Wireless Systems. Objectives of the course

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1 Wireless Systems Jerzy Dąbrowski Communication Systems Department of Electrical Engineering LinköpingUniversity Objectives of the course Understand operation principles of the wireless communication systems Learn techniques which enable wireless signal transmission in multi-user systems (coding, modulation, channel sharing, ) Understand physical limitations of the contemporary wireless systems 2 1

2 Organization of the course Lectures 9x2h Project work: Study on a modern communication standard Project presentation (VT2) Course book: Theodore S. Rappaport, Wireless Communications -Principles and Practice, Prentice Hall, 2002, ISBN: Written exam (VT2) 3 Overview of course content Wireless systems: underlying concepts and technologies Wireless communication channel Multiple access Signal modulation Equalization and diversity Speech coding Error control and source coding Case study examples (e.g. GSM, WCDMA, LTE) 4 2

3 Key invention - Radio G.Marconi, A.Popov(1895) Radio broadcasting, R.Fessenden(1906) Heterodyne, Armstrong (1918) FM radio, E.Armstrong(1933) Detector Resonant circuit 2πf 0 = 1 LC Headphones Z > 2kΩ Digital radio TRx PA RF Filter LNA LP Filter I I LO Q Q LP Filter Frequency synthesizer LP Filter ADC DAC Base-band processor 5 Wireless communication channel Information Source Transmitter Channel Receiver Information Sink Physical layer of WS Conveys bit-stream of data Channel issues: - Loss - Interference - Distortion - Time-varying nature - Noise Transmitter/Receiver: - Filtering - Amplification - Modulation - Demodulation - Synchronization - 6 3

4 OSI model 7 OSI /Data Link Layer Deals with packets of bits Provides block synchronization Detects and corrects data errors Responsible for Medium Access Control (FDMA, TDMA, CDMA, SDMA) Responsible for power control and handover (of mobile terminals) 8 4

5 OSI /Network Layer Delivers packets to their correct destination (routing) Determines QoS Controls flow in system to avoid congestions 9 OSI /Higher Layers Transport layer Provides end-to-end communication. TCP in TCP/IP belongs here. ARQ can also be used here. Session layer Opens, closes and manages a communication session. Presentation layer Translates data for communication. Application layer The actual purpose or usage. Examples: SSH, FTP, IMAP These layers are less affected by the transmission medium 10 5

6 Multiple access FDMA base-line technique TDMA N channels = band f f f N time slots = frame t t t t t t Users_operate simultanously on individual frequencies Users_share the channel in different time slots CDMA N codes in same band C1 C2 C3 Users_operate simultanously and share the channel using individual codes 11 Modulation Necessary to convert signal into radio-waves Amplitude, frequency, and phase Constant amplitude modulation Pulse shaping, MSK Quadrature carriers (sine, cosine) QAM Multiple carriers (OFDM) Sinusoidal Carrier : v C ( t) = V cos C ( ω t + φ ) Frequency Phase Amplitude Angle C C Issues: distortions, ISI, bandwidth, noise spectral efficiency vs power efficiency (advanced modulation schemes vs amp. Linearity) 12 6

7 Modulation/ M-ary QAM s QAM (t) = α i cosω c t + β i sinω c t β α High spectral efficiency, R/BW But susceptible to noise and distortion (needs linear amplification) 16-ary QAM constellation (4 bits are grouped in 1 symbol) (T S and T S > τ av ) 13 Modulation/ OFDM Multiple sub-carriers to transmit signal bits in parallel for very high throughput Spectra of different sub channels can partly overlap OFDM is usually combined with QAM or n-psk PSD f c1 f c2 f c3 Tone modulated by rectangular pulse with interval T S f Orthogonal -spaced by 1/T S BW on each carrier < channel coherence BW freq. sel. fading avoided Implementation technique: IFFT/FFT 14 7

8 Equalization and diversity Channel band limited and provides multiple signal paths ISI occurs which can be corrected by equalization filters (usually adaptive), T S < σ τ Signal impairments (fading) can be corrected by diversity (redundancy by multiple signal samples over each symbol interval) - space diversity (multiple antennas, MIMO) - frequency diversity (multiple carriers, freq. hopping) - time diversity (RAKE receiver, interleaving) - polarization diversity 15 Error control coding & Speech coding Detection and correction of errors incurred in transmission //Forward error correction (FEC) - Convolutional and Turbo codes / correction -Block codes / Error Detection -Automatic repeat request (ARQ) latency issue Support by Interleaving (splitting bursts of possible errors in single errors) To reduce data rate and save bandwidth various speech coding techniques (LPC, Vocoders, Time/frequency coders, ) 16 8

9 Lectures 1. Introduction 2. Channel model 3. Multiple access 4. Modulation techniques 5. Equalization and diversity 6. Speech coding 7. Error control coding 8. Mobile telephony /Evolution of Communication systems 9. Overview of contemporary wireless systems 17 Timeline 2016 When Wednesday, January 20 Wednesday, February 3 Friday, February 5 Weeks 6-7 Monday, February 22 Week 8 Weeks 9-15 Monday, April 18 Week 16. Weeks Monday, May 9 Friday, May 13 Week Deadline Deadline Deadline Deadline What Course start Project selection List of three topics by to Jerzy Dabrowski. Announcing project assignment Searching information, initial reading. Outline By as a PDF to your supervisor. Supervision sessions. Reading and writing. Beta version of the report as a PDF to Jerzy Dabrowski via Urkund. Supervision sessions. Reading and rewriting. Final version of the report as a PDF to Jerzy Dabrowski via Urkund. Announcing three chosen reports and publishing all reports. Presentation seminars. 4 9

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