Wireless Communication Engineering - Data Communications

Li-Der Jeng

Department of Electronic Engineering

Chung-Yuan Christian University

Chung-Li, Taiwan, ROC

TEL: (03) 265-4608

E-mail: lider@cycu.edu.tw

Contents

• Introduction to Data Communications

• Information Encoding

• Analog and Digital Transmission Methods

• Transmission Media

Introduction to Data

Communications

Fundamental concepts

• Communication can be defined as exchange of information between two humans.

• Data communications can be defined as the exchange of information between two computers.

• In its simplest form, the data communications can be shown as in the following figure.

Data Communication

Transmission medium

Source Destination

Real-life Data Communication Systems

Modem

Modem

Modem

Modem

Modem

Transmission medium

Mu

ltip

lexe

rD

emu

ltiplexer

Data communications

• In the simplest form, data communications involves the exchange of data between two computers.

• Computers work with a binary language consisting of zero and one.

• Therefore, a computer generates a stream of zeros and ones and sends it to another computer to which it is connected in some fashion.

• The connection can be either a simple wire or it can be through wireless media.

Data communications (I)

• For enabling data communications, a combination of hardware and software is essential. In any data communications system, three characteristics are described:– Correct delivery: When a sender transmits data for an intended

recipient, the data must reach only the intended recipient and not someone else.

– Accurate delivery: The data sent must be received in the same form as the one in which it was sent. There must not be any sort of alternations to it in transit.

– Timely delivery: The data must travel from the sender to the receiver in a finite amount of time. The term finite is quite vague, and would depend on the reasons why the data communication is taking place.

• Two key aspects of data communication systems need a good amount of understanding.– Transmission media: the physical path over which data

travels from the sender to the receiver. Ex: twisted-pair of copper wires, coaxial cable, optical fiber or wireless media such as radio waves.

– Protocol: a set of rules and conventions. Ex: The sender and the receiver, the two key parties in data communication must agree on a common set of rules, i.e. protocols before they can communicate with each other.

Data communications (II)

Protocols• A protocol defines the following:  

– Syntax (What is to be communicated)– The syntax defines the structure or format of data. This means that the order in which it is to be sent is decided. For instance, a protocol could define that the first 16 bits of a data transmission must always contain the receiver’s address. 

– Semantics (How it is to be communicated) – The semantics define the interpretation of the data that is being sent. For example, the semantics could define that if the last two bits of the receiver’s address field contain a 00, it means that the sender and the receiver are on the same network.

– Timing (When it should be communicated) – This refers to an agreement between the sender and the receiver about the data transmission rates and duration. For instance, a protocol could demand that the sender must send 1000 bytes and then wait for an acknowledgement from the receiver before sending any more data.

Standards• Standards are necessary in every walk of life. For instance, when

you want to replace a light bulb in your home because it has been damaged, you expect the new bulb to fit in the holder straightaway and work like the old bulb did. What is the use if the bulb does not fit in the holder, or if it fits in the holder but does not illuminate because it requires a different voltage level? Consequently, everything that we use in our daily life has some common features, some standards that every manufacturer must abide by. In the absence of standards, every manufacturer can theoretically manufacture a set of goods or services that are incompatible with other manufacturers.

• To avoid such anomalies, a set of standards is established, which governs the rules that manufacturers must obey. In exactly the same fashion, standards for data communications have been set. Consequently, a lot of incompatibility issues have no place in data communications, which is highly desirable.

Bandwidth of a signal and a medium

• The term bandwidth is very commonly used in data communication. The basic idea behind bandwidth can be understood quite easily with a simple example of pipes carrying water to our homes. What is the maximum amount of water a pipe can carry at any given time? The maximum capacity of the pipe at a given instance is its bandwidth.

Analog and digital signals

• Any signal can be classified into one of the two types: analog and digital.

• An analog signal is a continuously varying signal, similar to a sinusoidal waveform.

• A digital signal takes the form of pulses, where we have something or nothing.

Time

T e m pe

r a t ur

e

Analog Signal

V O L T A G E

Time

0 1 1 0 1 0

Digital Signal

Amplitude, period, frequency, phase

• Amplitude: the signal has maximum value• Period: the time taken for the completion of

one cycle• Frequency: the number of cycles or

revolutions that our particle would make in one second

• Phase: the phase of a signal is related to the position of a waveform relative to time zero

Fourier analysis and the concept of bandwidth of a signal

• Ex: A periodic signal has been decomposed using Fourier analysis to yield four sine waves of frequencies 100, 400, 600 and 800 Hz. What is the bandwidth of the resulting periodic signal? (800-100=700)

• Ex: A signal has a bandwidth of 20Hz and its highest frequency is 60Hz. What is the lowest frequency? (60-20=40)

0 1 0 0 0 1 0

Bandwidth 1500 Hz

Bandwidth 500 Hz

Bandwidth 2000 Hz

Bandwidth 2500 Hz

Bandwidth 3000 Hz

Bandwidth 5000 Hz

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Bandwidth Hz (h)

A Digital Signal With Infinite Bandwidth

Pulses before transmission :Bit rate:

2000 bits per second

Period (T)= 1 second 1 second

A Digital Signal of 1Hz

0 1 0 1 0 1 0 1 0

1 0

T = 1/10 secT = 1/10 sec

Time

1 0

0X

V

A Sinusoidal Wave with Frequency = 10 Hz

40 Hz: 20 bps (Channel 1)

 

 

40 Hz: 20 bps (Channel 0)

A Medium and Channels

Information Encoding

Introduction

• How computers store data?• Can a computer understand English?• Does it store data in some other language?• If a computer cannot understand English,

how can we codify the data to be stored in a fashion that the computer will be able to understand?

• Why a computer uses binary language?

The BCD Equivalent of Decimal Digits

Decimal Digits BCD Equivalent0 0000

1 0001

2 0010

3 0011

4 0100

5 0101

6 0110

7 0111

8 1000

9 1001

The BCD code

• Binary Coded Decimal (BCD) code Decimal 2 5 Binary 0010 0101• The BCD number for a decimal number 25 is

00100101 Decimal 1 0 Binary 0001 0000• The BCD number for a decimal number 10 is

00010000

Character ASCII (Binary)

ASCII (Decimal)

Character ASCII (Binary) ASCII (Decimal)

A 1000001 65 [ 1011011 91

B 1000010 66 \ 1011100 92

C 1000011 67 ] 1011101 93

Z 1011010 90 ^ 1011110 94

1 0110001 49 _ 1011111 95

2 0110010 50 ‘ 1100000 96

3 0110011 51 * 0101010 42

9 0111001 57 + 0101011 43

a 1100001 97 , 0101100 44

b 1100010 98 - 0101101 45

c 1100011 99 . 0101110 46

z 1111010 122 / 0101111 47

Portion of the ASCII Table

Portion of the EBCDIC Table

Decimal Digit EBCDICA 11000001

B 11000010

C 11000011

Z 11101001

0 11110000

1 11110001

2 11110010

9 11111001

Multimedia• These days, computers can also be used for the following:

– Drawing, storing and viewing pictures

– Storing sounds and playing them back

– Storing videos and playing them back

• However, pictures, videos and sounds are not made up of alphabets and numbers. How can a computer recognize and store them? How can we codify information about these so that a computer can store them?

• To solve this problem of codification of pictures, videos and sounds, the concept of multimedia came into being. As the name says, multimedia means multiple media.

Picture/Images

• Now let us imagine that we divide the picture by a number of horizontal and vertical lines to form a grid. Each rectangle is called picture element or pixel.

• As the number of pixels increases (also called higher resolution), the pixel size decreases.

• Ex: We choose the resolution such that each pixel has either a dot or a blank.

00000000 01100000 00000000 01100000 00001111 11110000 00010000 00001000 00100000 00000100 01000000 00000010 01000000 00000010 01111111 11111110 00100111 01110100

Graphics Hardware /

Software

Screen Output

Computer’s Memory

. . . . . . . . . . . . . . .

.

. . . . . . . . . . . . . . .

.

. . . . . . . . . . . . . . .

.

. . . . . . . . . . . . . . .

.

. . . . . . . . . . . . . . .

.

Pixels Being Mapped to Zeroes and Ones

• In practice, it is common to have 8, 16 or 24 bits to represent one pixel on the screen.

• It is well known that any color can be derived by adding or mixing various intensities of three basic colors: Red, Green, Blue – thus the name RGB.

• Many systems that use 24 bits to describe the color of one pixel use 8 bits each to describe the intensities of Red, Green, Blue.

Picture/Image

Video

• The basic principle behind video is the technology animation. The idea behind animation is very simple and is used in cartoons and films.

• If a set of pictures is shown rapidly, the human eye can be fooled into believing that the pictures are in motion.

• It has been proved that if 24 pictures are shown in succession in one second, our eyes sense it as a continuous motion.

Sound

• A sound wave (i.e. an audio signal) is continuous in nature.

• The continuity is in two respects: the strength of wave/signal (called amplitude) and time.

• In contrast, a computer works only with binary values: 0 and 1.

• If we want to translate an audio signal so that it can be mapped to the computer-recognizable data of 0 and 1, it should be clear that we must somehow map an analog signal as a digital signal.

Audio Signal in the Analog Form

Am

pli

tud

e

Time

Signal Representing Only Binary Values (0 and 1)

Amplitude

Time

0

1

Sound

• Sampling: measuring the audio signal at fixed intervals of time is called sampling. Thus, if we decide that the audio signal would be measured say 60 times a second, the sampling rate would be 60.

• Quantizing: having determined how many times the signal should be measured, the next step is to assess the range of amplitudes.

6 5 2 1 2 3 6 9 11 10 7

Original signal Sampling Measuring the signal  

Stored on the disk as numbers Quantizing

Sampling and Quantizing

5

4

3

2

1

0

Analog and Digital Transmission Methods

Introduction

• We have studied that the two major types of signals are analog and digital. However, the manner in which these two types of signals can be transmitted are also of the same types, that is analog and digital.

• We have four possible combinations:– Analog Signal, Analog Transmission– Digital Signal, Digital Transmission– Digital Signal, Analog Transmission– Analog Signal, Digital Transmission

Analog Signal, Analog Transmission

(a) Telephone (b) Analog signal

Analog signal, analog transmission• The term analog is very common and used for decades in

the field of telephony.

• The human voice generates an analog(i.e. continuously varying) signal, which is transmitted as an analog signal over the medium.

• On the way, the signal suffers attenuation.

• Amplifiers are used to overcome this problem, but then amplifiers amplify noise along with the original signal, too.

• The problem with this type of combination is that if the signal gets distorted, it cannot be reconstructed at all!

• This is the reason why this type is not used where a high level of accuracy is desired.

Digital signal, digital transmission

• We know that the information coming out of a computer is the form of digital signals.

• We also know that a digital signal has an infinite bandwidth, whereas any medium has only a limited bandwidth.

• Therefore, as the signal is generated and enters the medium, the signal is distorted.

• The hardware equipment called regenerative repeater or repeater is used to regenerate the signal.

Regenerative Repeaters From

Data

Processing

Machine

0 1 0 0 1 0 1

0 1 0 0 1 0 1 0 1 0 0 1 0 1

Regenerative

Repeater

A

B C

• The input to the regenerative repeater is a signal, which looks like a digital signal. Therefore, the repeater measures the signal values at regular intervals to recognize the 0s and 1s in the signal and regenerate them. Therefore, there is no loss of information.

• However, only one repeater will not do. You will require many such repeaters. The distance between the repeaters is very crucial. We may like to increase that distance as much as possible to reduce the cost but then there is also a disadvantage to this. (it may be difficult to differentiate 0 and 1.)

• Any line with repeaters placed at the appropriate distance is called a digital line.

• AT&T put such repeaters on the wire pairs used for telephonic conversations, separated by a distance of only 6000 feet. This digital line is called a T1 line, which can carry a data rate of 1,54,400 bits per second (1.544 Mbps).

Digital signal, digital transmission

DestinationSource

A T1 Line Contains Many Repeaters

Destination

Digital line

Repeater Repeater Repeater

Digital signal, analog transmission

• The designers had two choices for data communications between two computers.One was to create a new digital network with repeaters etc, or use the existing telephone network.

• When computers were invented, the telephone network was already in existence. However, telephones use analog signals and analog circuits. The problem: how to send a digital signals over an analog network?

• We use a modem for this purpose. The modem is derived from two components: a modulator and a demodulator.

Use of Modem for Sending Digital Data Over Analog Lines

modem

modem

Analog signal

Analog signalDigital signal

Digital signal

Network

• As the above figure shown, the digital signals originating from the computer go through the modem where they are converted (i.e., codified or modulated) into analog signals whose bandwidth is < 4000 Hz. This is because the channel for telephone conversation requires a bandwidth of 4000 Hz.

Digital signal, analog transmission

Modulation techniques• Amplitude Shift Keying: ASK• Frequency Shift Keying: FSK• Phase Shift Keying: PSK• Quadrate Amplitude Modulation: QAM

– The main limitation of PSK is the inability of the hardware equipment to distinguish small differences in terms of phase changes. This puts a limitation on its data rate.

– Combine ASK and PSK, makes higher data rates possible (since the bandwidth of the transmission medium is a major limitation, we cannot combine FSK with anything else)

Amplitude Shift Keying (ASK)

1 0 0 1 1 0 1 0 0 1 1

1

0

The frequency is between 0 and 4000 Hz

Frequency Shift Keying (FSK)

1 0 0 1 1 0 1 0 0 1 1

f1 f2 f2 f1 f2 f 1 f2 f1 f1 and f2 are between 0 and 4000 Hz

Phase Shift Keying (PSK)

1 0 0 1 1 0 1 0 0 1 1

Baud rate and bits per second• Many people confuse baud rate and bit rate or bits per

second (bps). There is a difference between them.• The baud rate is the number of times the signal level

changes in a channel per second. This signal level could be amplitude, frequency of phase.

• The bandwidth of a transmission medium is finite, how can we achieve higher data rates?

• By associating more than one bit for each signal level, one can achieve a higher data rate. That is, the bit rate will be higher that the baud rate in such a case. All this has to be built into the modem.

Single Bit Transmission by Using FSK

2200 Hz = 1

1200 Hz = 0

1700 Hz

ComputerModem

bit rate = baud rate

Double Bit Transmission by Using FSK

2000 Hz = 11

500 Hz = 00

1250 Hz

Computer Modem

1000 Hz = 01

1500 Hz = 10

bit rate = 2*baud rate

Analog signal, digital (storage and ) transmission

• This type of transmission is becoming very popular due to many reasons that we will discuss later.

• The idea is somehow to represent an analog signal into digital bits and then transmit it as a digital signal.

• There are several techniques that are possible to achieve this and we have discussed the general overview of the basic idea, but Pulse Code Modulation (PCM) is the most popular.

The basic steps in PCM

• At source– Sample the analog signal at regular interval say t.

(Sampling)

– Convert the analog signal into some discrete values. (Quantization)

– Convert these values into binary numbers by assigning a fixed number of bits for each value. (Encoding)

– Convert the binary numbers as a digital signal by concatenating all these binary numbers.

• At destination– Convert the digital signal into binary numbers.– Separate out the discrete values of signals by using the

number of bits for each discrete value.– Reconstruct the original analog signal

• We require an equipment called codec (Coder/Decoder) at both the source and destination to perform these functions. We can call it also as A/D (Analog to Digital) converter and D/A (Digital to Analog) converter.

The basic steps in PCM

Pulse Code Modulation (PCM)

t

1. 04 1.0

0.680.70

0.21

t

0.78 0.8

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.49 0.5

0. 83 0. 8

Time

0.2

1.0.1.1.1.1.1.1.

1.071.1

Pulse Code Modulation (PCM)

• The A/D process is called quantization.• The problem: quantization error.• In the whole process, we have saved a lot in the

number of bits that we needed to send. Thus, there is a trade-off between accuracy and cost or speed. The aim of any good PCM strategy would be to reduce the quantization noise to a negligible level without increasing the load on the network significantly.

• The current PCM standard assumes eight bits/sample.

Nyquist theorem• An interesting question is : How do we choose the time

interval for sampling or slicing the analog signal?• At higher speeds of sampling, the signal is more likely

to be reproduced faithfully than if the speeds are low• In fact, the sampling speed is related to the highest

frequency in a signal. Nyquist showed that the sampling speed should be 2*fmax where fmax represents the highest frequency in that signal resulting out of Fourier analysis. This is called Nyquist theorem.

Sampling Speeds for Different Frequencies

0 t 2t 3t 4t 5t

(a) Low frequencyAmplitude

Time t

0 t 2t 3t 4t 5t

(b) High frequency

Amplitude

1.0.1.1.1.1.2

x y z

Nyquist theorem

• Ex: if we want to sample a telephone voice with a maximum frequency of 4000 Hz, we must have a sampling rate of 8000 samples per second. This is exactly what is used in PCM standard.

• Video signals have a far higher bandwidth with signals at very high frequencies than voice signals. This is obvious from the data contents and rates of VCD and DVD players (for video disk) which are far higher as compared to that of a CD (Compact Disk) for music.

Nyquist theorem• The human voice has various frequency components in the

range of 0 to 20000 Hz. However, out of this range, the frequency range of 300-3300 Hz is sufficient to recognize the voice in a telephone conversation.

• The frequencies 0-300 Hz and 3300-4000 Hz act as guard bands, so that multiplexing of many signals in a single wire is possible. Therefore, the maximum frequency in this case is 4000 Hz.

• Using Nyquist theorem, we can conclude that to transmit human voice over digital telephone line, we must have a sampling rate of 4000*2=8000 samples per second. Moreover, if each sample consists of 8 bits, we can have the following equation for the bandwidth required of the telephone lines to carry digitized human voice:

Highest frequency of human voice * 2 * Number of bits in each such sample = 4000 * 2 * 8 = 64,000 bits per second = 64 Kbps

Transmission Media

Introduction

• Transmission media are the physical infrastructure components that carry data from one computer to another.

• Examples:– Telephone wires that connect telephones to the central

office– Coaxial cables that carry the cable television

transmission to homes

• Transmission media need not always in the form of a physical wire – they can be invisible as well.

Transmission Media

Guided Media Unguided Media

Categories of Transmission Media

Guided Media

Twisted-pair wires Coaxial Cables Optical fiber

Types of Guided Media

Twisted Pair Cable

Unshielded Twisted Pair (UTP) Shielded Twisted Pair (STP)

Categories of Twisted Pair Cable

Unshielded Twisted Pair (UTP)

Category Usage

1 The basic cable used in the telephone system. This is fine for voice communication, but is unsuitable for data communication, except at very low speed.

2 Suitable for voice and data communication up to the speed of 4 Mbps.

3 Can carry voice and data up to 10 Mbps. It requires minimum three twists per foot. Today, these are more regularly used in telephone networks.

4 These are similar to the category 3, but can handle data up to 16 Mbps.

5 Can handle data speed of 100 Mbps.

Categories of UTP

Shielded Twisted Pair (STP)

Metal shield Plastic coverInsulationCopper

Protective plastic coating

Outer conductor

Insulating material

Copper core

Coaxial Cable

Optical Fiber• Optical Fiber Structure

– Optical fibers use light instead of electrical signals as a means of signal propagation. They are made of glass fibers that enclosed in a plastic jacket. This allows the fibers to bend and not break.

– A transmitter at the sender’s end of the optical fiber sends a light emitting diode (LED) or laser to send pulse of light across the fiber.

– A receiver at the other end makes use of a light-sensitive transistor to detect the absence or presence of light to indicate 0 or 1.

Fiber Buffer Outer jacket

Optical Fiber

Propagation modes

Multimode Single mode

Step indexed Graded indexed

Propagation Modes

Multimode Step Index Fiber

Source Destination

Core Cladding

Source Destination

Core Cladding

Multimode Graded Index Fiber

Source Destination

Core Cladding

Single Mode Fiber

Advantages/Disadvantages of Optical fiber

• Advantages:– Resistance to noise– Huge bandwidth– Higher signal carrying capacity

• Disadvantages:– Fragility– Cost– Maintenance overhead

Unguided Media

• Unguided media, also called as wireless communication, transport electromagnetic waves without using a physical conductor.

• The signals propagate through air (or sometimes water).

• The communication band for unguided media is as shown in the following figure.

3 KHz 300 GHz

Radio communication

VLF LF MF HF VHF UHF SHF EHF

3 KHz

30 KHz

300 KHz

3 MHz

30 MHz

300 MHz

3 GHz

30 GHz

300 GHz

Radio Communications Band

Terrestrial Microwave Communication

Satellite Microwave Communication

Ground stations

Satellite

A B

Satellite Communication• Problem:

– If the earth along with its ground stations is revolving and the satellite is stationary, the sending and receiving earth stations and satellite can be out of sync over time. Therefore, normally Geosynchronous satellite are used, which move at the same Revolutions Per Minute (RPM) as that of the earth in the same direction, exactly like the earth.

• Frequency: SHF, 3 GHz to 30 GHz• Two frequency bands

– From the earth to the satellite (called uplink)

– From the satellite to the earth (called downlink)

Earth

Three Satellites to Cover the Planet

Access Methods• There are three methods for communication using

satellite. These three methods use principles that are similar in concept to normal wired communication. Like the wired world, satellite communication is also based on modulation techniques. The three primary modulation techniques are:– Frequency Division Multiple Access (FDMA)

– Time Division Multiple Access (TDMA)

– Code Division Multiple Access (CDMA)

• Multiple Access: This simply means that more than one user (multiple) can use (access) each cell.

Satellite

Ground stations

Frequency Group 1

Frequency Group 3

Frequency Group 2

 

Frequency Division Multiple Access (FDMA)

This is the most popular method for communication using satellites.

Satellite

Ground stations

Data packets

Time Division Multiple Access (TDMA)

This is the second most popular mechanism for communication using satellites.

Satellite

Ground stations

Code 1 Code 1Code 2

Code 2

Code Division Multiple Access (CDMA)

Cellular (Mobile) Telephones• First mobile telephone

– As early as 1946.

– The city of St. Louis in USA

– Half-duplex system, known as push-to-talk-system, was installed in the big cities in 1950s.

– Even today, taxi, CB-radio etc. use the same technology

• The second development took place in 1960s.– Improved Mobile Telephone System (IMTS)

– Full-duplex system: two frequencies are used

– 23 channels

– In IMTS, users had to wait for a long time to get a dial tone

• The third step: Advanced Mobile Phone System (AMPS) (TACS in England, MCS-L1 in Japan)– Cellular phones (Cell: radius 0~12 miles)– The cells are actually circular, they are shown as

hexagonal for conceptual clarity.– Each cell has an antenna and a cell office to control that

call.– A Mobile Telephone Switching Office (MTSO) control

various cell offices and coordinates the communication between them and Telephone Central Office (TCO) or a telephone exchange.

– TCO: a part of the wired land telephone system– The computer at MTSO is responsible for not only the

connections but also for the information and billing of the calls.

Cellular (Mobile) Telephones

Cell Office

Cell Office

Cell Office

Cell Office

Cell Office

Cell Office

Cell Office

Mobile Telephone Switching Office (MTSO)

Telephone Central Office (TCO)

To land telephone system

Cellular Phone System

Bands in Cellular Telephony

• Classically, analog transmission is used for cellular telephony. – Frequency modulation is used for communication

between the mobile phone and the cell office. Normally, two frequency bands are allocated for this purpose.

– For preventing interference, adjacent channels are rarely allocated.

– Some channels are also required for control purposes.

– The number of channel: 40 in USA

– In USA, two bands: 824-849 MHz and 869-894 MHz

F

E

B

D

G

A

C

F

A

E

D

GC

F

F

B

E

D

GA

B

Frequency Reuse

Calls Using Mobile Phones• A call is made from the mobile phone

– Entering a 7-, 8- or 10-digit phone number– Mobile phone cell office MTSO TCO. If the

party is available, CTO lets MTSO know. At this juncture, MTSO allocates an empty voice channel to the cell to establish the connection.

• When a land phone places a call to a mobile phone– TCO MTSO all cell (paging). The cell where the

mobile phone is currently located responds to the MTSO. The MTSO then transmit the incoming call signal to the mobile phone, and when the mobile phone is answered, the MTSO assigns a voice channel to the call, thus enabling the conversation.

MTSO

ACurrent path

The signal of unit 50 is very weak now. Please find another cell for the unit where the signal is stronger.

B

User of unit 50 moving from cell A

to B.

Handoff Part 1 - A Unit Becomes Weak in Cell A

MTSO

C B

Can any of you take up unit 50? It is very weak in cell A. No, it is weak

for me, too!Yes, I can take it.

Handoff Part 2 – MTSO Enquires to See If Anybody Can Take up Unit 50

MTSO

A

Current path

B

New path

 

Handoff Part 3 – MTSO Hands Over Unit 50 to Cell B

Medium Speed Cost Security Attenuation

UTP 1–100 Mbps Low Low High

STP 1–150 Mbps Medium Low High

COAX 1 Mbps–1 Gbps

Medium Low High

Fiber 10 Mbps–2 Gbps

High High Low

Radio 1–10 Mbps Medium Low High-Low

Terrestrial Microwave

1 Mbps–10 Gbps

High Medium Variable

Satellite Microwave

1 Mbps-10 Gbps

High Medium Variable

Cellular 1.6–1.2 Kbps High Low Low

Transmission Media Characteristics

New Developments• 1. Digital cellular telephone.• 2. The integration of cellular phones with

satellite communication. This will enable a person to have a unique but same telephone number throughout the world, unlike today, when we have different numbers for land phones and mobile phones.

• 3. The integration of mobile telephony with the PC. The scheme is called Mobile Personal Communication.