1. Lecture (April 11, 2000) Radio Spectrum Multiple Access Communication –TDMA –FDMA –CDMA

2. Review of Last Lecture Amplitude Modulation (AM) changes the amplitude of a sine wave Frequency Modulation (FM) changes the frequency of a sine wave Power spectrum represents the frequency content of a signal –Center Frequency and Bandwidth are two important power spectrum measurements

3. Review Logarithm to the base 2 Take notes on chalkboard

4. Power Spectrum Example Frequency (Hz) Bandwidth Center Frequency Bandwidth measures the width of the signal in frequency Center Frequency measures the center of the signal in frequency Noise Signal Power (Watts)

5. Radio Spectrum The Radio spectrum is decomposed into frequency bands Communication systems have the liberty to transmit signals at various frequencies –FCC regulates which frequencies to use Web Site –http://advanix.net/~neuhaus/fccindex/spectrum.html

6. Radio Spectrum Bands MF AM Radio Maritime HF Maritime Amateur Radio VHF Television FM radio Aviation UHF/SHF Satellite Television Cell Phones Microwave EHF Astronomy Low Frequency High Frequency

7. Considerations for Global Signal Propagation Inverse Square Law Curvature of the earth Signals reflect/bounce as they propagate through the atmosphere –Low frequency signals have a tendency to reflect and bounce through atmosphere –High frequency signals tend to go straight

8. Illustration of Global Low Frequency (MF/HF) Communication EarthA B Low frequency signals (MF/HF) bounce through atmosphere Used for AM radios, maritime communications and amateur radio

9. Illustration of Gloabal High Frequency (UHF/SHF/EHF) Communication EarthA B High frequency signals don’t bounce through atmosphere (go straight) Used for satellite communications, television, direct site microwave Satellite

10. Class Discussion Radio Spectrum Design Examples –Television –Line of Site Microwave –Cell Phones –Satellite Links

11. Multiple Access Techniques FDMA –Frequency Division Multiple Access TDMA –Time Division Multiple Access CDMA –Code Division Multiple Access

12. Illustration of FDMA Time Frequency User 1 User 2 Each user assigned a unique frequency Traditionally used for Analog Communications TV, AM/FM radio

13. Illustration of TDMA Time Frequency User 1 All users share the same frequency Users take turns using channel Commonly used for digital communications Satellite Broadcasting User 2User 1User 2

14. TDMA Example/ Class Discussion Digital Television and Fiber Optics

15. Begin CDMA Time permitting