1-2.IntroductiontoDigitalCommunicationSystems数字通信系统和WLAN(台湾).ppt

Introduction to Digital Communication Systems 陳棟洲 2006/01/04 Outline Block Diagram of Digital Communication Systems Spectrum Formatting (Sampling, Quantization) Source Coding Multiplexing and Multiple Access Pulse Modulation Demodulation/Detection Bandpass Modulation Channel Coding Interleaving Spread Spectrum Block Diagram of Digital Communication Systems Analog Communication System Block Diagram Modulation 什麼是Modulation? 為什麼要Modulation? Why digital? Regeneration The primary advantage is the ease with which digital signals, compared with analog signals, are regenerated. Digital Communication System Block Diagram Block Diagram of a Typical Digital Communication System Spectrum Fourier Series Periodic Signal g(t) = g(t + T0) Period: T0 Frequency: f0 = 1/ T0 Trigonometric Fourier Series Fourier Series Complex Exponential Fourier Series Euler’s Formula ejq = cosq + jsinq e-jq = cosq - jsinq Fourier Series Example: Sine Wave g(t) = cos(2pt) + cos(4pt) Fourier Series Example: Periodic Pulse Train T/T0 = 1/5 Fourier Transform Nonperiodic Signal Fourier Transform Fourier Transform Fourier Transform Example: Rectangular Pulse Fourier Transform Example: Sinc Pulse (Lowpass Filter) Duality: G(t) ? g(-f) Fourier Transform Example: RF Pulse Fourier Transform Example: Modulation Fourier Transform Example: Demodulation Power Spectral Density Power Signal Power PSD Power Spectral Density Random Signal Example: A binary random sequence with unit-amplitude bipolar pulses Bandwidth Formatting Formatting Baseband Systems Formatting Textual Data(Character Coding) 7-bit ASCII Messages, Characters, and Symbols Example: Transmitting the Word “CHU” Character Coding: Encode the word “CHU” into a sequence of bits, using 7-bit ASCII coding, followed by an eighth bit for error detection, per character. (even-parity code) 110000110001001010101010 4-ary PAM: Partition the bit stream into k = 2 bit segments. Represent each of the 2-bit segments as a symbol. s3 s0 s0 s3 s0