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Wireless Transmission

Wireless Transmission. The Electromagnetic Spectrum Radio Transmission Microwave Transmission Infrared and Millimeter Waves Lightwave Transmission. The Electromagnetic Spectrum. The electromagnetic spectrum and its uses for communication. Radio Transmission.

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Wireless Transmission

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  1. Wireless Transmission • The Electromagnetic Spectrum • Radio Transmission • Microwave Transmission • Infrared and Millimeter Waves • Lightwave Transmission

  2. The Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication.

  3. Radio Transmission (a) In the VLF, LF, and MF bands, radio waves follow the curvature of the earth. (b) In the HF band, they bounce off the ionosphere.

  4. Politics of the Electromagnetic Spectrum The ISM bands in the United States.

  5. Four possibilities to consider: • analog data via analog transmission “as is” (e.g., radio) • analog data via digital transmission sampling (e.g., voice, audio, video) • digital data via analog transmission broadband & wireless • digital data via digital transmission baseband (e.g., Ethernet)

  6. Common to both: 1)problem of attenuation. 2)decrease in signal strength as a function of distance.

  7. Increase strength of signal via amplifiers (analog) and repeaters(digital).

  8. Analog transmission of digital data : Three pieces of information to manipulate: amplitude , frequency , phase. 1. Amplitude modulation (AM): encode bits using amplitude levels. 2. Frequency modulation (FM): encode bits using frequency differences. 3. Phase modulation (PM): encode bits using phase shifts

  9. Bit Rate and Baud Rate Bit rate is the number of bits per second. Baud rate is the number of signal elements per second.

  10. AM with 8 levels or PM with 9 phases and if baud rate is 20 signals per seconds then find out bit rate of the AM or PMS Sol: 20*3 20*4

  11. Bit Rate(N)=Sxr Here S is number of signal per seconds r is the number of data elements or bits in one signal • Here r=Log2L. • Here L is number of levels or phases or number of frequency.

  12. An analog signal carries 4 bits per signal element. If 1000 signal elements are sent per second, find the bit rate. Sol:, r = 4, S = 1000, and N is unknown. We can find the value ofN from N=Sxr= 1000 x 4 =4000 bps

  13. Amplitude Shift Keying In amplitude shift keying, the amplitude of the carrier signal is varied to create signal elements. Both frequency and phase remain constant while the amplitude changes.

  14. We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What are the carrier frequency and the bit rate if we modulated our data by using ASK with d =I? Sol:The middle of the bandwidth is located at 250 kHz. This means that our carrier frequency can be at fe =250 kHz. We can use the formula for bandwidth to find the bit rate (with d =1 and r =1). B =(l +d) x S=2 x N X! =2 XN =100 kHz ...... N =50 kbps

  15. Frequency Shift Keying In frequency shift keying, the frequency of the carrier signal is varied to represent data. The frequency of the modulated signal is constant for the duration of one signal element, but changes for the next signal element if the data element changes. Both peak amplitude and phase remain constant for all signal elements.

  16. We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What should be the carrier frequency and the bit rate if we modulated our data by using FSK with d =1?

  17. Phase Shift Keying • In phase shift keying, the phase of the carrier is varied to represent two or more different signal elements. Both peak amplitude and frequency remain constant as the phase changes.

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