2.Signals.pdf

SIGNALS What is a signal??? a mathematical indicator conveys information anything that conveys information or broadcast a message in physical world between two observers How information is represented Entity that causes reaction or change What is a signal??? a gesture, acti...

SIGNALS What is a signal??? a mathematical indicator conveys information anything that conveys information or broadcast a message in physical world between two observers How information is represented Entity that causes reaction or change What is a signal??? a gesture, action, or sound that is used to convey information or instructions, typically by prearrangement between the parties concerned an electrical impulse or radio wave transmitted or received an electric current or electromagnetic field used to convey data from one place to another Any physical quantity that conveys information Types of Signals Analog – Continuous signals – Defined with respect to time – Uses sine waves – Examples: sound, thermometer, human voice, telephones (old landline) Types of Signals Digital – uses only two values : 0 and 1 – refers to data with discrete values – discontinuous signals – less accurate they are discrete samples of an analog signal taken over some period of time – not subject to noise – denoted by square waves  Analog and Digital Signals value 0 1 0 1 0 1 1 0 0 0 1 1 0 Logic Voltage Level 2 States of a wire: Voltage - is the electric energy charge difference of electric potential energy transported between two points – SI (International System of Units): volts Current – flow of electric charge – Rate of flow of electrical charge – SI : ampere (one coulomb per second) Current Resistor wire Where: V = voltage I = current R = resistance  i= 2 A 10 v R=? Formula of Ohm’s law: V = IR Power = VI R = V/I = 10v * 2A = 10v / 2A = 20 watts = 5 ohms or 5 Ω Definition of Terms: Voltmeter: measures the voltage (or potential difference) between two points in a system Ammeter: measures electric current (ampere) AC – Alternating Current – Movement of electric charge reverses direction – Electric power delivered to businesses and residences DC – Direct Current – Unidirectional flow of electric charge – Produced by batteries, solar cells Digital and Analog Signals Comparison element Analog signal Digital signal Analysis Difficult Possible to analyze Representation Continuous Discontinuous Storage Infinite memory Easily stored Subject to Yes No Noise/Distortion Original signal is Samples of the signal are Recording Technique preserved taken and preserved Human voice, Computers, Digital Examples Thermometer, Analog Phones, PDA’s, e.t.c phones, e.t.c https://www.diffen.com/difference/Analog_vs_Digital Digital and Analog Signals Comparison element Analog signal Digital signal - No guarantee for real - Real time time processing Bandwidth - Consumes less bandwidth - Can consume more bandwidth Storage - Wave signal - Bits Power Large power consumption Less power consumption Waves Sine waves Square waves Cost Low cost High cost Portability Portable Not easily portable Accuracy Less Accuracy Better accuracy https://www.diffen.com/difference/Analog_vs_Digital CHARACTERISTICS OF ANALOG SIGNAL 3 Parameters of Sine Wave 1. amplitude – value of intensity at time t 2. frequency – number of cycles completed by the wave per second 3. phase – describes the position of the waveform with respect to time – measured in degrees or radians Frequency and Period Frequency - number of cycles or vibrations per unit time - Number of waves that pass a fixed point in unit time - Expressed in Hertz (Hz) - 1 Hz = 1 cycle per second Period - –time taken by the wave to complete one second T = 1/f f = 1/T Example2: If the period of a signal is 100ms, what is its frequency? CHARACTERISTICS OF ANALOG SIGNAL Frequency 6 Hz Interactive q 3 Hz T = 1 sec Amplitude  Phase In phase – if the signals having the same frequency are aligned at the same time Out of phase – if the signals having the same frequency are not aligned at the same time Refer to the sample waves, are the waves the same or different in terms of: - Amplitude - Frequency - Phase Wavelength refers to the relationship between frequency (or period) and propagation speed of the wave through a medium distance a signal travels in one period is the physical length from one point of a wave to the same point on the next wave Represented by lowercase lambda λ Long wavelength → Short Frequency Short wavelength = High Frequency  Wavelength Formula for wavelength: 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑐 Wavelength or λ = or 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑓 – Measured in micrometers (microns) – Varies from one medium to another – Propagation speed = speed of light, depends on the medium Chart of Common Frequency Bands Source: http://www.antenna-theory.com/basics/freqBands.php Wavelength Example: In a vacuum, light is propagated at a speed of 3x108 m/s. What is the wavelength of red light in air? (f=4x1014 ) λ = c/f = 3x108 / 4x1014 = 0.75 x 10-6 m or 0.75 μm Time-Domain and Frequency-Domain Time-domain plot – shows changes in signal amplitude with respect to time; indicates time and amplitude relation of a signal Frequency-domain – shows signal frequency and peak amplitude Time-Domain and Frequency- Domain CHARACTERISTICS OF DIGITAL SIGNAL Discrete values Not continuous signal LEVEL-Information is represented in voltage levels  Bit Length or Bit Interval (Tb) – time to send one bit; measured in seconds Bit Rate: number of bits transmitted per second; expressed in bits per second (bps) Relation of bit rate and bit interval: Bit rate = 1/Bit interval Baud Rate: – Unit of measurement – Rate of signal speed (i.e. the rate at which the signal changes) – A digital signal with two levels 0 and 1 will have the same baud rate and bit rate MODULATION  Modulation Technique for impressing information such as voice, music, picture or data) on a radio-frequency carrier wave by varying one or more characteristics of the wave in accordance with the intelligence signal. Process of changing the parameters of the carrier signal, in accordance with the instantaneous values of the modulating signals (https://www.tutorialspoint.com/principles_of_communicatio n/principles_of_communication_modulation.htm) https://www.britannica.com/technology/modulation-communications Definition of Terms Modulating signal or message –signal which contains the message to be transmitted Carrier signal – high frequency signal which is used to carry the message Modulated signal – result of signal that has been modulated Forms of modulation – Amplitude – Frequency – Phase – Pulse sequence – Pulse duration  AM – Amplitude Modulation Oldest method of broadcasting radio programs auditory or visual information is impressed on a carrier wave by varying the amplitude of the carrier to match the fluctuations in the audio or video signal being transmitted Employed in long-distance shortwave radio broadcast and in transmitting the videos of tv programs https://www.britannica.com/technology/modulation-communications FM – Frequency Modulation the amplitude of the carrier is kept constant, but its frequency is altered in accordance with variations in the audio signal being sent Less susceptible to interference (storms, machineries) Phase Modulation Variation of FM Carrier wave is modulated by changing its phase to transmit the amplitude and pitch of the signal Applications: – radio waves transmissions – Used in wireless technologies coding schemes such as: WiFi Satellite tv SM coding schemes Pulse Code Modulation Converts analog signals to digital signals by converting the carrier into a series of spaced constant-amplitude pulses (1 or 0) These pulses are contained in coded form Examples: Baudot Code – Baudot Code – contains group of 5 with on and off signals (original) Application: Telkom system, digital audio recording, voice mails, receiver for remote-controlled cars, planes.  Pulse-Duration Modulation or Pulse-Width Modulation A method of controlling analog devices with digital output Example: – Controlling a servo motor and generating a digital output. – Turning a light on and off Servo with Robot arm using PWM https://learn.sparkfun.com/tutorials/pulse-width-modulation/all BANDWIDTH BANDWIDTH the range of frequencies within a given band used for transmitting a signal describes the maximum data transfer rate of a network amount of data that can be transferred from one point to another within a network in a specific amount of time Example: 25MBps = 25 Megabits per second Bandwidth of a Signal Frequency range over which a signal is transmitted Different types of signals have different bandwidth (voice, music..) Bandwidth of analog signal: frequency Bandwidth of digital signal: bit rate (bits per second, bps) Difference between he highest and the lowest frequencies or upper and lower frequencies Bandwidth of a Channel Medium through which the signal carrying information will pass In analog signal: bandwidth of a channel is the range of frequencies that the channel can carry In digital signal: bandwidth of a channel is the maximum bit rate supported by the channel (ex: the maximum amount of data that the channel can carry per second) Bandwidth of a Channel Bandwidth of the medium: should be greater than the bandwidth of the signal If bandwidth of the medium is less than the bandwidth of the signal: – signal attenuation – signal distortion – loss in information Maximum Data Rate of a Channel 3 factors Affecting Data Rate – Available bandwidth – Level of the signal – Quality of the channel 2 Types of Channel Quality 1. Noiseless or Perfect Channel – Ideal channel – Nyquist Bit rate gives the bit rate for Noiseless channel 2. Noisy Channel – Realistic channel – Shannon Capacity gives the bit rate for Noisy channel Nyquist Bit Rate is half of the sampling rate of a discrete signal processing system Used in the digitization of analog signals Bitrate = 2*Bandwidth * log2L Where: – Bitrate = bitrate of the channel in bps – Bandwidth = bandwidth of the channel – L = number of signal levels Nyquist Bit Rate Example: What is the maximum bit rate of a noiseless channel with a bandwidth of 5000 Hz transmitting a signal with two signal levels? Solution: Bitrate= 2 * bandwidth * Log2L = 2 * 5000 s Log2 2 = 10000 bps Shannon Capacity Theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise Capacity = bandwidth * log2 (1+SNR) Where: Capacity – capacity of the channel in bps Bandwidth – bandwidth of the channel; corresponds to image sharpness SNR – Signal to Noise Ratio Shannon Capacity Example: Calculate the bit rate for a noisy channel with SNR 300 and bandwidth of 3000Hz. Solution: Capacity = bandwidth x log2 (1+SNR) = 3000 * log2 (301) = 3000 * 8.23 = 24,690 bps Note: SNR of 300 : camera SNR = 300 to 1000 Baseband and Broadband Transmission Baseband Transmission without modulation Sends digital signal over single frequency as discrete electrical pulses The bandwidth of the signal to be transmitted has to be less than the bandwidth of the channel Bidirectional Signal can be regenerated Baseband Transmission Example: The bandwidth channel with lower frequency 0Hz and higher frequency 100Hz, – Bandwidth = higher frequency bandwidth – lower frequency bandwidth = 100Hz – Wideband channel : when a bandwidth channel is more than the bandwidth of the signal – Narrowband channel: when bandwidth channel is less than the bandwidth of the signal Broadband Transmission – With modulation – sends signals simultaneously over a range of different frequencies as electromagnetic waves – Can carry multiple, simultaneous data signals  IQ Modem Local Exchange Node Baseband Broadband Uses of Signals in Data Communication Communications Research Video Processing Image Processing Digital Signal Processing Video and image compression, multimedia authoring Resources https://en.wikiversity.org/wiki/Signal_Processing https://www.diffen.com/difference/Analog_vs_Digital https://www.britannica.com/science/frequency-physics http://www.techplayon.com/wavelength-frequency-amplitude- phase-defining-waves/ https://www.britannica.com/science/radio-wave https://www.britannica.com/technology/modulation- communications https://networkencyclopedia.com/baseband-transmission  https://www.analogictips.com/pulse-width-modulation-pwm/ https://networkencyclopedia.com/broadband-transmission/ https://www.elprocus.com/pulse-code-modulation-and- demodulation https://techterms.com/definition/bandwidth https://www.paessler.com/it-explained/bandwidth https://en.wikipedia.org/wiki/Baud https://www.tutorialspoint.com/principles_of_communication /principles_of_communication_modulation.htm