Data and Computer
Communications
Chapter 3 – Data Transmission
Chapter 3 – Data Transmission
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Understanding Data Transmission: Guided vs Unguided Media, Signals, and Impairments, Study notes of Computer Networks
An in-depth exploration of data transmission, focusing on transmission terminology, frequency domain representations, data rate and bandwidth, analog and digital data transmission, and transmission impairments. Topics include guided and unguided media, direct and point-to-point links, simplex and full duplex communication, and frequency domain representations of signals. The document also covers the relationship between data rate, bandwidth, and noise, as well as the advantages of digital transmission and transmission impairments such as attenuation, delay distortion, and noise.
What you will learn
- What are the differences between guided and unguided media?
- What are the key differences between analog and digital signals?
- What is the difference between simplex and full duplex communication?
- What are direct links, point-to-point, and multi-point connections?
- What is data transmission and how does it occur?
Typology: Study notes
2017/2018
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Data and Computer
Communications
Chapter 3 – Data Transmission Chapter 3 – Data Transmission
Transmission Terminology
- (^) data transmission occurs between a
transmitter & receiver via some medium
- (^) guided media
- (^) Guided along a physical path
- (^) eg. twisted pair, coaxial cable, optical fiber
- (^) unguided / wireless media
- (^) Transmits but do not guide
- (^) eg. air, water, vacuum
Transmission Terminology
- (^) simplex
- (^) one direction
- (^) eg. television
- (^) one direction
- (^) half duplex
- (^) either direction, but only one way at a time - (^) eg. police radio
- (^) full duplex
- (^) both directions at the same time
- (^) eg. telephone
- (^) both directions at the same time
Frequency, Spectrum and
Bandwidth
- (^) time domain concepts
- (^) analog signal
- (^) Intensity varies in a smooth way over time
- (^) digital signal
- (^) maintains a constant level then changes to another constant level
- (^) periodic signal
- (^) Signal pattern repeated over time
- (^) aperiodic signal
- (^) pattern not repeated over time
- (^) analog signal
Periodic
Signals
Periodic continuous signal Periodic discrete signal Signal s(t) is periodic if S(t+T)=s(t) -∞ < t < +∞ where T is the period
Sine Wave
- (^) Fundamental periodic signal
- (^) Three parameters
- (^) peak amplitude (A)
- (^) maximum strength of signal
- (^) volts
- (^) frequency (f)
- (^) rate at which signal repeats
- (^) Hertz (Hz) or cycles per second
- (^) period = time for one repetition (T)
- (^) T = 1/f
- (^) phase ()
- (^) relative position in time within a single period of a signal
- (^) peak amplitude (A)
Wavelength ()
- (^) is distance occupied by one cycle
- (^) Or distance between two points of
corresponding phase in two
consecutive cycles
- (^) assuming signal velocity v have = vT
- (^) or equivalently f = v
especially when v=c
(^) c = 3*10^8 ms-1^ (speed of light in free space)
Frequency Domain Concepts
- (^) signal are made up of many frequencies
- (^) components are sine waves
- (^) Fourier analysis can show that any signal is made up of component sine waves
- (^) Fourier analysis
- (^) Signal – components (sinusoid) at various frequencies
- (^) For each signal
- (^) Time domain function s(t) – amplitude at each instant
- (^) Frequency domain function s(f) – peak amplitude of the constituent frequencies of the signal 13
Frequency Domain Representations
- (^) freq domain func of Fig 3.4c
- (^) freq domain func of single square pulse 14
Signal with dc component
16
Data Rate and Bandwidth
- (^) Wave form may contain frequencies over a broad range
- (^) any transmission system can accommodate only a limited band of frequencies
- (^) this limits the data rate that can be carried 17
Contd..
- (^) Adding sine waves at different frequencies, the wave form approaches a square wave.
- (^) Frequency components of square wave with amplitudes A and –A s(t)= A * 4/ * sigma k odd, k=1 to ∞ sin(2kft)/k
- (^) square wave have infinite components and hence infinite bandwidth
- (^) Amplitude of kth component, kf = 1/k
- (^) so most energy in first few components 19
Data rate and bandwidth
- (^) Case I: Fig. 3.7a
- (^) f = 1 MHz i.e10 power 6 cycles/sec
- (^) T=1/ 10 power 6 = 10 power -6=1μs
- (^) One bit occurs every 0.5 μs
- (^) Bandwidth = 4 MHz
- (^) Data rate = 2 Mbps
- (^) Case II: Fig. 3.7a
- (^) f = 2 MHz, T=1/2MHz= 0.5 μs
- (^) One bit occurs every 0.25 μs
- (^) Bandwidth = 8 MHz
- (^) Data rate = 4 Mbps
- (^) Case III: Fig. 3.4c
- (^) f = 2 MHz
- (^) One bit occurs every 0.25 μs
- (^) Bandwidth = 4 MHz
- (^) Data rate = 4 Mbps 20