mobile communication full report
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1. The role of cellular phones has risen with improvement in services, reduction in service costs and the ever increasing services available through cell phones.Mobile Internet access is a global phenomenon with even great implications.Leading phone manufacturers such as Ericsson, Motorola, and Nokia have put a great deal of marketing effort behind the mobile Internet phenomenon, recognizing that adoption is a complex business proposition.
2. The most modern telephone is the cellular telephone, or commonly called a cell phone. A cellular telephone is designed to give the user maximum freedom of movement while using a telephone.The number of mobile communication devices users is growing very fast.
1. It was basically started in Germany in 1958.
2. In 1982 the European Conference of Postal and Telecommunications Administrations founded a working group.
3. 1987 the Global System for Mobile (GSM) communications standard was available.
4. 1991 in Switzerland the first devices are presented.
5. In 1995 SMS was available.
1. 1G cellular systems refer to the early analogue cellular phone technologies.
2. The early 1980â„¢s marked the first use of wireless cellular systems. It was typical for this kind of systems that the systems were quite limited.
3. 1G systems differed from the earlier radio networks in a couple of ways. The first generation (1G) cellular systems had increased capacity and greater mobility support than the early wireless radio networks.
4. The first generation of wireless consisted mostly of voice traffic handled with analog techniques.For example NMT and AMPS cellular technologies belong to this category.
1. Second generation (2G) cellular phone system use digital communication methods.
2. The second generation (2G) wireless systems are characterized by the use of digital radio transmission.
3. Examples of this series of systems include GSM, D-AMPS (TDMA/IS-136) and CDMA IS-95-A.
1. Third generation (3G) systems promise faster communications services, including voice, fax and Internet, anytime and anywhere with seamless global roaming.
2. ITUâ„¢s IMT-2000 global standard for 3G has opened the way to enabling innovative applications and services (e.g. multimedia entertainment, infotainment and location-based services, among others).
3. The first 3G network was devolped in Japan in 2001. 2.5G networks, such as GPRS (Global Packet Radio Service) are already available in some parts of Europe.
1. 4G refers to the fourth generation of cellular wireless and is a successor to 3G and 2G standards.
2. The rest of this article associates 4G with International Mobile Telecommunications-Advanced (IMT Advanced), though 4G is a broader term and could include standards outside IMT-Advanced.
3. A 4G system may upgrade existing communication networks and is expected to provide a comprehensive and secure IP based solution where facilities such as voice, data and streamed multimedia will be provided to users on an "Anytime, Anywhere" basis and at much higher data rates compared to previous generations
1. The idea behind cellular networks is the sub-division of a geographical area covered by a network into a number of smaller areas called cells. The frequencies allocated to one cell can be reused in other cells that are far enough not to disturb.
2. A fixed radio station called as a base station within each cell acts as a transmitter/receiver serving all the mobile stations inside the cell area.A base station controls a group of transmitting/receiving frequencies allocated by the network to that cell.
1. An antenna is fundamentally a transmission line that transforms information from electrical energy (current and voltage) into electromagnetic energy (RF waves)
2. Antennas are critical links in the wireless signal chain.Right antenna for the application yields a good signal coverage, increased S/N ratio, reduced bit error rate, and lower power consumption all at very low cost.As cellular telephones have evolved over the years, so have their components, particularly the antennas. Cellular phone used to have large external antennas, but nowadays most cellular phones use an internal antenna.
1. Secrets of the wireless elite: Mobile applications need scripting too! - Mobile game developer Tom Park believes that scripting for wireless devices is important for proficiency sake. And with the need to scale mobile applications across so many different platforms, proficiency is everything.
CELLULAR PHONE SAFETY
1. Cellular phones are electronic devices that commununicate with the ceullar system base station usign radio communications. This means that they contain both radio receiver and transmitter.
2. The transmitter cause RF field around the cellular phone.
3. . RF fields are non-ionizing radiations (NIR). ). Unlike X-rays and gamma rays, they are much too weak to break the bonds that hold molecules in cells together and, therefore, produce ionization.
4. RF fields may, however, produce different effects on biological systems such as cells, plants, animals, or human beings.
1. Bluetooth is a short-range radio technology that connects portable devices such as cell phones, handheld devices and notebook computers.
2. The technology has a range of up to 10 meters and wirelessly transfers data at rates of up to 720 kilobits per second.
3. The technology was originally developed by Ericsson. Bluetooth is now a global specification for wireless connectivity
1. GPRS is an extension of the GSM system, and uses the same channels, the same modulation, and the same network backbone as the existing GSM network.
2. GPRS is a general pocket radio service which is used such as a wireless internet and multimedia service. It is also known as GSM (INTERNET PROTOCOL)Because it will continue users directly to internet service provider.
SHORT MESSAGE SERVICE (SMS)
1. SMS is a bidirectional service for sending short alphanumeric (up to 160 bytes) messages in a store and forward fashion.
2. GSM Short Messages have a maximum length of 160 characters (from the SMS character set), or 140 octets. However, Short Messages can be concatenated to form longer messages.
1. The GSM system is the most widely used cellular technology in use in the world today. It has been a particularly successful cellular phone technology for a variety of reasons including the ability to roam worldwide with the certainty of being able to be able to operate on GSM networks in exactly the same way.
1. Multimedia Messaging is just around the corner. Multimedia Messaging Service (MMS) is a new prominent wireless standard for multimedia. The idea behind MMS is to enhance SMS type messagging to carry larger messages which can contain more text, images, sound and possibly animation. MMS is expected to become a very popular messaging service in the future in both today's GSM networks and 3G networks in the future.
1. It is the fastest way to communicate all around the world.
2. The cost of messaging and talking to people wirelessly is significantly lower.
3. It helps everyone in there daily life and its becomes a very essential part of our life .
4. Mobile Technology is playing an increasing role in disaster awareness.
5. We can use MMS, GPRS, WAP etc Services.
1. Mobile phone addiction is a big social problem.
2. Emergence of mobile phones is losing good habits, such as punctuality
3. People use the phone while they are driving, and this can cause problems.
4. Symptoms caused by the radiation of mobile phones are one of the most argued problems.
5. Cyber bullying is also another issue among the disadvantages of mobile phones.
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MOBILE COMMUNICATION .docx (Size: 161.73 KB / Downloads: 126)
MOBILE COMMUNICATION [EC 03]
G. DIVYA RAO
III B.Tech, E.C.E
III B.Tech, E.C.E
PRAGATI ENGINEERING COLLEGE
1-378, ADB Road, Surampalem â€œ 533 437, Near Peddapuram, E.G.Dt.(A.P).
In this paper a view of the world-wide developments in the field of wireless broadband
multimedia communications is given first. Taking this into account, a multi-disciplinary
approach is presented as a combination of: promising applications, novel user- interfaces,
compression, protocols geared to the mobile user and transmission techniques that give abundant
bandwidth to the user. The insights of each of the research topics that contribute on the path
towards the Fourth Generation Mobile Multimedia Communication is presented.
WIRELESS COMMUNICATIONS ARE UBIQUITOUS
This first section of Electromagnetics and Applications, focuses on wireless
communications, which can involve point-to-point communications, broadcasting (one point to
many), or passive sensing of natural or man-made signals. The original point-to-point wireless
communications links for telephone and telegraph circuits sometimes were direct line-of-sight or
diffracted paths and sometimes involved ionospheric reflections. They were largely superceded,
initially by coaxial cables and multi- hop microwave links that were later supplemented by
satellite links, and ultimately by optical fibers and cellular technology. Each technical advance
markedly boosted capacity and generally increased reliability.
Most homes and offices are currently served by twisted pairs of wires, each conveying
~50 kbs - 1 . 5 Mbps, although coaxial cables, satellite links, and even wireless services are
making inroads. The most common wireless services currently include cell phones, wireless
phones (within a home or office), walkie-talkies (dedicated mobile links), satellite links,
microwave tower links, and many specialized variations for private or military use. In addition,
optical or microwave line-of-sight links between buildings offer instant broadband connectivity
for the last mile to the consumer, which accounts for a significant fraction of all installed plant
cost. Weather generally restricts optical links to very short hops or to weather- independent
optical fibers. Specialized medical devices, such as RF links to video cameras inside swallowed
pills, are also being developed.
Broadcast services now include AM radio near 1 MHz, FM radio near 100 MHz and
higher frequencies, TV in several bands between 50 and 600 MHz for local over-the-air service,
and TV and radio delivered by satellite at many GHz. Shortwave radio below ~30 MHz also
offers global international broadcasts dependent upon ionospheric conditions, and is widely used
by radio hams for long-distance communications. The intensities of thermal and non-thermal
microwave radiation from the terrestrial atmosphere and surface can be passively sensed for
meteorological and other geophysical purposes. For example, almost all objects radiate radio
waves in proportion to their temperature, just as a bonfire radiates heat. More precisely, the
power P [W] radiated by any blackbody (reflectivity = 0) into a transmission line at radio or
microwave frequencies within a bandwidth B [Hz] is kTB, where T is the temperature of the
radiator [ K] and k = 1.38Ãƒâ€”10
[JK ] is Boltzmann's constant. Wireless services are so
ubiquitous today that we may take them for granted, forgetting that a few generations ago the
very concept would have been considered magic. Despite the wide range of services already in
wide use, it is reasonable to assume that over the next few decades numerous other wireless
technologies and services will be developed by todayâ„¢s engineering students.
B. COMMUNICATIONS REQUIRES POWER AND ENERGY
Even the best current radio receivers require a certain amount of energy per bit of
information, Eb, whether that information is analog or digital. The current nominal state-of-the-
art receivers require at least ~4Ãƒâ€”10
Joules per bit of information, and so the power required at
the receiver is simply EbM, where M is the bit rate per second. The remarkably low values for Eb
imply enormous data transfer rates are possible at very reasonable power levels that are easily
achieved via wire or fibers, and that useful data rates are possible even via air links that are
Although electromagnetic waves are slightly absorbed by losses in air, we shall ignore
these for now and shall assume power is conserved as it propagates, even though it may weaken
as it spreads out far from the transmitter. For example, a transmitter antenna radiating
isotropically PR watts would produce a wave in direction ,f having Pr(,f,r) [Wm ] = PR/4pr
at distance r [m]. It follows that PR =
Pr(,f,r) r sin d df. Most antennas are designed,
however, to concentrate their power in desired directions, offering some gain over isotropic:
gain is a dimensionless quantity. The shapes
antenna gain patterns are suggested below.
The upper illustration shows five microwave antennas operating near 1-cm wavelength
that use bulbous lenses to focus the radio waves in a 10Ã‚Âº beam. The middle illustration is of the
National Radio Astronomy 300- ft paraboloic radiotelescope (now dismantled) in Greenbank,
West Virgina; its beamwidth was ~/D
0.2/100 radians, or ~7 arc minutes (the sun and moon
have diameters of ~30 arc minutes). The bottom illustration is of a multi-aperture optical
interferometer that successfully measured the relative positions of two orbiting stars to ~100
micro-arc-seconds through the terrestrial atmosphere (the Hubble space telescope achieves ~100
The receiving properties of antennas are commonly characterized by their effective
area A(,f) [m ], where the power recieved P rec is simply the incident flux [Wm ] from
direction ,f times
the antenna effective area for that same
direction. That is,
We shall show later that there is, under most circumstances, a simple relation between the gain
and effective area
same shape such
of an antenna: they have the exact
With this simple definition we can now evaluate wireless communications links.
EVOLUTION OF THE MOBILE TECHNOLOGY
"If you can dream it, you can do it", according to this we can leap 3G to 4G along its features and
future trends in mobile technology. In wireless communication, mobile technology is advanced
and in this system 4G is the latest at present.
1G analog system for mobile communications saw two key improvements during the 1970s: the
invention of the microprocessor and the digitization of the control link between the mobilephone
and the cell site. AMPS ( Advance mobile phone system ) was first launched by US which is 1G
mobile system. It is best on FDMA technology which allows users to make voice calls within
2G digital cellular systems were first developed at the end of the 1980s. These systems digitized
not only the control link but also the voice signal. The new system provided better quality and
higher capacity at lower cost to consumers. GSM (Global system for mobile communication)
was the first commercially operated digital cellular system which is based on TDMA.
3G systems promise faster communications services, including voice, fax and Internet, anytime
and anywhere with seamless global roaming. ITUâ„¢s IMT-2000 global standard for 3G has
opened the way to enabling innovative applications and services (e.g. multimedia entertainment,
infotainment and location-based services, among others). The first 3G network was deployed in
Japan in 2001. 2.5G networks, such as GPRS (Global Packet Radio Service) are already
Available in some parts of Europe. 3G technology supports 144 Kbps bandwidth, with high
speed movement (e.g. vehicles), 384 Kbps (e.g. on campus) & 2 Mbps
for stationary (e.g.inbuilding)
At present the download speed for mode data is limited to 9.6 kbit/sec which is about 6
times slower than an ISDN (Integrated services digital network) fixed line connection. Recently,
with 504i handsets the download data rate was increased 3-fold to 28.8kbps. However, in actual
use the data rates are usually slower, especially in crowded areas, or when the network is
"congested". For third generation mobile (3G, FOMA) data rates are 384 kbps (download)
maximum, typically around 200kbps, and 64kbps upload since spring 2001. Fourth generation
(4G) mobile communications will have higher data transmission rates than 3G. 4G mobile data
transmission rates are planned to be up to 20 megabits per second.
Before understanding 4G, we must know what is 3G 3G initiative came from device
manufactures, not from operators. In 1996 the development was initiated by Nippon Telephone
& Telegraph (NTT) and Ericsson; in 1997 the Telecommunications Industry Association (TIA)
in the USA chose CDMA as a technology for 3G; in 1998 the European Telecommunications
Standards Institute (ETSI) did the same thing; and finally, in 1998 wideband CDMA (W-
CDMA) and cdma2000 were adopted for the Universal Mobile Telecommunications System
W-CDMA and CDMA 2000 are two major proposals for 3G. In this CDMA the
information bearing signal is multiplied with another faster ate, wider bandwidth digital signal
that may carry a unique orthogonal code. W-CDMA uses dedicated time division multiplexing
(TDM) whereby channel estimation information is collected from another signal stream. CDMA
2000 uses common code division multiplexing (CDM) whereby channel estimation information
ACCESS TECHNOLOGIES (FDMA, TDMA, CDMA) â€œ
FDMA: Frequency Division Multiple Access (FDMA) is the most common analog system. It is
a technique whereby spectrum is divided up into frequencies and then assigned to users. With
FDMA, only one subscriber at any given time is assigned to a channel. The channel therefore is
closed to other conversations until the initial call is finished, or until it is handed-off to a
different channel. A "full-duplex" FDMA transmission requires two channels, one for
transmitting and the other for receiving. FDMA has been used for first generation analog
TDMA: Time Division Multiple Access (TDMA) improves spectrum capacity by splitting each
frequency into time slots. TDMA allows each user to access the entire radio frequency channel
for the short period of a call. Other users share this same frequency channel at different time
slots. The base station continually switches from user to user on the channel. TDMA is the
dominant technology for the second generation mobile cellular networks.
CDMA: Code Division Multiple Access is based on "spread" spectrum technology. Since it is
suitable for encrypted transmissions, it has long been used for military purposes. CDMA
increases spectrum capacity by allowing all users to occupy all channels at the same time.
Transmissions are spread over the whole radio band, and each voice or data call are assigned a
unique code to differentiate from the other calls carried over the same spectrum. CDMA allows
for a soft hand-off, which means that terminals can communicate with several base stations at
the same time.
OVERVIEW OF MOBILE COMMUNICATION SYSTEMS
Mobile radio communication began with Guglielmo Marconiâ„¢s and Alexander Popovâ„¢s
experiments with ship-to-shore communication in the 1890â„¢s. Land mobile radiotelephone
systems have been used since 1921 when the Detroit City Police Department installed a system.
Radio systems have increased in importance since that time for both voice and data
communication. Modern mobile systems mostly use high frequencies (UHF and above) because
of the larger available bandwidth at these frequencies. In the United States this includes cellular
telephone systems operating at 800-900 MHz and personal communication systems (PCS) at
1800-2000 MHz, and a variety of unlicensed devices, including wireless LANs, in the ISM
bands at 902-928 MHz and 2.4-2.4835 GHz. Additional high speed, short-range digital
communications will use the unlicensed national information infrastructure (U-NII) bands at
GHz and 5.725-5.825 GHz. This chapter describes basic categories of wireless
communication systems and fundamental concepts.
2.1 The Wireless Communication Link
A wireless communication link includes a transmitter, a receiver, and a channel.
Adapted. Quantization, coding and decoding are only performed in digital systems. Most links
are full duplex and include a transmitter and a receiver or a transceiver at each end of the link.
2.2 Types of Systems
In a mobile communication system at least one of the transceivers is mobile. It
may be on board a vehicle that can move at high speeds, or it may be a handheld unit used by a
pedestrian. Basic types of systems include base/mobile, peer-to-peer, repeater, and mobile
satellite systems. In a base/mobile system, a base station connected to a public network
communicates with a mobile unit. This gives the mobile unit access to the public network. More
than one mobile at a time can be supported if a different channel (such as a narrow band of
spectrum) is assigned to each user. In most systems, channels are assigned to users as needed
rather than giving each user a dedicated channel that is reserved for that user at all times. This is
called trunking and allows large numbers of users to be supported with a limited number of
available channels, with a small probability that any given call will be blocked because all
channels are busy. Cellular telephony uses the base/mobile configuration to give mobile users
access to the public switched telephone network. In peer-to-peer systems, mobile Information
Source Quantizer/ Source Encoder Channel Encoder Modulator Discrete Channel Decoder
Demodulator Source Decoder Information Sink Transmitter Receiver RF Front End Channel
Amplifier (Amplifier/Filter/Mixer) 9 units communicate directly with each other. Mobile units
sharing a frequency channel can communicate with one another, and independent conversations
can take place on different channels. Many CB radio contacts fit into this peer-to-peer model. In
peer-to-peer systems, a mobile can sometimes hear only one of two other mobiles that are using
a channel, when a total of three users are active. Fig. 2-2 shows a repeater system. In this system,
all users transmit on one channel and listen on a second channel. The repeater, a transceiver that
is located at a high point, retransmits the signals with greater power on the second channel. In
this system, all users can communicate with each other using one pair of frequencies. A repeater
system allows communication over a much greater range than in a direct peer-to-peer system.
Repeaters are used for public services and some amateur radio operations at VHF and UHF
frequencies. A variation is a trunked radio system that uses several frequency pairs and assigns a
frequency pair for each conversation between mobiles. A trunked system can support many more
users than the number of frequencies available because all users typically do not operate at once.
In a mobile satellite system, one or more satellites relays signals between a mobile user and an
earth-based base station or gateway that connects to the public switched network, as shown in
Fig. 2-2. The large distances and high speeds of the satellites introduce some difficulties, but a
system of this type can provide worldwide coverage.
2.3 MULTIPLE ACCESS TECHNIQUES AND FREQUENCY REUSE
Both multiple access and frequency reuse are essential to providing radio
communication service simultaneously to many users over a wide area using a fixed bandwidth.
It is useful to make a distinction between the two approaches. Multiple access schemes allow a
frequency channel to be subdivided among many users. Frequency reuse strategies most
frequently use spatial separation to enable two or more channels in different areas (called cells)
to occupy the same spectrum with minimal interference between channels. The relationship
between the two is that frequency reuse increases capacity and multiple access is the allocation
of that capacity to multiple users.
All over the world and also within our Mobile Multimedia Communication project and implimentation solutions are
sought to make the combination of mobile and multimedia possible and affordable. In the
progress towards this goal, not only the evolution of existing systems will help but also the new
insights emerging from the
Multidisciplinary research reported in this paper. We have shown some new concepts of
multimedia systems. In the MMC project and implimentation, also an experimentation platform has been developed.
This common experimentation environment serves to link the contributions of the researchers. It
is a vehicle to demonstrate to other researchers and interested parties the state-of-the-art in the
different areas that were discussed in the previous sections. It also helps to get a feel for the
different mono-disciplinary contributions in a multidisciplinary context.
W. C. Jakes, Microwave Mobile Communications, AT&T.
J. G. Proakis, Digital Communications, McGraw-Hill.
J. D. Gibson, Ed., The Mobile Communications Handbook, CRC Press
.R. E. Blahut, Principles and Practice of Information Theory, Addison-Wesley.
Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion
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MOBILE COMMUNICATION paper.docx (Size: 73.72 KB / Downloads: 84)
3/4 B.TECH, ECE,
Firstly, in this paper, we present the uses of digital cellular telephone and how the cellular
technology works for mankind.As an initial, we define the cellular telephone codes and the
basic concepts of handoff and roaming...We define the basic steps involved in the reception
of a call.
We determine the evolution of the digital cellular technology by using the generations of
mobile technology.In first generation,we define the frequency division multiple
access(FDMA) and advance mobile phone service.In second generation,we define the
Time division multiple access(TDMA),and Global system for mobile
communication(GPRS).In 2.5 generation,we define the GPRS system and enhanced data
rates for global evolution.In third generation,the evolution of CDMA 2000
1XEVDO,CDMA 2000 1XEVDO,wideband CDMA technologies are explained.In fourth
generation,the nomadic/local area wireless access system. is defined.We conclude the
topic by giving applications to mobile communications and we explain how the mobile
communication technology is increasing in favour of mankind by giving some difference to
latest technologies differ from older technologies.
A cellular communication network is being pushed by the new or expanded
applications and features that it is providing to its users. The network is based
on digital instead of analog technology and it can transmit at much higher
speeds . They are not limited to voice communication alone.
Digital cellular telephones can be used to:
Browse the Internet
Access e- mail.
Participate in videoconferencing.
Receive travel, entertainment and other types of information
Run a variety of programs on the cellular devices.
HOW CELLULAR TECHNOLOGY WORKS?
The working of the cellular technology differs a lot from the usual wired
telephones. There are two keys to cellular telephone networks. The first is that
the coverage area is divided into smaller individual sections called cells. In a
typical city the cells, which are hexagon-shaped measure 10 square miles (26
square kilometers).At the center of each cell is a cell transmitter to which the
mobile devices in that cell send and receive radio frequency (RF) signals.
These transmitters are connected to a base station, and each base station is
connected to a mobile telecommunications switching office (MTSO). The
MTSO is the link between the cellular network and the wired telephone world
and controls all transmitters and base stations in the cellular network.
The second key to cellular telephone networks is that all of the transmitters
and the cell phones operate at a low power level. This enables the signal to
stay confined to the cell and not interfere with any other cells. Because the
signal at a specific frequency does not go outside of the cell area, that same
frequency can be used in other cells at the same time.
CELLULAR TELEPHONE CODES
All cell phones have special codes associated with them. These codes are used
to identify the phone, the phoneâ„¢s owner, and the carrier or service provider.
The following are the codes associated with the cell phones.
System Identification Code
Electronic Serial Number
The carrierâ„¢s unique
The cellular phoneâ„¢s unique
Mobile Identification Number 10digits
A unique number generated
from the phoneâ„¢s telephone
The ESN is permanently assigned to a specific cellular phone when it is
manufactured. The MIN and SID codes are programmed into the phone when
it is activated.
HANDOFF AND ROAMING:
When a cellular telephone user moves around within the same cell, the
transmitter and the base station for that cell handles all of the transmissions.
As the user moves toward the next cell, the cellular telephone will
automatically associate with the base station of that cell. This is known as
However, if the cellular user moves beyond the coverage area of the entire
network the cellular telephone would automatically connect with whatever
cellular network was in place in the remote area. The cellular network in the
remote area would communicate with the cellular network in the home area
verifying that the user can make calls and also charge for the calls. This is
known as ROAMING.
STEPS INVOVLED IN THE RECEPTION OF A CALL :
When the cell phone is turned on it listens for the SID being
transmitted by the base station on the control channel, which is a special
frequency that the phone and the base station use for setup. If the phone
cannot detect a control channel, it is out of range and displays a message to the
user such as No Service.
If the cell phone receives a SID, it compares it with the SID that was
programmed into the phone .If they match; the cell phone is in the network
owned by its carrier. The cell phone transmits a registration request number to
the base station that the MTSO uses to track in which cell the phone is located.
If the SIDs do not match, then the cellular phone is roaming. The
MTSO of the remote network contacts the MTSO of the home network, which
confirms that the SID of the phone is valid. The MTSO of the remote network
then tracks the phone and sends the information back to the home MTSO.
When the call comes in, the MTSO locates the phone through the
registration request and then selects a frequency that will be used for
The MTSO sends the frequency information to the phone over the control
channel. Both the phone and the transmitter switch to that frequency and the
connection is then completed.
As the user moves towards the edge of a cell, the base station notes
that signal strength is decreasing while base station in the next cell determines
that the phoneâ„¢s signal strength is increasing. The two base stationscoordinate
with each other through the MTSO. The cellular phone then gets a message on
the control channel to change frequencies as it is handed off into another cell.
DIGITAL CELLULAR TECHNOLOGY:
Cellular telephones have been available since 1980s in the United States. Most
industrial experts outline several generations of cellular telephony.
The first generation of wireless cellular technology is known appropriately
enough as First Generation (1G). 1G uses analog signals, which are radio
frequency (RF) transmissions sent in a wave-like form. The maximum
transmission speed of a 1G network is 9.6 Kbps.1G technology is based on the
Advanced Mobile Phone Service (AMPS). An AMP operates in the 800-900
MHz frequency spectrum. Each channel is 30 KHz wide with a 45 KHz pass
band (the additional space on each side of the transmission band). There are
832 frequencies available for transmission. For voice traffic there are 790
frequencies used and the remaining 42 frequencies are used for the control
channel. However, because two frequencies are for a cellular telephone
conversation (one to transmit and one to receive), there are actually 395 voice
channels and 21 are used for control channel functions.
AMPS uses Frequency Division Multiple Access (FDMA). FDMA is most
often used with analog transmissions. In FDMA the bandwidth of the
frequency is divided into several smaller frequencies. Each channel is
dedicated to one specific user. In FDMA transmissions take place at the same
time but at different frequencies.FDMA does, however, have some drawbacks.
One is that when signals are sent at frequencies that are closely grouped, an
errant signal may encroach on its neighborâ„¢s frequency. This phenomenon,
known as crosstalk, causes interference on the other frequency and may
disrupt the transmission.
The 30 KHz channels were chosen for AMPS because this gives voice quality
comparable to standard wired telephone transmission. AMPS were the first
wireless communications systems to use FDMA. Although today AMPS is not
commonly used, it still can be found in remote areas where digital service is
difficult to support. This is because using AMPS, mobile devices can switch
from a digital signal to an analog signal when necessary.Analog signals, the
basis for 1G cellular telephony, are prone to interference and do not have the
same quality as a digital signal. In addition, sending data over an analog signal
requires a modem or a similar device to convert the signals from digital to
analog and then back again.
The next generation of cellular telephony is known as Second Generation
(2G). 2G networks transmit data between 9.6 Kbps and 14.4 Kbps in the 800
MHz and 1.9 GHz frequencies. The only major feature that 2G systems share
with 1G system is that they are circuit-switched networks.
2G systems use digital instead of analog transmissions. Digital transmissions
provide several improvements over analog transmissions:
Digital transmission uses the frequency spectrum more efficiently.
Over long distances the quality of the voice transmission does not
degrade as with analog.
Digital transmissions are difficult to decode and offer better security.
On average, digital transmissions use less transmitter power.
Digital transmission enables smaller and less expensive individual
receivers and transmitters.
Another difference between 1G and 2G systems is that the carriers of 2G
cellular networks build their cellular networks around different multiple access
technologies. There are three different technologies that are used with 2G:
TDMA, CDMA, and GSM.
Time Division Multiple Access (TDMA):
In this the bandwidth is divided into several time slots. Each user is assigned
the entire frequency for the transmission for a fraction of time on a fixed,
rotating basis. Because the duration of the transmissions is so short, the delays
that occur while others use the frequency are not noticeable.
TDMA has several advantages over FDMA.TDMA uses bandwidth more
efficiently. Also, TDMA allows both data and voice transmissions to be mixed
using the same frequency.
Code Division Multiple Access (CDMA):
CDMA uses spread spectrum technology, which spreads the transmission over
a larger range of frequency. CDMA also uses unique digital codes, rather than
separate RF frequencies or channels, to differentiate between the different
transmissions. A CDMA transmission is spread across the frequency and the
digital codes are applied to the individual transmissions.
There are several advantages to CDMA.CDMA transmissions are much harder
to eavesdrop on, since a listener would have difficulty picking out one
conversation spread across the entire spectrum. Also, CDMA can carry up to 3
times the amount of data as TDMA.
Global Systems for Mobile Communication (GSM):
GSM uses a combination of FDMA and TDMA technologies. GSM systems
can transmit at speeds up to 9.6 Kbps.
The next interim step between 2G and 3G technology is 2.5 Generation
(2.5G).2.5G networks operate at a maximum speed of 384 Kbps.
The primary difference between 2G and 2.5G networks is that 2.5G networks
are packet-switched instead of circuit-switched. Although circuit switching is
ideal for voice communications, it is not efficient for transmitting data. This is
because data transmissions occur in bursts with periods of delay in between.
The delay results in time wasted while nothing is being transmitted. Packet
switching requires that the data transmission be broken
into smaller units or packets, and each packet is sent independently through
the network to reach the destination.
There are three 2.5G technologies. For TDMA or GSM 2G networks, the next
step would be to a 2.5G technology known as General Packet Radio Service
(GPRS). GPRS uses 8 time slots in a 200 KHz spectrum to transmit at a top
speed of up to 114 Kbps. The next step beyond GPRS is Enhanced Data
Rates for Global Evolution (EDGE). EDGE is considered a booster for
GPRS systems and can transmit up to 384 Kbps. EDGE, like GPRS, is based
on an entirely new modulation technique. If network transition is from a 2G
CDMA network, instead of migrating to GPRS, the transition would be to
CDMA2000 1XRTT. CDMA2000 1XRTT is designed to support 144 Kbps
packet data transmission and to double the voice capacity of current
generation CDMA networks.
3G is intended to be a uniform and global worldwide standard for cellular
wireless communication. The International Telecommunications Union (ITU)
has outlined the standard data rates for a wireless cellular digital network.
These rates are:
144 Kbps for a mobile user
386 Kbps for a slowly moving user
2 Mbps for stationary user
The technology of 3G depends on the technology on which the transition is
being made. If technology is made from CDMA2000 1XRTT, the next step
would be to CDMA2000 1XEVDO. This technology can transmit at 2.4
Mbps. However, it can only send data and not voice. CDMA2000 1XEVDO
must be coupled with CDMA2000 1XRTT if both types of data are needed to
be transmitted. The successor to CDMA2000 1XEVDO is CDMA2000
1XEVDV. Although it has no increase in speed over CDMA2000 1XEVDO,
it can send both data and voice transmissions.
If technology from which the transition is being made is EDGE, the next step
technology to bring it up to 3G is Wideband CDMA (WCDMA). WCDMA
adds a packet-switched data channel to a circuit-switched voice channel.
WCDMA can send at 2 Mbps in a fixed position and 300 Kbps when mobile.
Cultural differences also have an impact .In the U.S. the overall emphasis is
not focussed on the device that sends the message but on the content of that
FOURTH GENERATION SYSTEMS:
The fourth generation is to be put into practice in 2010. In this system, people
can set their data in the transmission rate of 100Mbit/s, which is equivalent
with the transmission of the optical fiber. (This transmission rate is 10,000
times that of the second-generation system and 50 times of that of the third
generation system.) The system is also capable of sending and receiving high
quality moving images even when the sender or the receiver is moving in a
high-speed vehicle. In addition, in the fourth generation mobile
communications system, people can use terminals freely without becoming
conscious of individual systems. This flexibility is realized by having a
connection with other mobile communications systems such as the
nomadic/local area wireless access system.
DIGITAL CELLULAR TECHNOLOGIES:
Cellular phone customers clearly have many different service choices that they
did not have several years ago. Furthermore, it is inevitable that as the
technology evolves, the quality of service will increase and the equipment cost
will decrease.The analysis in the "Cost Factors" section has demonstrated on a
theoretical level how newer technologies such as CDMA can give finer
control over the cost per user of providing service by regulating user capacity
as a function of signal noise. Although limiting factors still exist, the number
of frequency bands allocated in the total frequency range no longer fixes the
user capacity. This allows service providers to target a more optimum quality
of service and user load, which benefits both user and service provider.
By eliminating the requirement that towers transmit at constant power, CDMA
systems can better optimize their utilization. Other technologies such as
satellite networks and GSM improve their utilization by similarly exploiting
their advances over standard FDMA and TDMA networks. The result is that
newer cellular networks will be intelligent enough to improve their utilization
and quality of service, which in turn benefits the user.
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Two aspects of mobility:
user mobility: users communicate (wireless) “anytime, anywhere, with anyone”
device portability: devices can be connected anytime, anywhere to the network
Wireless vs. mobile Examples
û û stationary computer
û ü notebook in a hotel
ü û wireless LANs in historic buildings
ü ü Personal Digital Assistant (PDA)
Typical application: road traffic
Effects of device portability
limited computing power, low quality displays, small disks due to limited battery capacity
CPU: power consumption ~ CV2f
C: internal capacity, reduced by integration
V: supply voltage, can be reduced to a certain limit
f: clock frequency, can be reduced temporally
Loss of data
higher probability, has to be included in advance into the design (e.g., defects, theft)
Limited user interfaces
compromise between size of fingers and portability
integration of character/voice recognition, abstract symbols
limited value of mass memories with moving parts
Wireless networks in comparison to fixed networks
Higher loss-rates due to interference
emissions of, e.g., engines, lightning
Restrictive regulations of frequencies
frequencies have to be coordinated, useful frequencies are almost all occupied
Low transmission rates
local some Mbit/s, regional currently, e.g., 53kbit/s with GSM/GPRS
Higher delays, higher jitter
connection setup time with GSM in the second range, several hundred milliseconds for other wireless systems
Lower security, simpler active attacking
radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile phones
Always shared medium
secure access mechanisms important
Simple reference model used here
Influence of mobile communication to the layer model
new applications, multimedia
congestion and flow control
quality of service
addressing, routing, device location
media access control
Chapter 2: Wireless Transmission
Frequencies for communication
VLF = Very Low Frequency UHF = Ultra High Frequency
LF = Low Frequency SHF = Super High Frequency
MF = Medium Frequency EHF = Extra High Frequency
HF = High Frequency UV = Ultraviolet Light
VHF = Very High Frequency
Frequencies for mobile communication
VHF-/UHF-ranges for mobile radio
simple, small antenna for cars
deterministic propagation characteristics, reliable connections
SHF and higher for directed radio links, satellite communication
small antenna, beam forming
large bandwidth available
Wireless LANs use frequencies in UHF to SHF range
some systems planned up to EHF
limitations due to absorption by water and oxygen molecules (resonance frequencies)
weather dependent fading, signal loss caused by heavy rainfall etc.
physical representation of data
function of time and location
signal parameters: parameters representing the value of data
continuous time/discrete time
continuous values/discrete values
analog signal = continuous time and continuous values
digital signal = discrete time and discrete values
signal parameters of periodic signals:
period T, frequency f=1/T, amplitude A, phase shift j
sine wave as special periodic signal for a carrier:
s(t) = At sin(2 p ft t + jt)
Different representations of signals
amplitude (amplitude domain)
frequency spectrum (frequency domain)
phase state diagram (amplitude M and phase j in polar coordinates)
Composed signals transferred into frequency domain using Fourier transformation
Digital signals need
infinite frequencies for perfect transmission
modulation with a carrier frequency for transmission (analog signal!)
Signal propagation ranges
low error rate
detection of the signal
signal may not be
signal adds to the
Propagation in free space always like light (straight line)
Receiving power proportional to 1/d² in vacuum – much more in real environments
(d = distance between sender and receiver)
Receiving power additionally influenced by
fading (frequency dependent)
reflection at large obstacles
refraction depending on the density of a medium
scattering at small obstacles
diffraction at edges
Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction
Time dispersion: signal is dispersed over time
è interference with “neighbor” symbols, Inter Symbol Interference (ISI)
The signal reaches a receiver directly and phase shifted
è distorted signal depending on the phases of the different parts