1. Transmission Fundamentals & Principles

2. Class Contents: Analogue and Digital Data Transmission
Analogue and Digital Signals
Analogue and Digital Transmissions
Channel Capacity
Data Rate & Bandwidth
Channel Capacity – Nyquist and Shannon
Transmission Media
Guided and Unguided Media
Wireless Transmissions and Applications

3. Analogue and Digital Data Transmission
Analogue and Digital world:
The terms analogue and digital, corresponds roughly
to continuous and discrete,
Used in communications in 3 ways:
Data
Signals
Transmissions

4. Analogue and Digital Data Transmission
Data: are entries that convey meaning or information
Analogue Data: Is data that takes on continuous values
over a time interval.
Examples: Voice, video, sensor readings
such as temperature
Digital Data: Is data that takes on discrete values
over a time interval.
Examples: Text, integers

5. Analogue and Digital Data Transmission
Signals are electric or electromagnetic
representations of data
Data are propagated from one point to another by means of
electrical signals.
Analogue signal:
Is a continuously varying electromagnetic wave that can be propagated over a variety of media.
Digital Signal:
Is a series of voltage pulses that may be transmitted over a medium.

6. Analogue and Digital Data Transmission
Media are the places used to propagate the signals.
Guided Media: Copper Wire, twisted pair, coaxial cable
optical fibre.
Unguided Media: Atmosphere, vacuum and air.
The Course Focuses in unguided media transmissions or
WIRELESS TRANSMISSIONS

7. Transformations from Data to Signals
Analogue and digital data can be represented by both
analogue and digital signals
Analogue Data – Analogue Signals
Analogue data is a function of time and occupy a limited frequency spectrum.
Analogue data can be directly represented by an electromagnetic signal occupying the same spectrum
Example: Sound waves are voice data. Voice spectrum 20 Hz – 20 KHz
Spectrum for Voice Signal is 300 Hz to 3.4 KHz.

8. Transformations from Data to Signals
Digital Data – Analogue Signals
A process of modulation-demodulation is required.
A MODEM converts a series of binary data voltage pulses,
into an analogue signal. This process is done by modulating a
carrier frequency.
The spectrum of the modulated signal is centred around the
Example: Most common MODEMS represent digital data in the voice
signal spectrum, this data can then be propagated over telephone lines

9. Transformations from Data to Signals
Analogue Data – Digital Signals
Process is similar to Digital Data – Analogue Signal conversion.
Continuous data is codified into a digital bit stream using a
coding process.
A CODEC is used to convert analogue data to digital signals.
Example: The CODEC takes the analogue signal that directly represents the
voice data and approximates it by a digital stream..

10. Transformations from Data to Signals
Digital Data – Digital Signals
Process is equivalent to the analogue data – analogue signal
conversion.
Binary data is often encoded in a more complex form of binary signal to improve propagation characteristics of the signal.
Observation: Digital signals are generally cheaper to produce and
are less susceptible to noise interferences, however, they suffer
more attenuation than their analogue counterparts.

11. Analogue and Digital Signalling of Analogue and Digital Data

12. Analogue and Digital Transmissions
Analogue and digital signals may be transmitted on suitable
transmission media. The way the signals are treated is a
function of the transmission media:
In an Analogue Transmission an analogue signal is
transmitted without any regard to it’s content. Propagation
of the signal is done through AMPLIFIERS
Digital signals are not propagated using Analogue
Transmissions

13. Analogue and Digital Transmissions
In a Digital Transmission analogue and digital signals are transmitted. Signal content is important.
Signal Propagation: Digital
Digital signals can be propagated only a limited distance.
Attenuation endangers the integrity of the signal
A REPEATER is used to receive the signal, recover the string and generate a new signal to retransmit.

14. Analogue and Digital Transmissions
Signal Propagation: Analogue (Constructed from digital data)
Retransmitters (repeaters) are used instead of amplifiers.
The repeater recovers the digital data from the analogue signal
And uses it to generate a new, noise-free analogue signal

15. Summary Table 1: Data & Signals Analogue Signal Digital Signal
Analogue Data
Two alternatives:
a) Signal occupies same spectrum as the analogue data
b) Analogue data are encoded or modulated to occupy a different portion of the spectrum
Analogue data are encoded using a CODEC to produce a digital bit stream
Digital Data
Digital data are encoded using a MODEM to produce analogue signal
a) Signal consists of a two voltage levels to represent the two binary values
b) digital data are encoded to produce a digital signal with desired properties

16. Summary Table 2: Treatment of Signals Analogue Transmission
Digital Transmission
Analogue Signal
Is propagated through amplifiers: same treatment whether signal is used to represent analogue data or digital data
Assumes that the analogue signal represents digital data. Signal is propagated through repeaters; at each repeater, digital data are recovered from inbound signal and used to generate a new analogue outbound signal
Digital Signal
NOT USED
Digital signal represents a stream of 1s and 0s, which may represent digital data or may be an encoding of analogue data. Signal is propagated through repeaters: at each repeater, stream of 1s and 0s is recovered from inbound signal and used to generate a new digital outbound signal.

17. CHANNEL CAPACITY THEORY: Data Rate
Data Rate: Calculated using the time duration of a symbol

18. CHANNEL CAPACITY THEORY: Bandwidth
The bandwidth depends of the signal used.
For a binary bit stream, the square pulse A,-A is used as
The elemental signal. The data takes on the values A and –A
In a random way.
Fourier series expansion:
where
Notice that the Bandwidth is infinite.

19. CHANNEL CAPACITY THEORY: Bandwidth
The nth harmonic is represented by:
The amplitude of the nth harmonic
When n tends toward infinite is:
The signal has a “finite bandwidth” as defined by the
number of harmonics taken into consideration to build
the signal.

20. Examples of Data rate and bandwidth calculations:
Using a square wave (Amplitude 1) with a fundamental period
of 2 m seconds, and taking the first 2 harmonics into account
(n=3 and n=5):
Data Rate: 1 bit has a duration of 1 m sec ==> DR=1 Mbps
Bandwidth: Fundamental frequency = 500 KHz, frequency of
the 2nd harmonic is 5f0=2.5 MHz
BW=2.5 MHz – 0.5 MHz = 2 MHz

21. Examples of Data rate and Bandwidth calculations:
Data Rate: 1 Mbps
Bandwidth: 2 MHz

22. Examples of Data rate and Bandwidth calculations:
Changing the period of the signal to 1 m sec:
Data Rate: 2 Mbps
Bandwidth: 4 MHz

23. Examples of Data rate and Bandwidth calculations:
Keeping the period of the signal in1 m sec:
Data Rate: 2 Mbps
Bandwidth: 3 fo- fo = 2 MHz

24. Examples of Data rate and bandwidth calculations:
Changing the period of the signal to 0.5 m sec, and using one
harmonic:
Data Rate: 4 Mbps Bandwidth: 4 MHz

25. Data Rates & Bandwidth Facts
The greater the bandwidth, the greater the data rate that can be achieved.
The transmission system will limit the bandwidth
The greater the bandwidth, the greater the cost
The more limited the bandwidth, the greater the distortion and the potential for error by the receiver.

26. Noise Channel Capacity [bps]
It is defined as an unwanted signal that combines with and hence distorts the signal intended for transmission and reception
To make as efficient use as possible of a given bandwidth, the Maximum possible data rate must be achieved.
The Limitation to this is the quantity of noise present in the system
Channel Capacity [bps]
Is the maximum data rate at which information can be transmitted
over a given communications path or channel under given conditions.

27. Channel Capacity
There are 2 approaches in calculating Channel Capacity:
Nyquist Bandwidth Theorem
Shannon’s Capacity Formula
Shannon’s Formula takes noise into account.
Nyquist works with multilevel signals but does not take noise into account.
Both Methods give theoretical maximums to data rate given a bandwidth

28. Nyquist Bandwidth Theorem
For a signal made of M levels, and a bandwidth of B, using
a binary transmission system, the carrying capacity C of the
system is given by:
C = 2.B.log2 M
Calculation of Base b logarithm:
Taking logarithm base 10
in both sides:
Logby = x  bx = y
x log b = log y  x = log y / log b

29. Nyquist Bandwidth Theorem
In a binary systems (2 levels), the carrying capacity is
Twice the bandwidth
An information source is coded using a 6 bit word
that is to be propagated using a binary system. How
many levels are needed?. Find the carrying capacity
if the signal has a bandwidth of 5 MHz.
Example:
bits per word
levels of the system
M = 26 = 64
Binary System is represented by base 2
C = 2 . B . log2 64 = 2 . B . 6 = 60 Mbps

30. Shannon’s Capacity Formula
In a channel in the presence of noise, the carrying capacity
is adversely affected by the level of noise to signal that is
present in the communications channel.
Signal to Noise Ratio
Is a parameter used to measure the immunity of the signal power
to the noise power.
It is defined as the ratio of signal power to noise power that is
present at a particular point of the transmission:

31. Shannon’s Capacity Formula
Signal to Noise Ratio Characteristics:
The SNR is adimensional
It is usually expressed in dB

32. Shannon’s Capacity Formula
The Signal to Noise Ration (SNR), imposes the upper limit on
achievable data rate in a communications system
C = B . log2(1+SNR) [bps]
B is the signal bandwidth in Hz
This formula is also called:
ERROR-FREE CAPACITY

33. Shannon’s Capacity Formula
If the data rate of the channel is less than the error-free capacity,
then it is theoretically possible to use a suitable code to achieve
error-free transmission through the channel.
Observations
The data rate could be increased by increasing either the signal
strength or the bandwidth, however:
Increasing the bandwidth, increments the costs
Increasing the signal strength, increments the effects of
non-linearities in the system producing an increase in
inter-modulation noise.

34. Shannon’s Capacity Formula
Observations
Shannon, assumes the noise to be “white noise”, therefore, the wider the bandwidth, the more noise is admitted into the system
Shannon’s error-free capacity represents the theoretical maximum that can be achieved. In practice, only much lower rates are achieved because of factors such as impulsive noise, attenuation distortion and delay distortion, are not accounted for.

35. Example of Calculation
The spectrum of a communications channel has a
bandwidth of 6 MHz. A signal is transmitted through
the channel and received with a SNRdB of 24 dB.
Find the error-free capacity of the channel
and the number of signal levels that are required to
achieve that capacity and the number of bits used to
sample the signal.

37. WIRELESS TRANSMISSIONS
Transmission Media
Is the physical path between the transmitter and the receiver
in a communications system.
Guided Media:
twisted pair, coaxial cable, optical fibre.
Unguided Media:
Air (atmosphere), space (vacuum)
Unguided Media transmission are referred to as:
WIRELESS TRANSMISSIONS

38. Wireless Transmissions
The characteristics and quality of a data transmission are determined by the characteristics of the medium and the characteristics of the signal.
Guided Media: The medium is more important in determining the limitations of the transmission
Unguided Media: The bandwidth of the signal produced by the transmitting antennas is more important than the medium in determining transmission characteristics.

39. Unguided Media Communications
Transmission and reception of unguided media are achieved by means of an antenna.
The transmitting antenna radiates electromagnetic energy into the medium
The receiving antenna picks up electromagnetic waves form the surrounding medium

40. Frequency & Directionality
Directionality is a key property of a transmitter and is
achieved by means of an antenna.
Lower Frequencies
Signal are omnidirectional in nature: The propagation
occurs in all directions with the same intensity.

41. Frequency & Directionality
Higher Frequencies
It is possible to focus the signal in a directional beam:

42. The Frequency Spectrum

43. The Frequency Spectrum
There are several ranges that are interesting in wireless transmissions:
Broadcast Radio (radio range)
Microwave Frequencies
Terrestrial Microwave
Satellite Microwave
Infra-Red

44. Wireless Frequency Spectrum Distributions
The Radio Range:
Transmissions in the band of 30 MHz to 1 GHz
Suitable for omnidirectional applications (radio broadcast)
Applications
FM radio
UHF & VHF television
Some data networking applications

45. Wireless Frequency Spectrum Distributions
The Radio Range:
Transmission Characteristics
Effective range for broadcast communications
Ionosphere is transparent to radio waves above 30 MHz
Transmission is limited to line-of-sight.
Distant transmitters will not interfere with each other due
to reflection from the atmosphere

46. Wireless Frequency Spectrum Distributions
The Radio Range:
Transmission Characteristics
Radio waves are less sensitive to attenuation due to rainfall
Free space losses can be calculated using:
Wave length l can be calculated using the speed of light in
vacuum
l . f = c c = 3x108 m/s

47. Wireless Frequency Spectrum Distributions
The Radio Range:
Sources of Impairment:
Multi-path interference: Reflections from land, water and
human made objects, create multiple
paths between antennas

48. Wireless Frequency Spectrum Distributions
The Microwave Range:
Compromises frequencies between 1 GHz and 40 GHz
Possibility for highly directional beams
Mode of transmission is point to point
Classification:
Terrestrial Microwaves
Satellite Microwaves

49. Wireless Frequency Spectrum Distributions
Terrestrial Microwaves:
Typical antenna used is a parabolic dish with 3 metres in diameter
The antenna is fixed rigidly and focuses a narrow beam to achieve
line-of-sight transmission
Antennas are located at substantial heights above ground level
To achieve long distances, microwave relays towers
need to be used

50. Wireless Frequency Spectrum Distributions
Terrestrial Microwaves:
Applications and Frequency Bands
Long-Haul telecommunications services (voice and TV)
Short point-to-point links between buildings (CCTV, Data
links between LANs
Cellular systems and fixed wireless access
The microwave requires far fewer amplifiers or repeaters than an
equivalent coaxial cable system over the same distance

51. Wireless Frequency Spectrum Distributions
Terrestrial Microwaves:
Applications and Frequency Bands
Application
Band
Observations
Long-Haul Telecommunications
4 GHz - 6 GHz
Suffering from congestion. Increased chance for interference.
11 GHz band is coming into use.

52. Wireless Frequency Spectrum Distributions
Terrestrial Microwaves:
Applications and Frequency Bands
Application
Band
Observations
CATV Systems
12 GHz
Links used to provide TV signals to local cable TV installations (CATV). Signals are distributed to subscriber via coaxial cable
Short Point-to-point links
22 GHz
Used in building to building LAN applications.

53. Wireless Frequency Spectrum Distributions
Terrestrial Microwaves:
Transmission Characteristics
Main source for attenuation are free space losses
The higher the frequency, the higher the potential bandwidth,
thus the higher the data rate for some typical applications
Losses varies with the square of the distance. In twisted pair
and coaxial systems, it varies logarithmically with the distance
Repeater may be placed farther apart (typically Km)
Attenuation is increased with rainfall (noticeable above 10 GHz)

54. Wireless Frequency Spectrum Distributions
Satellite Microwaves:
A communications satellite is a microwave relay station used
to link 2 or more earth based microwave transmitter/receivers
known as EARTH STATIONS or GROUND STATIONS
Transmission is received in a frequency band called UPLINK,
the satellite amplifies or repeats the signal, and transmits it back
to earth using a different frequency band called DOWNLINK
A single satellite operates on a number of frequency bands called
TRANSPONDER CHANNELS
The electronics on the satellite that converts uplink to downlink are
called TRANSPONDER

55. Wireless Frequency Spectrum Distributions
Satellite Microwaves:

56. Wireless Frequency Spectrum Distributions
Satellite Microwaves:
Applications
TV distribution
Long-Distance telephone transmission
Private Business networks
Transmission Characteristics
Optimum frequency range: 1 GHz to 10 GHz
Typical uplink: 5.95 to GHz
4/6 GHz Band
Typical downlink: 3.7 to 4.2 GHz

57. Wireless Frequency Spectrum Distributions
Satellite Microwaves:
Transmission Characteristics – Sources of impairment:
Below 1 GHz: Noise from natural sources, including
galactic, solar and atmospheric noise.
Human made interference from electronic
devices
Above 10 GHz: Signal attenuation is severe. Also affected
by precipitation and atmospheric absortion.

58. Wireless Frequency Spectrum Distributions
Satellite Microwaves:
Properties of satellite communications
Propagation delay of 0.25 sec.
Problems in the areas of Error and Flow control.
Satellite microwave is a broadcast facility.
Many stations can transmit to the satellite.
Satellite transmission can be received by many stations.

59. Infrared
Achieved using transceivers (Tx/Rx) that modulate noncoherent IR light.
Must operate within line-of-sight (directly or by reflection from light coloured surface)
Does not penetrate walls  Security and interference problems encountered in microwaves are not present.

60. Recomemded Additional Reading
Multiplexing Techniques: Section 2.5 Stallings Wireless Communications Book
Frequency Division Multiplexing
Time Division Multiplexing