ECE 4371, Fall, 2013 Introduction to Telecommunication Engineering/Telecommunication Laboratory

1. ECE 4371, Fall, 2013Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 2 Aug. 28th, 2012

2. Baseband and Carrier Communication • Baseband: • Describes signals and systems whose range of frequencies is measured from 0 to a maximum bandwidth or highest signal frequency • Voice: Telephone 0-3.5KHz; CD 0-22.05KHz • Video: Analog TV 4.5MHz, TV channel is 0-6MHz. Digital, depending on the size, movement, frames per second, … • Example: wire, coaxial cable, optical fiber, PCM phone • Carrier Communication: • Carrier: a waveform (usually sinusoidal) that is modulated to represent the information to be transmitted. This carrier wave is usually of much higher frequency than the modulating (baseband) signal. • Modulation: is the process of varying a carrier signal in order to use that signal to convey information. • Example on the board.

3. Modulation • Modulation • A process that causes a shift in the range of frequencies of a signal. • Gain advantages • Antenna size: half of the antenna size. Thousands of miles for baseband • Better usage of limited bandwidth: less side lopes • Trade bandwidth for SNR: CDMA • Robust to inter-symbol-interference (multipath delay) • Robust to errors and distortions • Types • Analog: AM (DSB, SSB, VSB), FM, Delta modulation • Digital: ASK, FSK, PSK, QAM, … • Pulse modulation: PCM, PDM, … Fiber, phone • Advanced: CDMA (3G), OFDM (WLAN, WMAN), ….

4. Double Sideband • Modulation: m(t)cos(wct) 0.5[M(w-wc)+M(w+wc)] • LSB, USB, DSB • DSB-SC: suppressed carrier, no carrier frequency • Wc >= bandwidth of the signal to avoid aliasing. • Demodulation: e(t)=m(t)(cos(wct))^2=0.5(m(t)+m(t)cos(2wct)) E(w)=0.5M(w)+0.25(M(w+2wc)+M(w-2wc)) Low pass filter to remove the higher frequency • Coherent and non-coherent detection • Receiver can recover the frequency and phase of the transmitter by PLL. Error of timing can cause the performance error floor • Non-coherent receiver has 3dB worst performance than coherent. • Cheaper for Non-coherent receiver, Nextel.

5. AM-DSB-SC 0 0 Lower sideband (LSB) Upper sideband (USB) 0

6. Categories of Modulators • Multiplier Modulators • Multiply m(t) by cos(wct) • Hard for linearity for high energy. Expensive. e.g. sound system • Nonlinear Modulators • Example • Switching Modulators • FFT transform to series of frequencies • Series-bridge diode modulator, shunt-bridge diode modulator • Ring Modulators

7. Frequency Conversion • Move the signals to other frequency • Multiplying two sinusoids results in two frequencies which are the sum and difference of the frequencies of the sinusoids multiplied. • To change the carrier frequency c of a modulated signal to an intermediate frequency I we use an oscillator to generate a sinusoid of frequency MIX such that BPF@ I EXAMPLE : Let m(t) be as shown. m(t) (t) e1(t) SPECTRA 0 0 0

8. 0 0 Amplitude Modulation • Why DSB-SC not working: do not know the carrier frequency in receiver. • The last impulse functions indicate that the carrier is not suppressed in this case. For some M() shown, the modulated signal spectrum is as shown. • With this type of AM the demodulation can be performed with/without a local oscillator synchronized with the transmitter.

9. AM Example • m(t) has a minimum value of about -0.4. Adding a dc offset of A=1 results in A+m(t) being always positive. Therefore the positive envelope of is just A+m(t). An envelope detector can be used to retrieve this. A=1 m(t) A+m(t) 0.7 1. 0. -0.4

10. AM Example (cont.) • The choice of dc offset should be such that A+m(t) should always be positive. Otherwise envelope detector cannot be used, but coherent still ok • For example, the minimum value of m(t) = -0.4 . Therefore A > |min(m(t))| for successful envelope detection. What if A< |m(t) |. • In the previous example let A=0.3. A+m(t) m(t) 0.7 0 0. -0.4

11. m(t) Modulation Index • Let mp be the absolute negative peak of m(t). • EXAMPLE : Single-tone modulation. Let m(t)=2sin(20t)

12. Sideband and Carrier Power

13. + - m(t) AM output + - c cos(ct) AM Generator

14. Coherent detector for demodulating DSB-SC modulated wave.

15. + vc(t) - AM signal R C AM Decoder • Rectifier Detector: synchronous • Envelope Detector: asynchronous

16. RC Selection E(t)=A(1+cos(wct))

17. GPS Orbits

18. GPS Position • By knowing how far one is from three satellites one can ideally find their 3D coordinates • To correct for clock errors one needs to receive four satellites • Differential GPS: local FM

19. Type of waves

20. Radio Frequency Bands

21. Satellite Communications • Large communication area. Any two places within the coverage of radio transmission by satellite can communicate with each other.   • Seldom effected by land disaster ( high reliability) • Circuit can be started upon establishing earth station (prompt circuit starting) • Can be received at many places simultaneously, and realize broadcast, multi-access communication economically( feature of multi-access) • Very flexible circuit installment , can disperse over-centralized traffic at any time. • One channel can be used in different directions or areas (multi-access connecting).

22. Rain Attenuation