Lecture 1 principles of communication .pdf
- 1. Electronic and Communication Department Principles of Communication Systems (ECE 236) Power and Electrical Machines Department Communication Systems (ECE 238) Dr. Mohammed Faysal
- 2. Course Contents: Communication system elements Overview of current communication systems. Communication channels properties. Basics of analog communication: amplitude, angle, frequency and analog pulse modulation. Frequency division multiplexing. Basics of digital communication: sampling, quantization, pulse code modulation, Differential PCM, Delta Modulation. Sigma Delta Modulation Time division multiplexing, binary signal formats. Digital carrier modulation: ASK, PSK, FSK and QAM. Multiple - access techniques. Reference: Book: MODERN DIGITAL AND ANALOG COMMUNICATION SYSTEMS Fifth Edition
- 3. Assessment Criteria Student Activities and/or Practical Exam Mid-Term Exam Final Exam Final 35 25 60 120
- 4. Communication Models Communication is the transfer of information from one place to another. The Purpose of a communication system is to carry information from one point to another. A typical communication system consists of three main components: Source, Channel, Destination.
- 5. Communication System Broadcasting mode (one Tx, many Rx). Pear – to – pear mode (one Tx, one Rx).
- 6. Communication Process The generation of a message signal. The description of a message signal with a set of symbols The encoding of these symbols The transmission of the encoded symbols The decoding and the reproduction of the original symbols The reconstruction of the original message signal
- 7. Elements of a Communication system The block diagram on the top shows the blocks common to all communication systems Digital Analog
- 8. Elements of a Communication system Input Transducer: The message produced by a source must be converted by a transducer to a form suitable for the particular type of communication system. Example: In electrical communications, speech waves are converted by a microphone to voltage variation. Transmitter: The transmitter processes the input signal to produce a signal suits to the characteristics of the transmission channel. Signal processing for transmission almost always involves modulation and may also include coding. In addition to modulation, other functions performed by the transmitter are amplification, filtering and coupling the modulated signal to the channel.
- 9. Elements of a Communication system Channel: The channel can have different forms: The atmosphere (or free space), coaxial cable, fiber optic, waveguide, etc. The signal undergoes some amount of degradation from noise, interference and distortion Receiver: The receiver’s function is to extract the desired signal from the received signal at the channel output and to convert it to a form suitable for the output transducer. Other functions performed by the receiver: amplification (the received signal may be extremely weak), demodulation and filtering. Output Transducer: Converts the electric signal at its input into the form desired by the system user. Example: Loudspeaker, personal computer (PC), tape recorders.
- 10. Basic analog communications system Modulator Demodulator Transmission Channel Input transducer Transmitter Receiver Output transducer Carrier EM waves (modulated signal) EM waves (modulated signal) Baseband signal (electrical signal) Baseband signal (electrical signal)
- 11. Analog Modulation The purpose of a communication system is to transmit information signals (baseband signals) through a communication channel The term baseband is used to designate the band of frequencies representing the original signal as delivered by the input transducer For example, the voice signal from a microphone is a baseband signal, and contains frequencies in the range of 0-3000 Hz The “hello” wave is a baseband signal:
- 12. AM radio FM radio/TV Analog Modulation Since this baseband signal must be transmitted through a communication channel such as air using electromagnetic waves, an appropriate procedure is needed to shift the range of baseband frequencies to other frequency ranges suitable for transmission, and a corresponding shift back to the original frequency range after reception. This is called the process of modulation and demodulation Remember the radio spectrum: For example, an AM radio system transmits electromagnetic waves with frequencies of around a few hundred kHz (MF band) The FM radio system must operate with frequencies in the range of 88-108 MHz (VHF band)
- 13. Analog Modulation Since the baseband signal contains frequencies in the audio frequency range (3 kHz), some form of frequency-band shifting must be employed for the radio system to operate satisfactorily. Note that: wave speed = frequency × wavelength. v = f λ This process is accomplished by a device called a modulator The transmitter block in any communications system contains the modulator device The receiver block in any communications system contains the demodulator device The modulator modulates a carrier wave (the electromagnetic wave) which has a frequency that is selected from an appropriate band in the radio spectrum For example, the frequency of a carrier wave for FM can be chosen from the VHF band of the radio spectrum For AM, the frequency of the carrier wave may be chosen to be around a few hundred kHz (from the MF band of the radio spectrum) Note that: The wavelength of a wave is related to the wave's energy. Short-wavelength waves have more energy than long-wavelength waves of the same amplitude.
- 14. The demodulator extracts the original baseband signal from the received modulated signal To Summarize: Modulation is the process of impressing a low-frequency information signal (baseband signal) onto a higher frequency carrier signal Modulation is done to bring information signals up to the Radio Frequency (or higher) signal
- 15. Types of Analog Modulation Amplitude Modulation (AM) Amplitude modulation is the process of varying the amplitude of a carrier wave in proportion to the amplitude of a baseband signal. The frequency of the carrier remains constant Frequency Modulation (FM) Frequency modulation is the process of varying the frequency of a carrier wave in proportion to the amplitude of a baseband signal. The amplitude of the carrier remains constant
- 16. Amplitude Modulation Carrier wave Baseband signal Modulated wave Amplitude varying- frequency constant
- 17. Frequency Modulation Carrier wave Baseband signal Modulated wave Frequency varying- amplitude constant Large amplitude: high frequency Small amplitude: low frequency
- 18. AM vs. FM AM requires a simple circuit, and is very easy to generate. It is simple to tune, and is used in almost all short wave broadcasting. The area of coverage of AM is greater than FM (longer wavelengths (lower frequencies) are utilized-remember property of HF waves?) However, it is quite inefficient, and is susceptible to static and other forms of electrical noise. The main advantage of FM is its audio quality and immunity to noise. Most forms of static and electrical noise are naturally AM, and an FM receiver will not respond to AM signals. The audio quality of a FM signal increases as the frequency deviation increases (deviation from the center frequency), which is why FM broadcast stations use such large deviation. The main disadvantage of FM is the larger bandwidth it requires
- 19. Digital Modulation The previous section presented analog communication systems that transmit information in analog form using Amplitude or Frequency modulation Digital communication systems also employ modulation techniques, some of which include: Amplitude Shift Keying Frequency Shift Keying Phase Shift Keying
- 20. Basic digital communications system Modulator Demodulator Transmission Channel Input transducer Transmitter Receiver Output transducer Carrier EM waves (modulated signal) EM waves (modulated signal) Analog signal analog signal Digital signal digital signal
- 21. Some Types of Digital Modulation Amplitude Shift Keying (ASK) The most basic (binary) form of ASK involves the process of switching the carrier either on or off, in correspondence to a sequence of digital pulses that constitute the information signal. One binary digit is represented by the presence of a carrier, the other binary digit is represented by the absence of a carrier. Frequency remains fixed Frequency Shift Keying (FSK) The most basic (binary) form of FSK involves the process of varying the frequency of a carrier wave by choosing one of two frequencies (binary FSK) in correspondence to a sequence of digital pulses that constitute the information signal. Two binary digits are represented by two frequencies around the carrier frequency. Amplitude remains fixed
- 22. Amplitude Shift Keying Digital information 1 0 1 1 0 0 1 0 1 0 Carrier wave ASK modulated signal Carrier present Carrier absent Amplitude varying- frequency constant
- 23. Frequency Shift Keying Digital information 1 0 1 1 0 0 1 Carrier 1 (frequency #1) FSK modulated signal Carrier 2 (frequency #2) Frequency varying- amplitude constant