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MOBILE COMMUNICATION [EC 03]
AUTHORS:
G. DIVYA RAO
III B.Tech, E.C.E
P. DEEPIKA
III B.Tech, E.C.E
PRAGATI ENGINEERING COLLEGE
1-378, ADB Road, Surampalem “ 533 437, Near Peddapuram, E.G.Dt.(A.P).
ABSTRACT:
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.
INTRODUCTION:
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 They were largely superceded,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
o
-23
-1
radiator [ K] and k = 1.38×10
[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-
-20
art receivers require at least ~4×10
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
extremely weak.
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
1
-2
2
isotropically PR watts would produce a wave in direction ,f having Pr(,f,r) [Wm ] = PR/4pr
2
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:
Antenna
of typical
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 10º 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
milli-arc-second resolution).
The receiving properties of antennas are commonly characterized by their effective
2
-2
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
that:
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.
FIRSTGENERATION:-
1G analog system for mobile communications saw two key improvements during the 1970s: the
invention of the microprocessor and the digitization of the control page 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
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y
.
SECONDGENERATION:-
2G digital cellular systems were first developed at the end of the 1980s. These systems digitized
not only the control page 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.
THIRDGENERATION:-
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)
FOURTH GENERATION:-
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
(UMTS).
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
can
be
collected
with
the
signal
stream.
ACCESS TECHNOLOGIES (FDMA, TDMA, CDMA) “
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
systems.
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
5.15-5.35
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 page 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.
CONCLUSIONS:
All over the world and also within our Mobile Multimedia Communication project 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, also an experimentation platform has been developed.
This common experimentation environment serves to page 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.
REFERENCES
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.
