COMS REVIEWER (Caberte) PDF

AUGUST 24, 2024- 1ST MEET Information capacity, bits and bit rate Bits - The most basic digital symbol used to represent information. - Is a contraction of the term “binary digit” - A unit of information represented by either a ‘1’ or ‘0’ Bit rate Is simply the number of bits transmitted du...

AUGUST 24, 2024- 1ST MEET Information capacity, bits and bit rate Bits - The most basic digital symbol used to represent information. - Is a contraction of the term “binary digit” - A unit of information represented by either a ‘1’ or ‘0’ Bit rate Is simply the number of bits transmitted during one seconds and express in bit per seconds (bps) Hartley Law 1928, R. Hartley of Bell Telephone Laboratories - developed a useful relationship among bandwidth, transmission time and information capacity. I = information capacity (bits per second) B = bandwidth t = transmission time (seconds) Channel capacity Channel Capacity (C)- the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions Data rate (bps)- rate at which data can be communicated, impairments, such as noise, limit data rate that can be achieved Bandwidth (B)- the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz) Noise (N)- impairments on the communications path Error rate - rate at which errors occur (BER) Error- transmit 1 and receive 0; transmit 0 and receive 1 Reasons for choosing encoding techniques Digital data, digital signal - Equipment less complex and expensive than digital-to-analog modulation equipment Analog data, digital signal - Permits use of modern digital transmission and switching equipment Digital data, analog signal - Some transmission media will only propagate analog signals E.g., unguided media (air) Analog data, analog signal - Analog data in electrical form can be transmitted easily and cheaply E.g., AM Radio What is modulation ? - Adding information to a carrier signal - The sine wave on which the characteristics of the information signal are modulated is called a carrier signal Transmitting Information (Analog or Digital) Three characteristics of a signal that can be changed overtime: amplitude, phase, or frequency. However, phase and frequency are just different ways to view or measure the same signal change. Analog Modulation In AM, the amplitude of a high-frequency carrier signal is varied in proportion to the instantaneous amplitude of the modulating message signal. Frequency Modulation (FM) is the most popular analog modulation technique used in mobile communications systems. In FM, the amplitude of the modulating carrier is kept constant while its frequency is varied by the modulating message signal. Modulation 1 Motivation - Smaller antennas (e.g., λ /4 typical antenna size)  λ = wavelength = c/f, where c = speed of light, f= frequency.  3000Hz baseband signal => 15 mile antenna, 900 MHz => 8 cm - Frequency Division Multiplexing – provides separation of signals - medium characteristics - Interference rejection - Simplifying circuitry Modulation - shifts center frequency of baseband signal up to the radio carrier Basic schemes - Amplitude Modulation (AM) Amplitude Shift Keying (ASK) - Frequency Modulation (FM) Frequency Shift Keying (FSK) - Phase Modulation (PM) Phase Shift Keying (PSK) AUGUST 31, 2024- 2ND MEET Definition Digital Transmission- is the transmittal of digital signals between two or more points in a communication system Digital Transmission System- are used to carry not only digitally encoded voice and video signals but also digital source information directly between computer and computer networks. Use both metallic and optical cables for their transmission medium. Questions of Interest - How are errors detected and corrected? How long will it take to transmit a message? What transmission speed is possible over radio, copper - How many bits are in the message (text, image)? cables, fiber, infrared,...? - How fast does the network/system transfer information? Advantages of digital transmission Can a network/system handle a voice (video) Noise immunity - less susceptible call? Multiplexing - combination of digital signals - How many bits/second does voice/video require? Digital Signal Processing (DSP) At what quality? Regeneration - more resistant How long will it take to transmit a message without errors? Simpler to measure and evaluate - How are errors introduced? Easy to correct and detected error Digital Signal Processing( DSP) Disadvantages of digital transmission Is the processing of analog signals using digital methods and includes band limiting the signal More bandwidth- costly and limited with filters, amplitude equalization, and phase shifting. Precise time synchronization Signal Regeneration Incompatible of with older analog transmission system Digital transmission systems are more resistant to analog systems to additive noise "To be transmitted, data must be stransformed to electromagnetic signals." ANALOG AND DIGITAL Analog data- refers to information that is continuous. - ex. an analog clock, human voice Digital data- refers to information that has discrete states. - ex. an digital clock, data are stored in computer memory Data can be analog or digital. Analog data are continuous and take continuous values. Digital data have discrete states and take discrete values. Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital signals can have only a limited number of values. TWO FORMS OF ANALOG AND DIGITAL SIGNAL 1. Periodic signal completes a pattern within a measurable time frame, called a period, and repeats that pattern over subsequent identical periods. 2. Nonperiodic signal changes without exhibiting a pattern or cycle that repeats over time. ANALOG AND DIGITAL SIGNAL In data communications, we commonly use periodicanalog signals and nonperiodic digital signals. PERIODIC ANALOG SIGNALS Periodic analog signals can be classified as simple or composite. A simple periodic analog signal, a sine wave, cannot be decomposed into simpler signals. A composite periodic analog signal is composed of multiple sine waves. The sine wave is the most fundamental form of a periodic analog signal. When we visualize it as a simple oscillating curve, its change over the course of a cycle is smooth and consistent, a continuous, rolling flow. Three parameters of Sine Wave 1. peak amplitude 2. the frequency 3. the phase PERIOD AND FREQUENCY - Period refers to the amount of time, in seconds, a signal needs to complete 1 cycle. Change over a long span of time means low. Frequency refers to the number of periods in 1s frequency. If a signal does not change at all, its frequency is zero. If a signal changes instantaneously, its frequency is infinite. - Frequency is the rate of change with respect to time. Change in a short span of time means high frequency. Change over a long span of time means low frequency. If a signal does not change at all, its frequency is zero. If a signal changes instantaneously, its frequency is infinite. Phase The term phase describes the position of the waveform relative to time 0. If we think of the wave as something that can be shifted backward or forward along the time axis, phase describes the amount that shift. It indicates the status of the first cycle. Wavelength Wavelength is another characteristic of a signal traveling through a transmission medium. Wavelength binds the period or the frequency of a simple sine wave to the propagation speed of the medium. Bandwidth The range of frequencies contained in a composite signal is its bandwidth. The bandwidth of a composite signal is the difference between the highest and the lowest frequencies contained in that signal. SEPTEMBER 7, 2024- 3RD MEET BROADCASTING "To send out in all directions" The process of transmitting information (vojce, music or video signal) by radio or through television for reception by the general public. NATIONAL TELECOMMUNICATIONS COMMISSION NTC issues digital TV guidelines for future shift and mandated for standard Digital free TV) Percentage of TV Households in the Philippines Based on 2020 Philippine Statistics Authority (PSA) data,the total population ih the Philippines is 108,667,043. The average size of household in 17 regions is 4.1 persons while the total household is 95%. TWO STAGES PROCESS OF DTV SERVICE 1. Transition - Parallel broadcast of Analog TV broadcast with Digital TV broadcast 2. Migration - Analog broadcast shut-off and full DTV broadcast. - December 31, 2024 Shut-off of all Analog TV Station. What is Digital Television? Digital Television is a technology that allows broadcaster to deliver superior picture and audio quality to the viewers. ISDB-T A flexible Digital Television (DTV) transmission system that is capable of providing three (3) levels of hierarchical modulation that can carry audio, video and data services to fixed, mobile and handheld terminals using a single transmission facility with an integrated Emergency Warning System (EWBS). Single Frequency Network (SFN) SFN -a technique that enables transmission on the same frequency within the same coverage without interference. A key feature in DTV. MFN-a technique of providing coverage in a service area utilizing multiple frequencies, this technique is used in analog. LABORATORY: SEPTEMBER 28, 2024- 4TH MEET BINARY TRANSMISSION BIT - Is a contraction of the term "binary digit" - A unit of information represented by either a 'I' or "0" BIT RATE /DATA RATE - The number of O's and I's that pass on a communication charnel each second - Transmission rate in bits per second ERROR RATE - A measure of data connectivity's performance - Ofien the unit of measurement is bit error rate (BER), which probability of error - A BER of 1 in 10° means that there is a probability of one error will occur for every 100,000 bits BINARY INFORMATION CODES Types of Characters 1. Data Link Control Characters -used to facilitate the orderly flow of data from a source to a destination 2.Graphic Control Characters -involve the syntax or presentation of the data at the receive terminal 3.Alphanumeric Characters -used to represent the various symbols used for letters, numbers, and punctuation in the English language BINARY INFORMATION CODES Data Communication Codes 1. Baudot code 2. ASCII code 3. EBCIDIC BAUDOT CODE Jean-Maurice-Emile Baudot - The first fixed-length character code. It is a 5 bit character code, with a start bit and a 1.5 stop bits. - Pioneer in telegraph printing - French postal Engineer - Developed in 1875 PULSE MODULATION Consist essentially of sampling analog informatibn signals and then converting those samples into discrete pulses and transporting the pulses from a source to a destination over a physical transmission medium. FOUR METHODS OF PM 1. Pulse Width Modulation -PWM 2. Pulse Position Modulation - PPM 3. Pulse Amplitude Modulation -PAM 4. Pulse Code Modulation -PCM DEFINITIONS: 1. Pulse Width Modulation-PWM - Sometimes called pulse duration modulation (PDM) or pulse length modulation (PLM, as the width of a constant amplitude pulse is varied proportional to the amplitude of the analog signal at the time the signal is sampled. - The maximum analog signal amplitude produces the widest pulse whereas the minimum analog signal is the narrowest pulse. 2.Pulse Position Modulation -PPM - The position of a constant-width pulse within a prescribed time slot is varied according to the amplitude of the sample of the analog signal. - The highest amplitude sample produces a pulse to the far right whereas the lowest pulse to the far left.  3. Pulse Amplitude Modulation-PAM - The amplitude of a constant-width, constant position pulse is varied according to the amplitude of the sample of the analog signal. - Where it can be seen that the amplitude of a pulse coincides with of the analog signals 4. Pulse Code Modulation -PCM - The analog signal is sampled and then converted to a serial n-bit binary code for transmission. - Each code has the same number of bits and requires the same length of time for transmission. DIGITAL DATA-DIGITAL SIGNAL Digital or Analog is converted to digital signal for transmission Line coding is a technique for converting digital data into digital signal LINE CODING CHARACTERISTICS: - No of signal levels - Bit rate versus Baud rate - DC components - Signal Spectrum-Noise Immunity- Error Detection - Cost of Implementation LINE CODING SCHEMES Unipolar LINE CODING SCHEMES Characteristics of Unipolar Signal Characteristics of Biphase Encoding - Simple but obsolete - Two levels - It uses only one polarity of voltage level - No DC component - Bit rate same as data rate - Good synchronization - DC component present - Higher bandwidth due to doubling of bit rate with respect to data rate - Loss of synchronization for long sequences of 0' and I's