1.

1 Introduction
A mobile phone is a portable telephone that does not use a wired connection. It is also known as
a wireless phone, cell phone, or cellular telephone. In many developing countries, mobile technology is
a substitute for traditional fixed services. Worldwide the number of cellular phone users in the years
1984, 1994, and 1997 were 25,000, 16 million, and 50 million, respectively. In 2000, the number of
wireless users became equal to the wired users and this number increased to 1.9 billion worldwide in
the year 2005. The number of mobile users increased to 3 billion by 2007, which is almost half of the
world’s population. By 2011, the estimated mobile phone subscriber base in India will be 298 million
and India will become the second largest country in the world, next to China. The resulting cellular
penetration rate is 23.9 per cent of the nation’s population. Mobile technology extends access to
formerly unreserved population groups such as the urban poor and rural users. In addition to the
standard voice function, current mobile phones also support latest services such as short message
service (SMS), general packet radio service (GPRS), and multimedia service (MMS) for sending and
receiving photos and videos, e-mail, packet switching, wireless access protocol (WAP), and Bluetooth.
The cellular concept was developed by Bell Labs in 1960s–1970s.D
The evolution of cellular communication systems is commonly known by the 1G, 2G,
3G, and 4G designations.
We are currently in the third generation (3G) cellular communication systems. The cellular network
provides wireless connection between mobile phones or between a mobile phone and landline phone
using radio waves. These mobile phones connect to the cellular networks which are further connected
to the public switched telephone network (PSTN).
The cellular network uses a number of low-power transmitters called base stations (BSs) and each
BS covers a unit area called a “cell”.
The cellular network concept is against the use of a single high-power transmitter with antenna
mounted on a tall tower as is the case in the early mobile radios (shown in Fig. 1.1(a)) to cover a large
area. The difficulty in the early mobile radio systems was the reuse of same frequencies throughout
the system resulting in significant interference and lot of bandwidth being dedicated to a single call.
The cellular system shown in Figure 1.1(b) uses a number of low-power transmitters called BSs to
cover same area and to avoid the above difficulties.

Figure 1.1 Early mobile radio system and cellular system

This chapter introduces the different generations of cellular systems and their limitations, the
geometry of the cell, different performance improvement methods such as handoff, frequency reuse,
cell splitting, and so on, the principle of cellular radio systems, and also includes a brief overview of
the analogue and digital cellular mobile systems.

1.2 Generations of wireless mobile systems

Wireless communication is basically transmitting and receiving voice and data using electromagnetic
waves in open space. The origin of wireless communications can be traced back to the year 1857,
when the behaviour of electromagnetic waves was explained mathematically using four equations by
James Clerk Maxwell. Maxwell’s four equations describe the electric and magnetic fields arising from
varying distributions of electric charges and currents, and how those fields change with time.
The equations were the mathematical representation of decades of experimental observations of the
electric and magnetic effects of charges and currents. According to Maxwell, an accelerated charge
creates a magnetic field in its neighbourhood which in turn creates an electric field in the same area. A
moving magnetic field produces an electric field and vice versa. These two fields vary with time, so
they act as sources of each other. Thus, an oscillating charge having non-zero acceleration will emit an
electromagnetic (EM) wave and the frequency of the wave will be same as that of the oscillation of the
charge. Though the electromagnetic waves were first discovered as a communication medium at the
end of the nineteenth century, these were put in use for the masses later.

Figure 1.2 EM wave generation

Twenty years later, in the period 1879–1886, after a series of experiments, Heinrich Hertz came to
the conclusion that an oscillatory electrical charge q = q0sin t radiates EM waves and these waves
carry energy. Hertz was also able to produce EM waves of frequency 3 ×10 10 Hertz. The experimental
setup is shown in the Figure 1.2. To detect EM waves, he used a loop S, which is slightly separated
from EM wave generator as shown in the figure.
Hertz’s radio system consists of a switch and an induction coil to generate a spark across two
electrodes. The receiver was a loop(S) made from a copper wire around 35 cm in diameter, with a
small gap in the loop. When the “transmitter” generated a spark, a small spark was seen to jump the
gap in the receiving coil. This is the basis for the antenna theory. In 1895–1897, Jagdish Bose also
succeeded in generating EM waves of very short wavelength (∼25 mm).
The father of today’s mobile radio systems is G. Marconi, born in Italy in 1874. He demonstrated the
first radio-based wireless transmission successfully using electromagnetic waves in 1901 over a
distance of 1 mile. However, the bandwidth of these transmission systems was very small; the
transmission of information was very slow. Over the next couple of decades, Marconi was a leading
pioneer in establishing long-range wireless communication standards and his efforts led to the
deployment of first radio-based telephony system for conversations between ships in 1915.
A technological breakthrough was the development of frequency modulation (FM) in the mid-1930s
by Edwin Howard Armstrong. The Second World War battlefields were a major test bed for portable
two-way FM radio technologies. The first systems offering mobile telephone service (MTS) (car phone)
were introduced in the late 1940s in the United States and in the early 1950s in Europe. These single
cell systems were severely constrained by restricted mobility, low capacity, limited service, and poor
speech quality. Also, the equipment was heavy, bulky, expensive, and susceptible to interference.
In 1964, Bell Laboratories introduced the improved mobile telephone service (IMTS) which added full-
duplex features to the old MTS. In 1968 and 1970, the Federal Communication Commission (FCC)
realizing the huge potentials of mobile telephony, reallocated the frequency spectrum (40 MHz band in
the 800 to 900 MHz frequency range) for cellular use. The cell covers a service area where a group of
mobiles or terminals (referred to as users) are served primarily by one BS – usually located at the
centre of the cell.
In addition, AT&T proposed a cellular mobile scheme in 1968 to the FCC which was approved in
1974. The cellular concept of using the same frequency at different places was introduced by
MacDonald in 1979. The next evolutionary steps begin in the early 1980s with the deployment of
the first generation (1G) analogue networks based on frequency division multiplexing (FDM). In
addition to the original 40 MHz band, an additional 10 MHz band was allocated in 1988 and called as
the expanded spectrum (ES). Cellular communication is full duplex and the frequency band is divided
between both communications: 25MHz is allocated to the forward path or downlink, which is the path
for BS to mobile unit and the other half is for the mobile to BS. The paths are separated by a 45 MHz
guard band in order to avoid interference between transmission and reception channels.
The increased demand for mobile communication led to the evolution of second generation (2G)
digital networks in the early 1990s. The introduction oftime-division multiplexing (TDM) on top of the
existing FDM, an essential feature of 2G, increased the number of served subscribers per geographical
area. In addition, voice quality was improved as well, with the introduction of newer voice coding
algorithms. Finally, at the beginning of the third millennium, the first 2.5G networks, which are an
upgrade of 2G and the 3G networks were implemented in most countries worldwide. And now the
research is on the next-generation mobile technology with more advanced features, that is 4G, which
is expected to be available in the market by 2012–2015. For clear understanding of the evolution of
analogue and digital cellular technology, their broad features are illustrated in Figure 1.3.

1.2.1 First generation (1G)

The first 1G mobile phone system was introduced in 1980 in the United States. Before 1G, “0G” refers
to pre-cellular mobile telephony technology, such as radio telephones that we had in cars before the
advent of cell phones.
Analogue circuit-switched technology is used for this system, with frequency division multiple access
(FDMA), as an air channel multiple access technique, and worked mainly in the 800–900 MHz
frequency bands. The 1G mobile phone had only voice facility.
Examples of 1G system are analogue mobile phone systems (AMPS) and total access communication
systems (TACS). The AMPS was implemented in North America and the TACS was used in Europe.
 Figure 1.3 Evolution of cellular systems

In AMPS, two 25-MHz bands are allocated. One 25-MHz band is for communication from BS to mobile
unit and the other for communication from mobile unit to BS.
The following are the limitations of 1G:

 Supports only speech

 Low traffic capacity
 Unreliable handover
 Long-call setup time and frequent call drops
 Inefficient use of bandwidth and poor battery life
 Poor voice quality and large phone size
 Allows users to make voice calls in 1 country only

1.2.2 Second generation (2G)

The need for more user capacity per cell led to the development of 2G technologies. 2G systems
are digital cellular systems and were introduced in the late 1980s and were in use till the late 1990s.
2G technology supports data, speech, FAX, SMS, and WAP services. The frequency bands used by GSM
are 890–960 MHz and 1710–1880 MHz. In the 890–960 MHz frequency band, the band at 890–915 MHz
is dedicated to uplink communications from the mobile station (MS) to the BS, and the band at 935–
960 MHz is used for the downlink communications from the BS to the MS. 2G digital technology is
divided into two standards: time division multiple access (TDMA) and code-division multiple access
(CDMA).
Global system for mobile (GSM) was the first commercially operated digital cellular system and uses
TDMA/frequency-division duplexing (FDD)
IS-95 is commonly referred to as CDMA one standard and is used in North America and some parts of
Asia
The following are limitations of 2G:
 Provides low data rates ranging from 9.6 kbps to 28.8 kbps.
 Circuit-switched network, where the end systems are dedicated for the entire call session. This
causes reduction in usage of bandwidth and resources.
 Too many 2G standards globally (e.g. GSM, CDMA, PDC, and PHS )

1.2.3 Interim generation (2.5G)

The need for increased throughput data rates in data transfer (such as web browsing and e-mail) led
to the evolution of 2.5G which is between 2G and 3G.
The mobile technology using GPRS standard has been termed as 2.5G.
The 2.5G was started in 1998 with added GPRS and enhanced data rates for GSM evolution (EDGE). In
addition to the hyper text transfer protocol (HTTP), it supports the wireless access protocol (WAP)
through which web pages can be viewed on the small screen of a mobile phone or a handheld device,
which led to mobile commerce (m-commerce).

1.2.4 Third generation (3G)

The need for high-speed internet access, live video communications, and simultaneous data and voice
transmission led to the development of 3G cellular networks. The 3G technology has added
multimedia facilities to 2.5G phones. 3G operates in the frequency band of 1710–2170 MHz. It provides
high transmission rates from 348 Kbps in a moving vehicle to 2 Mbps for stationary or mobile users.
The aim of 3G systems is to provide communication services from person-to-person at any place
(global roaming) and at any time through any medium with guaranteed quality of service.
Examples of 3G system are universal mobile telecommunication systems (UMTS) and international
mobile telecommunications at 2,000 MHz (IMT-2000).
UMTS are designed to provide different types of data rates, based on the following circumstances: up
to 144 kbps for moving vehicles, 384 kbps for pedestrians, and 2 Mbps for indoor or stationary users.
UMTS will integrate all the services offered by different mobile communication systems such as mobile
phone, cordless telephone, and satellite radio in one service. Japan was the first country to introduce
3G system IMT-2000 network nationally, and in Japan the transition to 3G was completed in the year
2006.
 Figure 1.4 illustrates the mobile phone samples of 1G, 2G, and 3G cellular network
generations. Figure 1.4(a) is the first handheld device from Motorola Company which was available in
1984 in 1G network. Figure 1.4(b) is Ericsson GH218 which was introduced in 1994 and operated in 2G
networks. Figure 1.4(c) is the LG U8110 that was introduced in 2004 and is operating in 3G networks.
The following are the drawbacks of 3G system:

 High bandwidth requirement

 High spectrum licensing fees
 Expense and bulk size of 3G phones
 Lack of 2G mobile user buy in for 3G wireless service
 Lack of network coverage because it is still a new service
 High prices of 3G mobile services in some countries

1.2.5 Fourth generation (4G)

Even though the 3G networks have been deployed since 2001, the true broadband access will be
achieved with the 4G mobile phones. The 4G mobile communications will have transmission rates up
to 20 Mbps higher than that of 3G.
4G technology is expected to provide very smooth global roaming universally with lower cost.
Theoretically, 4G is set to deliver 100 Mbps to a roaming mobile device globally, and up to 1 Gbps to a
stationary device. 4G will bring almost the perfect real world wireless internetworking called
“WWWW:World Wide Wireless Web”
 Figure 1.4 Samples of mobile phones from the three generations

With the expected features in mind, 4G allows for video conferencing, streaming pictureperfect video
(e.g. tele-medicine and tele-geo processing application) and much more. Since the 4G is a research
item for the next-generation wide-area cellular radio, the technology is expected to be available
around 2012–2015. The following modulation techniques are proposed to be used in the 4G cellular
phones.

 Variable spreading factor-orthogonal frequency and code division multiplexing (VSF-OFCDM).

 Variable spreading factor code-division multiple access (VSF-CDMA).

A short history of cellular evolution from 1G to 4G cellular systems is shown in Table 1.1. From Table
1.1 we can observe that the 4G is not a single defined technology or standard, but rather a collection
of technologies and protocols aimed at creating fully packet-switched networks optimized for data.
Another major difference between 3G and 4G is that unlike the 3G networks which are a combination
of circuit-switched and packet-switched networks, 4G will be based on packet switching only. This will
allow low-latency data transmission.

Table 1.1 History of 1G, 2G, 3G, and 4G technologies

1.3 Cellular geometry
The main reason for defining cells in a cellular land mobile radio system is to outline areas in which
specific channels and specific cell sites are used. However, designers have realized that visualizing all
cells as having the same geometrical shape helps to ease the design of cellular systems, not only in
locating transmitter sites relative to one another and making economical use of equipment, but also in
making the adaptation to traffic much easier. From this point of view, cellular geometry helps to ease
the assessment of spectral efficiency of various cellular systems, in particular to calculate the
significant co-channel interference (CCI) in the system.

1.3.1 Cell shapes

There are only certain patterns of cells or tessellations which can be repeated over a plane: the
regular hexagon, the square, the circle, and the triangle.
The regular hexagon is favoured by system designers for the following reasons:
 It provides the best approximation to the circular omni-directional radio patterns achieved in
practice.
 It is more economical to use since a hexagonal layout requires fewer cells and hence fewer stations.
 It combines ease of geometry with the practical realization of overlapping circles.
 For a given distance between the centre of a polygon and its farthest perimeter points, the hexagon
has the largest area, and it almost approximates a circular radiation pattern.
Hexagons are generally used to represent the cells due to geometry considerations and
calculation purposes.
For example, in Figure 1.5 hexagons closely approximate the circle, which is used as a coverage area
by a BS that has transmission radius (range) R. More details are given in Chapter 2 about cell and
sector shapes by comparing the hexagonal and circular cell shapes.

1.4 Introduction to cellular concept

The cellular concept was developed in response to the limitations of conventional mobile radio
services. The main limitations of the previous mobile communication systems are as follows:
1. High-power transmitters were used to cover very large area.
2. Inefficient use of allocated radio spectrum.
3. If a user leaves the coverage area, they had to reinitiate the call on a different frequency
channel.
 Figure 1.5 Circle to hexagonal cell shape approximation

Figure 1.6 Conventional mobile radio service

In the beginning, there were no handoffs and the cellular system’s size depended on how much
power the centralized BS could transmit and receive. Users who stepped out of range of one system
had to re-establish the call in the next system (Fig. 1.6). The capacity of these systems was severely
limited because only a small number of radio channels (available bandwidth) were available for mobile
systems. Therefore, they had to find a way to reuse radio channels in order to carry more than one
conversation. Repeatedly reusing the radio frequencies over a given geographical area provides
number of simultaneous conversations. The basic idea of the cellular concept is frequency reuse.

1.4.1 Frequency reuse

Frequency reuse refers to the use of radio channels on the same carrier frequency to cover different
areas that are separated from one another by sufficient distances.
 Since the users in different geographical areas (cells) may simultaneously use the same frequency,
this technique maximizes the number of mobile phones served in a given geographical area and
spectrum efficiency. Frequency reuse causes CCI which is a trade-off link quality versus subscriber
capacity. This concept is shown in Figure 1.7 and is explained in greater detail in Chapter 2. Cells with
the same letter (A) use the same set of frequencies. A cell group or cluster is outlined in bold and
replicated over the coverage area. In Figure 1.7, the cluster size (N) is 7 and the frequency reuse
factor is 1/7 since each cell contains 1/7 of the total number of available channels.

1.4.2 Handoff
Notion of handoff is a crucial component in cellular concept. The mobile users by definition are mobile
i.e. they can move around while using the phone. Hence the network should be able to provide them
continuous access as they move. This will not be a problem if the user is moving within the same cell.
But when the user moves from one cell to another, a handoff is required.
Handoff is one of the important concepts in the cellular mobile communications. The mobile user can
move around while using the mobile phone, which is the main advantage of mobile phones. Even
when the mobile user is moving, the access to the network should be continuous. This problem does
not arise if the user is moving within the same cell, but when the user is moving from cell to cell,
a handoff is needed.

Figure 1.7 An illustration of the cellular frequency reuse concept

Handoff is the process of transferring an active call from one cell to another as the mobile unit
moves from the first cell to the other cell without disconnecting the call.
 When a mobile moves into a different cell while the call is in progress, the mobile switching centre
(MSC) automatically transfers the call to a new channel belonging to the new BS. Handoff operation
involves identifying a new BS along with the allocation of voice and control signals.
Example of a handoff process is given in steps with reference to mobile phone moving from one BS
to another as shown in Figure 1.8:

 A user is transmitting and receiving signals from a given BS (say BS1).

 Assume the user moves from the coverage area of one BS into the coverage area of a second BS
(BS2).
 BS1 notices that the signal from this user is degrading.
 BS2 notices that the signal from this user is improving.
 At some point, the user’s signal is weak enough at BS1 and strong enough at BS2 for a handoff to
occur.
 Specifically, if messages are exchanged between the user, BS1, and BS2 then the communication
to/from the user is transferred from BS1 to BS2.

Figure 1.8 Call handoff process

Figure 1.9(a) depicts an improper handoff scenario between two BSs (i.e. BS1 and BS2). When the
mobile user in a car is at point A in the coverage area of BS1, then the received signal strength (RSS)
is above the threshold level as shown in Figure 1.9(a). But if the mobile user in the car is moving
 towards point B in the coverage area of BS2, then the RSS received by the mobile due to the BS2 is
dropped below the minimum acceptable threshold level and the call is terminated. Figure
1.9(b) depicts the proper handoff scenario that has taken place when the mobile user’s car is moving
from BS1 to BS2. In this case, when the mobile user is at point A under the coverage area of BS1, then
the RSS is above the threshold level as shown in Figure 1.9(b). If the mobile user in the car is moving
towards point B in the coverage area of BS2, then the RSS received by the mobile due to the BS2 is
well above minimum acceptable threshold level, and therefore, the handoff is successful.

1.4.2.1 Types of handoff

Handoffs are broadly classified into two categories:
 Hard handoff
 Soft handoff (SHO)
Hard handoff is “break-before-make”, meaning that the connection to the old BS is broken before a
connection to the new BS is made. Hard handoff occurs when handoff is made between disjointed
radio systems, different frequency assignments, or different air-interface characteristics or
technologies.

Figure 1.9(a) Improper handoff

 Figure 1.9(b) Proper handoff

Usually, the hard handoff can be further divided into two different types: intracellular and
intercellular handoffs.
A handoff made within the currently serving cell (e.g. by changing the frequency) is called an
intracellular handoff. A handoff made from one cell to another is referred to as an intercellular handoff.
SHO is “make-before–break”, meaning that the connection to the old BS is not broken until a
connection to the new BS is made. In fact, more than one BS is normally connected simultaneously to
the MS. There are different types of SHO. When sectors of the same BS are involved in communication
with the MS, the handoff is called softer handoff. When one sector from each BS is involved, the
handoff is called soft handoff. When multiple sectors of one BS and one or more sectors of another BS
communicate with the MS, the resulting SHO is called softer-soft handoff.

1.4.2.2 Handoff strategies

Mobility in network is managed by two different handoff strategies, namely horizontal handoff and
vertical handoff.
 In case of horizontal handoff, handoff is between two network access points or BSs that use the same
wireless network access technology. The handoff is purely due to mobility of the MS. In case of vertical
handoff, handoff is between two network access points or BSs that use the different wireless network
access technology.
In the 1G analogue cellular systems, the RSS measurements are made by the BS and are supervised
by the MSC. In the 2G systems that use TDMA technology, mobile-assisted handoff (MAHO) is used. In
MAHO, every mobile phone measures the RSS from the surrounding BS and continuously reports the
RSS values to the corresponding BS. Further details of the handoff mechanism are presented
in Chapter 18.

1.4.3 Co-channel interference

For each cell, a set of frequencies is allocated.
Cells that use the same set of frequencies are denoted as co-channel cells and the interference
received from co-channel cells is called co-channel interference.
The CCI occurs mainly due to reusing an identical frequency channel. This has become a major
problem in the mobile cellular network. To reduce the CCI, minimum frequency reuse distance must be
used. If all cell sizes are fixed, CCI is independent of the transmitted power of each cell. One method to
reduce the CCI is by tilting down the BS antenna beam as shown in Figure 1.10 due to which the power
outside the cell causing CCI reduces. CCI in the cellular system is described in detail in Chapter 3.
The following five types of approaches are followed in cellular communications to increase the user
capacity.

Figure 1.10 CCI reduction using beam tilting

 Adding new channels: New channels are added between mobile unit & base station.
 Frequency borrowing: Frequencies are taken from adjacent cells by congested cells.
 Cell splitting: Cells in areas of high usage can be split into smaller cells.
 Cell sectoring: Cells are divided into a number of wedge-shaped sectors, each with their own set of
channels.
 Microcells: BS antennas move to buildings and lamp posts.

1.4.4 Cell splitting

Cell splitting is the process of dividing the radio coverage of a cell site into two or more new cell
sites. Cell splitting is performed to provide additional capacity (number of channels) within the region
of the original cell site by increasing the number of BSs.

Splitting a cell provides more number of cells,

reduction in the cell size, and
corresponding reduction in the antenna height and transmitter power

More number of cells gives more number of clusters, resulting in more number of channels and high
user capacity.
The cell radius (R) reduction by a factor of f reduces the coverage area and increases the required
number of BSs by a factor of f2.
Figure 1.11 illustrates how cells can be divided if higher capacity is needed in a spot. We need to go
locally to smaller cluster size (N). Figure 1.11 consists of three clusters and each cluster is a group of
seven cells. (http://www.wirelessdictionary.com/Wireless-Dictionary-Cell-Splitting- Definition.html). To
cover a smaller area, the radio coverage area of large cells sites are split by adjusting the power level
and/or using reduced antenna height. The radio coverage area of the cell site can be reduced by
changing the RF boundaries of the cell site. This is similar to placing the cells farther apart and
permitting new cells to be added. To use the cell resources efficiently the smaller cells can be either
activated or deactivated according to the traffic patterns. More details on cell splitting are discussed
in Chapter 3.
Figure 1.11 Cell splitting before and after in 3 clusters of size 7
.5 Principle of operation of a cellular mobile system
The most common example of a cellular network is a mobile phone (cell phone) network. A mobile
phone is a portable telephone used to receive or make calls through a cell site (BS), or transmitting
tower. Electromagnetic waves are used to transfer signals to and from the cell phone.
Modern mobile phone networks use cells because radio frequencies are 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. Figure 1.12 illustrates the cellular mobile network.
A cellular network is used by the mobile phone operator to achieve both coverage and capacity for
their subscribers. Large geographical areas are split into smaller cells to avoid line-of-sight (LOS)
signal loss and to support a large number of active phones in that area. All cell sites are connected to
telephone exchanges (or switches), which in turn connect to the public telephone network.
Coverage area of cells: In cities, each cell site may have a range of up to approximately 1/2 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.

1.5.1 Components of a cellular mobile network

A cellular network is formed by connecting the following five components as shown in Figure 1.12.

1. Mobile station (MS)

2. Base station (BS)
3. Mobile switching centre (MSC)
4. Base station controller (BSC)
5. Public switched telephone network (PSTN)

The function of each network component is described in the following:

Mobile station (MS): MSs are usually a mobile phone. Each mobile phone contains
a transceiver (transmitter and receiver), an antenna, and control circuitry. Antenna converts the
transmitted RF signal into an EM wave and the received EM waves into an RF signal. The same
antenna is used for both transmission and reception, so there is a duplexer switch to multiplex the
same antenna.
 Base station (BS): One of the important components in the cellular network is the BS.
BS provides direct communication with mobile phones and it defines the cell. When cells are grouped
together, a cluster is formed. Within a cluster, no channels are reused.

Figure 1.12 Cellular network

Two frequencies are required to establish communication between MS and BS: one from mobile
phone (MS) to BS (uplink channel) and inverse (downlink channel) as shown in Figure 1.13.
A group of BSs are in turn connected to a BSC. The BS is a transceiver station or system and consists
of a number of different elements.
 The first part of the BS is electronics section normally located in a container at the base of the
antenna tower. The various electronic devices for communicating with the mobile handsets include
RF amplifiers, radio transceivers, RF combiners, control, communication links, and power supplies
with backup.
 The second part of the BS is the antenna and the feeder to connect the antenna to the base
transceiver station itself. These antennas are visible on top of the masts and tall buildings enabling
them to cover the required area.
 It is important that the location, height, and orientation are all correct to ensure that the required
coverage is achieved.

 If the antenna is too low or in a poor location, there will be insufficient coverage, leaving a
coverage “hole”.
 If the antenna is too high and directed incorrectly, then the signal will be heard well beyond the
boundaries of the cell. This may result in interference with another cell using the same frequencies.
 Figure 1.13 Downlink and uplink channels

BS or cell site antenna: Either omni-directional or directional antennas are used as BS antennas in the
wireless industry. The typical directional antenna is shown in Figure 1.14. The cell site mast generally
has three “faces” each with several frequency agile, directional antennas. Each face covers
approximately 120° of the cell and each face uses a different subset of the cell’s assigned frequencies.
Usually, the antenna tower is at the centre of the cell.
Omni-directional antenna: Today, the omni-directional antenna shown in Figure 1.15a at BSs exists
only in rural areas for the most part. This is because of the lower subscriber densities in rural areas
and the lack of requirement for the increased capacity that is afforded by using directional antennas
and sectorized BSs. Omni-directional BSs are noted for their use of omni-directional antennas which
are slender, long, and tubular. There are always two receive antennas at every BS, which are known
as receive zero (Rx0) and receive one (Rx1). The purpose of having two receive antennas at every BS
is to provide for what is known as space diversity. Space diversity, also known as receive diversity,
compensates for Rayleigh fading in the uplink to the BS. Space diversity is a tool used to optimize the
signal received by a BS (transceiver); it counteracts the negative effects of Rayleigh fading. It ensures
that the best possible receive signal is used to process all wireless calls. A typical antenna
arrangement is shown in Figure 1.15(b).

Figure 1.14 3 face directional antenna as base station antenna

Figure 1.15a Horizontal view of tower mounting of omni directional BS antenna

 Figure 1.15b Typical antenna arrangement

Figure 1.16 Interconnection of BS and BSC

Base station controller (BSC): A number of BSs are connected to a BSC as shown in Figure 1.16. An
important function of BSC is that it manages the “handoff” from one BS to another as a subscriber
moves from cell-to-cell. The BSC contains logic to control each of the BSs. Also, a group of BSCs are in
turn connected to a MSC via microwave link or telephone lines.
Mobile switching centre (MSC): The MSC is the control centre for the cellular system. The MSC is also
known as mobile telephone switching office (MTSO). It coordinates the actions of the BSs providing
overall control and acts as a switch and connects into the PSTN. Various functions performed by a MSC
are as follows:
 It communicates with the BSs, routing calls and controlling them as required.
 It contains databases detailing the last known locations of the mobiles.
 It also contains facilities for authentication centre allowing mobiles onto the network.
 It contains facilities to generate billing information for individual accounts.

For this purpose, the MSC makes use of the three major components of the network subsystem
(NSS), that is HLR, VLR, and AUC.
Home location register (HLR): The HLR contains the information related to each mobile subscriber,
such as the type of subscription, services that the user can use, the subscriber’s current location, and
the mobile equipment status. The database in the HLR remains intact and unchanged until the
termination of the subscription.
Visitor location register (VLR): The VLR comes into action once the subscriber enters the coverage
region. Unlike the HLR, the VLR is dynamic in nature and interacts with the HLR when recoding the
data of a particular mobile subscriber. When the subscriber moves to another region, the database of
the subscriber is also shifted to the VLR of the new region.
Authentication centre (AUC): The AUC (or AC) is responsible for policing actions in the network. This
has all the data required to protect the network against false subscribers and to protect the calls of
regular subscribers. There are two major keys in the GSM standards: the encryption of
communications between mobile users and the authentication of the users. The encryption keys are
held both in the mobile equipment and the AUC and the information is protected against unauthorized
access.
PSTN is a cellular network that can be viewed as an interface between mobile units and a
telecommunication infrastructure (Fig. 1.17). Therefore, the PSTN network is nothing but the land-
based section of the network. It is necessary that the BSs are to be connected to a switching network
and that network is to be connected to other networks such as the PSTN, so that calls can be made to
and from mobile subscribers.
 Figure 1.17 PSTN to mobile station connectivity

1.5.2 Common air interface

Communication between the BS and the mobiles is defined by a standard common air interface (CAI)
that specifies four different channels. The channels used for voice transmission from the BS to mobiles
are called forward voice channels (FVC) and the channels used for voice transmission from mobiles to
the BS are called reverse voice channels (RVC). The two channels responsible for initiating mobile calls
are the forward control channels (FOCC) and reverse control channels (RECC). Control channels are
often called setup channels because they are only involved in setting up a call and moving it to an
unused voice channel. Control channels transmit and receive data messages that carry call initiation
and service requests, and are monitored by mobiles when they do not have a call in progress. FOCCs
also serve as beacons which continually broadcast all of the traffic requests for all mobiles in the
system.

1.6 Call transfer operation from one mobile phone to another

The operation of one phone placing a call to another mobile phone and the operation that takes place
when a MS receives an incoming call is described in this section. Before describing the call transfer
operation to/from one mobile to another mobile, the knowledge of the concept of duplex and
control/voice channels must first be understood.
 Figure 1.18(a) FDD

Figure 1.18(b) TDD

1.6.1 The duplex concept

One of the key elements of any radio communications system is the way in which radio
communications are maintained in both directions. The various types of mobile radio transmission
systems in use are simplex, half duplex, and full duplex.
Simplex: Communication is possible only in one direction (e.g. paging systems).
Half duplex: Two-way communication, but uses the same radio channel for both transmission and
reception. User can only transmit or receive information (e.g. walkie-talkie).
Full duplex: Simultaneous two-way radio transmission and reception between the subscriber and the
BS (e.g. FDD and time-division duplexing [TDD]).
 Similar to landline phones, cellular phones must also be full duplex. For cellular systems, it is
necessary to talk or to send data in both directions simultaneously and this places a number of
constraints on the schemes that may be used to control the transmission flow. Using the FDD and TDD
duplexing schemes, simultaneous two-way communication can be established.
FDD uses two separate frequencies for the uplink (from the mobile to the BS) and the downlink (from
the BS to the mobile).
TDD uses a single frequency to transmit signals in both the downlink and uplink directions.
In FDD information from the mobile handset to the BS is carried on one frequency and information
from the BS to the handset is carried on another (Fig. 1.18(a)). In TDD information from the handset to
the BS is transmitted at one time on one frequency and information from the BS to the handset is
transmitted at another time on the same frequency (Fig. 1.18(b)).

Example problem 1.1

The bandwidth allocated to a particular FDD cellular system is 33 MHz. It uses two 25 kHz simplex
channels to provide full duplex voice and control channels, compute the number of channels available
per cell if a system uses (a) 4 cell reuse and (b) 7 cell reuse (refer Section 1.6.1).

Solution
Total bandwidth allocated to cellular system = 33 MHz
Channel bandwidth required for duplex channel (uplink and downlink) =25 kHz × 2 = 50 kHz
Total number of available channels = 33,000,000/50,000 = 660

a. For cluster size N = 4, number of channels available per cell = 660/4 = 165
b. For cluster size N = 7, number of channels available per cell = 660/7 = 95

1.6.2 Control and voice channels

There are two general types of channels in a cellular system: control channels and traffic (voice)
channels.
Control channels: The control channels are referred to as setup channels and paging channels.
Control channels are also sometimes called paging channels in the case of downlink, and access
channels in the case of uplink. The paging channels are used to set up calls that originate from the BS,
while the access channel is used to set up calls that originate from the mobile. Paging channel is
designated as FOCC and the access channel as the RECC (Fig. 1.18(a)).
The FOCC and RECC establish the MS on the network (registration), to set up calls from the MS and
to set up calls coming in for a particular MS (called a mobile page). After a call is established using the
RECC and FOCC, the process switches to the voice channels.
Traffic channels: Traffic channels are active during voice conversations, but they also do contain the
digital information needed to keep a call up. A MS thus tunes to and receives either a control channel
or a traffic channel at any given moment.

1.6.3 Operation of one mobile phone placing a call to another mobile phone
The operation of one mobile phone placing a call to another involves two steps. One is the initialization
of the mobile system and the second is the establishment of the call.
Initialization of mobile system: Five basic steps are involved in the mobile initialization procedure.
They are power on, scanning, tuning, registering, and listening. When a mobile phone is turned on, it
scans and selects the strongest and best bit-error rate (BER) (control channel) signal sent by adjacent
BSs. Then a handshaking process takes place between the mobile phone and the MSC to identify the
user and register its location. This procedure is repeated periodically as long as the mobile unit is on to
monitor the location of the mobile.
Establishment of a call: If a user dials a number and presses START or TALK button, the mobile phone
initializes a call by sending a call initiation request to its nearest BS. This request is sent on a special
channel (RECC). The BS sends the request, which contains the telephone number of the called party,
to the MSC (http://onlinelibrary.wiley.com/doi/10.1002/9780470050118.ecse055/full). The MSC
validates the request and uses the number to make a connection to the called party via the PSTN.
Then PSTN first connects itself to the MSC of the called party, and then the MSC instructs the BS and
MS that placed the call to switch to voice channels. The MS that placed the call is then connected to
the called station, using unused forward and backward voice channels.

1.6.4 Operation that takes place when a mobile station receives an incoming call
The following operation takes place when a MS receives an incoming call is described in this section.
MSs continually scan the FOCC for paging signals from BSs. Paging signal informs the mobile phone
that it has a call coming in and should prepare the set up to receive it.
 When a MSC receives a request for a connection to a MS in its area, it sends a broadcast message to
all BSs under its control. The message contains the number of the MS that is being called. The BSs
then broadcasts the message on all FOCCs. The correct MS acknowledges the page, by identifying
itself over the RECC. The MSC receives the acknowledgment via the BS and instructs the BS and MS to
switch to an unused voice channel. A data message is then transmitted over the FVC which instructs
the mobile phone to ring.

Figure 1.19 Multiple access control

1.7 Multiple access schemes

The radio spectrum is a scarce resource. Without access to radio spectrum, there can be no mobile
communication. Multiple access refers to techniques that enable multiple users to share a finite
portion of given frequency spectrum efficiently. The sharing of frequency spectrum is required to
achieve high capacity by simultaneously allocating the bandwidth.
The multiple users will be assigned channels within that portion according to various techniques,
known as multiple access schemes. A channel can be thought of as merely a portion of the limited
radio resource (frequency slot or time slot or code), which is temporarily allocated for a specific
purpose, such as someone’s phone call. Multiple access control is shown in Figure 1.19.
 The five most common schemes are given below and are discussed in more detail in Chapter 16.

 Frequency division multiple access (FDMA), where the total spectrum assignment is divided into a
number of discrete frequencies.
 Time division multiple access (TDMA), where the total spectrum is divided in time between a number
of users.
 Code division multiple access (CDMA), where neither the frequencies nor the time are divided but
users are distinguished through the use of a special code.
 Orthogonal frequency division multiple access (OFDMA), where the spread spectrum technique
spreads the data over a number of carriers that are spaced apart at precise frequencies.
 Space division multiple access (SDMA), where different users will be served on same frequency
channel at the same time.

1.8 Analogue and digital cellular mobile systems

The 1G cellular mobile systems were introduced in the beginning of the 1980s. Examples of these
early analogue systems are AMPS and NMT. It used FDMA technology to achieve radio
communications. In the 1990s the analogue systems were replaced by digital technology,
which provided higher capacity, better quality, and new services. The most widely used 2G mobile
system is GSM. The deployment of the 3G mobile networks is now ongoing. The 3G offers new data
and multimedia services. The major 3G technology is called WCDMA. In this section, the analogue and
digital cellular systems are briefly introduced.

1.8.1 Analogue cellular mobile radio systems (AMPS)

During the early 1980s, there were analogue technologies and the 1G cellular system was designed for
analogue voice communications only. The following are examples of 1G cellular analogue radio
system:

 Advanced mobile phone system (AMPS) in the United States

 Total access communication systems (TACS) in the United Kingdom
 Nippon advanced mobile telephone system (NAMTS) in Japan
 AMPS are one of the leading analogue cellular phone systems in the United States. AMPS use the 800
MHz to 900 MHz band. It uses two separate analogue channels, one for forward (BS to MS) and the
other for reverse (MS to BS) communication. The 824–849MHz band is used for reverse communication
and the 869–894MHz band is for forward communication (Fig. 1.20). This spectrum is divided into 832
frequency channels consisting of 416 downlink and 416 uplink channels. The division of the spectrum
into sub-band channels is achieved by using FDMA.

Figure 1.20 Forward and reverse communication channels in AMPS

Salient features of analogue cellular mobile systems (AMPS)

 Frequency-division multiple access (FDMA) is the analogue cellular modulation standard.

 Cellular network uses a duplex mode of communication and two channels are required for each call:
one channel for transmitting and one channel for receiving.
 User’s mobile phone transmits on 824–849MHz band known as uplink or reverse channel.
 BS transmits on 869–894MHz band known as downlink or forward channel.
 In AMPS, the channel spacing is 30 kHz. Each uplink and downlink channel occupies 30 kHz of
bandwidth. Every AMPS cellular call actually occupies a total of 60 kHz.

Limitations of AMPS include

 Low calling capacity

 Limited spectrum
 Poor data communication
 Minimal privacy
 Inadequate protection
 Example problem 1.2
The American analogue technology standard, known as Advanced Mobile Phone Service (AMPS),
employs frequency modulation and occupies a 30 kHz frequency slot for each voice channel. Suppose
that a total of 30 MHz bandwidth is allocated to a particular cellular radio communication system with
cluster size 7. How many channels per cell does the system provide? (refer Section 1.8.1).

Solution
Allocation of 15 MHz each for forward and reverse links provides a little more than 1,000 channels in
each direction for the total system, and correspondingly a little less than 150 per cell.

IS-54/IS-136
This standard is based on the AMPS system and is commercially known as digital-AMPS (D-AMPS). It
introduces TDM in the AMPS channels. It uses digital modulation (π/4 QPSK with speech coding in
TDMA). It was standardized from the Telecommunications Industry Association (TIA) in 1990 and it
uses the same frequencies with AMPS as are used, but in every time slot up to three full rate or six half
rate users are multiplexed. The forward channel (downlink range) and reverse channel (uplink range)
frequency bands are 869–894 MHz and 824–849 MHz, respectively. The final version of IS-54 Rev-C
was called IS-136 and is still in use today.

1.8.2 Digital cellular mobile radio systems

While analogue cellular phone system (1G) was designed for analogue voice communication, the
digital cellular mobile radio system (2G) was mainly designed for digitized voice. There are a number
of different digital cellular technologies including the following:

 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)
 Digital enhanced cordless telecommunications (DECT)
 Digital AMPS (IS-136/TDMA)
 Integrated digital enhanced network (IDEN)

Two main groups have evolved in the digital cellular mobile radio system development. One group is
from Europe and another is from America. The digital cellular mobile radio systems developed by the
two groups are

 Global system for mobile communications (GSM) in Europe

 Code-division multiple access (CDMA)/Interim Standard (IS-95) in the United States

The above cellular systems (GSM and CDMA) are not compatible with each other.

1.8.2.1 Global system for mobile communications

It was developed in Europe in the year 1990. It provides a common 2G technology all over Europe.
GSM uses TDMA and FDMA techniques as access mechanism. In GSM, the bandwidth is divided into
time slots for better utilization of bandwidth. GSM operates in the 900 MHz band (890–915 MHz for
forward link and 935–960 MHz for reverse link channels) in Europe and Asia and in the 1,900 MHz band
in the United States. GSM uses two bands for duplex communication. Each band is 25 MHz in width,
shifted towards 900 MHz. Each band is divided into 125 channels of 200 kHz separated by guard bands
and each channel is subdivided into eight time slots or sub channels. One time slot must be allocated
for control channel purposes; therefore, up toseven subscribers can use a channel simultaneously.
GSM users are almost eight times in number than CDMA users worldwide and in India, Bharti Telecom
(Airtel) provides GSM standard. GSM mobile phone consists of two main components: handset and
subscriber identity module (SIM).
SIM: The handset in a GSM system is different from analogue phones in that the identification
information of the subscriber is programmed into a SIM module and not in the handset. The main
functions of the handsets are receive/transmit and encoding and decoding of the voice transmission.
The SIM is a microcontroller embedded into a small piece of plastic. The SIM card provides
authentication, information storage, subscriber account information, and data encryption. SIM chips
and handsets are swappable.
 GSM: This is a digital-wireless standard which uses TDMA technology as its air interface. GSM has
been deployed in the 900, 1,800, and 1,900 MHz bands. Each 25 MHz band provides a total of 125
forward channels and 125 reverse channels. Each channel has a bandwidth of 200 kHz (25 MHz
bandwidth/125 channels). Where each channel is subdivided into eight time slots, or sub channels and
the sub channel spacing is 25 kHz (200 kHz channel space divided by eight time slots). Each channel is
shared by eight users giving a total of 125 × 8 = 1,000 users per cell.

Example problem 1.3

The global system for mobile (GSM) communications utilizes the frequency band 935–960 MHz for the
forward link and frequency range 890–915 MHz for the reverse link. Each 25-MHz band is broken into
radio channels of 200 kHz. Each radio channel consists of eight time slots. If no guard band is
assumed,

a. Find the number of simultaneous users that can be accommodated in GSM.

b. How many users can be accommodated if a guard band of 100 kHz is provided at the upper and the
lower end of the GSM spectrum? (Refer Section 1.8.2.)

Solution

a. The number of simultaneous users that can be accommodated in GSM in the first case is equal to
b. In the second case the number of simultaneous users = 992.

Example problem 1.4

The 2G cellular system GSM 900 operates its 125 forward channels in the uplink frequency band
890.2–915 MHz and 125 reverse channels in the frequency band 935.2–960 MHz. Each channel has a
bandwidth of 200 kHz.

a. What is the bandwidth in the forward channels (uplink frequency band) and reverse channels
(downlink frequency band)?
b. If each channel is subdivided into 16 time slots, what is the sub channel spacing?
c. If each channel is shared by 16 users then compute the total number of users per cell? (Refer
Section 1.8.2.)
 Solution

a. Number of forward channels = Number of reverse channels = 125

Total number of channels = 125 + 125 = 250
Bandwidth of each channel allocated = 200 kHz
Bandwidth of uplink = bandwidth of downlink =
Number of channels × bandwidth of each channel = 125 × 200 kHz = 25 MHz
b. Number of time slots in each channel = 16
Sub channel spacing = channel space/time slots in each channel
= 200 kHz/16 = 12.5 kHz
c. Number of users shared in each channel = 16

Total number of users per cell = 125 channels 16 = 2000 users

1.8.2.2 CDMA or (IS-95)

The use of CDMA technology started in the United States in the year 1990. IS-95 is a standard for
CDMAone digital cellular where as CDMA2000 is a 3G specification (the North American version of
wideband CDMA), and is backward compatible with IS-95 systems. In India, Reliance Communications
(RCOM), BSNL, and Vodafone (formerly Hutch) serve more than 39.4 million subscribers using CDMA
technology.
CDMA is a unique access technology that separates subscriber calls from one another by a
pseudorandom noise (PRN) code instead of time or frequency. As a result, all available CDMA
frequencies can be used in every cell, thereby increasing the total number of available voice channels
and the overall system capacity.
CDMA is a wideband, spread-spectrum technology in which we allocate a unique code for every user
separately and allocate bandwidth to the user. Today, each CDMA carrier can support around 22 voice
calls. 3G CDMA2000 systems may deploy more carriers per BS, possibly six to eight carriers to
accommodate the additional bandwidth requirements. CDMA networks have pilot channels, which
carry no data but are used by the mobile phone to acquire the system and assist in the process of
SHOs and synchronization. Table 1.2 summarizes the differences among the basic analogue (AMPS)
and digital (GSM and CDMA) cellular systems that have been used. It gives an overview of the different
mobile phone systems or cellular technologies that are in use today and those that have been used
over the years. Although not every cellular technology is included, those that have been more widely
used are included.

Channel Spacing in CDMA systems

Channel spacing refers to the actual bandwidth space that is allocated for every wireless channel out
of the total amount of spectrum allocated to a wireless carrier. In AMPS, the channel spacing is 30 kHz.
Each uplink and downlink channel occupies 30 kHz of bandwidth. Every AMPS cellular call actually
occupies a total of 60 kHz. GSM systems allot their radio spectrum in 200 kHz carriers, where each
carrier allocates 25 kHz to uplink or downlink. CDMA, by definition, is unique when it comes to channel
spacing. In the most technical, literal sense, channel spacing in a CDMA system is 1.25 MHz because
all calls that are carried on a 1.25 MHz CDMA carrier are spread out over the entire swath of that
carrier. That is why CDMA is known as a spread spectrum technology.

Table 1.2 Comparison of AMPS, GSM, and CDMA standards

Details of Forward and Reverse CDMA Channels

The CDMA standard details are illustrated in Table 1.2. It uses two frequency bands (800 and 1900
MHz bands) for duplex communication. These bands are designated as ISM 800 MHz band or the ISM
1900 MHz band. Each band (25 MHz) is divided into 20 channels of 1.228 MHz each separated by
guard bands. Each service provider is allotted 10 channels. The forward and reverse CDMA channels
used in the ISM 800 MHz frequency band are 824–849/1850–1910 MHz for uplink/downlink
respectively. Similarly, the forward and reverse CDMA channels used in the ISM 1900MHz frequency
band are 869–894/1930–1990 for uplink/downlink, respectively.
A more detailed description about the analogue and digital cellular systems is given in Chapter 21.
All these methods rely on a distributed network of cell sites using frequency reuse concept.

1.9 Existing mobile communication technologies and current status

The following are some examples of mobile communication systems currently in use in addition to the
cellular radio networks.

1.9.1 Paging
Radio paging is a low-cost service used for sending information to a person on move. Paging system
consists of a BS that broadcasts the paging messages in the form of numeric digits (e.g. a telephone
number), alphanumeric text messages or even voice messages to a service area. From the radio
paging BS the transmission of data is one-way. The BS is interfaced to a paging controller (Fig. 1.21).
The message is composed by an operator who receives the message from a user through a telephone.
The message is broadcast through the BS using transmission medium. If the service area is very large,
this system requires high-powered transmitters and low data rates for maximum coverage of each
transmitter’s designated area.
 Figure 1.21 Paging system

The paging standard started in 1G and continued up to 2G systems.

Various pagers in use are numeric pager which displays only numeric data (such as a telephone
number), alphanumeric pager which displays alphanumeric text, and voice pager that supports voice
paging.

1.9.2 Communication satellites

A communication satellite provides long distance wireless communication and is similar to LOS
microwave transmission in which one of the stations is a satellite orbiting the earth. The satellite acts
like a tall antenna and repeater system (Fig. 1.22). Satellite system consists of number of
transponders which allow radio, television, and telephone transmissions to be sent live to anywhere in
the world. Satellite systems can make services available to airborne and sea-based users where
cellular mobile communication provides service to world’s land mass only.
Satellite systems are also playing a crucial role in mobile communications by providing coverage in
zones where land-based infrastructures are unable or ineffective to supply mobile services. Mobile
satellite communications began in 1976 with the launch by COMSAT of the MARISAT satellites to
provide communications to ships at sea. Mobile satellite communication systems are used for
transmitting point-to-point voice and data communications using a constellation of satellites. These
systems include a number of user terminals, several terrestrial ground stations or gateways and a
number of satellites for bi-directionally coupling the user terminals to terrestrial telecommunication
networks and the Internet via the gateways.
Mobile satellite communication system, for example, Iridium low earth orbit (LEO) satellite system
with 66 satellites, Globalstar satellites, and Ellipso mobile satellite system.
The main drawback of satellite communication systems is that they have quite a large propagation
delay due to the distances travelled by radio waves.
 Figure 1.22 Point to point communication through satellite

1.9.3 Wireless local loop (WLL)

Wireless local loop (WLL) is a cellular-like phone without mobility. These are designed for fixed
communications in situations where it is easier, cheaper, or more advantageous than wire
line connections and are often based on cellular or cordless technologies. WLL employs a cellular like
technology where the subscriber unit is fixed, like a wire line telephone, replacing the “local loop”
between the exchange and the subscriber’s home with a wireless link. They use the same basic
architecture and principles of radio transmission. There are a number of problems with WLL when
compared to the landline services. They are as follows:

 Voice quality is typically inferior.

 Data rates provided are typically lower.
 Call costs are typically more expensive.

1.9.4 Personal handy phone

Personal handy-phone system (PHS) has been in existence in Japan for years and operates in the
1880–1920 MHz spectrum. PHS is similar to cellular networks. However, PHS phones can also
communicate directly with one another when in range. This is an advantage over cellular phones,
which can only communicate with one another via BS transceivers. This system is very popular in
heavily populated metropolitan areas.
A PHS device functions as a cordless phone in the home and as a mobile phone elsewhere.
1.9.5 Mobile radio
Mobile radio is a half-duplex analogue communication system that uses single frequencies for sending
and receiving signals. In mobile radio system, a button must be pressed to switch modes ( Fig. 1.23).
They are used for emergency services such as police control rooms and the security industry.

Figure 1.23 Mobile radio

1.9.6 Cordless phones

These are designed for indoor and office applications. The initial application of cordless phones ( Fig.
1.24(a)) was as an extension to the fixed line in a home. The cordless BS is plugged into the home
phone socket and provides a radio link to the handset and does not transfer well to outdoor, cellular-
type systems. They are typically much simpler than cellular phones using lower power transmission
and higher bit-rate speech coders.

Figure 1.24(a) Cordless phone

 1.9.7 DECT
Digital enhanced cordless telecommunications (DECT) (Fig. 1.24(b)) is a multicarrier/TDMA/TDD radio
access system standard for cordless communications in residential, corporate, and public
environments. DECT system consists of three components: (i) phone network, (ii) a BS, which is
connected to the phone line socket and (iii) multiple number of mobile handsets. These mobile
handsets are used as normal “cordless” phones. DECT system allows several cordless telephones to
communicate with each other (internal) and to external network. The main advantage is that the
additional handsets do not require additional telephone sockets or additional transceivers.
DECT frequency band: DECT operates in the 1880–1900 MHz band and defines ten channels from
1881.792 MHz to 1897.344 MHz with a band gap of 1728 kHz. Each BS frame provides 12 duplex
speech channels with each time slot occupying any of channels.

Figure 1.24(b) A base station and multiple handsets in

The following are the advantages of DECT:

i. Security: All communications between base and handset are encrypted with a set of keys which are
renewed for each call.
ii. Long range without interference: DECT range is at least 300 m in free space (typical 450 m), and
reaches easily 50 m with an in-door base. It does not interfere with the 2.4 GHz WiFi band.
iii. Low power consumption: The DECT technology is simple and efficient. BSs use typically less than 3W
of operating power, and handsets operate with two AAA rechargeable batteries.
iv. High efficiency of spectrum use: It can manage without any frequency planning a full array of bases
every 10 m. No risk of interference, even if all neighbours are using DECT.
v. GSM/DECT internetworking: Part of the DECT standard describes how it can interact with the GSM
standard so that users can be free to move with a telephone from the outdoors (and GSM signals)
into an indoor environment (and a DECT system). It is expected that many GSM service providers
may want to extend their service to support DECT signals inside buildings. A dual-mode phone would
automatically search first for a DECT connection, then for a GSM connection if DECT is not available.
vi. Home cordless phones: A home owner could install a single-cell antenna within the home and use it
for a number of cordless phones throughout the home and garden.

1.9.8 Bluetooth
Bluetooth wireless technology is an open specification for a low-cost, low-power, short-range radio
technology for ad hoc wireless communication of voice and data anywhere in the world. It was
developed as a new cable replacement technology, which provides a short-range (<10 m), low bit rate
(<1 Mbps) access in the 2.4 GHz spectrum. It is also known as wireless personal area network (WPAN)
for short-range and low mobility applications around a room in the office or at home. A Bluetooth
WPAN involves up to eight devices, located within a 10 m radius personal operating space, that unite
to exchange information or share services (Fig. 1.24(c)). Because connectivity can be done
spontaneously according to immediate need, Bluetooth is also known as ad hoc networking. Because a
WPAN involves directly networking between different points, without the use of network infrastructure,
it is also referred to as a “point-to-point network”.
Laptop to mobile phone connectivity: A mobile phone can communicate with a computer through a
phone’s vendor-specific cable, infrared, or Bluetooth. The latter two depend on both devices’ hardware
capabilities. Figure 1.24(d) presents a typical scheme for a laptop connecting to a server through the
mobile phone and the cellular network. For laptop to mobile phone connectivity, the Bluetooth solution
was selected for the following reasons: (i) compared to infrared, it does not have the restriction of
having the phone being in the LOS of the laptop’s sensor, (ii) compared to cable, it does not require
the phone to be physically attached to the laptop and restricted to the cable’s length and (iii) with
Bluetooth, the phone only needs to be in a range of a few metres (<10) from the laptop.
Bluetooth uses a technique called spread-spectrum frequency hopping.
The important specifications of Bluetooth technology are illustrated in Table 1.3.
Advantages of Bluetooth technology are as follows:
 Wireless (no Cables)
 No setup needed
 Devices can be movable
 Industry wide support
 Easier synchronization due to omni-directional and no LOS requirement

Disadvantages of Bluetooth technology are as follows:

 Short range wireless radio technology operates in the range of 10 m

 Small throughput rates - data rate 1.0 Mbps
 mostly for personal use (PANs)
 fairly expensive

A more detailed description about Bluetooth technology is given in Chapter 27.

Figure 1.24(c) Bluetooth communication between portable devices

 Figure 1.24(d) Typical scheme for a laptop connecting to a server through the mobile phone and
the cellular network.

Table 1.3 Bluetooth technology specifications

Connection type Spread spectrum (Frequency hopping)

Multiple access control scheme FH-CDMA
Spectrum 2.4 GHz ISM
Modulation Gaussian frequency shift keying
Transmission power 1 mw-100 mw
Aggregate data rate 1 Mbps
Range 30 ft
Supported stations 8 devices
Voice channels 3
Data security- Authentication key 128 bit key
Data security-encryption key 8–128 bits (configurable)
1.9.9 Current status of cellular radio
Tremendous changes are occurring in the area of wireless communications. With the rising demand for
mobile communications, 3G systems have emerged, providing higher date rate to facilitate new
multimedia applications such as video telephony and wireless Internet access. There are three primary
standards that comprise 3G technology: W-CDMA, CDMA2000, and TD-CDMA. The mobile phone of
yesterday is rapidly turning into a sophisticated mobile device capable of more applications than PCs.
For example, the data rates provided by 3G networks enable a user to enjoy wireless access to the
Internet at speeds up to 1.8 Mbps. Further enhancements in high speed downlink packet access
(HSDPA) modulation schemes will soon increase this speed to greater than 10 Mbps.
Presently, we see 3G cell phones hitting the markets. In China, the 3G service is already in existence.
The 3G has also reached India recently. The existence of several diverse 3G standards limits
seamless global roaming between different cellular networks for a mobile user with a single handset.
In addition, there is a fundamental difference between wireless cellular networks (1G, 2G, or 3G) and
wireless data networks such as WLANs and PANs. The difference is that wireless cellular systems
are circuit-switched while wireless data networks are packet-switched. Convergence issues for these
differences between the wireless cellular systems and the wireless data networks will be addressed in
the design of 4G cellular networks. It is projected that 4G networks will provide users with seamless
wireless access to voice, data, and video services irrespective of which wireless network they belong
to. A 4G system will be able to provide a comprehensive IP solution where voice, data, and streamed
multimedia can be given to users on an “anytime, anywhere” basis, and at higher data rates than
previous generations. 4G will be capable of providing data rates between 100 Mbps and 1 Gbps both
indoors and outdoors.
As the 2G was a total replacement of the 1G networks and handsets and the 3G was a total
replacement of 2G networks and handsets, in the same way the 4G is also a complete replacement of
the current 3G networks and handsets. The ITU regulatory and standardization bodies are working for
commercial deployment of 4G networks roughly in the 2012–2015 time scale.