ECE 4371 Fall 2017 Introduction to Telecommunication EngineeringTelecommunication

ECE 4371, Fall, 2017 Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 3 Sep. 11 st, 2017

Overview l Homework – 4. 2. 1, 4. 2. 3, 4. 2. 5, 4. 2. 7, 4. 2. 9 – – – 4. 3. 3, 4. 3. 8 4. 4. 2, 4. 4. 4 4. 5. 2 4. 8. 1 Due 9/25/17 l FDM system, section 4. 7 Analog TV, section 4. 9 l Phase-locked loop, Section 4. 8 l FM basics 5. 1 -5. 3 l

Block diagram of FDM system.

FMA of SSB for Telephone Systems

Illustrating the modulation steps in an FDM system

AM Broadcasting l History l Frequency – Long wave: 153 -270 k. Hz – Medium wave: 520 -1, 710 k. Hz, AM radio – Short wave: 2, 300 -26, 100 k. Hz, long distance, SSB, VOA l Limitation – Susceptibility to atmospheric interference – Lower-fidelity sound, news and talk radio – Better at night, ionosphere.

Superheterodyne vs. homodyne l Move all frequencies of different channels to one medium freq. – In AM receivers, that frequency is 455 k. Hz, – for FM receivers, it is usually 10. 7 MHz. – Filter Design Concern – Accommodate more radio stations – Edwin Howard Armstrong

Television Digital Display (CRT) Analog Display (TV) Eliminate flicker effects

Deflection Signal and Synchronization Deflection signal and synchronization signal 525 30=8. 27 M

Solar Power and Human Eye

RGB, LIQ m. L=0. 3 mr+0. 59 mg+0. 11 mb m. I=0. 6 mr+0. 28 mg-0. 32 mb m. Q=0. 21 mr-0. 52 mg+0. 31 mb

Bandwidth VSB and QAM

Comb Filtering

NTSC, PAL, and SECAM l National Television System Committee – Low complexity, higher vertical color resolution – 525 line/60 Hz(30 frames per second) l Phase Alternative Line: PAL – The phase of the color components is reversed from line to line – Robust to Multipath, phase distortion – 625 line/50 Hz(25 frames per second), slightly larger bandwidth l SECAM – Requires the receiver to memorize the content of each line l Mono when used for different standards

TV standards in the world

Carrier Recover Error l DSB: e(t)=2 m(t)cos(wct)cos((wc+ w)t+ ) e(t)=m(t) cos(( w)t+ ) – Phase error: if fixed, attenuation. If not, shortwave radio – Frequency error: catastrophic beating effect l SSB, only frequency changes, f<30 Hz. – Donald Duck Effect l Crystal oscillator, atoms oscillator, GPS, … l Pilot: a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes.

Phase-Locked Loop l Can be a whole course. The most important part of receiver. l Definition: a closed-loop feedback control system that generates and outputs a signal in relation to the frequency and phase of an input ("reference") signal l A phase-locked loop circuit responds both to the frequency and phase of the input signals, automatically raising or lowering the frequency of a controlled oscillator until it is matched to the reference in both frequency and phase.

Voltage Controlled Oscillator (VCO) l W(t)=wc+ce 0(t), where wc is the free-running frequency l Example

Ideal Model Si Sp Sv LPF So VCO – Si=Acos(wct+ 1(t)), Sv=Avcos(wct+ c(t)) – Sp=0. 5 AAv[sin(2 wct+ 1+ c)+sin( 1 - c)] – So=0. 5 AAvsin( 1 - c)=AAv( 1 - c) l Capture Range and Lock Range

Phase and Frequency Acquisition

Carrier Acquisition in DSB-SC l Signal Squaring method l Costas Loop l SSB-SC not working

PLL Applications l Clock recovery: no pilot l Deskewing: circuit design l Clock generation: Direct Digital Synthesis l Spread spectrum: l Jitter Noise Reduction l Clock distribution

FM Basics l VHF (30 M-300 M) high-fidelity broadcast l Wideband FM, (FM TV), narrow band FM (two-way radio) l 1933 FM and angle modulation proposed by Armstrong, but success by 1949. l Digital: Frequency Shift Key (FSK), Phase Shift Key (BPSK, QPSK, 8 PSK, …) l AM/FM: Transverse wave/Longitudinal wave

Angle Modulation vs. AM l Summarize: properties of amplitude modulation – Amplitude modulation is linear u just move to new frequency band, spectrum shape does not change. No new frequencies generated. – Spectrum: S(f) is a translated version of M(f) – Bandwidth ≤ 2 W l Properties of angle modulation – They are nonlinear u spectrum shape does change, new frequencies generated. – S(f) is not just a translated version of M(f) – Bandwidth is usually much larger than 2 W

Angle Modulation Pro/Con Application l Why need angle modulation? – Better noise reduction – Improved system fidelity l Disadvantages – Low bandwidth efficiency – Complex implementations l Applications – – – FM radio broadcast TV sound signal Two-way mobile radio Cellular radio Microwave and satellite communications

Instantaneous Frequency • Angle modulation has two forms - Frequency modulation (FM): message is represented as the variation of the instantaneous frequency of a carrier - Phase modulation (PM): message is represented as the variation of the instantaneous phase of a carrier

Phase Modulation l PM (phase modulation) signal

Frequency Modulation l FM (frequency modulation) signal (Assume zero initial phase)

FM Characteristics l Characteristics of FM signals – Zero-crossings are not regular – Envelope is constant – FM and PM signals are similar

Relations between FM and PM

FM/PM Example (Time/Frequency)

Frequency Modulation l FM (frequency modulation) signal (Assume zero initial phase)

Example Consider m(t)- a square wave- as shown. The FM wave for this m(t) is shown below. m(t) 0 T 2 T

Frequency Deviation l Frequency deviation Δf – difference between the maximum instantaneous and carrier frequency – Definition: – Relationship with instantaneous frequency – Question: Is bandwidth of s(t) just 2Δf? No, instantaneous frequency is not equivalent to spectrum frequency (with non-zero power)! S(t) has ∞ spectrum frequency (with non-zero power).

Modulation Index l Indicate by how much the modulated variable (instantaneous frequency) varies around its unmodulated level (message frequency) A l Bandwidth

Narrow Band Angle Modulation Definition Equation Comparison with AM Only phase difference of Pi/2 Frequency: similar Time: AM: frequency constant FM: amplitude constant Conclusion: NBFM signal is similar to AM signal NBFM has also bandwidth 2 W. (twice message signal bandwidth)

Example

Block diagram of a method for generating a narrowband FM signal.

A phasor comparison of narrowband FM and AM waves for sinusoidal modulation. (a) Narrowband FM wave. (b) AM wave.

Wide Band FM l Wideband FM signal l Fourier series representation

Example

Bessel Function of First Kind

Spectrum of WBFM (Chapter 5. 2) l Spectrum when m(t) is single-tone l Example 2. 2

Bandwidth of FM l Facts – FM has side frequencies extending to infinite frequency theoretically infinite bandwidth – But side frequencies become negligibly small beyond a point practically finite bandwidth – FM signal bandwidth equals the required transmission (channel) bandwidth l Bandwidth of FM signal is approximately by – Carson’s Rule (which gives lower-bound)

Carson’s Rule l Nearly all power lies within a bandwidth of – For single-tone message signal with frequency fm – For general message signal m(t) with bandwidth (or highest frequency) W