Introduction to Mobile

Communication

- Dr. Rasika B. Naik

Course Code: Course Title Credit

ECC702 Mobile Communication System 3

Prerequisite:
Principles of Communication Engineering,
Digital Communication,
Computer Communication and Networks
 Course Objectives

1 To understand the cellular fundamentals and different types of radio

propagation models.
2 To study evolution of 2G and 3G mobile technologies.
3 To illustrate the working principle of LTE
4 To learn the concepts of emerging technologies for 4 G standards and
beyond
 Course Outcomes

1 Explain the cellular fundamentals and estimate the coverage and capacity
of cellular systems.
2 Classify different types of propagation models and analyze the link budget.
3 Compare and contrast GSM, GPRS, HSCSD, EDGE and IS-95 Technologies.
4 Apply the concepts of 3G technologies for UMTS and CDMA 2000.
5 Describe the features and working principle of 3GPP LTE
6 Discuss the emerging technologies for upcoming mobile communication
systems
1 Fundamentals of Mobile Communications 07
1.1 The Cellular Concept System Design Fundamentals: Evolution of
Cellular Technology, Frequency Reuse, Channel assignment
Strategies, Handoff, Interference and system Capacity, Trunking and
Grade of Service, Improving Coverage and Capacity in Cellular
Systems and related problems

1.2 Features of all conventional multiple access Techniques: Frequency

Division Multiple access, Time Division Multiple access, Spread
Spectrum Multiple access (SSMA), Space Division Multiple access
(SDMA), and Orthogonal Frequency Division Multiple Access
(OFDMA), OFDM-PAPR
2 Mobile Radio Propagation 08
2.1 Large scale fading: Introduction to radio wave propagation, Free
space Propagation model, Basic propagation mechanisms:
reflection (Ground Refection (two- ray) Model), diffraction (Knife
edge and multiple Knife edge Diffraction Model), scattering (Radar
Cross Section Model), Practical Link budget design using path loss
models and related problems.
2.2 Outdoor Propagation Model: Longley Rice Model, Durkin's Model
Indoor Propagation Model: Partition losses (same floor and
between floors), Ericsson Multiple Breakpoint Model
2.3 Small scale fading: small Scale multipath Propagation, parameter
of multi-path channels, types of small scale fading, Rayleigh and
Ricean distributions.
3 2G Technologies
3.1 GSM: GSM Network architecture, air interface
specifications, GSM signalling protocol architecture, 08
identifiers, GSM channels, GSM Multiframe
structure, authentication and security in GSM,
handoff procedures in GSM
3.2 GSM evolution: GPRS, HSCSD and EDGE
Architecture, radio specifications
3.3 IS-95 : CDMA Air interface, CDMA channels, power
control in CDMA system handoff, and RAKE receiver
4 3G and 4G Technologies
4.1 Universal Mobile Telecommunication System (UMTS): network
architecture, air interface specifications, security procedure, W- 07
CDMA air interface, attributes of W-CDMA system
4.2 cdma2000 cellular technologies: Handoff and Power control
4.3 Long Term Evolution: network structure, protocol structure,
modulation, Coding, Power control and handover.
4.4 4G Technology: Multi-antenna Techniques: Smart antennas,
Multiple input Multiple Output systems. Cognitive Radio:
Architecture, Spectrum sensing , Software Defined Radio (SDR):
Components and Applications
5 5G Architecture 06
5.1 5G Network Architecture, Cloud RAN(C-RAN), Definitions of
Heterogeneous Networks, Radio Resource, Interference
Management, mobility management, handover and Traffic
offloading scenarios for heterogeneous networks.
5.2 Small cell deployments: Different types, Deployment scenarios,
performance and analysis, Energy efficient mechanism with BS
sleep mode in green small cell networks
6 Advanced Techniques for 5G Deployment and 06
beyond
6.1 Non orthogonal Multiple Access (NOMA): Non orthogonal
Multiple Access (NOMA), Different Types: power domain NOMA
and code domain NOMA, Difference between Orthogonal multiple
access and NOMA,
6.2 Trends in 5G: 5G NR, Carrier Aggregation in 5G, Open RAN, Use
cases of 5G: eMBB, URL LC and mMTC, introduction to Software
Defined Networking, Network Function Virtualisation (NFV).
6.3 Advance applications: Robotic surgery, driverless car and Industrial
IoT(IIoT), Tactile Internet, 5G-IoT applications, AR/VR in 5G
Textbooks:

1 T. L. Singal “wireless communications”, Mc Graw Hill Education.

2 Theodore S. Rappaport “wireless communications - principles and

practice”, PEARSON, Second edition.

3 Andreas F. Molisch “wireless communications” WILEY INDIA PVT LTD,

Second edition.
Reference Books:
1 Upena Dalal “Wireless and Mobile Communications”, Oxford
university Press
2 Vijay K. Garg “Wireless Communications and Networking” ,Morgan–
Kaufmann series in Networking-Elsevier.
3 J. H. Reed, Software-Defined Radio, Prentice-Hall, 2002
4 W. C. Y. Lee, Mobile Communication, Wiley
5 David T., Pramod Viswanath “Fundamentals of Wireless
Communication ” published by Cambridge University Press
 Internal Assessment
Assessment consists of :
 Mid Term Test of 20 marks
 Continuous Assessment of 20 marks.
Mid Term test is to be conducted when approx. 50% syllabus is
completed Duration of the midterm test shall be one hour.
 Continuous Assessment
Sr.no Assessment Tools Marks
1. Certificate course for 4 weeks or more:- 10 marks
NPTEL / Coursera / Udemy /any MOOC

2. Wins in the event/competition/ hackathon 10 marks

3. Content beyond syllabus presentation 10 marks
4. Creating Proof of concept 10 marks
5. Mini Project / Extra Experiments/ Virtual Lab 10 marks
6. GATE Based Assignment test/Tutorials etc. 10 marks
7. Participation in event/workshop/talk/ competition followed by 5 marks
small report and certificate of participation relevant to the
subject(in other institutes)

8. Multiple Choice Questions (Quiz) 5marks

End Semester Theory Examination:
1 Question paper will be of 60 marks
2 Question paper will have a total of five questions
3 All questions have equal weightage and carry 20 marks each
4 Any three questions out of five needs to be solved.
 Lab Code Lab Name Credit
ECL702 Mobile Communication System Lab 1

Term Work:
1 Term work should consist of 8 experiments.
2 Journal must include at least 2 assignments.
3 The final certification and acceptance of term work ensures satisfactory
performance of laboratory work and minimum passing marks in term work.
4 Total 25 Marks
(Experiments: 10-marks, Mobile App Development: 15-marks)
Continuous assessment exam
1 Based on the subject and related labs.
Terminology
 Mobile:
Any radio terminal that could be moved during operation. (earlier
Definition)
 A Radio terminal that is attached to a high speed mobile
platform.
 Portable: A radio terminal that can be handheld and used by
someone at walking speed. (e.g. walkie talkie, cordless)
 Subscriber: A user who pays subscription charges for using
Mobile communication system. (e.g. mobile user, portable user)
Terminology
 Base Station (BS):
Mobile communicates to fixed BS which are connected to a commercial
power source and a fixed backbone network.
BS consists of a transceiver and channel multiplier with antennas mounted
on the tower.
BS located at the center or on the edge of a coverage area.
Mobile Station (MS) or Subscriber Unit:
MS communicates to BS which in turn communicates to a desired user at the
other end.
MS consists of transceiver, control circuitry, duplexer and an antenna.
 Classification of Mobile Radio
Transmission System:

1. Simplex:
Unidirectional, eg PAGER

2. Half Duplex:
Non-simultaneous, eg
Walkie talkie (push –talk,
release - Listen)

3. Full Duplex:
bidirectional simultaneous,
eg telephone
Cellular Telephone System
1.1 Cellular Concept SYSTEM DESIGN
FUNDAMENTALS
 Flow oF today’s lecture

֍ How to make a call (from mobile and from landline)

֍ Cellular Telephone Systems (across the countries)

֍ Cellular Concept –Important for exams

֍ Frequency Reuse –Problems to solve

Timing Diagram : how a call is initiated by a Landline phone
Timing Diagram : how a call is initiated by a mobile
Cellular Telephone System
Standard Type Multiple Frequency Modulation Channel Country
Access Band Bandwidth
AMPS Cellular FDMA 824-894 MHz FM 30KHz North America
USDC Cellular TDMA 824-894 MHz π/4-DQPSK 30kHz North America
NAMPS Cellular FDMA 824-894 MHz FM 10KHz North America
CDPD Cellular FHI 824-894 MHz GMSK 30kHz North America
IS-95 Cellular CDMA 824-894 MHz QPSK/ BPSK 1.25 MHz North America

1.8-2.0 GHz
E·TACS Cellular FDMA 900 MHz FM 25KHz Europe
NMT-450 Cellular FDMA 450-470 MHz FM 25KHz Europe
NMT-900 Cellular FDMA 890-960 MHz FM 12.5KHz Europe
GSM Cellular TDMA 890-960 MHz GFSK 200KHz Europe
C-450 Cellular FDMA 450-465 MHz FM 20KHz/10KHz Europe

JTACS Cellular FDMA 860-925 MHz FM 25kHz Japan

PDe Cellular TDMA 810-1501 MHz π/4- DQPSK 25kHz Japan
NTT Cellular FDMA 400/800 MHz FM 25kHz Japan
NTACS Cellular FDMA 843-925 MHz FM 12.5 kHz Japan
Cellular Evolution Timeline
Cellular Architecture

❖ Why cell shape is Hexagonal?

 In practice the cells are not regular hexagons, but instead are distorted and
overlapping areas.

 The hexagon is an ideal choice for representing macro cellular coverage

areas, because it closely approximates a circle and offers a wide range of
tessellating (a regular tiling of polygons) reuse cluster sizes.
 Frequency Reuse
• Cellular Concept: is a system level idea which calls for

replacing a single, high power transmitter (large cell) with many

low power transmitter (small Cell) each providing coverage to

only a small portion of service area.

• Objective: To increase system capacity and minimize interference.

• Frequency reuse: The design process of selecting and

allocating channel groups for all the cellular base stations

within a system is called frequency reuse or frequency planning.

• Footprint: The actual Radio coverage of a cell is known as the

footprint.
 Cellular Concept
Frequency Reuse:

N = cluster size
System Design Using Frequency Reuse:
► Placement of Base station:
✔ centre-excited cells

✔ Corner excited cells

✔ edge-excited cells

► Most system designs permit a base station to be positioned

up to one-fourth the cell radius away from the ideal location.
System Design using Frequency Reuse:
• Consider a cellular system with S = total no of duplex channels available.
• If each cell is allocated a group of ‘k’ channels (k < S) and if ‘S’ channels are
divided among ‘N’ cells into unique and disjoint channel groups which each have
the same number of channels,
• Total no of available radio channels i.e. S = kN
• Total number of duplex channels ‘C’ can be used as a measure of capacity given by

C = MkN = MS
Where M= Number of times cluster is replicated. C ∝ M
N = cluster size, typically equal to 4, 7 or 12
• smallest possible value of N is desirable in order to maximize the capacity over a
given coverage area.
System Design Using Frequency Reuse:

Some values of N are:

 Capacity of system (C)
Capacity(C) is directly proportional to the number of times a cluster is
replicated (M) in a fixed service area.
If cluster size N is reduced (keeping cell size constant), more clusters (M) are
required to cover a given area and hence capacity will increase.
If cluster size is increased, the ratio between the cell radius and the distance
between co-channel cell is small. But a small cluster size indicates that co
channel cells are located much closer together.
The value of N is a function of how much interferences a mobile or base station
can tolerate while maintain a sufficient quality of communication.
So From a design point of view, the smallest possible value of N is desirable in
order to maximize the capacity over a given coverage area.
Method of Locating co-channel cells

To Find Nearest co-channel

neighbors of a particular
cell:
1. Move i cell along any
chain of hexagon
2. Turn 600 counter
clockwise and move j cells
Examples of co-channel cells
Example 1
Example 2
 Channel Assignment Strategies

To increase capacity and minimization of interference

1. Fixed channel Assignment strategy

Problem- blocked call
Remedy- borrowing strategy
2. Dynamic channel Assignment strategy
Advantage- increases trunking capacity, increase channel utilization
Problem- increase storage and computational load

42
Handoff /Handover

43
Handoff
Strategies

45
 Handoff Strategies
 Once a particular signal level is specified as the minimum usable signal for acceptable
voice quality at the base station receiver (normally taken as between –90 dBm and –100
dBm), a slightly stronger signal level is used as a threshold at which a handoff is made.

 This margin, Δ = Pr handoff – Pr minimum usable, cannot be too large or too small.
 If Δ is too large, unnecessary handoffs which burden the MSC may occur,
 If Δ is too small, there may be insufficient time to complete a handoff before a call is
lost due to weak signal conditions.

 Therefore, Δ is chosen carefully to meet these conflicting requirements.

47
Handoff Strategies
 Prioritizing Handoff

 Guard Channel Concept: A fraction of the total available channels in a cell is reserved
exclusively for handoff

 Disadvantage: Reduce total carrier traffic as fewer channels are allocated to originating calls.

 Queuing Concept: Tradeoff between the decrease in probability of forced termination and
total carrier traffic.

 Disadvantage: not guaranteed a zero probability of forced termination

Practical Handoff considerations
Umbrella Cell Approach

50
 Cell Dragging
• Results from pedestrian users that provide a very strong signal to the BS.
• Such situations occurs mostly in urban environment when there is a LOS
radio path between the subscriber and BS.
• Even when the user has traveled well beyond the designed range of the call,
the received signal at BS may be above the handoff threshold and thus
handoff may not be made.
• Creates a potential interference and traffic management problem since user
has meanwhile traveled deep within a neighboring cell.
• To solve this problem, handoff thresholds and radio coverage parameters must
be adjusted carefully
To solve cell dragging problem,
Handoff thresholds must be adjusted carefully in 1G and 2G

Time to make a handoff Value of ∆

First Generation analog 10 seconds 6dB to 12dB

cellular system (1G)

Digital Cellular system as 1 or 2 seconds 0 dB & 6dB

GSM

Dwell Time : The time over which a call may be maintained within
a cell, without hand-off, is called the dwell time
52
SOFT Handoff HARD Handoff
(break after make) ( break before make)

53
 Interference and system Capacity
Interference –
 major limiting factor in performance of cellular radio system.
 Major bottleneck in increasing capacity
 Often responsible for dropped calls.
 More severe in urban areas due to greater RF noise floor and large no. of base stations and mobiles

Four major Sources of Interference-

 another mobile in the same cell
 a call in progress in a neighboring cell
 other base stations operating in same frequency band
 any noncellular system which leaks energy into cellular frequency band

 Interference on Voice CH : cross talk

 Interference on control CH : missed or blocked calls
Two major types of Interference
1) Co-channel interference (CCI)
2) Adjacent channel interference (ACI)
54
Co-channel interference (CCI) and system capacity

 By increasing the ratio D/R, the spatial separation

between co channel cell relative to the coverage distance
of a cell is increased and thus interference is reduced.

55
 Co- channel reuse ratio (Q)

• A small value of Q provides larger capacity since the cluster

size N is small

• Large value of Q improves the transmission quality, due to a

smaller level of co-channel interference

• A trade-off must be made between these two objectives in actual

cellular design
Mathematical Analysis
of S/I or SIR:
Io= no. of co channel interfering cells
S = designed signal power from desired BS
Ii =Interference power caused by the ith interfering
co channel cell BS
Pr =average received power
D = distance
Po = power received at a close-in reference
point in far field region of antenna at a small
distance do
n = path loss exponent, 2 & 4 in urban area
Di = distance of ith interferer from mobile

NOTE: for clear Audible FM signal, signal power should

be at least 60 times higher that the noise/interference
power SIR=10 log 60=17.78dB = 18dB 57
Co-channel Interference

First Tier
Interfering cells
Worst Case co-channel Interference

N= 7, Q= 4.6
Find S/I =? S/I=49.56=17.8dB Slightly < 18dB
So increase N to nearest largest size…if
N=12(i=j=2) spectrum utilization=1/12 and
when N=7, spectrum utilization =1/7

Trade off between N & C (system capacity) 59

SELF Reflection

1.What is system capacity?

2.How is it linked to CCI?

Example
Solution
Solution
 Channel Planning for wireless system
Control Channel Data Channel
5% of entire mobile 95% of entire mobile spectrum
Required for initiating, requesting dedicated to carry revenue generating traffic
21 cell reuse 7 cell reuse
 Channel Planning In CDMA:
Cluster size N=1

Limited frequency reuse where propagation conditions are ill behaved in a particular market. eg- in
the vicinity of bodies of water

f1/f2 cell planning – where nearest neighboring cell use different radio channels. Such freq planning
requires CDMA phones to make hard handoffs.
64
 Breathing cell

 In CDMA, a single 1.25 MHz radio channel carries the simultaneous transmissions of the
single control channel with up to 64 simultaneous voice channels.
 In 200 kHz GSM TDMA systems, the coverage region and interference levels are well
defined when specific radio channels are in use, the CDMA system instead has a
dynamic, time varying coverage region which varies depending on the instantaneous
number of users on the CDMA radio channel.
 This effect, known as a breathing cell, requires the wireless engineer to carefully plan the
coverage and signal levels for the best and worst cases for serving cells as well as nearest
neighbor cells, from both a coverage and interference standpoint.

65
 Breathing cell

 The breathing cell phenomenon can lead to abrupt dropped calls resulting from abrupt
coverage changes simply due to an increase in the number of users.

 Thus, instead of having to make careful decisions about the channel assignment schemes
for each cellular base station, CDMA engineers must instead make difficult decisions
about the power levels and thresholds assigned to control channels, voice channels, and
how these levels and thresholds should be adjusted for changing traffic intensity

66
 Breathing Cell

• When a cell becomes heavily loaded, it

shrinks.
• Subscriber traffic is then redirected to a
neighboring cell that is more lightly
loaded, which is called load balancing.
• Cell breathing is a common phenomenon
of 2G and 3G wireless systems including
code-division multiple access (CDMA).
• Cell breathing is a mechanism which
allows overloaded cells to offload
subscriber traffic to neighboring cells by
changing the geographic size of their
service area.
 Adjacent Channel Interference (ACI)
Results from imperfect receiver filters which allows nearby frequencies to leak into the
pass band.
 Near Far effect:
1. Case1 : The Mobile receiver is captured by the unintended, unknown transmitter, instead of
the desired base station
2. Case 2: The Base Station faces difficulty in recognizing the actual mobile user, when the
adjacent channel bleed over is too high.

68
 Adjacent Channel Interference (ACI)
To minimize

 Careful filtering and channel assignments

 Keeping large frequency separation

 If N is small, the separation between adjacent channel at BS may not be sufficient to

keep the adjacent channel interference level within tolerable limits.

 If a close in mobile is 10 times as close the BS as another mobile and has energy spill
out of its passband, the SIR at BS for the weak mobile is approx.

For a path loss exponent n=4, S/I = - 52 dB

9/1/2025 69
 Trunking and Grade of service (GOS)
Trunking:
 A means for providing access to users on demand from available pool of channels.
Trunking theory is about how a population can be handled by a limited number of servers.

70
Terminology:
1. Traffic intensity : average channel occupancy measured in Erlangs
• One Erlang: amount of traffic intensity in a completely occupied channel.
• 0.5 Erlang: channel occupied for 30 minutes in an hour.
2. Grade of Service (GOS): probability that a call is blocked (or delayed). OR is a measure
of ability of a user to access a trunked system during the busiest hour.
3. Set-Up Time: time required to allocate a trunked radio channel to a requested user.
4. Blocked Call: Call that cannot be completed at time of request due to congestion. Also
referred to as Lost Call.

5. Holding Time: (H) average duration of typical call.

6. Load: Traffic intensity across the entire trunked radio system.

7. Request Rate: (λ) average number of call requests per unit time.
71
 Traffic Intensity
The traffic intensity offered by each user is equal to the call request rate multiplied by the
holding time. That is, each user generates a traffic intensity of Au Erlangs given by,

H is the average duration of a call

λ is the average number of call

For a system containing U users and an unspecified number of channels, the total
offered traffic intensity A , is given as

In a C channel trunked system, if the traffic is equally distributed among the channels,
then the traffic intensity per channel, Ac is given as

9/1/2025 72
Trunking Systems
• There are two types of trunked systems which are commonly used.
 Blocked calls cleared (no queuing )
 Blocked calls Delayed (queuing)
Blocked calls cleared (Erlang B):
 If no channel are available, the requesting user is blocked without access and is free to try again.
 It is assumed that there are infinite number of users as well as the followings
a) There are memoryless arrivals of requests implying that all users, including blocked users may
request a channel at any time.
b) Probability of a user occupying a channel is exponentially distributed so that longer calls are
less likely to occur as described by exponential distribution.
c) There are a finite number of channels available in the trunking pool.
 This is known as M/M/m/m queue and leads to the derivation of the Erlang B formula.

9/1/2025 73
SELF Reflection

1.Which technology gets most affected by

‘Near and Far’ concept? How can it be solved?

2.How does Trunking make the system more

efficient?
 Erlang B formula

C = number of trunked
channels offered by a trunked
radio system
A= total offered traffic

9/1/2025 75
GOS

A
9/1/2025 76
Blocked calls Delayed (Erlang C):
• A different type of trunked system queues blocked calls–Blocked Calls Delayed.
This is known as an Erlang C model.

• Procedure:
• Determine Pr[delay> 0] = probability of a delay from the chart.
• Pr[delay > t | delay > 0 ] = probability that the delay is longer than t, given
that there is a delay
Pr[delay > t | delay > 0 ] =exp[-(C-A)t /H ]
• Conditional Probability of delay > t :
Pr[delay > t ] = Pr[delay > 0] Pr[delay > t | delay > 0 ]
• Average delay time D = Pr[delay> 0] H/ (C-A)

77
 Erlang C Formula
• The likelihood of a call not having immediate access to a channel is
determined by Erlang C formula:

C = number of trunked channels offered by a trunked radio system

A= total offered traffic
9/1/2025 78
9/1/2025 79
 Numerical on Trunking

Ex.1
Solution
Example 2
Solution:
solution continued…
solution continued…
solution continued…
Example 3
Solution
solution continued…
Example 4
Solution
solution continued…
Improving coverage & capacity in cellular system

• Cellular design techniques are needed to provide more channels per unit coverage area.
• Techniques to expand the capacity of the cellular system :
 Cell Splitting - increases number of BS to increase capacity
 Cell sectoring – uses directional antennas to control interference and frequency reuse of
channels.
 Coverage zone / microcell Zone concept – distribute the coverage of a cell and extend the cell
boundary to hard to reach places.
Cell Splitting
Process of subdividing a congested
cell into smaller cells, each with its
own BS and the corresponding
reduction in antenna height and
transmitter power.
Increases capacity by increasing
number of times channel are reused.
Radius of new microcell is half that
of original cell.
 The transmit power must be reduced
Cell Splitting by 12dB in order to fill in the
original coverage area with
microcells while maintaining S/I
requirement.
Pt2= Pt1/16 indicated we cannot use
original transmit power for all new
cell or vice versa.
Channels must be broken into two
channel groups.one for smaller cell
reuse requirements and other for
larger cell reuse requirements.
Antenna Down tilting is used to limit
the radio coverage of newly formed
microcells.
It increases capacity by rescaling the
system.
Cell Sectoring
Keeping cell radius unchanged
another method is used to decrease
D/R ratio.
It increases SIR using bidirectional
antennas then capacity
improvement is achieved by
reducing the number of cells in a
cluster. Thus increasing the
frequency reuse.
In sectoring channels broken down
into sectored groups
If N=7, Io=6 but now it will be
io=2
Cell Sectoring

SIR = 24.2dB significant improvement over

omnidirectional case (17dB)
Disadvantages of sectoring

1) Increased number of antennas

2) Decrease in trunking efficiency
3) Increased number of hand off

Advantage: Sectoring reduces interference which amounts

to an increase in capacity by a factor of 12/7 = 1.714
Microcell Zone Concept  Increased number of handoffs
requiring in sectoring results in
increased load on switching and
control link elements of the mobile
system.
Solution is Microcell zone
concept
3 zone sites are connected to a
single BS and a same radio
equipment.
The zones are connected by
coaxial cables, fiber optics cable or
microwave link to the BS.
 Cell= multiple zones and a single
BS.
 As mobile travels within the cell,
it is served by a zone with the
strongest signal.
Advantage of microzone cell concept
• Superior to sectoring because antennas are placed at the outer edges of the cell.
• As mobile travels from one zone to another within the cell it retains the same channel.
Thus unlike in sectoring a handoff is not required at MSC when mobile travels between
zones within the cell.
• BS simply switches the channel to a different zone site.
• In this way a given channel is active only in the particular zone in which mobile is
travelling and hence BS radiation is limited and interference is reduced.
• The channels are distributed in time and space by all 3 zones and are also reused in co
channel cells in the normal fashion. This technique is relatively useful along highways or
along urban traffic corridors
• While cell maintains a particular coverage radius, the co channel interference in the cellular
system is reduced, it increases capacity without degradation in trunking efficiency..
 Extent of Capacity Increase
Suppose the desired S/I=18 dB with path loss exponent of n=4 .
For a system of N=7, D/R of 4.6 was shown to achieve this.
How much capacity increase can occur if we use Microcell Zoning of 3 zones/cell???
Extent of Capacity Increase
In zone microcell system, transmission at any instant is confined to one
zone. Therefore, Dz /Rz=4.6
Each hexagon represents a zone and 3 hexagons represent a cell
 Zone radius=One hexagon radius
Capacity of system related to distance between co-channel cells and not
zones. Shown as D.
Value of co channel reuse is 3. D/R = 3 corresponds to N=3 Reduction in
cluster size from N=7 to N=3 Increase in capacity is 7/3=2.33 times
Repeaters for Range Extension
Useful for hard to reach areas
Buildings
Tunnels
Valleys
 Radio transmitters called Repeaters can be used to provide coverage in
these area
 Repeaters are bi-directional
Rx signals from BS
Amplify the signals
Reradiate the signals
Received noise and interference is also reradiated.
 Multiple
Access
Techniques
Multiple access Techniques (MAT)

⮚ MATs are used to allow many mobile users to share a finite amount of radio
spectrum simultaneously.
⮚ Duplexer- A device with duplex channel (two simplex channels- a forward and
a reverse)
⮚ Duplexing may be done using frequency (FDD) or time domain techniques
(TDD).

#See the video https://youtu.be/1DwogdEdm_M-

 Multiple Access Techniques
• Multiple Accessing Techniques :
❖ Frequency division multiple access (FDMA)
❖Time division multiple access (TDMA)
❖Spread spectrum multiple access (SSMA) :
e.g. Code division multiple access (CDMA)
❖Space division multiple access (SDMA)
⮚ These techniques can be grouped as
A. Narrowband system
B. Wideband system
Multiple Access Techniques in Mobile communication System

Cellular System Multiple Access Technique

AMPS FDMA/FDD
GSM TDMA/FDD
USDC (IS-54 and IS-136) TDMA/FDD
PDC TDMA/FDD
CT2 Cordless Phone FDMA/TDD
DECT Cordless Phone FDMA/TDD
US IS-95 CDMA/FDD
W-CDMA CDMA/FDD
CDMA/TDD
cdma2000 CDMA/FDD
CDMA/TDD
Spread Spectrum Multiple Access (SSMA)
► SSMA uses signals which have a transmission BW that is several orders of magnitude
greater than the minimum required RF BW.

► A pseudo-noise (PN) sequence converts narrowband signal to a wideband noise like

signals before transmission.

► Application: developed for military applications for

► Security

► Undetectability: minimum probability of being detected

► Robust against intentional jammers

 Spread Spectrum Multiple Access
Two techniques:
⮚ Frequency Hopped Multiple Access (FHMA)
⮚ Direct Sequence Multiple Access (DSMA) -Also called Code Division
Multiple Access (CDMA)
Code Division Multiple Access (CDMA)
Code Division Multiple Access (CDMA)

■ In CDMA, the narrowband message signal is multiplied by a very large

bandwidth signal called spreading signal (code).

■ Spreading signal is a pseudo noise code sequence that has a chip rate which
is orders of magnitude greater than the data rate of the message.

■ CDMA is also called Direct Sequence Spread Spectrum(DSSS). DSSS is a

more general term.

■ Message consists of symbols ,symbol period and hence, symbol rate

Example of DSSS used in CDMA
Code Division Multiple Access (CDMA)
■ Spreading signal (code) consists of chips

⮚ Has Chip period and chip rate

⮚ Spreading signal use a pseudo-noise (PN) sequence (a pseudo-random sequence)

⮚ PN sequence is called a codeword

⮚ Each user has its own cordword

⮚ Codewords are orthogonal. (low autocorrelation)

⮚ Chip rate is oder of magnitude larger than the symbol rate.

▪ The receiver correlator distinguishes the senders signal by examining the wideband signal
with the same time-synchronized spreading code

▪ The sent signal is recovered by despreading process at the receiver.

 Code Division Multiple Access (CDMA)
▪ Low power spectral density
Signal is spread over a larger frequency band
❑ Other systems suffer less from the transmitter

▪ Interference limited operation

❑ All frequency spectrum is used

■ Privacy
❑ The codeword is known only between the sender and receiver. Hence other
users can not decode the messages that are in transit
■ Reduction of multipath affects by using a larger spectrum
Code Division Multiple Access (CDMA)

■ Random access possible

❑ Users can start their transmission at any time

■ Cell capacity is not fixed like in TDMA or FDMA systems. has soft capacity.
■ Higher system capacity than TDMA and FDMA
■ No frequency management
■ No equalizers needed
■ No guard time needed
■ Enables soft handoff
Near Far Problem and Power Control
❑ At a receiver, the signals may come
from various (multiple) sources.

❑ The strongest signal usually captures

the modulator. The other signals are
considered as noise

❑ Each source may have different

distances to the base station
 Space Division Multiple Access (SDMA)

• Use spot beam antennas

• The different beam area can use
TDMA, FDMA, CDMA
spot beam
antenna
• Sectorized antenna can be thought of
as a SDMA
• Adaptive antennas can be used in the
future (simultaneously steer energy in
the direction of many users)
Space Division Multiple Access (SDMA)
 Features of SDMA
• A large number of independently steered high-gain beams can be formed
without any resulting degradation in SNR ratio.

• Beams can be assigned to individual users, thereby assuring that all links
operate with maximum gain.

• Adaptive beam forming can be easily implemented to improve the system

capacity by suppressing co channel interference.
 SELF Reflection

1.Write a note on SSMA and its

types.

2.What is Hybrid Multiple

Access technique, explain its
significance.

https://www.youtube.com/watch?v=fIZhDl35_XY (FDM TDM)

https://www.youtube.com/watch?v=5plZGFd-cWc (CDMA)
https://www.youtube.com/watch?v=oYRMYSIVj1o
(FDMA/TDMA/CDMA/OFDMA)
https://www.youtube.com/watch?v=CkhA7s5GIGc
8/1/2022
(FHSS)