This document provides an overview of analog signal communication systems. It discusses how baseband signals need to be modulated to higher frequencies suitable for transmission over a channel. It introduces multiplexing as a way to send multiple signals simultaneously. It describes the main types of analog modulation: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). It compares AM and FM and discusses their advantages and disadvantages. It also provides a brief overview of noise in communication systems and how it can degrade performance.

1. Analog signal
Shahad hussian && Ahmed shamel
supervised by:
Dr.En.Muyad sadik

2. Outline
 Communication Systems
 Multiplexing
 Analog communication
 Types of Analog Modulation
 Noise

3. Communication Systems
 Communication system aims to transmit information
signals (baseband signals) through a communication
channel.
 The term baseband is used to designate the band of
frequencies representing the original signal as
delivered by the input transducer
 For example, the voice signal from a microphone is a
baseband signal ,and contains frequencies in the
range of 0-3000 Hz.

5. Baseband Communications
• Signal strength attenuates with distance. Needs repeaters to
amplify the signals in stages
• Received signal is corrupted by noise
– R(t)=A S(t)+ n(t)
• Received signal quality depends on channel noise and noise
between repeaters.
• To transmit a signal with bandwidth B, we need >= B Hz in
channel bandwidth
• If the signal is low-pass (0-B), must the channel operate at 0-B
range of frequency?
• How do we send multiple signals over the channel?

6.  Since this baseband signal must be transmitted
through a communication channel such as air
using electromagnetic waves, an appropriate
procedure is needed to shift the range of
baseband frequencies to other frequency ranges
suitable for transmission, and a corresponding
shift back to the original frequency range after
reception. This is called the process of modulation
and demodulation.

7. Why do we need “modulation”
 A communication channel only operates at a certain frequency
range.
 telephone cables, terrestrial (over the air broadcast), Ethernet, optical
fiber, etc.
 Modulation translates a signal from its baseband to the operating
range of the channel
 In other words we can say that modulation is used because the some
data signals are not always suitable for direct transmission, but the
modulated signal may be more suitable.
 By modulating different signals to different frequency bands, they
can be transmitted simultaneously over the same channel.
frequency division multiplexing

8. Modulation = Frequency Shifting

9. Multiplexing
 When required to transmit several signals on the
same channel, Baseband transmission fails.
 To encounter this problem Multiplexing is
employed.
 Multiplexing is a way of sending multiple signals or
streams of information over a communications
link at the same time in the form of a single; the
receiver recovers the separate signals, in a
process called demultiplexing.

10.  Tow types of Multiplexing:
 Frequency Deviation Multiplexing (FDM) : is the
method of transmitting several channels
simultaneously
 Time Deviation Multiplexing (TDM) : is the
method of allotting a time slot for each signal
and it gets repeated cyclically.

11. Analog communication
 Information is encoded in a continuous
amplitude, continuous time signal.
 Analog systems are less tolerant to noise.
 make good use of bandwidth.
 easy to manipulate mathematically.

12.  However, analog signals require hardware receivers and
transmitters that are designed to perfectly fit the
particular transmission. If you are working on a new
system, and you decide to change your analog signal,
you need to completely change your transmitters and
receivers.

14. Types of Analog Modulation
 Amplitude Modulation (AM)
 Frequency Modulation (FM)
 Phase Modulation (PM)

15. The choice of the type of modulation is based on
several factors, such as :
 the amount of bandwidth allocated.
 the types of noise and interference that the signal
encounters in transmission over the channel.

16. Amplitude Modulation (AM)
 In AM, the information signal varies with the
amplitude of the carrier sine wave.
 The instantaneous value of the carrier amplitude
changes in accordance with the amplitude and
frequency variations of the modulating signal.
 The carrier frequency remains constant during the
modulation process, but its amplitude varies in
accordance with the modulating signal.
 An increase in the amplitude of the modulating
signal causes the amplitude of the carrier to
increase.

17. Normal (Am) modulation

21. Single-Sideband (SSB) Modulations

22. Vestigial-Sideband (VSB) Modulations

23. Frequency Modulation (FM)
 Frequency modulation is a form of analog angle
modulation in which the baseband information
carrying signal, typically called the message or
information signal m(t), varies the frequency of a
carrier wave.
 the frequency of the carrier, varies in a continuous
manner. Thus, there are infinitely many possible
carrier frequencies.
 The amount by which the signal frequency varies is
very important. This is known as the deviation and is
normally quoted as the number of kiloHertz
deviation.

25. AM vs. FM
 AM requires a simple circuit, and is very easy to
generate.
 It is simple to tune, and is used in almost all short
wave broadcasting.
 The area of coverage of AM is greater than FM
(longer wavelengths) (lower frequencies) are
utilized.
 However, it is quite inefficient, and is susceptible to
static and other forms of electrical noise.

26. AM vs. FM
 The main advantage of FM is its audio quality and
immunity to noise. Most forms of static and electrical
noise are naturally AM, and an FM receiver will not
respond to AM signals.
 The audio quality of a FM signal increases as the
frequency deviation increases (deviation from the center
frequency), which is why FM broadcast stations use such
large deviation.
 The main disadvantage of FM is the larger bandwidth it
requires.

27. Phase Modulation
 Frequency modulation (FM) and Phase modulation (PM)
have much in common and they are usually concluded as
angle modulation, i.e., it is impossible to tell them apart
without knowledge about the modulation function.
 Phase modulation is the process of varying the of a carrier
wave in proportion to the amplitude of a baseband signal.
The amplitude of the carrier remains constant .
 A strong motivation for FM and PM is that the amplitude is
constant and the transmitter’s power amplifier can work at a
constant high amplification level.

30. Noise
 Noise is unwanted signal that affects wanted signal.
 Noise is random signal that exists in communication
systems
 Noise:
 Internal:
 due to random movement of electrons in electronic
circuits
 Major sources are resistors, diodes, transistors etc.
 Thermal noise or Johnson noise for e.g shot noise .

31.  External
 Man- made and natural resources .
 Sources over which we have no control .
Examples are Motors, generators, atmospheric sources.
Noise level in system is proportional to:
 Temperature and bandwidth
 Amount of current
 Gain of circuit
Resistance of circuit Effect of noise
 Degrades system performance (Analog and digital)
 Receiver cannot distinguish signal from noise
 Efficiency of communication system reduces

33. Thank you