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Lecture 4. Review of Lecture 3 Transmission medium Signal encoding techniques Digital data into digital signals Digital data into analog signals Analog data into digital signals . Line Encoding. Encoding data into signals Digital data into digital signal

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Lecture 4 l.jpg
Lecture 4

  • Review of Lecture 3

  • Transmission medium

  • Signal encoding techniques

    • Digital data into digital signals

    • Digital data into analog signals

    • Analog data into digital signals

ECS 152A Computer Networks


Line encoding l.jpg
Line Encoding

  • Encoding data into signals

    • Digital data into digital signal

    • Analog data into digital signal

    • Digital data into analog signal

    • Analog data into analog signal

ECS 152A Computer Networks


Analog and digital data transmission l.jpg
Analog and Digital Data Transmission

  • Data

    • Entities that convey meaning

  • Signals

    • Electric or electromagnetic representations of data

  • Transmission

    • Communication of data by propagation and processing of signals

ECS 152A Computer Networks


Slide4 l.jpg
Data

  • Analog

    • Continuous values within some interval

    • e.g. sound, video

  • Digital

    • Discrete values

    • e.g. text, integers

ECS 152A Computer Networks


Signals l.jpg
Signals

  • Means by which data are propagated

  • Analog

    • Continuously variable

    • Various media

      • wire, fiber optic, space

    • Speech bandwidth 100Hz to 7kHz

    • Telephone bandwidth 300Hz to 3400Hz

    • Video bandwidth 4MHz

  • Digital

    • Use two DC components

ECS 152A Computer Networks


Data and signals l.jpg
Data and Signals

  • Usually use digital signals for digital data and analog signals for analog data

  • Can use analog signal to carry digital data

    • Modem

  • Can use digital signal to carry analog data

    • Compact Disc audio

ECS 152A Computer Networks


Encoding digital data into digital signal l.jpg

0

1

0

1

1

1

1

0

0

Unipolar

NRZ

Polar NRZ

NRZ-Inverted

(Differential

Encoding)

Bipolar

Encoding

Manchester

Encoding

Differential

Manchester

Encoding

Encoding digital data into digital signal

ECS 152A Computer Networks


Key design issues l.jpg
Key Design Issues

  • Bandwidth

  • Timing information

  • Immunity to noise

  • Signal power

  • Error detection

ECS 152A Computer Networks


Power spectrum of different encoding schemes l.jpg
Power spectrum of different encoding schemes

  • NRZ has spectrum that is concentrated at the lower frequencies

  • Bipolar codes are designed for bandpass channels

  • Manchester encoding requires higher bandwidth

ECS 152A Computer Networks


Differential encoding l.jpg
Differential Encoding

  • Detecting transitions is more immune to noise

  • Differential encoding

    • The signal level or the transition depends on the preceding sequence of bits

    • Error occur in pairs

ECS 152A Computer Networks


Bit error rate and eb no l.jpg
Bit Error Rate and Eb/No

  • Different encoding schemes need different amount signal power for a given probability of bit error.

ECS 152A Computer Networks



Encoding digital data into analog signals l.jpg
Encoding Digital Data into Analog Signals

ECS 152A Computer Networks


Modulating a signal l.jpg

1

0

1

1

0

1

(a) Information

+A

+A

(b) Baseband

Signal Xi(t)

(c) Modulated

Signal Yi(t)

t

6T

2T

4T

5T

T

3T

0

6T

2T

4T

5T

3T

T

0

-A

-A

t

6T

2T

4T

5T

3T

T

0

+2A

(d) 2Yi(t) cos(2fct)

t

-2A

Modulating a signal

ECS 152A Computer Networks


Multilevel psk l.jpg

Bk

Bk

Ak

Ak

16 “levels”/ pulse

4 bits / pulse

4W bits per second

4 “levels”/ pulse

2 bits / pulse

2W bits per second

Multilevel PSK

ECS 152A Computer Networks


Other constellation l.jpg

Bk

2-D signal

2-D signal

Ak

Bk

Ak

16 “levels”/ pulse

4 bits / pulse

4W bits per second

4 “levels”/ pulse

2 bits / pulse

2W bits per second

Other constellation

ECS 152A Computer Networks


Analog data to digital signals l.jpg
Analog Data to Digital Signals

  • Analog data is digitized to digital data – codec (coder/decoder)

  • Digital data can be encoded to digital signals

  • Digital data can also be encoded into analog signal

ECS 152A Computer Networks


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Pulse Amplitude Modulation

  • The signal is sampled at a rate higher than twice the maximum frequency – Nyquist Sampling Theorem

ECS 152A Computer Networks


Pulse code modulation l.jpg
Pulse Code Modulation

  • Pulse amplitude modulation

  • Quantization

    • Quantization error for n bit quantized sample

    • SNR(db) = 6.02n + 1.76bB

ECS 152A Computer Networks


Nonlinear encoding l.jpg
Nonlinear Encoding

  • In linear encoding the quantization levels are equally spaced

  • Lower amplitude values have higher errors

  • Companding (Compressing-expanding)

ECS 152A Computer Networks


Delta modulation l.jpg
Delta Modulation

ECS 152A Computer Networks