1 A first course in Telecommunications: a top-down approach Peter Driessen Faculty of Engineering University of Victoria

2 Outline u Introduction u Traditional course curriculum u New course curriculum –Systems –Link budget –Modulation –Spectra u Discussion

3 Introduction u The traditional first course in telecommunications –Analog modulation: AM, SSB, FM –Noise, threshold effect, capture effect u New top-down approach –Baseband digital –Link budget –General amplitude/phase modulation –AM and FM as special cases

4 Telecommunications courses Signals, spectra, AM, SSB, FM Digital modulation Coding Microwave components Fiber optics Antennas Networks and protocols Wireless systems 3rd year 4th year Digital filters

5 Traditional course curriculum First course in telecommunications –Signals and spectra –Linear filtering –Analog modulation: AM, SSB, FM –Noise, threshold effect, capture effect

6 Top down course curriculum u Definition of telecommunications u Idea of carrier wave u Link budget u Baseband message signals u General amplitude/phase modulation u General demodulation u AM, FM, PSK etc as special cases

7 Definition of telecommunications u Science and technology of communications at a distance by electronic transmission … –(Webster’s)

8 Telecommunications system u Convert from human readable form –Speech, music, image, video, text, data) u To electronic form u Transmit over a distance (between points A and B) via some channel (electronic pathway) u Convert back to human readable form

9 Channel u The electronic pathway between points A and B may be –Wire (twisted pair) –Coaxial cable –Fiber optics –Free space (wireless) u A carrier wave is needed (in most cases) to carry the message over a distance via the channel

10 Networks u Networks consist of nodes and channels u Messages may be sent from node A to node B via intermediate nodes C, D, … A C D B node channel

11 Carrier frequencies u The radio spectrum from DC to daylight –Long wave, AM broadcast, shortwave, TV, FM broadcast, two-way radio, more TV, cellphones, GPS, more cellphones, microwave ovens, wireless LANs, police radar, infrared, lightwave, ultraviolet, xrays, …

12 Link budget u To find out how much distance we can cover with the carrier wave u Available resources –Transmit power – bandwidth u Obstacles –Noise – interference

13 Link budget 2 u P_r,o –Receive power needed for acceptable quality u P_r,n –Receive power obtained via the channel u For the link to work u M = P_r,o - P_r,n > 0

14 Link budget 3 u P_r,o = P_T + G_T + G_R - L_0 u P_r,n = (S/N) + W + F - k u Examples –Range of cellphone from tower –Data rate of images from Saturn –Transmit power of FM and TV broadcast –Size of antenna needed for one-mile wireless LAN link

15 Analog and digital messages u Sine wave message may be –Fourier component of analog message –Filtered one-zero data pattern ….

16 Modulation General amplitude/phase modulation s(t) = a(t) cos[2pi f t + phi(t)] = x(t) cos[2pi f t] - y(t) sin[2pi f t] Special cases AM: a(t) = 1 + m(t), phi(t) = constant SSB: x(t) = m(t), y(t) = hilbert[m(t)] FM: a(t) = constant, phi(t) = integral[m(t)]

17 3-D signal representation u Side views: x(t), y(t) u End view: a(t), phi(t) x(t) y(t) t

18 Demodulation - receivers u General I-Q receiver yields x(t), y(t) u Envelope a(t) = sqrt[ x^2(t) + y^2(t) ] u Phase phi(t) = arctan[y(t)/x(t)] u Frequency f(t) = d phi(t)/ dt u Traditional analog demodulation circuits implement these equations u Digital demodulators program these equations in software or firmware

19 General orthogonal modulator structure u QAM on 4 carriers u 8 - dimensional signalling space u In each dimension during each symbol time, can send –0 –0 or 1 –+1 or -1 –Multilevel +3/+1/-1/-3 u Mapper takes 1,2,4,8 or 16 bits per symbol

20 90 f2 90 f4 90 f3 90 f1 Bits in Waveform out Demux map General modulator - up to 8 orthogonal streams

21 General orthogonal modulator structure 2 u Mapper takes 1,2,4,8 or 16 bits per symbol u 1 bit: –binary FSK, ASK, PSK u 2 bits: –4 level ASK, 4-PSK (QPSK) –Binary ASK or PSK on two carriers –FSK (two carriers at one time, choose (f_1 or f_2) and (f_3 or f_4) –MFSK (choose one out of 4 carriers) u 4 or more bits: many combinations

22 Signal spectra u Compute spectra using sine wave messages m(t) u Illustrate concept of sidebands with audio demo u 220 Hz 440 Hz u AM u FM

23 AM/FM spectra u Bell sound using combined AM/FM u s(t) = a(t) cos[2pi fc t + b(t) sin 2pi fm t] u a(t) = exp(-t/t1) u b(t) = b0 exp (-t/t2) shortlong

24 Discussion u Top-down approach creates motivation, context and structure u Link budget provides intuition about tradeoffs between power, bandwidth and distance u General modulator unifies AM, FM, PSK etc.