There are basically two types of transmission systems depending on the range of frequencies over which transmission takes place.
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Requirements of Pass band Transmission:-
1. Maximum data transmission rate.
2. Minimum transmitted power.
3. Minimum probability of error Pe.
4. Minimum Circuit complexity.
5. Maximum Channel Bandwidth.
Advantages of Pass band Transmission over Base band Transmission:-
1. Long distance transmission is possible.
2. Analog channels can be used for transmission.
3. Multiplexing techniques can be used for Band width Conservation.
4. Problems such as inter symbol interference and Cross talk are absent.
5. Pass band transmission can take place over wireless channels also. therefore Large variety of modulation techniques are available.
Drawbacks of pass band Modulation:-
Modulation and demodulation equipment imparts transmitting & receiving antennas which increase the system complexity. i.e, pass band systems are complex systems.
Coherent and Non-Coherent modulation schemes:-
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Advantages of Digital Communication systems over analog Communication systems:-
|Analog Communication Systems(ACS)||Digital Communication Systems(DCS)|
|1. Generation of analog signals involves a complex mechanism over Digital signals||1. Generation of digital signals is much easier when compared to Analog signals.|
|2. Regenerative repeaters are not used in ACS||2. DCS has a flexibility in terms of usage of regenerative repeaters at regular intervals along Transmission system.|
|3. Analog circuits are more subjected to distortion and noise||3. Digital circuits are less subjected to distortion and interference than are analog circuits, because of two state operation of digital circuits( i.e, fully on /fully off).|
|4. Error detection and error correction methods are not available in ACS.||4. Error detection and error correction methods makes DCS preferable over ACS, with this one can expect low error rates and high signal fidelity in DCS.|
|5. Reliability is less for analog circuits. cost is high for analog hardware.||5. Digital circuits are more reliable and can be produced at lower cost.|
|6. Multiplexing of analog signals using Frequency Division Multiplexing is complex.||6.Combining of digital signals using Time Division Multiplexing is simpler.|
|7. Encryption and privacy are not possible for analog modulation techniques||7. Encryption and privacy can be possible for digital techniques.|
|8. analog systems are not signal processing intensive.||8. Digital systems are very signal processing intensive.|
|9. AC is non-adaptive to DSP,DIP etc.||9. DC adaptive to other advanced branches of data processing such as DSP, DIP, data compression etc.|
|10. wide dynamic range is not possible with analog signals.||10. wide dynamic range is possible since the data is converted to the digital form.|
11. low speed data transmission is possible with analog communication.
|11. High speed and reliable data transmission is possible with digital communication.|