Chapter 11

Electronic Communications

Understanding Communication Systems

• Key ideas:– Information and communication technologies

include the inputs, processes, and outputs associated with sending and receiving information.

– Information and communication systems allow information to be transferred from human to human, human to machine, machine to human, and machine to machine.

Understanding Communication Systems (cont’d.)

• Key ideas (cont’d.):– Communication systems are made up of a

source, encoder, transmitter, receiver, decoder, storage, retrieval, and destination.

– At the source, a modem modulates an analog carrier signal to encode digital information.

• At the destination or receiver, a modem demodulates the signal to decode the transmitted information and receive the message.

Communication Systems• Made up of building blocks:

– Consider instant messaging• Input, transmit (process), output, feedback

• Communication process includes:• A source• An encoder• A channel• A decoder• A receiver

Communication Systems (cont’d.)

Figure 11.5 Communication process consists of a source, encoder, transmitter, receiver, decoder, storage, retrieval, and destination.

Identifying Types of Communications• Key ideas:

– Information and communication systems can be used to inform, persuade, entertain, control, manage, and educate.

– There are many ways to communicate.– Technological knowledge and processes are

communicated using symbols, measurements, conventions, icons, graphic images, and languages that incorporate a variety of visual, auditory, and tactile stimuli.

Identifying Types of Communications (cont’d.)

• Key ideas (cont’d.):– Graphical analysis and presentation can be

divided into two general types: qualitative and quantitative.

– Oral presentations to bosses, teachers, customers, or colleagues at meetings or conferences can be used to share information, or sell an idea, a product, or even yourself (for example, a job interview).

Types of Communications • How we communicate our message depends

on the communication medium.– Graphic communications:

• Words and pictures convey a message.

– Electronic communications:• Electrical signals, pulses of light, or radio waves carry

messages.

Graphical Communication• Technical communication:

– Sharing technical information through graphs, graphics, and other visual tools.

– Computer-Aided Design programs are used to create blueprints.

– Qualitative information: • Drawings, bar graphs, and pie charts

– Quantitative information: • Tables and line graphs

Oral Communication• Steps to improve:

– Preparation:• Jot down facts and create an outline.• Identify theme.• Split into 15-20 minute chunks and practice.

– Visual aids:• PowerPoint/KeyNote.

– Presentation techniques:• Look presentable, neat, and well dressed• Speak clearly and loud enough.

Defining Telecommunications• Key ideas:

– Telecommunications is a very broad term that implies transmission of messages at a distance

• Could include transmission of signals via smoke (smoke signals), sound (drums), flags (semaphore), and even reflected sunlight (heliograph).

– Modern telecommunications involves some combination of an electronic transmitter and receiver.

Defining Telecommunications (cont’d.)• Key ideas (cont’d.):

– Communication technology and the ability to communicate electronically provide a competitive advantage.

– Digitizing voice data allows telecommunications carriers to use a single common digital infrastructure for voice, video, and data.

– A basic communications system consists of:• A transmitter to send the message, media over which

to send it, and a receiver of the information.

Telecommunications

• Telecommunication:– Ability to connect with voice, video, and data– Global telecommunications market:

• Three percent of the gross world product

Figure 11.17 Modern communication is shifting from old media (such as CNN.com) to new media (such as blogs).

Figure 11.21 The developing world lags behind the rest of the world in fixed telephone use.

Figure 11.22 Internet access is also less frequent in the developing world than in other countries.

Telecommunications (cont’d.)• Telegraphy:

– Transmission of messages as a series of dots and dashes (i.e., Morse code).

• Replaced with telephony (Bell and Gray).

• Telephony:– Switchboard

• Switches established a connection.

– Analog • Public Switched Telephone Network (PSTN) dominant

protocol is Asynchronous Transfer Mode (ATM).

Telecommunications (cont’d.)• Basic elements:

– All communication systems can be modeled with the core components (transmitter, media, receiver).

– Transceiver:• Transmitter and receiver

Analog Versus Digital

Figure 11.25 If you move a garden hose slowly up and down, the water stream shows low-frequency peaks.

Figure 11.26 By moving the hose faster, you create waves of higher frequency.

Figure 11.29 You can use the stream from the hose to simulate binary 1s and 0s.

Figure 11.31 The difference between an analog signal and a digital signal is dramatic.

Channels• Each network or station broadcasts its own

signal in a very specific communications channel, usually associated with a frequency– Frequency division multiplexing:

• Multiplex: bundled channels together• Demultiplex: unbundle channels after receiving them

– Time division multiplexing:• “Chop” time into slices or slots and assign each

conversation its own time slot

Carrier Waves• Carrier waves:

– Analog signal or waveform acts as a carrier.

• Modulation:– How the signal

is carried.

Figure 11.36 In frequency modulation (FM), the frequency of the carrier wave is modified.

Satellite Communications• Key ideas:

– In communications, a satellite is a manmade object positioned in the Earth’s orbit to facilitate communication on the Earth.

• A satellite usually travels in either a geostationary, elliptical, or low Earth orbit (LEO).

– A satellite constellation is a group of satellites working together.

Global Positioning Systems• Key ideas:

– The Global Positioning System (GPS) uses a constellation of at least twenty-four medium Earth orbit satellites to transmit microwave signals to a GPS receiver.

– Civilian GPS is only accurate within 15 meters because of a combination of factors:

• Errors due to atmospheric conditions, multipath effects, clock drift in the satellite’s onboard clock, selective availability, and relativistic errors.

Satellite Communications• Satellite:

– Celestial body orbiting Earth or other planet– Usually categorized by their orbits (e.g.

geostationary, elliptical, or low Earth orbits)• Sputnik I• Explorer I

– Variety of applications– Satellite constellation:

• A group of satellites working together

Figure 11.41 Various types of orbits include geosynchronous, medium Earth, and low Earth orbits.

Figure 11.42 Satellite orbits can be polar, high incline, or low incline.

Global Positioning Systems • Enables a user to accurately determine

location, speed, direction, and time– Receiver identifies satellites within range and

calculates its position relative to three or more of them

Figure 11.45 A constellation of satellites helps to operate the Global Positioning System.

Figure 11.46 Atmospheric effects and errors have the greatest effecton GPS accuracy when satellites are near the horizon.

Exploring Digital Media • Key ideas:

– The shift from analog to digital information has forever altered the way we view sound, images, and video, and has opened up entirely new methods of communication and connectivity.

– Digital media is made up of ones and zeroes, and is measured in bits, bytes (8 bits), kilobytes (103

or 1,000 bytes), megabytes (106 or

1,000,000 bytes), and gigabytes (109 or 1,000,000,000 bytes or 1,000 megabytes).

Exploring Digital Media (cont’d.)• Key ideas (cont’d.):

– With analog media, we record sound by “scratching” an analog signal, created by your voice or a musical instrument, onto a surface and playing it back following the grooves we created.

– The MP3 file format uses a compression algorithm to reduce the size of a song while retaining near-CD sound quality, compressing a 32-MB song to 3 MB.

Exploring Digital Media (cont’d.)• Key ideas (cont’d.):

– Digital cameras and camcorders function by focusing light onto a small semiconductor image sensor that filters the light into the three primary colors, records the colors, and combines them to create a full-color image.

Exploring Digital Media (cont’d.)• Most devices are built around the same basic

process: – Converting analog into digital information

• ADC (analog-to-digital converter)• DAC (digital-to-analog converter)

• Digital media is made up of ones and zeroes– When we refer to digital media, we refer to bits,

bytes, kilobytes, megabytes, and gigabytes.

Exploring Digital Media (cont’d.)• Digital media includes:

– Audio, images, video– Digital cameras and camcorders focus light onto

a small semiconductor image sensor• Often, this sensor is a charge-coupled device (CCD)• CCD consists of a 1-cm panel of hundreds of

thousands of light-sensitive diodes called photosites• High-end cameras and camcorders use three

sensors, as well as three filters with a beam splitter to direct light to the different sensors.