EST a311 PRINCIPLES OF COMMUNICATIONS INTRODUCTION TO ELECTRONIC COMMUNICATIONS BY ENGR. JTM OBJECTIVES At the end of the topic…… ❑Be familiar with the basic principles of electronic communications. ❑Determine which frequency band a type of communication service is included. ❑Express the relationship of information capacity, time and bandwidth. DEFINITIONS Communications • The basic process of exchanging information • Transfer of information from one place to another Electronic Communications • It is the transmission, reception and processing of information by electronic means Perfect communications system • The received information is the exact replica of the transmitted information Elements of communications system Transmitter Elements of communications system Communication Channel TYPES OF COMMUNICATIONS CHANNEL 1. Physical/ Guided ( Wired) a. Metallic/ conductors – Metallic transmission lines b. Non- Metallic – Fiber optic transmission media 2. Non- Physical/ Unguided (Wireless) Elements of communications system Receiver Block diagram of a communication system Source (information) transmitter Message for human application Communications medium receiver Noise Classifications of communications systems(one way/two way) One-way • Simplex Two-way • Half-duplex • Full-duplex • Full-full duplex Simplex A communication mode in which a there is only transmitter and many receivers, i.e. broadcasting Half- duplex • A transmitter can also be a receiver but not at the same time. • Ex. Two way radio Full duplex • Transmission and reception at the same time • Ex. Wire telephony, cellular telephony Full Full duplex • Transmission and reception at the same time in telephony (voice) and data • Example: cellular telephony ( 2G and GPRS, 3G and HSPA) Classifications of communications systems (signals) Analog Signals Digital Signals Classifications of communications systems(signals) Baseband • Carrier • Modulating signal Modulated Classifications of communications systems(modulation) Analog • AM • Angle Modulation (FM, PM) Digital • ASK • FSK • PSK • QAM Classifications of communications systems(modulation) Classifications of communications systems(modulation) Classifications of communications systems(Transmission) Analog Digital 1. Digital Radio 2. Digital Transmission Reasons why modulation is necessary in electronic communications International Telecommunications Union ( ITU ) • Is an international agency in control of allocating frequencies and services within the overall frequency spectrum. Federal Communications Commission ( FCC ) • In the United States, assigns frequencies and communications services for free-space radio propagation. National Telecommunications Commission ( NTC ) The radio frequency spectrum Emission classifications • Radio transmitter classifications according to bandwidth, modulation scheme, and type of information. • The first symbol is a letter that designates the type of modulation of the main carrier. • The second symbol is a number that identifies the type of emission. • The third symbol is another letter that describes the type of information being transmitted. Basic Emission Classification First Symbol – Type of Modulation of the Main Carrier Emission of unmodulated carrier N Emission in which the main carrier is amplitude -> Double – sideband A -> Single – sideband, full carrier H -> Single –sideband, reduced or variable level carrier R -> Single – sideband, suppressed carrier J -> Independent sideband B -> Vestigial sideband C Emission in which the main carrier is angled modulated -> Frequency Modulation F -> Phase Modulation G First Symbol – Type of Modulation of the Main Carrier Emission in which the main carrier is angled and amplitude modulated simultaneously D Emission of pulses -> Sequence of unmodulated pulses P -> Sequence of pulses ->> Modulated in amplitude K ->> Modulated in width/duration L ->> Modulated in position/phase M ->> The carrier is angle – modulated during the period of the pulse Q ->> Combination of the foregoing or is produced by other means V Cases not covered above or combination of two or more of the following modes: amplitude, angle, angle and phase W Cases otherwise not covered X Second Symbol – Nature of the Signals Modulating the Main Carrier No modulating signal 0 Digitally keyed carrier 1 Digitally keyed tone 2 Analog 3 Multichannel digital 7 Multichannel analog 8 Combination 9 Cases not otherwise covered X Third Symbol – Type of Information to be Transmitted No information transmitted N Telegraphy – for aural reception A Telegraphy – for automatic reception B Facsimile C Data transmission, telemetry, telecommand D Telephony (including sound broadcasting) E Television (video ) F Combination of the above W Cases otherwise not covered X Fourth Symbol – Details of Signals Two – condition code with elements of differing numbers and/or durations A Two – condition code with elements of the same number and duration without error correction B Two – condition code with elements of the same number and duration with error correction C Four – condition code in which each condition represents a signal element D Multicondition code in which each condition represents a signal element E Multicondition code in which each condition or combination of conditions represents a character F Fourth Symbol – Details of Signals Sound of broadcasting quality (monophonic) G Sound of broadcasting quality (stereophonic or quadraphonic) H Sound of commercial quality J Sound of commercial quality with the use of frequency inversion or band splitting K Sound of commercial quality with separate frequency – modulated signals to control the levels of demodulated signal L Monochrome M Color N Combination of the above W Cases not otherwise covered X Noise and bandwidth The two most significant limitations in the performance of communications systems Noise • Is any unwanted electrical signals that interfere with the information signal. Bandwidth • The difference between the highest and lowest frequencies contained in the information. Passband • The bandwidth of a communications channel is the difference between the highest and lowest frequencies that the channel will allow to pass through it. Information Theory Information Theory • A highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems. Information Capacity • The measure of how much information can be propagated through a communications system and is a function of bandwidth and transmission time. Binary Digit/ Bit • The most basic digital symbol used to represent information. Information Theory Bit Rate • The number of bits transmitted during one second and is expressed in bits per second (bps). Hartley Law • In 1928, R. Hartley of Bell Telephone Laboratories developed a useful relationship among bandwidth, transmission time, and information capacity. Information Theory Shannon limit for information capacity • In 1948, mathematician Claude E. Shannon published a paper in the Bell System Technical Journal relating the information capacity of a communications channel to bandwidth and signal-to-noise ratio.
