EEE 409 - COMMUNICATION PRINCIPLES
email: alex_olawole@oauife.edu.ng March
Prerequisites
Ø Signal and Systems EEE 204 & EEE 309.
Suggested Text / Readings
1) Communication Systems, Bruce Carlson et al.
2) Analog and Digital Communication Systems, K. Sam Shanmugam
3) Modern Analog and Digital Communication Systems. B.P. Lathi
4) Analog and Digital Communication, Hwei P. Hsu. (Schaum’s)
INTRODUCTION
P.I
Introduction
● Communication
Taking message from point A to point B
Past: Messages are carried by runners, carrier pigeons, drum beats etc.
Present: Electrical communication systems
ØCan transmit message (signals) over much longer distances and at the speed of light.
ØIt is reliable and economical
• Communication technology thus alleviates the energy crises by trading information
processing for a more rational use of energy resources.
Introduction
● Communication System
Input Input Output Output
message signal Communication signal Ouput message
Input
transducer System transducer
Transmitted Received
signal signal
Transmitter Channel Receiver
Distortion
Fig. 1: Communication System & Noise
Introduction
● Components of Communication System
q The source: originates a message (e.g., human voice, a television picture or data) - If
message is non-electrical, it converts it using the input transducer into electrical
waveform referred to as baseband signal or message signal.
q The transmitter: modifies the baseband signal for efficient transmission (more
discussion later)
q The channel: medium through which the transmitter output is sent.
Ø Guided medium: wire, twisted-pair, coaxial cable, waveguide, optical fibre
Ø Unguided medium (wireless): radio link
q The receiver: operates on the output signal from the channel. Operation includes:
Ø Amplification (to compensate for transmission loss),
Ø Demodulation and Coding to reverse the signal processing performed at the
transmitter.
Ø Filtering
Introduction
● Fundamental Limitations
The fundamental limitations of information transmission by electrical means include:
i) Bandwidth, ii) Noise
Bandwidth: applies to both signal and systems as a measure of speed.
o When signal changes rapidly with time, its frequency content (spectrum) extends
over a wide range resulting in large bandwidth.
o The ability of a system to follow signal variations is reflected in its usable frequency
response or transmission bandwidth.
Ø All electrical systems contain energy-storage elements and stored energy cannot be
changed- instantaneously. Consequently, communication system has a finite
bandwidth B that limits the rate of signal variation.
Ø Lack of sufficient transmission bandwidth to accommodate signal spectrum results in
distortion. E.g. Bandwidth of several MHz is needed for a TV video signal while a
few kHz is needed for voice
Introduction
Fundamental Limitations
The time required to transmit a given amount of information is inversely proportional
to bandwidth B
Noise: At temperature above absolute zero, thermal energy causes microscopic
particles to exhibit random motion. The random motion of charged particles generates
random current or voltages called thermal noise. There are other types of noise but,
thermal noise appears in every communication system.
Signal-to-Noise Ratio (SNR or S/N): Noise power relative to an information signal
power.
q Increases with transmission range.
q For sufficiently long distance link SNR could becomes very small and amplification
at the receiver is then to no avail, since noise would be amplified with the signal.
Introduction
● Fundamental limitations
Taking both limitations into accounti.e., bandwidth ‘B’ and noise ‘N’, Shannon stated
that the rate R of information transmission cannot exceed the channel capacity
� = � ��� 1 + � � (1)
where C is the information capacity of the channel.
q Equation (1) expresses the maximum rate at which information can be transmitted
across the channel without error.
q SNR is usually expressed in decibel (dB).
q The relationship known as the Hartley-Shannon law sets an upper bound on the
performance of a communication system with a given bandwidth and SNR.
q Message signal can be transmitted without error provided � ≤ �
q The actual quantity of information transmitter can be expressed as
�� = � � ��� 1 + � � (2)
where � is the duration of transmisson.
Introduction
● Modulation
o Operation performed at transmitter to achieve efficient and reliable transmission
o Involves two waveforms: a modulating signal/intelligent message and a carrier wave
that suits the particular application
o A modulator systematically changes the carrier wave in corresponding with the
variation of modulating signal. The reverse of this (i.e., demodulation) is needed to
retrieve the message at the receiver.
o Most long-distance transmission system employ a sinusoidal carrier modulation or
continuous wave (CW) modulation with carrier frequency much higher than the
highest frequency component of the modulating signal. The spectrum of the
modulated signal consists of band of frequency components clustered around the
carrier frequency. This results in frequency translation.
o Pulse modulation (discuss later), does not result in frequency translation needed for
effiecient signal transmission
Introduction
● Modulation Benefits and Applications
Primary purpose is to generate a modulated signal suited to the characteristics of the
transmission channel.
Some of its benefits includes:
ü Efficient transmission
ü To overcome hardware limitations
ü To reduce effect of noise and interference
ü For frequency assignment
ü For multiplexing
More discussion in class!
Introduction
Radio Frequency Spectrum
v The Radio Frequency (RF) spectrum is a natural resource;
v The electromagnetic spectrum that has been investigated experimentally extends from
very low frequencies through radio, television, microwave, infrared, visible light,
ultraviolet, X-ray, and gamma ray frequencies exceeding 1024 �� .
v All electromagnetic waves in whatever frequency range propagate in a medium with
the same velocity, � = 1
��
In free space, � = 3 × 108 � �;
v Table 1 shows the electromagnetic spectrum divided into frequencies and wavelength
ranges on logarithmic scale. The term ‘microwave’ is somewhat nebulous and
imprecise, it could mean electromagnetic waves above a frequency of 1 GHz, and all
the way up to the lower limit of infrared band, encompassing UHF, SHF, EHF, and
mm-wave regions.
v The radio frequency spectrum is the part of the electromagnetic spectrum.
Introduction
Radio Frequency Spectrum
The radio frequency is a range of frequency spectrum from 30kHz to 300GHz that may
essentially be used for wireless communication.
The spectrum is partitioned into band, where each band is useful for specific purpose.
Fig. 1: Radio Frequency Spectrum
The data carrying capacity of the spectrum increases with frequency, but the ability to
refract and diffract over obstacles reduces with frequency since wavelength is inversely
proportional to frequency. As such the higher frequency signals tends to depend more
on the line-of-sight propagation.
Introduction
Radio Frequency Spectrum
The radio frequency spectrum is divided into a number of bands which have been given
designations such as LF, MF, HF, etc. for ease of reference. Based on ITU Radio
Regulations (ITU 2012), No. 2.1 (Article 2, provision 1), Table 1.1 specifies the symbols of
the radio frequency bands.
Table 1: Radio Frequency Spectrum Bands
v Frequencies below the VLF range are seldom used for wireless transmission
because: (1) Huge antennas would be needed for efficient radiation
(2) Very low data rate only possible at these low frequencies.
