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

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.

Brief History in Communication Year Events Telegraph Telephone AM Radio Television FM Radio 1962 Satellite 1966 Optical links using laser and fiber optics 1972 Cellular Telephone

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

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.

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

Elements of Communication System(CS)

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

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

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

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.

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

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.

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.

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.

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.

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

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

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

EM Frequency Spectrum(cont’d)

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

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.

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