TRUYỀN THÔNG SỐ DIGITAL COMMUNICATION ppt

TRUYỀN THÔNG SỐ DIGITAL COMMUNICATION 30 tiết, 2 tín chỉ 1 Mục tiêu: • Học phần này, tiếp theo học phần Các hệ thống truyền thông, có mục tiêu cung cấp cơ sở cho các học phần Truyền thông không dây, Truyền thông di động. Đánh giá kết quả học tập: • Bài tập ở nhà nộp cho giảng viên: 30% tổng điểm • Thi hết môn học: 70% Tài liệu tham khảo: – Bài giảng (Dựa trên bài giảng của Uppsala University và cuốn 1) – 1. Digital Communications Fundamentals and Applications, Bernard Sklar – 2. “Digital Communications”, Jonh G. Proakis, McGraw-Hill, 2001 – Internet 2 What is Digital Communication? • Digital Communication is any message passed through digital devices • Digital Communication can be easy and quick to use • E.g. of digital communication are: – E-mailing - Computers – Texting - Cell Phones 3 Receiver Transmitter A basic digital communication system Source Encoder Source Decoder Channel Encoder Channel Decoder Demodulator Data Sink Data Source Modulator channel 4 Bit Error Rate (BER) / Symbol Error Rate (SER) Nội dung môn học Contents of the course 1. Source coding / Mã hóa nguồn 2. Channel coding / Mã hóa kênh 3. Modulation (Baseband and passband signaling) / Điều biến 5 Week 1: • Need to know before studying a DCS – Classification of signals – Random process – Autocorrelation – Power and energy spectral densities – Noise in communication systems – Signal transmission through linear systems – Bandwidth of signal 6 7 Key blocks: • Formatting: transforms the source information into bits. • Modulation: the process by which message symbols or channel symbols are converted to waveforms that are compatible with the requirements imposed by the transmission channel. • Pulse modulation: transform each symbol from a binary representation to a baseband waveform. 8 Key blocks: • Bandpass modulation: basepand waveform g i (t) is frequency translated by a carrier wave to a frequency that is much larger than g i (t), called bandpass waveform s i (t), i = 1, … , M. (M-ary pulse waveform types). • Source coding: converts A/D (for analog souces) and removes redundant information  formatting transformation (for digizing). • Channel coding, for a given data rate, can deduce the probability of error, P E, at the expense of transmission BW or decoder complexity. 9 Classification of signals • Deterministic and random signals – Deterministic signals: whose values are completely specified for any given time. Thus, a deterministic signal can be modeled by a known function of time. • E.g. x(t) = 5.cos10t – Random signals: also called non deterministic signals are those signals that take random values at any given time and must be characterized statistically . • E.g. Noise in electronic circuits 10 [...]... (d) (e) 50dB 29 • Half-power BW: Gx(f) drop to half-power or -3 dB • Noise equivalent BW: Wn = Px/Gx(fc); Px is total signal power over all freq • Null-to-null BW: the most popular measure of BW for digital communications is the width of the main spectral lobe, where most of the power is contained • Fractional power containment BW: the band leaves 0.5% of the signal power above the upper band limit and... lower band limit • Bounded power spectral density: the band leaves a certain stated level Typical attenuation levels = 35 or 50 dB • Absolute bandwidth = infinite 30 Conclusion • Important features of digital communication systems • Some basic concepts and definitions as signal classification, spectral density, random process, linear systems and signal bandwidth 31 ... dt = ∑n =-∞ cn 2 ∞ 2 – Power spectral density (PSD): • Random process: – Power spectral density (PSD): 20 Fig Autocorrelation and Power Spectral Density 21 Bài tập Tìm Ex hay Px tương ứng 22 Noise in communication systems   Thermal noise is described by a zero-mean Gaussian random process, n(t) Its PSD is flat, hence, it is called white noise [w/Hz] Power spectral density of white noise Probability . TRUYỀN THÔNG SỐ DIGITAL COMMUNICATION 30 tiết, 2 tín chỉ 1 Mục tiêu: • Học phần này, tiếp theo học phần Các hệ thống truyền thông, có mục tiêu cung cấp cơ sở cho các học phần Truyền thông. 1) – 1. Digital Communications Fundamentals and Applications, Bernard Sklar – 2. Digital Communications”, Jonh G. Proakis, McGraw-Hill, 2001 – Internet 2 What is Digital Communication? • Digital Communication. Communication? • Digital Communication is any message passed through digital devices • Digital Communication can be easy and quick to use • E.g. of digital communication are: – E-mailing - Computers – Texting