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  • Slide 1
  • Transmission Fundamentals & Principles
  • Slide 2
  • Analogue and Digital Data Transmission Analogue and Digital Data 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 Class Contents:
  • Slide 3
  • Analogue and Digital world: The terms analogue and digital, corresponds roughly to continuous and discrete, Analogue and Digital Data Transmission Used in communications in 3 ways: Data Signals Transmissions
  • Slide 4
  • 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 Analogue and Digital Data Transmission
  • Slide 5
  • Signals are electric or electromagnetic representations of data Analogue signal: Digital Signal: Data are propagated from one point to another by means of electrical signals. Is a continuously varying electromagnetic wave that can be propagated over a variety of media. Is a series of voltage pulses that may be transmitted over a medium. Analogue and Digital Data Transmission
  • Slide 6
  • 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 Analogue and Digital Data Transmission
  • Slide 7
  • 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. Transformations from Data to Signals
  • Slide 8
  • 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 carrier frequency. Example: Most common MODEMS represent digital data in the voice signal spectrum, this data can then be propagated over telephone lines
  • Slide 9
  • 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.. Transformations from Data to Signals
  • Slide 10
  • 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. Transformations from Data to Signals
  • Slide 11
  • Analogue and Digital Signalling of Analogue and Digital Data
  • Slide 12
  • 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 its content. Propagation of the signal is done through AMPLIFIERS Digital signals are not propagated using Analogue Transmissions Analogue and Digital Transmissions
  • Slide 13
  • 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.
  • Slide 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
  • Slide 15
  • Analogue SignalDigital 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 Two alternatives: 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 Summary Table 1: Data & Signals
  • Slide 16
  • 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 USEDDigital 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. Summary Table 2: Treatment of Signals
  • Slide 17
  • Data Rate: Calculated using the time duration of a symbol CHANNEL CAPACITY THEORY: Data Rate
  • Slide 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.
  • Slide 19
  • CHANNEL CAPACITY THEORY: Bandwidth The amplitude of the n th 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. The n th harmonic is represented by:
  • Slide 20
  • Using a square wave (Amplitude 1) with a fundamental period of 2 seconds, and taking the first 2 harmonics into account (n=3 and n=5): Data Rate: 1 bit has a duration of 1 sec ==> DR=1 Mbps Bandwidth: Fundamental frequency = 500 KHz, frequency of the 2 nd harmonic is 5f 0 =2.5 MHz BW=2.5 MHz 0.5 MHz = 2 MHz Examples of Data rate and bandwidth calculations:
  • Slide 21
  • Data Rate: 1 Mbps Bandwidth: 2 MHz Examples of Data rate and Bandwidth calculations:
  • Slide 22
  • Changing the period of the signal to 1 sec: Data Rate: 2 Mbps Bandwidth: 4 MHz Examples of Data rate and Bandwidth calculations:
  • Slide 23
  • Keeping the period of the signal in1 sec: Data Rate: 2 Mbps Bandwidth: 3 f o - f o = 2 MHz Examples of Data rate and Bandwidth calculations:
  • Slide 24
  • Changing the period of the signal to 0.5 sec, and using one harmonic: Data Rate: 4 Mbps Bandwidth: 4 MHz Examples of Data rate and bandwidth calculations:
  • Slide 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.
  • Slide 26
  • Channel Capacity [bps] Is the maximum data rate at which information can be transmitted over a given communications path or channel under given conditions. Noise 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
  • Slide 27
  • There are 2 approaches in calculating Channel Capacity: Nyquist Bandwidth Theorem Shannons Capacity Formula Shannons 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 Channel Capacity
  • Slide 28
  • 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.log 2 M Calculation of Base b logarithm: Log b y = x b x = y Taking logarithm base 10 in both sides: x log b = log y x = log y / log b Nyquist Bandwidth Theorem
  • Slide 29
  • In a binary systems (2 levels), the carrying capacity is Twice the bandwidth Example: An information source is coded using a 6 bit word that is to be propagated usin

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