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Module-3 : Transmission

Module-3 : Transmission. Marc Moonen Dept. E.E./ESAT, K.U.Leuven marc.moonen@esat.kuleuven.ac.be www.esat.kuleuven.ac.be/sista/~moonen/. Module-3 : Transmission. Module 1: Introduction to Telecommunications & Networks Module 2: Telecommunication Networks and Technologies

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Module-3 : Transmission

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  1. Module-3 : Transmission Marc Moonen Dept. E.E./ESAT, K.U.Leuven marc.moonen@esat.kuleuven.ac.be www.esat.kuleuven.ac.be/sista/~moonen/ Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven/ESAT-SISTA

  2. Module-3 : Transmission • Module 1: Introduction to Telecommunications & Networks • Module 2: Telecommunication Networks and Technologies • Module 3: Transmission Techniques • Module 4: Transmission of Sound, Video & Data Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  3. Aims/Scope • Basic Digital Communication principles modulation/demodulation, detection (for the regraders/sidegraders) • New/Advanced Topics CDMA, multicarrier modulation, smart antennas (for the regraders/upgraders) • Mostly `bird’s-eye view’ skip mathematical details (if possible) selection of topics (non-exhaustive) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  4. New/Advanced Topics? • Analog & 1G Digital Communication Systems: communication over fairly `simple’ (e.g. AWGN) channels emphasis on modulation/demodulation/timing/etc... circuitry • Present Day/Future Communication Systems = box full of mathematics & signal processing for communication over highly bandwidth constrained channels, fading channels, etc... Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  5. New/Advanced Topics ? • Example: Telephone Line Modems voice-band modems : up to 56kbits/sec in 0..4kHz band ADSL modems : up to 8Mbits/sec in 30kHz…1MHz band VDSL modems : up to 52Mbits/sec in …10MHz band xDSL communication impairments: channel attenuation/distortion, echo, cross-talk, RFI,... see Lecture-7/8 x 1000 Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  6. New/Advanced Topics? x 40 • Example : Wireless Communications Typical spectral efficiency : ...1 bits/sec/Hz MIMO-transmission (`smart antennas’ & co): example : V-BLAST (Lucent Techn. 1998) …40bits/sec/Hz exploits a `rich scattering environment’ see Lecture-2, Lecture-10 Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  7. New/Advanced Topics? Enabling Technology is • Signal Processing 1G-SP: analog filters 2G-SP: digital filters, FFT’s, etc. 3G-SP: full of mathematics, linear algebra, statistics, etc... • VLSI • etc... Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  8. Overview (I) • 20/4/2000 Lecture-1 : General Intro Lecture-2 : Limits of Communication • 27/4/2000 Lecture-3 : Transmitter Design/Modulation Lecture-4 : Receiver Design/Detection • 4/5/2000 Lecture-5 : Channel Equalization Lecture-6 : Adaptive Equalization Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  9. Overview (II) • 11/5/2000 Lecture-7 : Multicarrier Modulation (I) Lecture-8 : Multicarrier Modulation (II) • 18/5/2000 Lecture-9 : Multiple Access/CDMA Lecture-10: Smart Antennas/MIMO-transmission Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  10. Assignments & Exam • Assignments Pen & paper exercises Self-study material • Exam 25/5/2000 • WWW-site : telecom.europace.be Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  11. Prerequisites • Module-1 - M. Goossens : Yes (?) • Module-2 - P. DeMeester : No • Digital Communications Background : No (?) • Mathematics Background : Yes statistics, linear algebra -> see assignments • Signal Processing Background : Yes digital filters, transforms, stochastic processes -> see assignments Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  12. Literature • E.A. Lee & D.G. Messerschmitt `Digital Communication’(Kluwer AP 1994) • J.G. Proakis `Digital Communications’(McGraw Hill 1989) • B. Sklar `Digital Communications’(Prentice-Hall 1988) • S. Haykin `Communication Systems’(Wiley 1994) • H. Meyr, M. Moeneclaey & S. Fechte `Digital Communication Receivers’(Wiley 1998) • etc... Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  13. Acknowledgement Many of the slides/text/figures/graphs are adopted from the handouts of Module T2 `Digital Communication Principles’ M.Engels, M. Moeneclaey, G. Van Der Plas 1998 Postgraduate Course on Telecommunications Special thanks to Prof. Marc Moeneclaey Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  14. Lecture-1 : General Introduction • Analog vs. Digital Communication • Digital Communication Systems Description Transmitter Channel Receiver • Preview Lectures 2->10 Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  15. Analog vs. Digital Communication (I) Analog Communication: • Transmission of signals that are inherently analog (speech, video, etc..) • Baseband or passband (AM, FM, ..) • Bandwidth = signal bandwidth Example: speech signal 0..4kHz -> BW=4kHz • Received signal subject to channel impairments, transmitter/receiver impairments, etc.. Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  16. Analog vs. Digital Communication (II) Digital Communication: • Transmission of signals that are inherently digital (`data’) or analog (speech, video, etc..) • Analog signals are converted into digital signals by sampling & quantization (A-to-D conversion) Example : - speech 0…4kHz - sampled at 8kHz (cfr. Nyquist criterion), - each sample converted into 8 bits number-> 64kbits/sec =PCM (pulse code modulation) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  17. Analog vs. Digital Communication (III) Digital Communication • What? A principle feature of a digital communication system is that during a finite interval of time, it sends a waveform from a finite set of possible waveforms. The objective of the receiver is not to reproduce the transmitted waveform, but (only) to determine which of the possible waveforms has been sent. Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  18. Analog vs. Digital Communication (IV) x 3 Digital Communication Key Features: • source coding/compression: Example: speech signal 64kbits/sec-> 11kbits/sec…4kbits/sec (through `signal modeling’) • channel coding/error correction see also Module-4 • increased spectral efficiency through coding, signal processing, etc. Example: v.34 voice-band modem 33.6 kbits/sec in 4kHz voice-band (=8bits/sec/Hz) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  19. Digital Communication System (I) • Block Diagram • Digital Information is digital signal (data) or `sampled+quantized’ analog signal (speech,..) continuous-time channel digital information digital information s(t) r(t) Tx Rx channel Transmitter with D-to-A Receiver with A-to-D Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  20. Digital Communication System (II) Transmitter • converts bit sequence into waveform s(t) (=`modulation’) • bits are grouped into `symbols’ (n bits per symbol, hence M=2^n different symbols) (=`symbol alphabet’, `constellation’) • each symbol corresponds to a different waveform segment • symbol rate = # transmitted symbols/sec = Rs (`Baud rate’, after Baudot, French telegraph engineer) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  21. Digital Communication System (III) Channel • physical medium : twisted pair, coax, optical fiber, radio • channel impairments : noise, attenuation/distortion, cross-talk, interference, etc… Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  22. Digital Communication System (IV) Receiver • Converts received signal r(t) into bit sequence (=`demodulation/detection’) • Receiver performance : Bit Error Probability (BEP) or Bit Error Rate (BER) BER = (#bit errors) / (#transmitted bits) example : voice : BER <1E-3 data : BER <1E-10 Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  23. Transmitter (I) • Transmitted bits are grouped into symbols (n bits per symbol, hence M=2^n symbols) • Transmitted symbols are • Transmitted signal is where p(t) is transmit pulse, and is symbol energy ( and p(t) are energy-normalized), Ts is symbol period Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  24. Transmitter (II) • Transmitted signal is • Linear modulation (e.g. PAM, QAM, PSK) all signal segments are proportional to the same pulse p(t) see Lecture-3 for pulse design • Non-linear modulation (e.g. FSK) emphasis on this see assignments Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  25. Transmitter (III) • Constellations for linear modulation (=`symbol alphabet’) PAM PSK QAM pulse amplitude modulation phase-shift keying quadrature amplitude modulation 4-PAM (2bits) 8-PSK (3bits) 16-QAM (4bits) ps: complex constellations for passband transmission (see Lecture-3) I I I R R R Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  26. Channel (I) Channel impairments: • attenuation/distortion (linear/non-linear) • noise (linear/non-linear) • cross-talk (1 or many) • echo (e.g. hybrid impedance mismatch) • RFI (e.g. amateur radio) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  27. s(t) Ho + channel n(t) Channel (II) • Mostly simple linear channel models • Example: AWGN-channel (additive white Gaussian noise channel) n(t) is zero-mean Gaussian process with power spectrum No/2 for |f|<B (B=bandwidth) (example: satellite communication channel) r(t)=Ho.s(t)+n(t) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  28. R(f)=H(f).S(f)+N(f) H(f) s(t) + channel Channel (III) • PS: Gaussian noise model justified through central limit theorem (ex: 1 cross-talker is non-Gaussian, 30 cross-talkers approx. Gaussian) • PS: `White’ actually means `white within useful bandwidth’ i.o. truly `white’ (->infinite power hence ill-defined) • Example: frequency-selective channel frequency-dependent channel attenuation/phase distortion (example: twisted pair, coax) n(t) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  29. Receiver (I) • Receiver retrieves transmitted symbols from received signal r(t) • This leads to an optimization problem Example: minimum distance receiver where p’(t) is transmit pulse p(t), modified by channel Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  30. 1/Ts Receiver (II) • For AWGN channels (<->frequency-selective channels), a receiver may consist of : - (a front-end `(whitened) matched filter’, WMF) - a symbol-rate sampler (i.e. 1 sample/symbol interval) - a (memory-less) decision device that decides on the nearest symbol in the symbol alphabet • Timing instant for symbol-rate sampling is crucial, hence synchronization scheme needed ! r(t) WMF see lecture 3-4 Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  31. Receiver (III) • For frequency-selective channels, the receiver may consist of - WMF + symbol-rate sampling front-end, or - anti-alias filtering + Nyquist-rate sampling front-end followed by more complicated processing: - Maximum-likelihood sequence estimation (e.g. Viterbi algorithms) - Equalization + decision device - … • See Lecture 4-5 Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  32. Preview Lectures 2->10 Lecture-2 : Limits of Communication • Given a communication channel, an amount of transmit power and transmit bandwidth, what is the maximum achievable transmission bit-rate (bits/sec), for which the bit-error-rate is sufficiently (infinitely) small ? • Shannon theory (1948) • Recent topic: MIMO-transmission (e.g. V-BLAST, cfr. supra) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  33. Preview Lectures 2->10 Lecture-3 : Transmitter Design/Modulation • Baseband vs passband modulation • Constellations for linear modulation • Transmit pulse p(t) design: `(root) raised cosine pulses’ • Simple receiver structures, eye diagrams, etc. Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  34. Preview Lectures 2->10 Lecture-4 : Receiver Design/Detection • Inter-symbol interference • Receiver front-ends : - (whitened) matched filtering + symbol-rate sampling - anti-alias filtering + Nyquist-rate sampling • Optimum detection - MAP/Maximum Likelihood-detection - MLSE/Viterbi algorithm Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  35. Preview Lectures 2->10 Lecture-5 : Receiver Design/Equalization • Equalization vs. inter-symbol interference • Equalizer structures : - Linear equalizers - Decision-feedback equalizers - Fractionally spaced equalizers • Design criteria - Zero-forcing equalization - Minimum-mean-squared-error (MMSE) equalization Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  36. Preview Lectures 2->10 Lecture-6 : Adaptive Equalization • Equalization when channel is unknown and/or time-varying • Least-mean squares algorithm (Widrow 1965) - MMSE and stochastic gradient • Recursive Least Squares algorithms - Least squares criterion - Introduction to Fast RLS algorithms Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  37. Preview Lectures 2->10 Lecture-7/8 : Multicarrier Modulation • Applications - ADSL modems (VDSL modems) • Combination of frequency-shift keying (FSK) and quadrature amplitude modulation (QAM) • Multicarrier modulation/demodulation based on fast Fourier transforms IFFT/FFT • Alleviate (?) equalization problem through usage of cyclic prefix - Time vs. frequency domain equalization Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  38. Preview Lectures 2->10 Lecture-9 : Multiple Access/CDMA • Multiple Access: - TDMA/FDMA (e.g. GSM) - CDMA (e.g. IS-95, 3G mobile comms) • CDMA code sequences • CDMA receivers - Single-user detection - Multi-user detection Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  39. Preview Lectures 2->10 Lecture-10 : Smart Antennas/MIMO transmission • Antenna array receivers - Beamforming - Channel modeling • SDMA : `spatial dvision multiple access’ allows different users to use the same frequencies/codes at the same time. Signal separation performed based on spatial properties. • MIMO-transmission (e.g. V-BLAST) Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

  40. Preview Lectures 2->10 Lecture-10 (reserve) : Echo Cancellation • Echo generation in full-duplex modems - Line echo - Acoustic echo • Echo cancellation • Adaptive echo cancellation Module-3 Transmission Marc Moonen Lecture-1 Introduction K.U.Leuven-ESAT/SISTA

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