The document provides information about cellular networks and technologies. It discusses how cellular networks use cells served by base stations to provide radio coverage over a wide area. This allows many portable transceivers like mobile phones to communicate through the network. It then describes some key components of cellular networks like base stations, mobile switching offices, and mobile devices. The document also summarizes different cellular network access technologies including AMPS, TDMA, and CDMA.

1. NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY
Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite
ASSIGNMENT # 1
Cellular Technology
Valladolid, Charles Edison October 03, 2011
Communications 1/ BSECE 41A1 Score:
Eng’r. Grace Ramones
Instructor
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2. Cellular Networks and Access to Public Networks
A cellular network is a radio network distributed over land areas called cells, each served by at
least one fixed-location transceiver known as a cell site or base station. When joined together
these cells provide radio coverage over a wide geographic area. This enables a large number of
portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with
fixed transceivers and telephones anywhere in the network, via base stations, even if some of the
transceivers are moving through more than one cell during transmission.
Cellular networks offer a number of advantages over alternative solutions:
increased capacity
reduced power use
larger coverage area
reduced interference from other signals
An example of a simple non-telephone cellular system is an old taxi driver's radio system where
the taxi company has several transmitters based around a city that can communicate directly with
each taxi.
Cellular networks consist of cellular base stations, mobile telephone switching offices (MTSO),
and mobile communication devices. Each base station contains a radio transceiver and controller
and provides radio communication to the mobile units located in its cell. The cells are arranged
in a honeycomb pattern in order to provide local, regional, or national cellular coverage. The
MTSO links calls together using traditional copper, fiber optic, or microwave technology and
acts as a central office exchange allowing users to place a call on the local and long distance
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3. public telephone systems. It also allows mobile communication devices in the cell to dial out and
alerts devices in the cell of incoming calls. The MTSO continuously monitors the quality of the
communications signal and transfers the call to another base station which is better suited to
provide communication to the mobile device.
The mobile communication devices consist of hand held phones, car phones, notebook
computers, personal digital assistants, pen-based computers, palm-top computers, and portable
data collection devices. Since only two percent of the cellular traffic is d ata, the most popular
mobile units are cellular telephones (Gareiss, 1995). When these mobile units communicate to
the network, they must register with the system by subscribing to a carrier service. Most carrier
services have arrangements with other pr oviders allowing users to roam. Roaming occurs when
the mobile unit is outside the coverage of their cellular service provider and an alternative
cellular provider places the call.
Cellular technology extends the bounds of a corporation's existing telecommunications
infrastructure by connecting mobile units to the public network operated by the local exchange or
long distance carriers. The cellular users have special features an d functions specific to cellular
customers but they can also use the features and functions of the public phone systems. This
allows cellular technology to be flexible enough to take advantage of features and functions of
almost any public or private net work.
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4. Fundamental Concepts in Cellular Technology
The radio spectrum contains many bands that are allocated and used for commercial, personal,
and military applications. Fifty (50) MHz of spectrum allocated to cellular networks exists in the
824-849 MHz and the 869-894 MHz bands (Pagett, 1995). These bands are then further
subdivided into 832 channels allowing many users in the same area to simultaneously access the
network (DeBelina, 1995).
Types of Cellular Network Access
The types of network access in the United States are advanced mobile phone systems (AMPS),
time division multiple access (TDMA), and code division multiple access (CDMA). AMPS is the
cellular standard that has been extensively deployed in North America and has been
commercially available since 1983 (Khan & Kilpatrick, 1995). The current cellular standard
describing access methods to the network is IS-553 and divides 50 MHz of spectrum into 832
frequency channels, each 30 KHz wide (Amin, 1995; Pagett, 1 995; Pagett, Gunther, & Hattori,
1995). Organizations such as the Portable Computer and Communications Association (PCCA)
consist of modem manufacturers, computer manufactures, and service providers work together in
defining the IS-553 interoperability s tandard (Khan & Kilpatrick, 1995).
Time Division Multiple Access (TDMA) is a digital access method that allocates time slots to
different users allowing them to share similar radio frequency channels. TDMA divides each
frequency channel into six time slots and allocates two slots to each user increasing the network
capacity by 300% (Pagett et al., 1995). Standard IS-54 describes a dual mode network access
method allowing mobile units the choice of using TDMA or AMPS operation (Amin, 1995;
Honig & Madhow, 1990; Khan & Kilpatrick, 1995; Tawfik, 1993; Sasaoka, 1993; Williams &
Ong, 1995).
Code Division Multiple Access (CDMA) sends multiple messages over a wide frequency
channel that is decoded at the receiving end. Each mobile unit in a cell is assigned a different
spreading sequence and allows multiple users to share the same frequency spectrum improving
network capacity over the AMPS systems by a factor of ten (DeBelina, 1995; Pagett et al., 1995;
Pagett, 1995). The details for CDMA network access are referenced in standard IS-95 which
describes the mobile unit's access to the cellula r network (Honig & Madhow, 1990; Khan &
Kilpatrick, 1995; Sasaoka, 1993; Williams & Ong, 1995).
Although TDMA and CDMA digital access methods are just starting to be deployed in the
United States (Tawfik, 1993), this author believes these access methods will become widely
deployed because of their superior performance characteristics. These networ ks have a higher
capacity, improved voice quality, encryption for communication privacy, and integration with
digital terrestrial networks (Padgett, Gunther, & Hattori, 1995). Digital access has its advantages,
but it does not have the ubiquitous access that AMPS systems have (Amin, 1995). Therefore, to
take advantage of the widely available coverage of today's cellular services, portable units need
to be compatible with the analog AMPS systems.
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5. Cell signal encoding
To distinguish signals from several different transmitters, frequency division multiple access
(FDMA) and code division multiple access (CDMA) were developed.
With FDMA, the transmitting and receiving frequencies used in each cell are different from the
frequencies used in each neighbouring cell. In a simple taxi system, the taxi driver manually
tuned to a frequency of a chosen cell to obtain a strong signal and to avoid interference from
signals from other cells.
The principle of CDMA is more complex, but achieves the same result; the distributed
transceivers can select one cell and listen to it.
Other available methods of multiplexing such as polarization division multiple access (PDMA)
and time division multiple access (TDMA) cannot be used to separate signals from one cell to
the next since the effects of both vary with position and this would make signal separation
practically impossible. Time division multiple access, however, is used in combination with
either FDMA or CDMA in a number of systems to give multiple channels within the coverage
area of a single cell.
Cellular Digital Packet Data (CDPD)
Cellular Digital Packet Data (CDPD) is a technology standard sponsored by the regional bell
operating companies and McCaw Cellular. CDPD was introduced by IBM, overlays packet
switching onto the existing cellular voice network, and transmits data packet s over the idle
capacity. This packet overlay is based on transmission control protocol/internet protocol
(TCP/IP) and does not need the call setup procedures required for switched voice calls. This
makes CDPD ideal for short bursty message applications such as point-of-sale (POS) credit card
verification, vehicle dispatch, package tracking and e-mail (Gareiss, 1995). Although this
complex overlay generally increases the network utilization, excessive data traffic may cause
interference with existing cellular calls (Lee, 1993). Therefore, managers should examine the
traffic of voice and data users in a particular service area before designing applications that put a
large load on the network.
Competing Wireless Communications Technologies
The advancement of radio technology has resulted in the development and deployment of many
forms of wireless communication systems. The most formidable competitors of cellular
communications are personal communications systems (PCS), cordless telephones , paging,
specialized mobile radio (SMR) and satellite communication (Perry, 1993).
PCS is a wireless communications network which operates at a radio frequency of 1850-1990
MHz and has a greater capacity for carrying voice and data traffic. Currently, a cellular mobile
unit's throughput peaks at 14.4 K bps (Gareiss, 1995) where curren t PCS systems using the
personal access communications services (PACS) standard have channel throughput of 384 K
bps with an upside potential of 25 M bps (Raychaudguri, 1995). PCS allows greater data
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6. throughput over the air links whereas the existing cel lular infrastructure is insufficient to carry
the growth of bandwidth intensive applications (Colmenares, 1994; Tang & Sobol, 1995; Kobb,
1993). Therefore, PCS is well positioned to handle the bandwidth intensive applications of the
future.
PCS will be less expensive than cellular communication because of government regulation
promoting and increasing competition (Bernier, 1995). Government regulators will effect
competition by assigning each major trading area (MTA) with five PCS provider s compared to
the traditional two cellular providers in each MTA. Additionally, cellular providers will not be
permitted to provide PCS service in areas where they provide cellular service (Novak, 1995).
Some members of congress are trying to remove the restrictions that prevent cellular carriers
from owning and operating PCS networks in areas they provide cellular service because they
believe these restrictions "will impede the development of PCS." (Congressional Record, 1993).
This author believes PC S will capture the growth of new subscribers and cut into the imbedded
base of cellular subscribers because of the PCS networks' (PCN) cost and performance
advantages over cellular networks.
Another competing wireless technology is cordless telephony which provides wireless
communications between a handset and a base station connected to the public phone system. The
main differences between cellular and cordless technologies are the single cell architecture of
cordless and the fact that the two systems operate at different frequencies. Although cordless
telephones are inexpensive, they are not as suited to business applications as cellular telephones
because of the cordless telephones' lim ited range and their lack of privacy. There are however,
handsets on the market that have dual mode (cordless and cellular) operation that may be used in
business situations to take advantage of both technologies. (Pagett, 1995; Pagett et al., 1995).
Paging is a wireless communication technology that provides an inexpensive one way
transmission of alpha numeric and full text data. It is a viable alternative to cellular specifically
when data needs to be transmitted in one direction, to the mobile us ers. [Since this paper was
written, companies, such as SkyPage and MCI, have introduced two-way paging services.] For
two-way real time, communication, users need to have access to some form of service such as
common business phone lines or cellular phones. There are many mobile users who use both
paging and cellular with cellular allowing the mobile user to c all back and respond to the page.
When used properly, paging may provide similar results as cellular when users are in paging
range and have access to communications resources. The major difference between paging and
cellular is that cellular provides tw o way direct communication while paging provides one way
direct communication.
Specialized Mobile Radio (SMR) is a wireless communication technology that operates in the
800 Mhz range and was designed for integrating voice and data over the same wireless network.
SMR supports voice dispatch, wireless phone, voice mail, and data tr ansmission applications. It
is capable of transmitting data at 4.8 K bps with the ability of going up to 64 K bps in certain
metropolitan areas. SMR does have some limitations for business applications because it does
not have wide coverage, deep in-bui lding penetration coverage, is available in only a few
metropolitan areas, and is limited in its ability to interoperate with other networks.
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7. Satellite communication provides wireless communication with base stations in orbit around the
earth. This technology is very expensive and has high network and handset costs. There are
many vendors such as GTE Airfone, TRW, Motorola, and GlobalStar, w ho are developing
satellite communication systems that can be accessed from almost anywhere in the world. One
example is Globalstar which will have a global, wireless, low-earth-orbit, satellite-based
telephone system operational by 1998 (Loral Annual Re port, 1995).
A new technology called software defined radio allows users to redefine the operation of a
mobile unit to allow interoperability with any of the aforementioned communications
technologies (Mitola, 1995). It is this author's belief that once software def ined radios are
commercially available and cost competitive, portable units will be able to seamlessly
interoperate with many other networks. If there are different network technologies in a specific
geographical area, the handsets will be programmed to s elect the least expensive, most private,
or highest bandwidth service. For example, a user's handset will operate in cordless mode when
at home or in the office, in PCS mode when in PCS capable cells, in cellular mode when driving
regionally, and in sate llite mode when traveling internationally or in remote areas.
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8. Example of a cellular network: the mobile phone network
The most common example of a cellular network is a mobile phone (cell phone) network. A
mobile phone is a portable telephone which receives or makes calls through a cell site (base
station), or transmitting tower. Radio waves are used to transfer signals to and from the cell
phone.
Modern mobile phone networks use cells because radio frequencies are a limited, shared
resource. Cell-sites and handsets change frequency under computer control and use low power
transmitters so that a limited number of radio frequencies can be simultaneously used by many
callers with less interference.
A cellular network is used by the mobile phone operator to achieve both coverage and capacity
for their subscribers. Large geographic areas are split into smaller cells to avoid line-of-sight
signal loss and to support a large number of active phones in that area. All of the cell sites are
connected to telephone exchanges (or switches) , which in turn connect to the public telephone
network.
In cities, each cell site may have a range of up to approximately ½ mile, while in rural areas, the
range could be as much as 5 miles. It is possible that in clear open areas, a user may receive
signals from a cell site 25 miles away.
Since almost all mobile phones use cellular technology, including GSM, CDMA, and AMPS
(analog), the term "cell phone" is in some regions, notably the US, used interchangeably with
"mobile phone". However, satellite phones are mobile phones that do not communicate directly
with a ground-based cellular tower, but may do so indirectly by way of a satellite.
There are a number of different digital cellular technologies, including: Global System for
Mobile Communications (GSM), General Packet Radio Service (GPRS), Code Division Multiple
Access (CDMA), Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution
(EDGE), 3GSM, Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-
136/TDMA), and Integrated Digital Enhanced Network (iDEN).
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9. 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)
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