final

Mobile Computing Unit 1

Sikkim Manipal University Page No.: 1

Unit 1 Introduction to Mobile Computing

Structure:

1.1 Introduction

Objectives

1.2 Radio Basics

Electromagnetic energy

Frequency and Wavelength

1.3 Spectrum Management

Managing a natural resource

Allocation, Allotment, Assignment

1.4 The Cell Approach

System identification code

Cellular access technologies

1.5 Summary

1.6 Terminal Questions

1.7 Answers

1.1 Introduction

One of the most vibrant areas in the communication field today is Wireless

communication. While it has been a topic of study since the 1960s, the past

decade has seen a surge of research activities in the area. There are

several factors behind this. First, there has been an explosive increase in

demand for wireless connectivity, driven so far mainly by cellular telephony

but expected to be soon eclipsed by wireless data applications. Second, is

the dramatic progress in VLSI technology, which enabled small-area and

low-power implementation of sophisticated signal processing algorithms and

coding techniques. Third, is the success of second-generation (2G) digital

wireless standards, in particular, the IS-95 Code Division Multiple Access

(CDMA) standard, providing a concrete demonstration that good ideas from

communication theory can have a significant impact in practice.

We begin, this unit with the basic terms and concepts relevant to radio

spectrum and cellular infrastructure. Spectrum is the foundation for mobile

communications and much of the significant social, economic, and political

aspects of the wireless sector are rooted in these technical dimensions of



radio systems. This unit provides a basic vocabulary and perspective on

spectrum management on which much of the rest of the SLM is built.

Objectives:

After studying this unit, you should be able to:

discuss Radio basics

explain spectrum management

define terms like wavelength, Cell and SID

discuss Cellular Access technologies

1.2 Radio Basics

The term radio spectrum is used by scientists, engineers and policymakers

to classify a vast and otherwise undifferentiated swath of electromagnetic

energy that exists in the universe. This kind of energy makes possible the

development and use of technologies such as, garage door openers,

broadcast radio and TV, remote controlled toy airplanes, geographic

positioning systems (GPS) and mobile phones. In fact, none of these

technologies would be possible without the pioneering work of people like

the French mathematician Jean-Baptiste Fourier (17681830), who first

theorized an idea of radio spectrum or the entrepreneurship of Guglielmo

Marconi (18741937) who is credited with the first successful experiments in

wireless telegraphy in the late 19th century.

With a growing stock of theoretical and practical knowledge in the technique

of wireless transmission, entrepreneurs in the early 20th century developed

the first reliable radio systems and the spectrum (sometimes called RF for

radio frequency) quickly became recognized as a radically new means by

which human beings could communicate. This recognition would bring

immense changes to maritime communications and military strategy; it

would also inspire the birth of new forms of entertainment, revolutionize

industrial techniques and inaugurate a major globalization initiative to

coordinate its use within and across international borders.

In the early years there was little need to differentiate between various

sections of the radio spectrum because there was relatively modest demand

for access to it. At that time anybody could build and operate a radio

system. Soon, however, the growing popularity of amateur and broadcast

radio stations created interference problems and led to political pressure to



manage this resource so that it could meet growing demand, particularly for

commercial interests in an emerging broadcasting industry. Over the past

century, nationally and internationally supervised spectrum management

programmes have become the means by which access to the radio

spectrum is controlled. At the heart of these programmes is a system for

dividing radio spectrum into discrete bands of frequencies, and then

allocating those frequencies for specific types of use.

One of the reasons for dividing the radio spectrum into discrete bands is

because radio energy possesses both electrical and magnetic properties.

This makes different portions of the spectrum suitable for different purposes.

In fact, it is the interaction of the electrical and magnetic properties of radio

energy combined with changing social demands for particular kinds of radio

communications systems that makes spectrum management a socio-

technical undertaking, often of considerable complexity and controversy.

1.2.1 Electromagnetic energy

We begin to understand how radio energy is harnessed for human

communication with a simple rule of physics: as materials vibrate they

transfer energy to their surroundings. This energy transference can take the

form of either compressional waves or transverse waves. Sound is

transmitted through the air by means of compressional waves like, for

example, when we speak and our mouth expels air from our lungs. These

waves travel through the air and eventually to a listeners ears. The air acts

as a medium that enables these compressional waves to propagate from

one place to another. Sound waves can also travel through other media,

such as water, oil, concrete, wood or many other physical materials.

However, the specific properties of a material will have an transducer,

which is a device more commonly known as a microphone. Once converted

into the transverse waves of electromagnetic energy, the spoken word can

then be transmitted over the air to be received by the taxi fleet. Radios

installed in the taxis then convert the electromagnetic energy back into

acoustic compressional waves so that the taxi driver can hear the

dispatchers voice through a speaker (another type of transducer). This

process of conversion from one type of energy into another, and back again,

is known as modulation and demodulation, and is very important in mobile

communications systems. In fact, modem comes from the coming together



of terms modulation-demodulation, and describes a device for computers

that converts sound energy into electromagnetic energy.

Another reason to make this distinction between natural sound and

electromagnetic energy is that many of the same terms and concepts such

as frequency and wavelength are used to describe both types of energy,

even though compressional and transverse waves have very different

properties. It is important to recognize that radio waves are not the same

form of energy as sound waves. Radio waves travel at the speed of light

and can pass through a vacuum, such as outer space. Sound waves move

much slower and require a physical medium such as air or water in order to

propagate from one place to another.

Recalling the basic rule of physics when materials vibrate they transfer

energy to their surroundings is also helpful in understanding the terms and

concepts used to measure and classify radio energy. Radio waves are the

result of a vibrating magnetic field that is created by a pulsating electrical

signal. Hence they are a form of electro-magnetic energy. The function of an

antenna on a radio is to concentrate and direct these vibrations in a

particular direction either from the radio into its surrounding environment

(transmission) or from the surrounding environment into the radio

(reception). The tempo at which the electromagnetic field vibrates

determines whether the transverse waves are longer or shorter and, in turn,

dictates the portion of the spectrum that a radio system will occupy. As you

might imagine, this relationship between wavelength and spectrum is a

primary consideration in the design and regulation of all radio

communication technologies, including mobile phone networks.

1.2.2 Frequency and Wavelength

The length of a radio wave is a property that allows us to classify the radio

spectrum according to frequency. During transmission or reception, the

number of energy vibrations reaching an antenna each second is measured

as the frequency of the signal. One vibration per second is known by the

term Hertz (Hz), named after Heinrich Rudolf Hertz (184794) the German

physicist who was the very first person to send and receive radio waves in

the laboratory. The range of electromagnetic energy designated specifically

as the radio spectrum is measured in thousands, millions or billions of



vibrations per second. Table 1.1 shows the correct terms and abbreviations

for each range of frequencies.

Table 1.1: Radio waves measured as frequencies

The frequency of a radio wave will determine whether it is longer or shorter,

which provides another measure known as wavelength. As a rule, the longer

the wavelength, the lower the frequency; and the shorter the wavelength,

the higher the frequency. We can work out this relationship more specifically

with simple mathematics. Recalling that radio waves travel at the speed of

light, we can divide it by the number of waves measured per second (Hertz)

to arrive at a calculation for wavelength.

Figure 1.1: Wavelength equation

Wavelength is an important measure because it tells us something about

the useful value of any frequency being considered for radio

communications. For instance, shorter wavelengths (higher frequencies)

have difficulty passing through solid objects. If the wavelength is very short

then, the presence of rain or fog might create interference to transmission

or reception because water droplets suspended in the air can cause the

radio waves to be absorbed or scattered. Direct to home (DTH) satellite

television (operating frequency about 12GHz) is a case in point, where trees

or heavy rain may cause interference to the signal being received at the



television (in the case of rain this is sometimes called rain fade). Higher

frequencies therefore tend to be most useful for line of sight radio

communications, where there is a low likelihood of objects standing in the

way of the transmission path. On the other hand, longer wavelengths have

quite different propagation properties and in some instances can travel great

distances without suffering interference. It is therefore the lower frequencies

that tend to be used in very long range communications, such as short wave

radio (3000kHz to 30MHz) or for military submarines operating in the deep

ocean (40 to 80Hz).

In most countries around the world, it has been agreed that the portion of

the electromagnetic spectrum generally used for radiocommunications is the

range of frequencies between 9kHz to 275GHz. This classification is based

on a longstanding arrangement established through the International

Telecommunications Union and is referred to formally as the radio

spectrum in order to differentiate it from other types of electromagnetic

energy such as visible light or X-rays.

The radio spectrum itself is then divided into eight separate frequency bands

that are in turn subdivided into smaller groupings of frequencies according

to the purpose for which they are intended to be used. Most of the radio

spectrum allocated to mobile telephone service falls within the Ultra High

Frequency (UHF) band. By contrast, satellite and fixed wireless services

tend to fall within the Super High Frequency (SHF) band. AM radio

broadcast is located within the Medium Frequency (MF) band and FM radio

broadcast radio is located within the Very High Frequency (VHF) band.

Self Assessment Questions

1. One vibration per second is known by the term _____________.

2. The electromagnetic spectrum generally used for radio communications

is the range of frequencies between 9kHz to 275GHz. (True /False)

1.3 Spectrum Management

While people have long known about electromagnetic energy and have

experimented with its effects, it is only within the last century or so that it has

come to be thoroughly exploited by humans as a naturally occurring

resource for communication and other purposes. We use it in our homes in

the form of commercial electricity to run our dishwashers, vacuum cleaners



and other appliances (alternating current (AC) in North America has a

frequency of 60Hz). We also use radio energy to cook food directly in our

microwave ovens (microwave energy in the 2GHz band), to open our

garage doors (40MHz), and for playing with remote controlled cars and

model airplanes (75MHz). With so many different types of devices using the

radio spectrum, the problem of unwanted interference needs to be

managed. You may have experienced unwanted radio interference, perhaps

when watching television and somebody in another room starts up the

vacuum cleaner or a power tool. The disruption to the signal on the TV is

interference, and in some cases it could be more than a minor nuisance

when, for instance, it interrupts radio communications for emergency

services dispatch such as police, fire or ambulance.

Radio interference is a problem related to both the physical properties of the

radio spectrum and to the equipment used to transmit and receive radio

signals. Together, these combined factors place constraints on how

effectively spectrum can be shared among different users. Based on the

current understanding and accepted practice, the radio spectrum is widely

considered a finite natural resource that is infinitely renewable. In other

words, it is possible to run out of usable frequencies in the spectrum

because of congestion and interference from many users making demands

for it. This possibility leads to a situation of spectrum scarcity. Unlike some

other natural resources, however, the radio spectrum will never be depleted

over the course of time because the moment a radio system stops

transmitting, that frequency becomes available for someone else to use it.

The radio spectrum is therefore a renewable resource. This possibility of

frequency sharing or frequency re-use is very important for the design of

mobile phone networks and for the prospects of future radio technologies.

1.3.1 Managing a natural resource

Like other natural resources, the radio spectrum has an influence over the

daily lives of all of us. Its proper management is an important factor in

balancing the social and economic needs of a modern society. First and

foremost, the radio spectrum is a central factor in maintaining national

sovereignty and security, and governments ultimately retain the right to

control access to it. In fact a considerable amount of radio spectrum is

allocated for government purposes, in large part to support radio



communications for national security and public safety activities. In the

United States, for example, it is estimated that there are some 270,000

frequency assignments to federal agencies. In addition to government

services, the radio spectrum supports a wide range of scientific research

activities, such as wildlife radio-collar tracking or radio astronomy.

In the private sector, the radio spectrum supports a wide range of

businesses, such as mobile telephony or radio dispatch. It also enables the

dissemination of culture through broadcast radio and television and drives a

multibillion dollar industry in the form of communications equipment

manufacturing. Some of the more commonly known manufacturers of radio

equipment around the world include Motorola (USA), Nortel (Canada), Sony

Ericsson (Sweden), Nokia (Finland) and Fujitsu (Japan).

Consumers and industry organizations are all counting on well managed

radio spectrum to give them confidence to invest in research and

development efforts in wireless systems. In fact, it may be useful to think of

the radio spectrum as the real estate of the wireless communications

sector every service provider requires a plot of frequencies on which to

build a network. Without timely management of this valuable property there

would likely be no mobile phone service today. This situation has led to

some important debates about how the radio spectrum should be managed,

what kinds of principles spectrum management should follow and what

objectives it should seek to achieve in a world where radio is more important

to the global economy than ever.

1.3.2 Allocation, Allotment, Assignment

In virtually all countries around the world, the radio spectrum is considered a

public resource, meaning that no one single person can own it.

Governments license its use to private firms or public groups, but no single

company or individual person can claim an inalienable right to the radio

spectrum or any portion of it.

Spectrum management generally involves a three-step process of

allocation, allotment and assignment. First, the radio spectrum must be

divided up into frequency bands that are allocated to various categories of

services, such as broadcasting, navigation or mobile telecommunications.

Second, specific blocks of frequencies are then allotted within each band

according to a specific type of service and its unique technical requirements.



Finally, allotments are then assigned to a specific type of service, such as a

direct to home satellite TV provider or a mobile phone carrier. This is usually

done by means of a government-led licensing or authorization process.

Licenses are often limited to specific geographical areas and usually must

be renewed after a expiry date.

Each step in this process of allocation, allotment and assignment must take

into account competing interests in economic, technical and public policy.

Engineers and planners involved in spectrum management refer to the

importance of balancing economic and technical efficiency, while taking into

account public interest obligations. Striking a balance between technical and

economic efficiency means achieving the most effective use of spectrum

without creating unwanted interference, while ensuring that it is allocated

and assigned in a way that will also meet the needs of those who will

provide the greatest value from it. However, these efficiencies must be

counter-balanced with public policy goals that in some instances may

override both technical and economic considerations. Public policy goals

might include the provision of radio communications for public safety,

national defence and public service broadcasting.

In recent years, the challenge of achieving this balance of objectives has

become more difficult than ever for a number of reasons. First, the demand

for access to the radio spectrum in the past decade has been greater than in

the entire preceding history of radio. This growth in demand is partly a result

of the worldwide explosion of mobile phones and other wireless

communication technologies.

Another factor in the growing demand for access to spectrum is the wave of

regulatory reform in the telecommunications sector that has taken place

starting in the mid1980s. This had led to increased competition in the supply

of both radio equipment and in demand for wireless services from

businesses and individual consumers. The appearance of new technologies,

such as the Geographic Positioning System (GPS) and Radio Frequency

Identification Tags (RFID) have been instrumental in creating new demand

for access to the radio spectrum.

In most countries, the responsibility for balancing these priorities falls under

national government jurisdiction and usually within the portfolio of a



department that is also responsible for other communication concerns, such

as radio and TV licensing, and perhaps telecommunications.


3. The radio spectrum is widely considered an infinite natural resource that

is finitely renewable. (True/False)

4. GPS stands for _____________.

1.4 The Cell Approach

One of the most interesting things about a cell phone is that it is really a

radio an extremely sophisticated radio, but a radio nonetheless. Alexander

Graham Bell invented the telephone in 1876, and wireless communication

can trace its roots to the invention of the radio in 1894, by a young Italian

named Guglielmo Marconi. It was only natural that these two great

technologies would eventually be combined! Before cell phones become

popular, people who really needed mobile communications ability installed

radiotelephones in their cars. In the radio telephone system, there was one

central antenna tower per city, and perhaps 25 channels available on that

tower. This central antenna meant that the phone in your car needed a

powerful transmitter big enough to transmit 40 or 50 miles. It also meant

that not many people could use radiotelephones because there weree just

were no enough channels.

The genius of the cellular system is the division of a city into small cells.

This allows extensive frequency reuse across a city, so that million of people

can use cell phones simultaneously. In a typical analog cell phone system in

the United States, the cell phone carrier receives about 800 frequencies to

use across the city. The carrier chops up the city into cells. Each cell is

typically sized at about 10 square miles (26 square kilometers). Cells are

normally thought of, as hexagons on a big hexagonal grid.



Because cell phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent cells. The two dark shaded cells can reuse the same frequencies.

Figure 1.2: Structure of a cell

A single cell in an analog system uses one-seventh of the available duplex

voice channels. That is, one cell, plus the six cells around it on the

hexagonal grid, each using one-seventh of the available channels so that

each cell has a unique set of frequencies and there are no collisions:

A cell phone carrier typically gets 832 radio frequencies to use in a city.

Each cell phone uses two frequencies per call a duplex channel so

there are typically 395 voice channels per carrier. (The other 42

frequencies are used for control channels.)

Therefore, each cell has 56 or so voice channels available. In other

words, in any cell, 56 people can be talking on their cell phones at one

time. With digital transmission methods, the number of available

channels increases. For example, a TDMA-based digital system can

carry three times as many calls as an analog system, so each cell would

have about 168 channels available.



Cell phones have low-power transmitters in them. Many cell phones have

two signal strengths: 0.6 watts and 3 watts (for comparison, most CB radios

transmit at 4 watts). The base station is also transmitting at low power.

Low-power transmitters have two advantages:

The transmissions of a base station and the phones within its cell do not

make it very far outside that cell. Therefore, in the figure above, both of

the dark shaded cells can reuse the same 56 frequencies. The same

frequencies can be reused extensively across the city.

The power consumption of the cell phone, which is normally battery-

operated, is relatively low. Low power means small batteries, and this is

what has made handheld cellular phones possible.

The cellular approach requires a large number of base stations in a city of

any size. A typical large city can have hundreds of towers. But because so

many people are using cell phones, costs remain low per user. Each carrier

in each city also runs one central office called the Mobile Telephone

Switching Office (MTSO). This office handles all of the phone connections to

the normal land-based phone system, and controls the entire base stations

in the region.

1.4.1 System Identification Code

All cell phones have special codes associated with them. These codes are

used to identify the phone, the phone's owner and the service provider. Let's

say you have a cell phone, you turned it on, and here is what happens when

someone tries to call you on mobile:

When you first power up the phone, it listens for a SID (System

Identification Code) on the control channel. The control channel is a

special frequency that the phone and base station uses to talk to one

another about things like call set-up and channel changing. If the phone

cannot find any control channels to listen to, it knows it is out of range,

and displays a "no service" message.

When it receives the SID, the phone compares it to the SID programmed

into the phone. If the SIDs match, the phone knows that the cell it is

communicating with is part of its home system.

Along with the SID, the phone also transmits a registration request, and

the MTSO keeps track of your phone's location in a database. This way,

the MTSO knows which cell you are in when it wants to ring your phone.



The MTSO gets the call, and it tries to find you. It looks in its database to

see which cell you are in.

The MTSO picks a frequency pair that your phone will use in that cell to

take the call.

The MTSO communicates with your phone over the control channel to

tell it what frequencies to use, and once your phone and the tower

switch on those frequencies, the call is connected. You are talking by

two-way radio to a friend!

As you move toward the edge of your cell, your cell's base station will

note that your signal strength is diminishing. Meanwhile, the base station

in the cell you are moving toward (which is listening and measuring

signal strength on all frequencies, not just its own one-seventh) will be

able to see your phone's signal strength increasing. The two base

stations coordinate themselves through the MTSO, and at some point,

your phone gets a signal on a control channel telling it to change

frequencies. This hand off switches your phone to the new cell.

As you travel, the signal is passed from cell to cell.

Figure 1.3: Signal passing from cell to cell

Roaming

If the SID on the control channel does not match the SID programmed into

your phone, then the phone knows it is roaming. The MTSO of the cell that

you are roaming in contacts the MTSO of your home system, which then



checks its database to confirm that the SID of the phone you are using is

valid. Your home system verifies your phone to the local MTSO, which then

tracks your phone as you move through its cells. And the amazing thing is

that all of this happens within seconds!

1.4.2 Cellular Access Technologies

There are three common technologies used by cell phone networks for

transmitting information:

Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

Code Division Multiple Access (CDMA)

Although these technologies sound very intimidating, you can get a good

sense of how they work just by breaking down the title of each one.

The first word tells you what the access method is and the second word,

division, lets you know that it splits calls based on that access method.

FDMA puts each call on a separate frequency.

TDMA assigns each call a certain portion of time on a designated

frequency.

CDMA gives a unique code to each call and spreads it over the available

frequencies.

The last part of each name is multiple access. This simply means that more

than one user (multiple) can use (access) each cell.

Frequency Division Multiple Access::

FDMA separates the spectrum into distinct voice channels by splitting it into

uniform chunks of bandwidth. To better understand FDMA, think of radio

stations. Each station sends its signal at a different frequency within the

available band. FDMA is used mainly for analog transmission. While it is

certainly capable of carrying digital information, FDMA is not considered to

be an efficient method for digital transmission.



Figure 1.4: Frequency Division Multiple Access

Time Division Multiple Access:

TDMA is the access method used by the Electronics Industry Alliance and

the Telecommunications Industry Association for Interim Standard 54

(IS-54) and Interim Standard 136 (IS-136). Using TDMA, a narrow band that

is 30 kHz wide and 6.7 milliseconds long is split time-wise into three time

slots. Narrow band means channels in the traditional sense. Each

conversation gets the radio for one-third of the time. This is possible

because voice data that has been converted to digital information is

compressed so that it takes up significantly less transmission space.

Therefore, TDMA has three times the capacity of an analog system using

the same number of channels. TDMA systems operate in either the 800

MHz (IS-54) or 1900 MHz (IS-136) frequency bands.

TDMA is also used as the access technology for Global System for Mobile

communications (GSM). However, GSM implements TDMA in a somewhat

different and incompatible way from IS-136. Think of GSM and IS-136 as

two different operating systems that work on the same processor, like

Windows and Linux both working on an Intel Pentium III. GSM systems use

encryption to make phone calls more secure. GSM operates in the 900 MHz

and 1800 MHz bands in Europe and Asia and in the 1900 MHz (sometimes



referred to as 1.9 GHz) band in the United States. It is used in digital cellular

and PCS-based systems. GSM is also the basis for Integrated Digital

Enhanced Network (IDEN), a popular system introduced by Motorola and

used by Nextel.

GSM is the international standard in Europe, Australia and much of Asia and

Africa. In covered areas, cell-phone-users can buy one phone that will work

anywhere else the standard is supported. To connect to the specific service

providers in these different countries, GSM-users simply switch subscriber

identification module (SIM) cards. SIM cards are small removable disks that

slip in and out of GSM cell phones. They store all the connection data and

identification numbers you need to access a particular wireless service

provider.

Code Division Multiple Access :

CDMA takes an entirely different approach from TDMA. CDMA, after

digitizing data, spreads it out over the entire bandwidth it has available.

Multiple calls are overlaid on the channel, with each assigned a unique

sequence code. CDMA is a form of spread spectrum, which simply means

that data is sent in small pieces over a number of the discrete frequencies

available for use at any time in the specified range.

Figure 1.5: Code Division Multiple Access



All the users transmit in the same wide-band chunk of spectrum. Each

user's signal is spread over the entire bandwidth by a unique spreading

code. At the receiver, that same unique code is used to recover the signal.

Because CDMA systems need to put an accurate time stamp on each piece

of a signal, it referes the GPS system for this information. Between eight

and 10, separate calls can be carried in the same channel space as one

analog AMPS call. CDMA technology is the basis for Interim Standard 95

(IS-95) and operates in both the 800 MHz and 1900 MHz frequency bands.

Ideally, TDMA and CDMA are transparent to each other. In practice, high

power CDMA signals will raise the noise floor for TDMA receivers, and high

power TDMA signals can cause overloading and jamming of CDMA

receivers.


5. SID stands for ____________.

6. ____________ technology is the basis for Interim Standard 95 (IS-95)

and operates in both the 800 MHz and 1900 MHz frequency bands.

1.5 Summary

The radio spectrum is a term that scientists, engineers and policymakers

use to classify a vast and otherwise undifferentiated swath of

electromagnetic energy that exists in the universe. One reason for dividing

the radio spectrum into discrete bands is because radio energy possesses

both electrical and magnetic properties, which makes different portions of

the spectrum suitable for different purposes.

The process of conversion from one type of energy into another, and back

again, is known as modulation and demodulation, and is very important in

mobile communications systems. Modem is a device for computers that

converts sound energy into electromagnetic energy. In a cellular system the

coverage area is divided into small geographical area called a cell. Each cell

is typically sized at about 10 square miles (26 square kilometers). Cells are

normally thought of, as hexagons on a big hexagonal grid. There are three

common technologies used by cell phone networks for transmitting

information FDMA, TDMA and CDMA.



1.6 Terminal Questions

1. Discuss Spectrum Management.

2. Explain FDMA and TDMA concepts.

3. How is the CDMA approach different from TDMA technology?

1.7 Answers


1. Hertz (Hz)

2. True

3. False

4. Geographic Positioning System

5. System Identification Code

6. CDMA

Terminal Questions

1. The radio spectrum is a renewable resource, and the possibility of

frequency sharing or frequency re-use is very important for the design of

mobile phone networks and for the prospects of future radio

technologies. (Refer section 1.3)

2. FDMA puts each call on a separate frequency. TDMA assigns each call

a certain portion of time on a designated frequency. (Refer section 1.4.2)

3. Ideally, TDMA and CDMA are transparent to each other. In practice,

high power CDMA signals will raise the noise floor for TDMA receivers,

and high power TDMA signals can cause overloading and jamming of

CDMA receivers. (Refer section 1.4.2)

Documents

final