX Advanced Features
• Voice mail
• Routes incoming calls to the best station set (automatic call
distribution)
• Provides recorded messages and responds to touch-tone requests
(automated attendant)
• Access to database storage and retrieval (interactive voice
response)

PBX Components
• CPU, memory, telephone lines, trunks
• Switching network
• Supporting logic cards
• Main distribution frame
• Console or switchboard
• Battery back-up system

Cordless system
•What is cordless system?
•History of cordless system.
•Frequencies
•Performance
•Wireless phone handsets
•Types of cordless system
● Analog
● Digital

What is cordless system?
• Cordless system is basically general term of cordless
telephones and cordless telecommunication systems.
•Cord means “wire” , so cordless system means
wireless system.

Cordless telephone with
base

Definition:
• A cordless telephone or portable telephone is a
telephone with a wireless handset that
communicates via radio waves with a base station
connected to a fixed telephone line, usually within a
limited range of its base station (which has the
handset cradle). The base station is on the
subscriber premises, and attaches to the telephone
network the same way a corded telephone does.

• Current cordless telephone standards, such as PHS
and DECT, have blurred the once clear-cut line
between cordless and mobile telephones by
implementing cell handover, various advanced
features, such as data-transfer and even, on a
limited scale, international roaming.

• Unlike a corded telephone, a cordless telephone
needs mains electricity to power the base station.
The cordless handset is powered by a rechargeable
battery, which is charged when the handset sits in
its cradle.

Limitations:
• Residential – a single base station can provide
in-house voice and data support
• Office
A single base station can support a small office
Multiple base stations in a cellular configuration can
support a larger office
• Telepoint – a base station set up in a public
place, such as an airport

Frequencies
• In the US, seven frequency bands have been allocated by
the FCC for uses that include cordless phones. These
are:
1. 1.7 MHz (1.64 MHz to 1.78 MHz & up to 5 Channels, AM
System)
2. 43–50 MHz (Base: 43.72-46.97 MHz, Handset: 48.76-
49.99 MHz, allocated in 1986 for 10 channels, and later 25
Channels, FM System)
3. 900 MHz (902–928 MHz) (allocated in 1990)
4. 1.9 GHz (1880–1900 MHz) (used for DECT
communications outside the U.S.)

5. 1.9 GHz (1920-1930 MHz) (developed in 1993 and
allocated U.S. in October 2005)
6. 2.4 GHz (allocated in 1998)
7. 5.8 GHz (allocated in 2003 due to crowding on the
2.4 GHz band).

Types (standards) of
Cordless telephone
• Digital cordless phones
(i) Digital Enhanced Cordless
telecommunication(DECT)
(ii)Personal Handy-Phone System(PHS)
• Analog cordless phones
The main distinction among types of cordless phones
is the way to transmit their signals.

Application of DECT
• Domestic cordless telephony, using a single base
station to connect one or more handsets to the
public telecoms network.
• Enterprise premises cordless PABXs and wireless
LANs, using many base stations for coverage. Calls
continue as users move between different coverage
cells, through a mechanism called handover. Calls
can be both within the system and to the public
telecoms network.
• Public access, using large numbers of base stations
to provide high capacity building or urban area
coverage as part of a public telecoms network.
• “Fido”

Features of DECT
Typical abilities of a domestic DECT Generic Access
Profile (GAP)
System include:
• Multiple handsets to one base station and one
phone line socket. This allows several cordless
telephones to be placed around the house, all
operating from the same telephone jack.
• Interference-free wireless operation to around 100
metres (109 yards) outdoors, much less indoors when
separated by walls .
- For instance, generally immune to interference
from other DECT systems, Wi-Fi networks, video
senders, Bluetooth technology, baby monitors and
other wireless devices.

Mobile Telephone Systems

Early Cellular Telephone Systems –
Advanced Mobile Phone System
(AMPS)

Problem with AMPS

New Mobile Telephone Switching Office
(MTSO) Systems

FDMA in Mobile Phones
• Frequency division multiple access (FDMA)
systems are like frequency division multiplexing
in that they allow many users to share a block of
spectrum by simply dividing it up into many
smaller channels.
• Each channel of a band is given an assigned
number or is designated by the center frequency
of the channel.
• One subscriber is assigned to each channel.
Typical channel widths are 30kHz, 200kHz,
1.25MHz and 5MHz.

FDMA Process
1. A base station can receive radio signals in a given band of
spectrum
2. The band of frequency is broken up into smaller bands
(subbands)
3. Each transmitter (user) transmits to the base station using
radio waves in its own subband
4. When a user is assigned to a subband, it transmits to the
base station using a sine wave with the center frequency in
that band
5. When the base station is tuned to the frequency of the desired
user, it receives no portion of the signal transmitted by
another in-cell user.
6. Multiple local transmitters in a cell do not interfere with one
another.

Time division Multiplexing
(TDMA)

TDMA Process
1. Time is broken into time slots (small, equal-length
intervals)
2. Assume there are N users in the cell
3. Base station groups N consecutive slots into a frame
4. Each user is assigned one slot per frame. This slot
assignment stays fixed as long as the user
communicates with the base station (the length of the
phone conversation)
5. In each time slot, the assigned user transmits a radio
wave using a sine wave at the center frequency of the
frequency band assigned to the base station.

Code division Multiple Access
(CDMA)

CDMA Method 1 (frequency
hopping Method)
1. Each user is assigned a frequency hopping
pattern (a fixed set of frequency values)
2. Time is divided into slots
3. In the first time slot, a given user transmits to
the base station using the first frequency in its
frequency hopping sequence.
4. In the next time interval, it transmits using the
second frequency value in its frequency hope
sequence, and so on. This way the transmit
frequency keeps changing in time.

Satellite Movement

Satellite Formulas

Satellite Formulas
Kepler’s third Law:

Example – Satellite
Calculations

Solution

Communication Satellites
• Communication satellites are not
originators of the signal to be transmitted
• Act as relay stations for earth sources
• The satellite contains a receiver that picks
up the transmitted signal, amplifies it, and
translates it to another frequency (uplink –
6GHz). The signal is then retransmitted to
the receiving stations on earth (downlink –
4 GHz). Known as transponder.

Satellite Bands and
Frequencies
As C Band is full, most modern satellite systems use the Ku Band:

The C Band

Example
• A mobile transponder operates in the C band. Assume a
local oscillator frequency of 2GHz.
– What is the uplink receiver frequency if the downlink transmitter
is on channel 4?
– What is the maximum theoretical date rate if one transponder is
used for binary transmission?

Solution
• The downlink frequency of channel 4 is 3840 MHz. The
downlink frequency is the difference between the uplink
frequency fu and the local oscillator frequency, fLO
• The bandwidth of one transponder channel is 36MHz.
For binary transmission, the maximum theoretical data
rate or channel capacity C for a given bandwidth B is:
•
• C=2B
• =2(36)=72Mbps

TDMA, FDMA, CDMA
• To maximize the use of the available
spectrum in satellite transponders and to
ensure access for as many users as
possible, all satellites use some form of
multiplexing.
• Frequency-division multiplexing (FDMA)
was used in early satellites. Time division
multiple access (TDMA) is used in newer
satellites.

TDMA, FDMA, CDMA
• TDMA assigns each user a time slot on the full
bandwidth of the transponder channel. Modulation
methods are BPSK and QPSK, although multilevel QAM
(16 QAM, 32 QAM, 256 QAM) is used to increase digital
transmission speeds at a given bandwidth.
• Code-division multiple access (CDMA) spreads the
signals of multiple users over the full transponder
channel bandwidth and sort them by the use of
pseudorandom codes. CDMA also provides security and
provides multiple access while conserving spectrum.

Thank you!

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