1. REVIEW TO COMMUNICATION SYSTEM
Transfer of Information from one place to another.
Should be efficient, reliable, and secured.
COMMUNICATION SYSTEM:
components/subsystems act together to accomplish information transfer/exchange

2. Need For Communication
2 main BARRIERS: Language & Distances
Importance of communication:
exchange of information between two parties separated in distances in a more faster and reliable way.

3. Brief History in Communication
Year Events
Telegraph
Telephone
AM Radio
Television
FM Radio
Satellite
1966 Optical links using laser and fiber optics
1972 Cellular Telephone

4. Analog vs Digital Analog -Continuous Variation
-Assume the total range of frequencies/time
-All information is transmitted
Digital
-Takes samples:-non continuous stream of on/off pulses
-Translates to 1’s and 0’s

5. Analog vs Digital (Advantages& Disadvantages)
Digital CS
Advantages:
-Inexpensive
-Privacy preserved(data encrypted)
-Can merge different data
-error correction
Disadvantages:
-Larger bandwidth
-synchronization problem is relatively difficult
Analog Cs
Disadvantages:
-expensive
-No privacy preserved
-Cannot merge different data
-No error correction capability
Advantages:
-smaller bandwidth
-synchronization problem is relatively easier.

6. Basic Requirements of Communication System
Rate of information transfer:
-how fast the information can be transferred
Purity of signal received:
-whether the signal received is the same as the signal being transmit
Simplicity of the system
-The simpler the system, the better
reliability

7. Elements of Communication System(CS)

8. Elements of CS(cont’d)
Information source:
any source of information; i.e human voice, music, etc
Input transducer:
convert message to a form suitable for the particular type of communication system. Eg: speech waves are converted to voltage variation by a microphone

9. Elements of CS(cont’d)
Transmitter:
Processes input signal to produce a transmitted signal that suited the characteristic of transmission channel. Eg: modulation, coding, mixing, translate
Other functions performed: Amplification, filtering, antenna

10. Elements of CS(cont’d)
Channel(transmission media):
a medium that bridges the distance from source to destination. Eg:Atmosphere (free space), coaxial cable, fiber optics, waveguide
signals undergoes degradation from noise , interference and distortion

11. Elements of CS(cont’d)
Receiver: to recover the message signal contained in the received signal from the output of the channel, and convert it to a form suitable for the output transducer. Eg: superhetrodyne, mixing, demodulation, decoding
Other functions performed: Amplification, filtering.

12. Elements of CS(cont’d)
Output transducer:
converts the electrical signal at its input into a form desired by the system used.
Eg:Loudspeaker, PC, and tape recorders, cd burners

13. Simplex and Duplex
Simplex: a one way communication. Info travels in one way directions. Eg: TV broadcasting and radio.
Half duplex: two ways comm but only one party can transmit in one time. eg:radio for military, police, etc.
Full duplex: two ways, can transmit and receive simultaneously. Eg:mobile phone.

14. Baseband Signals
Any original signals, regardless of whether it is analog/digital, referred as base band signals.
In Comm Sys, some info signals may be transmitted directly by themselves over the medium or using modulation.
Putting the original signal directly to the medium is called base band transmission.

15. Modulation Process What is modulation?
-a process of changing one or more properties of the analog carrier in proportion to the information signal.In other word : Modulation is the process of shifting a message signal to a higher frequency.
Techniques using modulation is called broadband.

16. Modulation Process(cont’d)
Why modulation is needed?
-it is impractical to propagate information signals over standard transmission media.Thus, the signal need to be modulate with a higher frequency, called the carrier. This carrier signals will carry the information through the system.

17. Noise, interference and distortion
Noise:unwanted signals that coincide with the desired signals. Noise is random, undesirable electric energy.
Two type of noise:internal and external noise.
Internal noise: Caused by internal devices/components in the circuits.
External noise:noise that is generated outside the circuit. Eg: atmospheric noise,solar noise, cosmic noise, man made noise.
Interference-one type of external noise
Distortion: signal being distorted

18. Limitations in communication system
Physical constraint
-Delay, attenuation, bandwidth limitation, etc
Technological constraint
hardware.
Expertise
- economy, law

19. EM Frequency Spectrum
electromagnetic spectrum: The range of frequencies of electromagnetic radiation from zero to infinity.

20. EM Frequency Spectrum(cont’d)

21. Various types of communication system
Broadcast: radio and television
Mobile communications
Fixed communication system- land line
Data communication-internet

22. Frequency Spectrum &Bandwidth
The frequency spectrum of a waveform consists of all frequencies contained in the waveform and their amplitudes plotted in the frequency domain.
The bandwidth of a frequency spectrum is the range of of frequencies contained in the spectrum.It is calculated by subtracting the lowest frequency from the highest.

23. Frequency Spectrum &Bandwidth (cont’d)
Bandwidth of the information signal equals to the difference between the highest and lowest frequency contained in the signal.
Similarly, bandwidth of communication channel is the difference between the highest and lowest frequency that the channel allow to pass through it