ITS323 Data Transmission Terminology Time Domain Frequency Domain Data Transmission Analog and Digital Impairments Capacity ITS323: Introduction to Data Communications Sirindhorn International Institute of Technology Thammasat University Prepared by Steven Gordon on 5 August 2014 ITS323Y14S1L03, Steve/Courses/2014/s1/its323/lectures/transmission.tex, r3262
ITS323 Contents Data Transmission Terminology Transmission Terminology Time Domain Frequency Domain Analog and Digital Time Domain Concepts Impairments Capacity Frequency Domain Concepts Analog and Digital Data Transmission Transmission Impairments Channel Capacity
ITS323 Transmission Terminology Data Transmission ◮ Data transmission occurs between a transmitter and Terminology receiver via some medium Time Domain ◮ Communication is in form of electromagnetic waves or Frequency Domain signals Analog and Digital ◮ Medium may be: Impairments Guided: wires/cables, e.g. twisted pair, coaxial cable, Capacity optical fiber Unguided: wireless, e.g. air, water, vacuum ◮ Configuration may be: Point-to-point: only 2 devices share medium Multipoint: more than 2 devices share medium ◮ Direction of communications may be: Simplex: one direction, e.g. television Half duplex: either direction, but only one way at a time, e.g. police radio Full duplex: both directions at the same time, e.g. telephone
ITS323 Frequency, Spectrum and Bandwidth Data Transmission ◮ Transmitter generates electromagnetic signals, which is Terminology transmitted over medium Time Domain ◮ Electromagnetic signals represent data Frequency Domain Analog and Digital ◮ Electromagnetic signal consists of one or more Impairments component signals Capacity ◮ Electromagnetic signals can be viewed in two domains: Time domain: signal intensity vs time Frequency domain: Peak signal intensity of component vs frequency
ITS323 Contents Data Transmission Terminology Transmission Terminology Time Domain Frequency Domain Analog and Digital Time Domain Concepts Impairments Capacity Frequency Domain Concepts Analog and Digital Data Transmission Transmission Impairments Channel Capacity
ITS323 Analog and Digital Waveforms Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity Analog signal varies in continuous manner over time Digital signal maintains constant level for some period then changes to another constant level, in a discrete manner
ITS323 Examples of Periodic Signals Data Transmission Any signal is either periodic (the following two) or aperiodic Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Sinusoid Signals Data Transmission ◮ Sine wave is the fundamental periodic signal Terminology Time Domain s ( t ) = A sin (2 π ft + φ ) Frequency Domain ◮ Communication signals are made up of sinusoid signals Analog and Digital Peak amplitude, A : maximum strength of signal over Impairments time [volts] Capacity Frequency, f : rate at which signal repeats [cycles per second or Hertz] Phase, φ : relative position signal has advanced (or shifted) to some origin (usually 0) [radians] ◮ Other parameters: Period, T : time for one repetition or cycle; T = 1 / f Wavelength, λ : distance occupied by one cycle; λ = c / f where c is speed of light ( ≈ 3 x 10 8 m/s)
ITS323 Sinusoid Signal Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Contents Data Transmission Terminology Transmission Terminology Time Domain Frequency Domain Analog and Digital Time Domain Concepts Impairments Capacity Frequency Domain Concepts Analog and Digital Data Transmission Transmission Impairments Channel Capacity
ITS323 Frequency Domain Concepts Data Transmission ◮ Communication signals are composed of many Terminology component sinusoid signals at different frequencies, e.g. Time Domain Frequency Domain s ( t ) = (4 /π ) × [sin (200 π t ) + (1 / 3) sin (600 π t )] Analog and Digital Impairments ◮ Or, if f = 100 Hz : Capacity s ( t ) = (4 /π ) × [sin (2 π ft ) + (1 / 3) sin (2 π (3 f ) t )] ◮ When all frequency components of signal are integer multiple of one frequency, that one is called fundamental frequency; the others are harmonic frequencies ◮ Period of resulting signal is equal to period of fundamental frequency component ◮ By adding together sine waves with different amplitudes, frequencies and phases, any desired communications signal can be constructed
ITS323 Addition of Frequency Components Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Frequency Domain Representations Data Transmission Frequency domain function, S ( f ), specifies peak amplitude Terminology of component frequencies of signal Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Frequency Domain Representations Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Spectrum, Bandwidth and Data Rate Data Transmission ◮ Spectrum of a signal is range of frequencies it contains Terminology ◮ Absolute bandwidth is width of spectrum Time Domain ◮ If signal contains component with zero frequency, signal Frequency Domain Analog and Digital has dc component Impairments ◮ Many signals have infinite absolute bandwidth, but Capacity most of the signal energy is contained in narrow band of frequencies; called Effective Bandwidth or just Bandwidth ◮ In practice, transmission system can only carry limited band of frequencies ◮ Bandwidth limit of system determines data rate
ITS323 Signal with dc Component Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Frequency Components of Square Wave: (a) Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Frequency Components of Square Wave: (b) Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Example: Bandwidth and Data Rate Data Transmission Digital transmission system can transmit signals with Terminology bandwidth of 4MHz. What is the maximum data rate? Time Domain What if bandwidth increased to 8MHz? Frequency Domain Analog and Digital Impairments Capacity
ITS323 Effect of Bandwidth on a Digital Signal Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Tradeoffs Data Transmission Bandwidth Terminology Time Domain ◮ Digital signal has infinite bandwidth; transmission Frequency Domain systems impose limits on bandwidth of transmitted Analog and Digital signals Impairments ◮ Bandwidth is a limited resource Capacity ◮ Greater the bandwidth, greater the cost Data Rate ◮ Digital data is approximated by signal of limited bandwidth ◮ Greater the bandwidth, greater the data rate Accuracy ◮ Receiver must be able to interpret received signal, even with transmission impairments
ITS323 Contents Data Transmission Terminology Transmission Terminology Time Domain Frequency Domain Analog and Digital Time Domain Concepts Impairments Capacity Frequency Domain Concepts Analog and Digital Data Transmission Transmission Impairments Channel Capacity
ITS323 Analog and Digital ... Data Transmission Data Terminology Time Domain ◮ Entities that convey meaning or information Frequency Domain ◮ Analog data take continuous values over time, e.g. Analog and Digital voice, video, sensor data Impairments Capacity ◮ Digital data take discrete values, e.g. text, integers Signals ◮ Electric or electromagnetic representations of data Transmission ◮ Communication of data by propagating and processing signals
ITS323 Example of Analog Data: Audio Data Transmission Acoustic Spectrum of Speech and Music Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
ITS323 Example of Digital Data: Text Data Transmission Terminology First 3 bits 000 001 010 011 100 101 110 111 Time Domain p 0 @ 0000 NUL DLE SP P Frequency Domain ‘ q 1 a SOH DC1 ! A Q 0001 Analog and Digital r STX DC2 2 B R b 0010 " Impairments c s ETX DC3 # 3 C S 0011 Capacity $ EOT DC4 4 D T d t 0100 e u ENQ NAK % 5 E U 0101 v ACK SYN & 6 F V f 0110 g Last 4 bits w BEL ETB 7 G W 0111 ’ x BS CAN ( 8 H X h 1000 y HT EM ) 9 I Y i 1001 : j z 1010 LF SUB J Z * ; + [ { 1011 VT ESC K k , < | 1100 FF FS L \ l = − ] m } 1101 CR GS M . > n SO RS N ~ 1110 ^ _ o SI US / ? O DEL 1111
ITS323 Analog vs Digital Signals Data Transmission ◮ Electric or electromagnetic representations of data Terminology ◮ Analog signal is continuously varying electromagnectic Time Domain wave Frequency Domain Analog and Digital ◮ Digital signal is sequence of voltage pulses Impairments ◮ Digital signals generally cheaper and less susceptible to Capacity interference ◮ Digital signals suffer more from attenuation
ITS323 Analog Signaling of Analog and Digital Data Data Transmission Terminology Time Domain Frequency Domain Analog and Digital Impairments Capacity
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