Telecommunication network lecture notes.pdf

Samara University Telecommunication Network(Eceg4282) Lecture Notes
Department Of Electrical& Computer Engineering Prepared By:Mohammedhayat A. @ 2023
SAMARA UNIVERSITY
COLLEGE OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
COURSE TITLE: TELECOMMUNICATION NETWORK
COURSE CODE: ECEG4282
ACADEMIC YEAR: IV (COMMUNICATION ENGINEERING)
SEMESTER: II
INSTRUCTOR NAME: MOHAMMEDHAYAT ALI
COURSE MATERIAL

CHAPTER 1: INTRODUCTION TO TELECOMMUNICATION SYSTEM
What Is Telecommunications?
• A technology concerned with communicating from a distance
• we can categorize it in various ways.
Significance of Telecommunications
• Many different telecommunications networks have been interconnected into a
continuously changing and extremely complicated global system
• Telecommunications networks make up the most complicated equipment in the world.

• Let us think only of the telephone network, which includes more than 2 billion fixed and
cellular telephones with universal access.
• When any of these telephones requests a call, the telephone network is able to establish a
connection to any other telephone in the world. In addition, many other networks are
interconnected with the telephone network.
• This gives us a view of the complexity of the global telecommunications network—no other
system in the world exceeds the complexity of telecommunications networks
• Other than this….
❖ Telecommunications services have an essential impact on the development of a
community
• In the developing countries: -Tele density, is fewer than 10 telephones per 1,000
inhabitants
in developed countries: - Tele density 500 to 600 fixed telephones per 1,000 inhabitants
❖ The operations of a modern community are highly dependent on telecommunications
• We can hardly imagine our working environment without telecommunications services.
❖ Telecommunications plays an essential role on many areas of everyday living.
❑ Here are some examples of services that depend on telecommunications:
• Banking, automatic teller machines, telebanking;
➢ Aviation, booking of tickets;
➢ Sales, wholesale and order handling;
➢ Credit card payments at gasoline stations;

➢ Booking of hotel rooms by travel agencies;
➢ Material purchasing by industry;
➢ Government operations, such as taxation.
Historical Perspective
Standardization
❖ Standards enable competition
❖ Standards lead to economies of scale in manufacturing and engineering
❖ Political interests often lead to different standards in Europe, Japan, and the United States.
• International standards are threats to the local industries of large countries but
opportunities to the industries of small countries
• Standards make the interconnection of systems from different vendors possible
• Standards make users and network operators vendor independent and improve availability
of the systems

• Standards make international services available
• Many organizations are involved in standardization work. We look at them from two points
of view: (1) the players in the telecommunications business involved in standardization and
(2) the authorities that approve official standards.
Interested Parties
❑ Network operators support standardization for these reasons:
✓ To improve the compatibility of telecommunications systems;
✓ To be able to provide wide-area or even international services;
✓ To be able to purchase equipment from multiple vendors.
❑ Equipment manufacturers participate in standardization for these reasons:
✓ To get information about future standards for their development activities as early as
possible;
✓ To support standards that are based on their own technologies;
✓ To prevent standardization if it opens their own markets.
❑ Service users participate in standardization for these reasons:
✓ To support the development of standardized international services;
✓ To have access to alternative system vendors (multivendor networks);
✓ To improve the compatibility of their future network systems.

CHAPTER 3: BASIC TELECOMMUNICATIONS NETWORK
The basic purpose of a telecommunications network is to transmit user information in any
form to another user of the network.
• These users of public networks, for example, a telephone network, are called subscribers.
• User information may take many forms, such
voice or data
subscribers may use different access network technologies to access the network, for
example, fixed or cellular telephones.
Technologies
• The three technologies needed for communication through the network are (1)
transmission, (2), switching, and (3) signaling
• Each of these technologies requires specialists for their engineering, operation, and
maintenance.
• Transmission: Transmission is the process of transporting information between end points
of a system or a network
Transmission
• Transmission systems use four basic media for information transfer from one point to
another
1. Copper cables, such as those used in LANs and telephone subscriber lines;
2. Optical fiber cables, such as high-data-rate transmission in telecommunications networks;
3. Radio waves, such as cellular telephones and satellite transmission;
Free-space optics, such as infrared remote controllers

Switching
Signaling
• Signaling is the mechanism that allows network entities (customer premises or
network switches) to establish, maintain, and terminate sessions in a network
• Some examples of signaling examples on subscriber lines are
▪ Off-hook condition: The exchange notices that the subscriber has raised the
telephone hook (dc loop is connected) and gives a dial tone to the subscriber.
▪ Dial: The subscriber dials digits and they are received by the exchange.
▪ On-hook condition: The exchange notices that the subscriber has finished the call
(subscriber loop is disconnected), clears the connection,
and stops billing.
Telephone Numbering

Telephone Exchange
• The main task of the telephone or ISDN exchange is to build up a physical
connection between subscriber A, the one who initiates the call, and subscriber B
according to signaling information dialed by subscriber A.
• The speech channel is connected from the time when the circuit was established to
the time when the call is cleared. This principle is called the circuit switching concept
and is different from packet switching, which has been used in data networks.
• This kind of exchange is called a stored program control (SPC) exchange
• The control unit of the local exchange receives the subscriber signaling, such as
dialed digits, from the subscriber line and makes consequent actions according to its

program. Usually the call is routed via many exchanges and the signaling information
needs to be transmitted from one exchange to another. This can be done via channel
associated signaling (CAS) or common channel signaling (CCS) methods
CASbetweenexchanges
CCSbetweenexchanges
LocalExchange:-Local or subscriber loops connect subscribers to local exchanges, which are the
lowest-level exchanges in the switching hierarchy
• The main tasks of the digital local exchange are
✓ Detect off-hook condition, analyze the dialed number, and determine
if a route is available.
✓ Connect the subscriber to a trunk exchange for longer distance calls.
✓ Connect the subscriber to another in the same local area
✓ Determine if the called subscriber is free and connect ringing signal
to him/her.
✓ Provide metering and collect charging data for its own subscribers.

✓ Convert 2W local access to 4W circuit of the network
Convert analog speech into a digital signal (PCM).
TRUNKNETWORK
InternationalNetwork
Transmission

• Transmission is the process of transporting information between end points of a
system or network.
• In radio transmission we have to transfer the spectrum of the message into the radio-
frequency band for transmission.
• For this we use continuous or carrier wave (CW) modulation.
The primary purpose of CW modulation in a communication system is to generate a modulated
signal suited to the characteristics of a transmission channel

CHAPTER 3: -MULTIPLEXING
 Multiplexing describes how several users can share amedium with
minimum or no interference
 Example: lanes in a highway
◼ Cars in different lanes (space division multiplexing)
◼ Cars in a line but at different times (time division
multiplexing)
 Multiplexing in 4 dimensions
◼ space (s)
◼ time (t)
◼ frequency (f)
◼ code (c)
 Important: guard spaces needed!
Space Division Multiplexing (SDM)
 Different channels for communications are allocated to different
spaces
 With this space only three channels can be separated
Example 1: each subscriber of an analogue telephone system is given a different wire
Example 2: FM stations can transmit only in a certain region
 SDM is the simplest and
Inefficient

 Usually associated with other methods.
Frequency Multiplex
 Separation of the whole spectrum into smaller frequency bands  A
channel gets a certain band of the spectrum for the whole time
Advantages:
 no dynamic coordination necessary
 works also for analog signals
Disadvantages:
 waste of bandwidth if the traffic is distributed unevenly
 inflexible
 guard spaces
Time Multiplex
➢ A channel gets the whole spectrum for a certain amount of time
Advantages:
➢ only one carrier in the medium at any time
throughput high even for many users
Disadvantages:
➢ Precise synchronization necessary (clocks)
➢ Guard space
Time and Frequency Multiplex
➢ Combination of both methods
➢ A channel gets a certain frequency band for a certain amount of time
Advantages:
➢ better protection against tapping

➢ protection against frequency selective interference
➢ higher data rates compared to code multiplex
➢ but: precise coordination required
Code Multiplex
➢ Each channel has a unique code: a vector of 1 and -1,
➢ These vectors are orthogonal and have a large autocorrelation (norm of the vector)
➢ All channels use the same spectrum at the same time
Advantages:
➢ bandwidth efficient
➢ no coordination and synchronization necessary
➢ good protection against interference and tapping
Disadvantages:
➢ lower user data rates
➢ more complex signal regeneration
Medium Access Control
➢ Medium access control comprises all mechanisms that regulate user access to a medium
using SDM, TDM, FDM or CDM
➢ MAC is a sort of traffic regulation (as traffic lights in road traffic)
➢ MAC belongs to layer 2 (OSI Model): data link control layer
➢ The most important methods are TDM
➢ TDM is convenient because the systems stay tuned on a given frequency and the us the
frequency only for a certain amount of time (GSM)
Access methods SDMA/FDMA/TDMA
SDMA (Space Division Multiple Access)
➢ segment space into sectors, use directed antennas
➢ cell structure
FDMA (Frequency Division Multiple Access)
➢ assign a certain frequency to a transmission channel between a sender and a receiver
permanent (e.g., radio broadcast), slow hopping (e.g., GSM), fast hopping (FHSS,
Frequency Hopping Spread Spectrum)

TDMA (Time Division Multiple Access)
➢ assign the fixed sending frequency to a transmission channel between a sender and a
receiver for a certain amount of time.
CHAPTER 4: -CELLULAR SYSTEM BASICS
➢ The spatial frequency reuse concept led to the development of the cellular principle, which
allowed a significant improvement in the economic use of frequencies. The essential
characteristics of the cellular network principle are as follows: The area to be covered is
subdivided into cells (radio zones). These cells are often modelled in a simplified way as
hexagons (Figure 4.1) with a base station located at the center of each cell. Assume that the
operator has a license on a set of channels, called, for example, set S.
➢ To each cell i a subset of the frequencies Si is assigned from the total set (bundle), which is
assigned to the respective mobile radio network. In the GSM system, the set of frequencies
assigned to a cell is called the Cell Allocation (CA). Under normal circumstances the
number of channels in a subset Si is driven by traffic capacity requirements.
➢ Neighboring cells do not normally use the same frequencies since this would lead to severe
co-channel interference from the adjacent cells.
Figure 4.1 Model of a cellular network with frequency reuse. Shadowed hexagons
represent cells with the same set of allocated frequencies.

❖ Only at distance D (the frequency reuse distance) can a frequency from the set Si be reused
(Figure 4.1); that is, cells with distance D to cell i can be assigned one or all of the
frequencies from the set belonging to cell i. When designing a mobile radio network, D
must be chosen to be sufficiently large, such that the co-channel interference remains small
enough not to affect speech quality.
❖ When a mobile station moves from one cell to another during an ongoing conversation, an
automatic channel/frequency change may occur (handover), which maintains an active
speech connection over cell boundaries. The spatial repetition of frequencies is done in a
regular systematic way; that is, each cell with the cell allocation sees its neighbors with the
same frequencies again at a distance D (Figures 4.1 and 4.2). Therefore, exactly six such
neighbor cells exist. The first ring in the frequency set always contains six co-channel cells
in frequency reuse system independent of the form and size of cells, not just in the hexagon
model.
Carrier-to-Interference Ratio
The signal quality of a connection is measured as a function of received useful signal power
and interference power received from co-channel cells and is given by the Carrier-to-
Interference Ratio (CIR or C/I):

The intensity of the interference is essentially a function of co-channel interference depending
on the frequency reuse distance D. From the viewpoint of a mobile station, the co-channel
interference is caused by base stations at a distance D from the current
Figure 4.2 Frequency reuse and cluster formation

base station, see Figure 4.1. A worst-case estimate for the CIR of a mobile station at the border
of the covered area at distance d = R from the base station can be obtained by assuming that all
six neighboring interfering transmitters operate at the same power and are approximately
equally far apart (a distance D that is large compared with the cell radius R).
Formation of Clusters
The regular spatial repetition of frequencies results in a clustering of cells. The cells within a
cluster must each be assigned different sets of channels, while cells belonging to neighboring
clusters can reuse the channels in the same spatial pattern. The size of a cluster is characterized
by the number of cells per cluster k, which determines the frequency reuse distance D when
the cell radius R is given. Figure 4.2 shows some examples of clusters. The numbers designate
the respective frequency sets Si used within the single cells. For each cluster, the following
holds:
❖ A cluster can contain all of the frequencies of the mobile radio system.
❖ Within a cluster, no frequency can be reused. The frequencies of a set Si may be
reused at the earliest in the neighboring cluster.
❖ The larger the cluster is, the larger the frequency reuse distance and the larger the CIR.
However, the larger the values of k, the smaller the number of channels and the
number of supportable active subscribers per cell.
The geometry of hexagons sets the relationship between the cluster size and the reuse
distance as: D = R √3k
The CIR is then given by CIR = 1/ 6 (R/ D)−𝛾 = 1 /6 (3k) −𝛾∕2
assuming the propagation attenuation exponent 𝛾 = 4, CIR = 3∕2k2. For example, if the
system can achieve acceptable quality provided the C/I is at least 18 dB, then the
required cluster size is 6.5. Hence, a cluster size of k = 7 would fit. Not all cluster sizes
are possible due to the restrictions of the hexagonal geometry. The hexagon geometry
results in following equation for cluster size k = i 2 + ij + j 2,
where i, j are integers. Possible values of k include 3, 4, 7, 12, 13, 19 and 27. The
smaller the value of C/I, the smaller the allowed cluster size. Hence the available
channels can be reused on a denser basis, serving more users and producing an
increased capacity. In the example here, had the path loss dependence on radius been

slower (i.e. the propagation exponent was less than 4), the required cluster size would
have been greater than 7, so the path loss
characteristics have a direct impact on the system capacity. Another constraint on the
value of cluster size is that each base-station site often serves a cloverleaf of three cells.
(This can be designated, for example, by specifying 21 cells as a 3 × 7 cluster.)
Commonly used cluster sizes are multiples of three.
Sectorization
One way to reduce cluster size, and hence increase capacity, is to use sectorization. The
group of channels available at each cell is split into three cells (sectors), each of which is
confined in coverage to one-third of the cell area by the use of directional antennas, as
shown in Figure 3.4. Interference now comes from just two rather than six of the first-
tier interfering sites, reducing interference by a factor of three and allowing cluster size
to be increased by a factor of √ =1.72 in theory.
Sectorization has some disadvantages:
➢ Mobiles have to change channels more often, resulting in an increased signaling
load on the system.
➢ The available pool of channels has to be reduced by a factor of 3 (in a three-
sector site) for a mobile at any particular location; this reduces the trunking
efficiency given same cell size. Despite these issues, sectorization is used very
widely in modern cellular systems, particularly in areas requiring high traffic
density. More than three sectors can be used to further improve the
interference reduction. The effective radiated power and, consequently, CIR
can be increased with directional antennas. In a three-sector site the radiation
pattern of sector antenna spans 120∘ in the horizontal plane, as shown in Figure
3.4. In fact, the horizontal lobe of the sector antenna extends over 120∘ creating
overlapping regions between site sectors where a mobile can receive a signal
from both sectors. These regions facilitate an intra-sector handover; that is, they
enable an MS travelling between sectors to be switched from one sector to
another. While sectorization does significantly increase the CIR, it often
decreases the carried traffic in time-division multiple access (TDMA) and
frequency division multiple access (FDMA) systems. For example, an

omnidirectional site is allocated N frequency channels and carries a traffic A
omni Erlang with a defined probability of cell blockage. After sectorization,
each sector may be allocated N∕3 channels and may carry traffic of as Erlang per
sector with the same probability of cell blockage as the omnidirectional cell.
One may observe that Aomni > 3As, where Aomni is the traffic carried by the
omnidirectional site. The reason is that the traffic in Erlangs is non-linearly
related to the number of channels, and as each sector only has N∕3 channels,
then each sector carries less than a third of Aomni. This effect is known as
trunking efficiency. In CDMA systems, the situation is very different. Given the
orthogonality of the cell codes, the same frequency channels can be reused in
each sector without loss in trunking efficiency. In a system with perfect
sectorization the increase in capacity at a cell site will be equal to the number of
sectors; that is, a three-fold increase for three sectors. In practice, interference
caused by overlapping antenna patterns and side and back lobes reduces this
gain to around 80% of the ideal case.
Figure 4.3 Sectorization.

Figure 4.4 Antenna patterns for a cell site with three 120∘ sectors.
Frequency Allocation
The reuse of frequencies in TDMA/FDMA systems may result in increasing co-channel and
adjacent channel interference, especially with tight frequency reuse. If a large reuse distance is
applied, the interference levels will be decreased, but the capacity is too. A short reuse distance is
beneficial for the system capacity, but the interference will increase. The trade-off between capacity
and quality is resolved in frequency planning. A better frequency plan will offer a higher capacity at
maintained quality. One base-station site is often used to serve three cells by means of sector
antennas. For instance, a cluster of 7 × 3 cells implies seven sites each serving three cells (see
Figure 4.5). The respective channel allocation is given in Table 4.1. The shaded area inside the
thick border in the figure comprises a cluster of cells. The cluster contains seven base-station sites,
A–G, with each site having three groups of channels numbered 1–3. If, for example, 10 channels
per cell are needed to handle the traffic, each base-station site must be allocated 30 channels.
Adjacent clusters can use the same radio channels, as the reuse distance between nearby co-
channel cells is such that co-channel interference causes only negligible degradation of the
transmission quality. This is known as geographical reuse of frequencies or channels. Thus, the
system needs a total allocation of 30 × 7=210 channels irrespective of how many times the cluster
pattern is repeated.

Trunking Effect
In a traditional public switched telephone network, each subscriber has a dedicated wire
connection to the local switch, but the number of lines continuing from the local switch towards
the next bigger switch is typically much smaller than the sum of subscribers served in that area.
The same applies to cellular networks as well, although the traditional subscriber line has been
replaced with wireless access to the base station. This phenomenon is known as the trunking effect.
In fact, the trunking effect reduces the number of lines at every network element concentrating
traffic (merging several lines) if the number of incoming lines is big enough. One can assume that
calls take place during the busy hour and that the duration of each call is constant. Subscribers
initiate calls randomly during the observation time. On one occasion, the traffic is increased by the
number of one new call (top row in the Figure 4.6). Apparently, with a sufficient number of
available lines (channels) there might be communication gaps available for placement of new calls
as illustrated in Figure 4.6. In example shown in Figure 4.6, allocation of new traffic was possible
with the minimum of seven channels available. This became feasible because randomly arriving
calls of a fixed duration create a randomly distributed ‘silent’ gaps of random duration; that is,
random intervals when the channel is not occupied. During those gaps, the available channel can
be assigned to carry a newly arrived call. While the number of simultaneous calls cannot exceed
the number of channels, the number of users using the same pool of the channels over a period of
time may exceed the number of lines due to the fixed duration of each call and random
distribution of time of arrival. This is what is called a trunked effect, meaning that, given the
random nature of call duration and time of arrival, the number of users may exceed the number of
available lines. The trunking effect takes place in all traffic concentrating points when the pool of
resources (number of channels or lines) is rather large. In a cellular system, the first such
concentration point is the air interface. A fixed but sufficiently large number of traffic channels
available in a transceiver can support large number of users camping on the cell; this number is
much greater than the number of traffic channels available in the cell

Figure 4.6 Illustration of the trunking effect.
Erlang Formulas
The trunking effect need to be estimated quantitatively in order to calculate the number of
resources (channels, lines) to meet traffic demand from users of a communications system. The
estimate of channel resources depends on many statistical factors related to traffic, such as call
duration, time distributions of call arrivals and other statistical parameters. The unit of traffic is the
Erlang (named after Agner Krarup Erlang (1878–1929) who invented it). One Erlang equals the
maximum traffic available on one line. The traffic is calculated using a simple formula:
x Erlangs = (calls per hour) × (average conversation time) /3600 Seconds.
It means that one call of a duration of 3600 seconds (i.e. 1 hour) produces 1 Erlang of traffic.
Erlang derived two formulas for different systems:
▪ If all resources are used, additional calls are lost (Erlang B case). This is the case for voice
calls in mobile cellular systems.

▪ If calls are put into a queue for certain time and will be served sequentially as resources
become free again, the traffic capacity is described by Erlang C formulas. This is applicable
to many trunked radio systems.
Erlang B Formula
The Erlang B formula determines the probability that a call is blocked. This probability
defines a measure for the Grade of Service (GOS) for a trunked system that provides no
queuing for blocked calls (i.e. blocked calls are instantly lost). The Erlang B formula uses the
following assumptions:
Call requests are memoryless. That is, all users, including blocked users, may request
a channel at any time all free channels are fully available for calls until all channels are
occupied.
Probability of channel holding (i.e. usage) times is exponentially distributed. That is,
longer calls are less likely to happen than short calls.
A finite number of channels available in the resources pool time between channel
requests follow a Poisson distribution (inter-arrival times). • Inter-arrival times of call
requests are independent of each other.
The number of busy channels is equal to the number of busy users. Offered traffic (in
Erlangs) A is related to the call arrival rate, 𝜆, and the average call-holding time, h, by
A = 𝜆h
Let us define 𝜆 as a call arrival rate, h, mean holding time (duration of the call), then
𝜆hT is a mean operating time of a single user during period T, also called the time of
occupancy of the channel.
Relative operation time 𝜆hT∕T = 𝜆h = 𝛼 is a traffic load from a single user measured in
Erlangs, 0 ≤ 𝛼 ≤ 1. The traffic load from N users is then A = N𝛼, also called offered traffic: we
have assumed that statistical characteristics of all calls by any user are the same. Under all the

assumptions here, the probability that in a system with n channels, k channels are occupied is
given by the Erlang formula: Pk = Ak ∕k! /∑n
m=1 Am
∕m!
The probability that all n channels are busy and, therefore, a new call is blocked is called the
blocking probability and is given by the Erlang blocking formula (Erlang B):
Pn = An
∕n! ∑n
m=1 Am
∕m!
The Erlang B formula shows relations between offered load A and blocking probability with a
total number n of available channels. Given a fixed amount of resources, the higher the
acceptable blocking probability, the more traffic could be offered. Figure 4.7 illustrates, using a
dashed line, the occurrence of blocking when at one instance all channels n = 6 are occupied.
Note that call arrival rate is often called BCHA (busy call hour attempt). Erlang values for a
given set of resources are often tabulated in telecommunication engineering handbooks. The
target blocking probability in a system is called Grade of Service, GOS, and is a percentage
measure of service performance in mobile communication systems. For instance, GOS=1%
corresponds to an Erlang blocking probability of 0.01. A sample of an Erlang B table is
presented in Table 4.2.
Figure 4.7 Blocking an incoming call.

Table 4.2 Erlang B table

CHAPTER 5: INTRODUCTION TO CELLULAR RAN
Wireless Communications
It is a communication while moving with wireless transmission medium.
It refers to the transfer of info. b/n 2 or more points that are not physically connected.
e.g. Cellular Networks/Mobile networks.
The 3 broad categories of wireless transmission media are:
Radio waves:
EM wave frequencies ranging from 3KHz to 1GHz
use omnidirectional antennas.
The radio wave band is under government regulation.
used for multicast communications, such as radio & television, & paging systems
They can penetrate through walls.
 Micro Waves:
◼ EM waves between 1 & 300GHz
◼ Microwaves are unidirectional; propagation is line of sight.
◼ Use directional antennas - point to point line of sight communications.
◼ The parabolic dish antenna & the horn antenna is used for transmission &
reception of microwaves.
◼ Used for unicast communication such as cellular telephones, satellite networks,
& wireless LANs.
◼ Higher frequency ranges cannot penetrate walls.

Infrared Waves: IR
◼ Infrared Waves => 300 GHz to 400 THz
◼ for short-range communications such as b/n a PC & a peripheral device.
◼ Small distance, typically no more than 10m.
◼ Line of sight (or reflection) propagation, blocked by walls e.g. TV remote
control, IRD port

GERAN: GSM-EDGE RAN

UTRAN: UMTS RAN

CHAPTER 6: GSM (GLOBAL MOBILE COMMUNICATION) BASICS

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