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Session 2. Objectives: By the end of this session, the student will be able to: Distinguish between data and signals. Cite the advantages of digital data and signals over analog data and signals Identify the 3 basic components of a signal
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Objectives: By the end of this session, the student will be able to: • Distinguish between data and signals. Cite the advantages of digital data and signals over analog data and signals • Identify the 3 basic components of a signal • Discuss the bandwidth of a signal & how it relates to data transfer speed • Identify signal strength and attenuation, and how they are related • Outline the basic characteristics of transmitting analog data with analog signals, digital data with digital signals, digital data with analog signals and analog data with digital signals • List and draw diagrams of the basic digital encoding techniques, and explain the advantages and disadvantages of each • Identify the different shift keying (modulation) techniques and describe their advantages, disadvantages, and uses • Identify the two most common digitization techniques and describe their advantages and disadvantages • Discuss the characteristics and importance of spread spectrum encoding techniques • Identify the different data codes and how they are used in communication systems
Analog Signals Frequency Amplitude Spectrum? Bandwidth? Effective bandwidth? 8
Analog Signals B Y X A Spectrum Human Voice Spectrum: 300Hz – 3400Hz Bandwidth: 3100Hz Bandwidth = Y – X Effective Bandwidth = B - A 9
Attenuation / Amplification dB = 10log10(P2 / P1) P1 – power level at transmitter P2 – power level at receiver A loss of 50% power is -3dB. Whether the loss is from 1000W to 500W or from 10W to 5W. 11
Digital Encoding Schemes NRZ-L (Non-Return to Zero Level) Binary 0 – represented by presence of voltage Binary 1 – represented by absence (or low) voltage 14
Digital Encoding Schemes NRZ-I (Non-Return to Zero Inverted) Binary 0 – represented by no voltage change at the time mark Binary 1 – represented by a change in voltage at the time mark What happens to NRZ-I and NRZ-L encoding when transmitting a long series of binary zeros? 15
Digital Encoding Schemes Manchester Binary 0 – represented by change from high to low in the middle of the time mark Binary 1 – represented by a change from low to high in the middle of the time mark 16
Digital Encoding Schemes Differential Manchester Binary 0 – represented by change at the beginning of the time mark Binary 1 – represented by no change at the beginning of the time mark What happens to Manchester and Differential Manchester encoding when transmitting a long series of binary zeros? Self-clocking 17
Bipolar-AMI • Bipolar-AMI Digital Encoding • 3 voltage levels: • binary 0 = zero voltage • binary 1 = positive or negative voltage sent depending on last binary 1 sent (negative voltage last sent -> positive voltage sent this time) 18
Pulse Code Modulation • Twice the sample rate 28
EBCDIC 32
ASCII 33
Review NRZ-L NRZ-I Manchester DiffManchester Bipolar-AMI 4B/5B Encoding 0V 0V 0V 0V 0V 34 0V