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.