1 Introduction Introduction Communication System Baseband an - PDF document

Introduction Introduction Physical Layer Mobile network Global ISP  Provides the means to transmit bits Basic Concepts of from sender to receiver, Data Transmission  Defines the mechanical, electrical, and Home network timing interfaces to the network, Regional ISP  Involves Yanmin Zhu  Transmission media Institutional network Department of Computer  How to use (analog) signals for digital Science and Engineering information  Techniques such as modulation techniques (the actual encoding), multiplexing, and switching CSE Department CSE Department 1 2 Introduction Introduction Basic Concepts of Data Fourier Analysis Transmission Any reasonably behaved periodic function,  Fourier Analysis g(t) with period T can be constructed as the  Data Transmission sum of a (possibly infinite) number of sines  Bandwidth & the Maximum Data Rate of and cosines: a Channel  Asynchronous and Synchronous 1 g t ( ) c a sin(2 nft ) b cos(2 nft ) Communication n n 2 n 1 n 1  Serial and Parallel Communication where f = 1/T is the fundamental frequency, a n and b n are the sine and cosine amplitudes of the n th harmonics , and c is a constant CSE Department CSE Department 3 4 Introduction Introduction Basic Concepts of Data Fourier Analysis Transmission  Fourier Analysis  Data Transmission  Bandwidth & the Maximum Data Rate of a Channel  Asynchronous and Synchronous Communication  Serial and Parallel Communication CSE Department CSE Department 5 6 1

Introduction Introduction Communication System Baseband  an adjective that describes signals and noise systems whose range of frequencies is measured from close to 0 channel source transform transform destination hertz to a cut-off frequency, a maximum bandwidth or highest  source ： analog signal, digital signal signal frequency;  transformation ： modulation, multiplexing,  a band of frequencies encoding starting close to zero.  channel ： bandwidth, bit-rate CSE Department CSE Department 7 8 Introduction Introduction Passband Modulation  Baseband (DC) signaling is not suitable for  A passband is the range of frequencies long distance transmission or wavelengths that  because of its wide frequency spectrum can pass through a  a continuous tone called sine wave carrier (AC filter without being signaling) is introduced attenuated.  its amplitude, frequency, or phase can be modulated to transmit information  Three basic forms of modulation: amplitude modulation, frequency modulation and phase modulation. CSE Department CSE Department 9 10 Introduction Introduction Carrier Signal: Three Parameters Let’s start with Analog signals transmission Carrier signal for analog data CSE Department CSE Department 11 12 2

Introduction Introduction Illustration of AM AM CSE Department CSE Department 13 14 Introduction Introduction FM PM CSE Department CSE Department 15 16 Introduction Introduction Data Transmission  Analog signals transmission for digital data: ASK(Amplitude Shift Keying)  FSK(Frequency Shift Keying)  PSK(Phase Shift Keying)  Analog signals transmission QPSK(Quadrature Phase Shift Keying)  for digital data  Digital signals transmission for digital data Non-return-to zero encoding  Return-to zero encoding  Manchester encoding  4B/5B   Digital signals transmission for analog data Pulse Code Modulation  CSE Department CSE Department 17 18 3

Introduction Introduction Three Types of Modulations QPSK (Quadrature Phase Shift Keying) QPSK QAM-16 QAM-64 2bit/signal 4bit/signal 6bit/signal CSE Department CSE Department 19 20 Introduction Introduction NRZ-L ( Non-Return-to-Zero-Level ) Uses two different voltage levels (one positive and one negative) as the signal elements for the two binary digits. Digital signals transmission Amplitude for digital data Time CSE Department CSE Department 21 22 Introduction Introduction NRZ-I ( Non-Return-to-Zero- RZ (Return-to-Zero) Invert) NRZI is a differential encoding (i.e., the signal is decoded  Uses two different voltage levels (one positive by comparing the polarity of adjacent signal elements.) and one negative)  existence of a signal transition at the middle 1  existence of a signal transition at the beginning of the bit time of the bit time (high-to-zero or low-to-zero) (either a low-to-high or a high-to-low transition) 0  no signal transition at the beginning of the bit time Amplitude Voltage Level Low duty cycle Time Time USB CSE Department CSE Department 23 24 4

Introduction Introduction Manchester encoding Manchester Encoding Example  Straight binary encoding with 0 volts for a 0 bit and 5 volts for a 1 bit because it bit 流 1 0 0 0 0 1 0 1 1 1 1 0 leads to ambiguities. 二进制编码  Different clock speeds can cause the receiver and sender to get out of synchronization about where the bit boundaries are Ethernet 曼切斯特编码  Manchester encoding is introduced for receivers to unambiguously determine the start, end, or middle of each bit without 差分曼切斯特编码 reference to an external clock. bit 与 bit 之间有跳变，下一个 bit bit 与 bit 之间无跳变，下一个 bit 为 0 为 1 CSE Department CSE Department 25 26 Introduction Introduction Pulse Code Modulation AD Transformation: sampling 、 quantifying 、 encoding Digital signals transmission for analog data PCM forms the heart of the modern telephone system ： Sampling period :125us ， 256 level quantifying ， Bit Rate ： 8*8000=64Kbps CSE Department CSE Department 27 28 Introduction Introduction Bandwidth and Bandwidth-Limited Basic Concepts of Data Transmission Signals  The range of frequencies transmitted  Fourier Analysis without being strongly attenuated is called  Data Transmission the bandwidth.  Bandwidth & the Maximum Data Rate of  The bandwidth is a physical property of a Channel the transmission medium  Asynchronous and Synchronous  usually depends on the construction, thickness, Communication and length of the medium.  Serial and Parallel Communication  A wide band signal will be distorted when transmitted thru relatively narrower band channel  with the higher harmonics cut off or hold back. CSE Department CSE Department 29 30 5

Introduction Introduction Symbol, Baud Rate and Bit Rate Maximum Data Rate  For the maximum data rate for a finite  The baud rate is the number of samples/sec bandwidth noiseless channel, Nyquist's theorem made. states:  Each sample sends one piece of information, Maximum data rate=2Hlog 2 V (b/s) that is, one symbol. The baud rate and symbol Where H is the Bandwidth and V is the discrete rate are thus the same. levels of the signal.  The modulation technique (e.g., QPSK)  Shannon's major result is that the maximum determines the number of bits/symbol data rate of a noisy channel whose bandwidth is  The bit rate is the amount of information sent H Hz, and whose signal-to-noise ratio is S/N, is over the channel given by  equal to the number of symbols/sec times the Maximum data rate = Hlog 2 (1+S/N) number of bits/symbol. S/N （ dB ） = 10log 10 S/N CSE Department CSE Department 31 32 Introduction Introduction Impact of Bandwidth on Digital Basic Concepts of Data Transmission Transmission  Fourier Analysis  Data Transmission  Bandwidth & the Maximum Data Rate of hz a Channel hz  Asynchronous and Synchronous Communication hz  Serial and Parallel Communication hz hz CSE Department CSE Department 33 34 Introduction Introduction Asynchronous and Synchronous Basic Concepts of Data Communication Transmission  Synchronous Communication:  Fourier Analysis  sender and receiver should synchronize before each transmission.  Data Transmission  The data transmitted contain information that the  Bandwidth & the Maximum Data Rate of receiver can use to determine where individual bits begin and end. a Channel  It is useful for system which always have data ready to send, e.g. the PSTN.  Asynchronous and Synchronous  Asynchronous Communication: Communication  sender and receiver don’t need to coordinate before  Serial and Parallel Communication data can be transmitted.  Thus a sender can wait arbitrarily long between transmissions, and can transmit whenever data becomes ready.  Useful for devices such as keyboards which don’t always have data ready to send. CSE Department CSE Department 35 36 6

Introduction Introduction Serial and Parallel Communication Mobile network Global ISP Advanced Home network Regional ISP Institutional network Serial: sent Parallel: send over a single multiple bits at a channel one time over multiple bit at a time lines CSE Department CSE Department 37 38 7