Modulation and Multiplexing PDF

Modulation and Multiplexing Communication Systems Theory Modulation and Multiplexing Modulation and multiplexing are electronic techniques for transmitting information efficiently from one place to another. Modulation makes the information signal more compatible with the medium. Multiplex...

Modulation and Multiplexing Communication Systems Theory Modulation and Multiplexing Modulation and multiplexing are electronic techniques for transmitting information efficiently from one place to another. Modulation makes the information signal more compatible with the medium. Multiplexing allows more than one signal to be transmitted concurrently over a single medium. 36  Modulation: Broadband Transmission In many instances, baseband signals are incompatible with the medium. As a result, the baseband information signal is normally used to modulate a high-frequency signal called a carrier. The higher-frequency carriers radiate into space more efficiently than the baseband signals themselves. EM Signal Source AM Signal ---> electrical energy ---> amplify Figure 1-5: Modulation at the Transmitter 37 Modulation (characters) Modulation is simply the process of changing one or more properties of the analog carrier in proportion with the information signal. The information signal is usually called the modulating signal, and the higher-frequency signal which is being modulated is called the carrier or modulated wave. The carrier is usually a sine wave generated by an oscillator, which is M1.1 mathematically expressed as: 𝑣 = 𝑉𝑝 sin 2𝜋𝑓𝑡 + 𝜃 eto rin yung v(t) na discuss a while ago 38 Practical Reasons for Modulation Interference Information signals often occupy the same frequency band and, if signals from two or more sources are transmitted at the same time, they would interfere with each other. Tx Rx Tx Antenna in terms length it's very impractical w/o modulation It is extremely difficult to radiate low frequency signals from an antenna in the form of electromagnetic energy. 39  Types of Modulation Modulation Analog Digital Continuous-wave Pulse carrier Modulation Modulation Considered as Considered as Analog Digital Info. Analog Digital ASK PWM PCM AM Angular FSK PPM Delta Modulation FM PM PSK PAM comms 1 comms 2 40 *SK. - Shift Key Types of Modulation The three ways to make the baseband signal change the carrier sine wave are to vary its amplitude, vary its frequency, or vary its phase angle. In amplitude modulation (AM), the baseband information signal varies the amplitude of the higher-frequency carrier signal. carrier (a) (b) Figure 1-6: Example of (a) information signal 41 (b) AM signal Types of Modulation In frequency modulation (FM), the information signal varies the frequency of the carrier and the carrier amplitude remains constant. FM varies the value of f in the first angle term of the sinusoidal signal. (a) (b) higher freq low freq Figure 1-7: Example of (a) information signal (b) FM signal 42  Types of Modulation Varying the phase angle produces phase modulation (PM). In this case, the second term 𝜃 of the sinusoidal signal is made to vary by the intelligence signal. Phase modulation produces frequency modulation. EQN of Angle modulated signal v(t) = Vc sin (wct +msinw_mt) Recap: AM - amplitude varies, phase freq is constant the idea is: *as the freq is varied, phase is also varied. FM - freq is varied (also phase varied) PM - phase is varied(also freq. is varied); amplitude is constant 43  comm 1 comm 2 info Types of Modulation carrier info carrier If the information signal is digital and the amplitude of the carrier is varied proportional to the information signal, it is referred to as amplitude shift keying (ASK). If the frequency of the carrier is varied, it is referred to as frequency shift keying (FSK). If the phase of the carrier is varied, it is referred to as phase shift keying (PSK). (info) (a) FSK Figure 1-8: Example of im-phase Digital Modulation Scheme (b) PSK 44 Demodulation Demodulation is the reverse process of modulation and converts the modulated carrier back to the original information. Demodulation is performed in a receiver circuit called a demodulator. End of modulation stage - Antenna info weak signal info (another term) AM - Figure 1-9: Example of Demodulation process at the Receiver side 45 Multiplexing Multiplexing is the process of allowing two or more signals to share the same medium or channel. A multiplexer converts the individual baseband signals to a composite signal that is used to modulate a carrier in the transmitter. modulated signal previously: audio amp. microphone Figure 1-20: Example of Multiplexing at the Transmitter 46 Multiplexing At the receiver, the composite signal is recovered at the demodulator, then sent to a demultiplexer where the individual baseband signals are regenerated. same process and diagram for demodulation individual Figure 1-20: Example of demultiplexing at the Receiver 47  MUX ANALOG DIGITAL Types of Multiplexing FDM TDM CDM There are three basic types of multiplexing: frequency division, time division, and code division. NON-OVERLAPPING Frequency Division Multiplexing (FDM) In FDM, the intelligence signals modulate subcarriers on different frequencies that are then added together, and the composite signal is used to modulate the carrier. freq. allocation *while overlapping is OFDM (used in 5g networks) Signal 1 guardband (spacing bet. two freq to avoid interference) Signal 2 Frequency Signal 3 Frequency Frequency Figure 1-21: FDM technique 48  Types of Multiplexing Time Division Multiplexing (TDM) uses - timeslot In TDM, the multiple intelligence signals are sequentially sampled, and a small piece of each is used to modulate the carrier FDM - x'msn at diff freq but at same time Ex. cable TV, TV and FM broadcasting timeslot TDM - x'msn at same freq. but at different timeslot Source Figure 1-22: Simple rotary-switch multiplexer 49 Types of Multiplexing Power Frequency Time Frequency Division Multiplexing (FDM) Power Frequency Time Figure 1-23: FDM and TDM techniques Time Division Multiplexing (TDM)  Types of Multiplexing Code Division Multiplexing (CDM) combination of FDM and TDM In CDM, the signals to be transmitted are converted to digital data that is then uniquely coded with a faster binary code. The unique coding is used at the receiver to select the desired signal. application: cellular mobile comm. chip code 51 Electromagnetic Spectrum Communication Systems Theory  spectra - single freq spectrum - many Electromagnetic Spectrum EM The information is converted into electromagnetic signals that consists of both electric and magnetic fields. These signals oscillates and varies sinusoidally which may occur at a very low or at an extremely high frequency. This entire range of frequencies is referred to as the electromagnetic spectrum. increase in freq., decrease in lambda lambda = c/f 53 Figure 1-24: The Electromagnetic Spectrum Electromagnetic Spectrum Figure 1-25: The Electromagnetic Spectrum visualization 54  Electromagnetic Spectrum The electromagnetic frequency spectrum is divided into subsections or bands, with each band having a different name and boundary. Europe The International Telecommunications Union (ITU) is an standard giving international agency in control of allocating frequencies and services bodies within the overall frequency spectrum. In United States, the Federal Communications Commission (FCC) assigns frequencies and communications services for free-space radio propagation. The National Telecommunication Commission (NTC) is an attached agency of the Department of Information and Communications Technology (DICT). It oversees telecommunications services, radio, and television networks throughout the country. 55 Radio Frequency Spectrum The total usable radio frequency (RF) spectrum is divided into narrower frequency bands. Frequency Range Name 30Hz to 300Hz Extremely Low Frequencies (ELF) 300Hz to 3kHz Voice Frequencies (VF) 3kHz to 30kHz Very Low Frequencies (VLF) 30kHz to 300kHz Low Frequencies (LF) 300kHz to 3MHz Medium Frequencies (MF) 3MHz to 30 MHz High Frequencies (HF) 30MHz to 300MHz Very High Frequencies (VHF) 300MHz to 3GHz Ultra High Frequencies (UHF) 3GHz to 30GHz Super High Frequencies (SHF) 30GHz to 300GHz Extremely High Frequencies (EHF) 56 Figure 1-26: The Radio Frequency (RF) Spectrum Radio Frequency Spectrum Extremely Low Frequency (ELF) ELF include ac power line frequencies (50 and 60 Hz are common), as well as those frequencies in the low end of the human audio range. Voice Frequency (VF) This is the normal range of human speech. Although human hearing extends from approximately 20 to 20,000 Hz. Very Low Frequency (VLF) also used by submarine Many musical instruments make sounds in this range as well as in the ELF and VF ranges. The VLF range is also used in some government and military communication. Low Frequency (LF) The primary communication services using this range are in aeronautical and marine navigation. 57 Radio Frequency Spectrum Medium Frequency (MF) The major application of frequencies in this range is AM radio broadcasting (535 to 1605 kHz). High Frequency (HF) These are the frequencies generally known as short waves. All kinds of simplex broadcasting and half duplex two-way radio communication take place in this range. Very High Frequency (VHF) This popular frequency range is used by many services, including mobile radio, marine and aeronautical communication, FM radio broadcasting (88 to 108 MHz), and television channels 2 through 13. analog TV Ultra High Frequency (UHF) It includes the UHF TV channels 14 through 51, and it is used for land mobile communication and services such as cellular telephones as well as for military communication. 58 Radio Frequency Spectrum 300MHz to 300GHz Microwave and Super High Frequency (SHF) Frequencies between the 1000-MHz (1-GHz) and 30-GHz range are called microwaves. Microwave ovens usually operate at 2.45 GHz. These microwave frequencies are widely used for satellite communication and radar. Wireless local-area networks (LANs) and many cellular telephone systems also occupy this region. Extremely High Frequency (EHF) Electromagnetic signals with frequencies higher than 30 GHz are referred to as millimeter waves. 40 to 300GHz ISM band (unlicensed band) = 2.45GHz {WiFi; Bluetooth; microwave oven) Industrial, scientific and medical 59 The Optical Spectrum Right above the millimeter wave region is what is called the optical spectrum, the region occupied by light waves. There are three different types of light waves: infrared, visible, and ultraviolet. signal are expressed in terms of wavelength Infrared Infrared occupies the range between approximately 0.1 millimeter (mm) and 700 nanometers (nm), or 100 to 0.7 micrometer (μm). Infrared is the basis for all fiber optic communication. 60 The Optical Spectrum The Visible Spectrum Light is a special type of electromagnetic radiation that has a wavelength in the 0.4- to 0.8-μm range (400 to 800 nm). 10^-10 meter Light wavelengths are usually expressed in terms of Angstroms (Å). 61 Figure 1-27: The Visible Spectrum The Optical Spectrum (freq is at THz) The Visible Spectrum The visible range is approximately 8000 Å (red) to 4000 Å (violet). Red is low-frequency or long-wavelength light, whereas violet is high- frequency or short-wavelength light. The great advantage of light wave signals is that their very high frequency gives them the ability to handle a tremendous amount of information. Ultraviolet Spectrum UV covers the range from about 4 to 400 nm. Ultraviolet is not used for communication; its primary use is in the medical field. 62 Frequency and Wavelength In electronics, frequency is the number of cycles of a repetitive wave that occurs in a given time period. (one second) Frequency is measured in cycles per second (cps) or Hertz (Hz). Wavelength is measured between identical points on succeeding cycles of a wave. V 𝜆 t 𝜆 one cycle Sinusoidal Signal Figure 1-28: Sinusoidal signal’s Frequency and Wavelength 63 Frequency and Wavelength Electromagnetic waves travel at the speed of light, or 299,792,800 m/s. The speed of light and radio waves in a vacuum or in air is usually rounded off to 300,000,000 m/s (3x108 m/s), or 186,000 mi/s and designated as . The frequency and wavelength are related by the equation: 𝑣 "nu" somehow same as "c" 𝜆= 𝑓 lambda = c/f parin ang susundan 64 EXAMPLE#1: Determine the wavelength in meters for following frequencies: (a) 1 kHz, (b) 100 kHz, and (c) 10 MHz. b Sol'n f = 100kHz a. lambda =c/f lambda = 3x10^8 m/s / 100x10^3Hz lambda = 3000m f = 1kHz c lambda = ( 3x10^8 m/s )/(1x10^3Hz) f = 10MHz = 300,000m lambda = 3x10^8 m/s / 10x10^6 Hz lambda = 30m 65 Bandwidth and Information Capacity Communication Systems Theory Bandwidth Bandwidth (BW or B) of an information signal is simply the difference between the highest and the lowest frequencies contained in the information. The bandwidth of a communications system is the minimum passband (range of frequencies) required to propagate the source information through the system. 𝐵𝑊 = 𝑓2 − 𝑓1 or 𝐵𝑊 = 𝑓𝐻𝐼𝐺𝐻 − 𝑓𝐿𝑂𝑊 Figure 1-29: This is the voice frequency bandwidth. 67  range of freq. that the channel allows to pass thru B = f2-f1 Bandwidth and Channel Bandwidth "value" The term bandwidth refers to the range of frequencies that contain the information. The term channel bandwidth refers to the range of frequencies required to transmit the desired information. Signals transmitting on the same frequency or on overlapping frequencies interfere with one another. Ex: VHF band = 30 to 300Mhz channel BW BW = 300MHz =30MHz BW = 270MHz 68  "lightwave" in THz (x10^12 Hz) Bandwidth *optical fiber has the highest BW to offer The benefit of using the higher frequencies for communication carriers is that a signal of a given bandwidth represents a smaller percentage of the spectrum at the higher frequencies than at the lower frequencies. Example: 10 kHz signal at 1 MHz and 1 GHz * The higher the no. of channels allocated for information; the greater (info) amount of info can be x'mitted 10 𝑘𝐻𝑧 %= = 1% 1 𝑀𝐻𝑧 10 𝑘𝐻𝑧 %= = 0.001% 1 𝐺𝐻𝑧 This implies that there are many more 10-kHz channels at the higher frequencies than at the lower frequencies. 69 EXAMPLE#2: (a) Calculate the bandwidth if a frequency range from 902 MHz to 928 MHz is available. (b) If an analog television (TV) signal covers a bandwidth of 6 MHz and the low frequency limit of channel 2 is 54 MHz, determine the upper frequency limit. (a) range: 902 to 928 MHz BW = 928 - 902 MHz BW = 26MHz (b) chan.2 ans. 54 MHz f2 = 60 MHz BW = 6MHz 70 Information Theory Information theory is a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems. info bits per symbol A key measure in information theory is entropy. Entropy quantifies the amount of uncertainty involved in the value of a random variable or the outcome of a random process. 71  bits/sec (bps) bit rate/data rate K is constant (or channel) Information Capacity C = KBT I or C is directly proportional to Bandwidth and Transmission time Information capacity is a measure of how much information can be propagated through a communications system and is a function of bandwidth and transmission time. It represents the number of independent symbols that can be carried through a system per unit time. The most basic digital symbol used to represent information is the binary digit or bit. Information capacity is conveniently expressed as bit rate which is the number of bits transmitted per second (bps). 72 Information Capacity Claude E. Shannon published a paper relating the information capacity to bandwidth and signal-to-noise ratio entitled “A Mathematical Theory of Communication.” Information capacity is expressed mathematically as 𝑺 𝑪 𝒐𝒓 𝑰 = 𝑩 𝐥𝐨𝐠 𝟐 𝟏+ 𝑵 where I = information capacity or Channel capacity (bps) B = bandwidth (Hz) S/N = signal to noise ratio (unitless) 73 Challenges in Communication System Communication Systems Theory Primary Resources Communication systems are designed to provide efficient utilization of two primary communication resources: 1. Transmit Power 2. Channel Bandwidth Transmit power is defined as the average power of the transmitted signal. Channel bandwidth is the width of the passband channel. 75 Channel Classification Communication channels can be classified as follows: Power-limited channels Wireless channels, where it is desirable to keep the transmitted power low to prolong battery life. Satellite channels, where the available power on board the satellite transponder is limited, which necessitates keeping the transmitted power on the downlink at a low level. solar panels Bandwidth-limited channels Telephone channels, where, in a multi-user environment, the requirement is to minimize the frequency band allocated to the transmission of each voice VC signal. BW= 4kHz Television channels, where the available channel bandwidth is limited by regulatory agencies. BW = 6MHz 76 Challenges in Communication Systems The design of communication systems is complex and challenging due to the following factors: 1. Limited Spectrum 2. Power Consumption 3. Interference 4. Seamless Access 5. System on Chip Design 77 Limited Bandwidth 78  Limited Bandwidth https://region7.ntc.gov.ph/images/LawsRulesAndRegulations/Others/frequencyallocation_freq_alloc.jpg 79 Features of Good Communication Systems A good communication system will strike a balance between: 1. Small signal power (measured in W or dBm) M2 2. Small bandwidth (measured in Hz) 3. Large data rate (measured in bps) C = Blog2(1+S/N) 4. Low distortion (measured in SNR or BER) Bit error rate (digital) SNR --> analog 5. Low cost (complex systems with low cost) 80 Some Research Areas 6G Systems NW --> network Figure 1-30: Requirements for 6-G Wireless Technology 81 Some Research Areas millimeterwave multiple-input, multiple-output mmWave MIMO Systems LOS - line of sight Qualcomm Figure 1-31: Example of MIMO System 82 Some Research Areas Cognitive Radios (CR) is a radio that can change its transmitter parameters based on interaction with the environment in which it operates. Power Frequency Time Spectrum in use (Primary Users) Spectrum hole (Secondary Users) 83 Figure 1-32: Sample concept of CR’s