The document discusses cellular technology and mobile phone networks. It provides details on: - How early mobile phones worked and the development of modern cellular networks. - The basic components and functions of a cellular network including radio base stations, mobile switching centers, and connections to the public telephone network. - Concepts of cellular networks like frequency reuse, cells, and handovers that allow calls to be switched between cells as users move. - Factors that influence cellular network performance like frequency choice, interference, and coverage depending on frequency used.

1. NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY
Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite
ASSIGNMENT 1
CELLULAR TECHNOLOGY
Agdon, Berverlyn B. October 03, 2011
Communications 1/ BSECE 41A1 Score:
Engr. Grace Ramones
Instructor

2. A mobile phone allows calls into the public switched telephone system over a radio link. Early
mobile phones were usually bulky and permanently installed in vehicles; they provided limited
service because only a few frequencies were available for a geographic area. Modern cellular
"cell" phones or hand phones make use of the cellular network concept, where frequencies are
re-used repeatedly within a city area, allowing many more users to share access to the radio
bandwidth. A mobile phone allows calls to be placed over a wide geographic area; generally the
user is a subscriber to the phone service and does not own the base station. By contrast, a
cordless telephone is used only within the range of a single, private base station.
A mobile phone can make and receive telephone calls to and from the public telephone network
which includes other mobiles and fixed-line phones across the world. It does this by connecting
to a cellular network provided by a mobile network operator.
In addition to telephony, modern mobile phones also support a wide variety of other services
such as text messaging, MMS, email, Internet access, short-range wireless communications
(infrared, Bluetooth), business applications, gaming and photography. Mobile phones that offer
these more general computing capabilities are referred to as smartphones.
The first hand-held mobile phone was demonstrated by Dr Martin Cooper of Motorola in 1973,
using a handset weighing 2 1/2 lbs (about 1 kg). In 1983, the DynaTAC 8000x was the first to be
commercially available. In the twenty years from 1990 to 2010, worldwide mobile phone
subscriptions grew from 12.4 million to over 4.6 billion, penetrating the developing economies
and reaching the bottom of the economic pyramid

3. Structure of the mobile phone cellular network
A simple view of the cellular mobile-radio network consists of the following:
A network of Radio base stations forming the Base station subsystem.
The core circuit switched network for handling voice calls and text
A packet switched network for handling mobile data
The Public switched telephone network to connect subscribers to the wider telephony
network
This network is the foundation of the GSM system network. There are many functions that are
performed by this network in order to make sure customers get the desired service including
mobility management, registration, call set up, and handover.
Any phone connects to the network via an RBS (Radio Base Station) at a corner of the
corresponding cell which in turn connects to the Mobile switching center (MSC). The MSC
provides a connection to the public switched telephone network (PSTN). The link from a phone
to the RBS is called an uplink while the other way is termed downlink.
Radio channels effectively use the transmission medium through the use of the following
multiplexing schemes: frequency division multiplex (FDM), time division multiplex (TDM), code
division multiplex (CDM), and space division multiplex (SDM). Corresponding to these
multiplexing schemes are the following access techniques: frequency division multiple access
(FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and
space division multiple access (SDMA).

4. Cellular handover in mobile phone networks
As the phone user moves from one cell area to another cell whilst a call is in progress, the
mobile station will search for a new channel to attach to in order not to drop the call. Once a
new channel is found, the network will command the mobile unit to switch to the new channel
and at the same time switch the call onto the new channel.
With CDMA, multiple CDMA handsets share a specific radio channel. The signals are separated
by using a pseudonoise code (PN code) specific to each phone. As the user moves from one
cell to another, the handset sets up radio links with multiple cell sites (or sectors of the same
site) simultaneously. This is known as "soft handoff" because, unlike with traditional cellular
technology, there is no one defined point where the phone switches to the new cell.
In IS-95 inter-frequency handovers and older analog systems such as NMT it will typically be
impossible to test the target channel directly while communicating. In this case other techniques
have to be used such as pilot beacons in IS-95. This means that there is almost always a brief
break in the communication while searching for the new channel followed by the risk of an
unexpected return to the old channel.
If there is no ongoing communication or the communication can be interrupted, it is possible for
the mobile unit to spontaneously move from one cell to another and then notify the base station
with the strongest signal.

5. Cellular frequency choice in mobile phone networks
The effect of frequency on cell coverage means that different frequencies serve better for
different uses. Low frequencies, such as 450 MHz NMT, serve very well for countryside
coverage. GSM 900 (900 MHz) is a suitable solution for light urban coverage. GSM 1800
(1.8 GHz) starts to be limited by structural walls. UMTS, at 2.1 GHz is quite similar in coverage
to GSM 1800.
Higher frequencies are a disadvantage when it comes to coverage, but it is a decided
advantage when it comes to capacity. Pico cells, covering e.g. one floor of a building, become
possible, and the same frequency can be used for cells which are practically neighbours.
Cell service area may also vary due to interference from transmitting systems, both within and
around that cell. This is true especially in CDMA based systems. The receiver requires a certain
signal-to-noise ratio. As the receiver moves away from the transmitter, the power transmitted is
reduced. As the interference (noise) rises above the received power from the transmitter, and
the power of the transmitter cannot be increased any more, the signal becomes corrupted and
eventually unusable. In CDMA-based systems, the effect of interference from other mobile
transmitters in the same cell on coverage area is very marked and has a special name, cell
breathing.
One can see examples of cell coverage by studying some of the coverage maps provided by
real operators on their web sites. In certain cases they may mark the site of the transmitter, in
others it can be calculated by working out the point of strongest coverage.

6. Coverage comparison of different frequencies
The concept
In a cellular radio system, a land area to be supplied with radio service is divided into regular
shaped cells, which can be hexagonal, square, circular or some other irregular shapes, although
hexagonal cells are conventional. Each of these cells is assigned multiple frequencies (f1 - f6)
which have corresponding radio base stations. The group of frequencies can be reused in other
cells, provided that the same frequencies are not reused in adjacent neighboring cells as that
would cause co-channel interference.
The increased capacity in a cellular network, compared with a network with a single transmitter,
comes from the fact that the same radio frequency can be reused in a different area for a
completely different transmission. If there is a single plain transmitter, only one transmission can
be used on any given frequency. Unfortunately, there is inevitably some level of interference
from the signal from the other cells which use the same frequency. This means that, in a
standard FDMA system, there must be at least a one cell gap between cells which reuse the
same frequency.
In the simple case of the taxi company, each radio had a manually operated channel selector
knob to tune to different frequencies. As the drivers moved around, they would change from
channel to channel. The drivers knew which frequency covered approximately what area. When
they did not receive a signal from the transmitter, they would try other channels until they found
one that worked. The taxi drivers would only speak one at a time, when invited by the base
station operator (in a sense TDMA).

7. Frequency reuse
The increased capacity in a cellular network, comparing to a network with a single transmitter,
comes from the fact that the same radio frequency can be reused in a different area for a
completely different transmission. If there is a single plain transmitter, only one transmission
can be used on any given frequency. Unfortunately, there is inevitably some level of
interference from the signal from the other cells which use the same frequency. This means
that, in a standard FDMA system, there must be at least a one cell gap between cells which
reuse the same frequency.
The frequency reuse factor is the rate at which the same frequency can be used in the network.
It is 1/n where n is the number of cells which cannot use a frequency for transmission.
Code division multiple access based systems use a wider frequency band to achieve the same
rate of transmission as FDMA, but this is compensated for by the ability to use a frequency
reuse factor of 1. In other words, every cell uses the same frequency and the different systems
are separated by codes rather than frequencies.
Depending on the size of the city, a taxi system may not have any frequency reuse in its own
city, but certainly in other nearby cities, the same frequency can be used. In a big city, on the
other hand, frequency reuse could certainly be in use.

8. Frequency Division Multiple Access or FDMA is a channel access method used in multiple-
access protocols as a channelization protocol. FDMA gives users an individual allocation of one
or several frequency bands, or channels. It is particularly commonplace in satellite
communication. FDMA, like other Multiple Access systems, coordinates access between
multiple users. Alternatives include TDMA, CDMA, or SDMA. These protocols are utilized
differently, at different levels of the theoreticalOSI model.
Disadvantage: Crosstalk may cause interference among frequencies and disrupt the
transmission.
FREQUENCY DIVISION MULTIPLE ACCESS
FDMA is distinct from frequency division duplexing (FDD). While FDMA allows multiple users
simultaneous access to a transmission system, FDD refers to how the radio channel is shared
between the uplink and downlink (for instance, the traffic going back and forth between a
mobile-phone and a mobile phone base station). Frequency-division multiplexing (FDM) is also
distinct from FDMA. FDM is a physical layer technique that combines and transmits low-
bandwidth channels through a high-bandwidth channel. FDMA, on the other hand, is an access
method in the data link layer.
FDMA also supports demand assignment in addition to fixed assignment. Demand
assignment allows all users apparently continuous access of the radio spectrum by assigning
carrier frequencies on a temporary basis using a statistical assignment process. The first
FDMA demand-assignment system for satellite was developed byCOMSAT for use on
the Intelsat series IVA and V satellites.
There are two main techniques:
 Multi-channel per-carrier (MCPC)
 Single-channel per-carrier (SCPC)

9. Time division multiple access (TDMA) is a channel access method for shared medium networks.
It allows several users to share the same frequency channel by dividing the signal into different
time slots. The users transmit in rapid succession, one after the other, each using its own time
slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency
channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular
systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital
Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT)
standard for portable phones. It is also used extensively in satellite systems, combat-net
radio systems, and PON networks for upstream traffic from premises to the operator. For usage
of Dynamic TDMA packet mode communication.
TDMA is a type of Time-division multiplexing, with the special point that instead of having
one transmitter connected to one receiver, there are multiple transmitters. In the case of
the uplink from a mobile phone to abase station this becomes particularly difficult because the
mobile phone can move around and vary the timing advance required to make its transmission
match the gap in transmission from its peers.
Code division multiple access (CDMA) is a channel access method used by various radio
communication technologies. It should not be confused with the mobile phone
standards called cdmaOne, CDMA2000 (the 3G evolution of cdmaOne) and WCDMA (the 3G
standard used by GSM carriers), which are often referred to as simply CDMA, and use CDMA
as an underlying channel access method.
Space-Division Multiple Access (SDMA) is a channel access method based on creating parallel
spatial pipes next to higher capacity pipes through spatial multiplexing and/or diversity, by which
it is able to offer superior performance in radio multiple access communication systems. In
traditional mobile cellular network systems, the base station has no information on the position
of the mobile units within the cell and radiates the signal in all directions within the cell in order
to provide radio coverage. This results in wasting power on transmissions when there are no
mobile units to reach, in addition to causing interference for adjacent cells using the same
frequency, so calledco-channel cells. Likewise, in reception, the antenna receives signals
coming from all directions including noise and interference signals. By using smart
antenna technology and differing spatial locations of mobile units within the cell, space-division
multiple access techniques offer attractive performance enhancements. The radiation pattern of
the base station, both in transmission and reception, is adapted to each user to obtain highest
gain in the direction of that user. This is often done using phased arraytechniques.

10. The Major Advantages of Cellular Technology
Apps for mobile phones is one of the major advantages to being mobile and on the go,
especially to places we are unfamiliar with, is what is known as the GPS, or global positioning
system. Some of the more sophisticated cellular devices come with a GPS option, so you can
always find your way. Today’s GPS is like road maps used to be without all the clutter and
information that you don’t need.
Cellular technology is entertaining. Though you can tell a joke through texting or live during a
phone call, the other possibilities are endless: music, music videos, movies, photographs, video
games, word games and television programs are just a few of the ways that you can keep
yourself entertained. They key to this technology is how long your batter life is and keeping
your cellular device charged.
None of this would have been possible without cellular technology, which is practically
synonymous with being on the move. Being on the move is total freedom, not being tied to a
specific location for anything. In the past, vocations and careers stated that we sometimes had
to stay in one location and for some, that is still the case. But most of us can work, be
entertained and socialize from the road thanks to cellular devices.