Lecture 1 - EEL 3552C Analog and Digital Communications Dr...

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EEL 3552C Analog and Digital Communications Dr. Lei Wei Lecture 1: Chapter 1 1) Introduction a) The need to communicate Human to human (face to face) Voice, gestures, etc Human to human (long distance) Ancient methods: Runner, drum, flag, torch, pigeons, smoke (wolf dung) Modern long distance communications Radios
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Figure 1.1 Some examples of communications systems.
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Figure 1.2 Communication system. b) Typical Communication Systems Information source TX media RX Information sink Radio Communication Systems
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Figure 1.2 Communication system. b) Typical Communication Systems media RX Information sink Radio Communication Systems
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Device functionality examples Input transducer Converts information source into an electrical waveform, (baseband signal, or message) Microphone for Voice, ?? for TV picture, ?? telegraphy, data Transmitter Modifies the baseband signal for efficient transmission (modulator) Modem, codec channel A medium which passes signals from one end to the other Wire, optical fiber, radio, cable receiver Converts the modulated signal back to the message signal Modem, codec Output transducer Converts the baseband signal back to the original information source Speaker for voice ??
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type definition examples analog Values vary over a continuous range Sine digital Values are constructed with a finite number of symbols. M-ary messages noise Unwanted, from other sources, other users, (random, unpredictable Thermal noise Desired signal Intentional transmitted signal Sine wave random Unpredictable, unknown Thermal noise Deterministic signal Predictable, known Sine wave, pulse waveform Continuou s time Signal has nonzero values for infinite time slots Sine Discrete time signal Signal has nonzero values only for finite sampling times PAM
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Figure 1.3 (a) Transmitted signal. (b) Received distorted signal (without noise). (c) Received distorted signal (with noise). (d) Regenerated signal (delayed).
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Figure 7.31 (a) The modulating signal m(t) . (b) PSK: the modulated signal m(t) cos ω c t . (c) FSK: the modulated signal.
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Why Digital Communication? Not analog? Perfectly construct the original signal Encryption Perfectly control the signal quality Easy to store the data Cheap DSP chips Better channel bandwidth efficiency
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Analog to digital conversion A/D conversion Sampling Covert signal in continuous time to discrete time signal No quality loss if sampling rate is fast enough From continuous analog signal to discrete analog signal Quantization Convert signal in analog form into digital format Controllable quality in term of quantization noises Linear vs non-linear quantization methods
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Figure 1.4 Analog-to-digital conversion of a signal.
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Figure 1.5 Example of PCM encoding.
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Key factors in communication system design Channel bandwidth (B) Smaller the bandwidth required, the better Transmission rate (R) Faster, the better Signal to noise ratio (SNR)
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Lecture 1 - EEL 3552C Analog and Digital Communications Dr...

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