現代通信原理課件(英文版)(ppt 35頁)

What must be considered when you design a communication system?
1. Selection of the information-bearing waveform
2. Bandwidth and power of the waveform
3. Effect of system noise on the received information
4. Cost of the system
Function of transmitter ：
1）signal processor
In analog system it may be an analog low-pass filter; In hybrid one, it may be analog-to-digital converter(ADC)
2)Function of signal-processing block in hybrid one Source coding Channel coding(adding parity and others)
3) Function of Carrier Circuits modulation
Channel：
1） Classification: wire and wireless
Wire channel including twisted-pair telephone line/Coaxial cables,waveguides and fiber-optic cables
Wireless channel having air,vacuum and seawater
2) Note: The general principles of digital and analog modulation apply to all types of channels, although channel characteristics may impose constraints that favor a particular type of signaling
Receiver：
The receiver takes the corrupted signal at the channel output and converts it to a baseband signal that can be handled by the receiver baseband processor, and then the receiver baseband processor estimate the source information and output the estimation result
Summary：
The goal is to design communication system that transmit information to the receiver with as little deterioration as possible while satisfying design constrains such as allowable transmitted energy,allowable signal bandwidth and cost.
In digital system measure of deterioration is taken to be bit error rate(BER),while in analog system the performance measure is usually taken to be the signal-to-noise ratio(SNR) at the receiver output.

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