Module No.1: Introduction to Communication Systems Theory PDF

Module No.1: Introduction to Communication Systems Theory (ECE 21118: Communication Systems Theory) Outline 1. Historical Background 2. Electronic Communication Systems 3. Modulation and Multiplexing 4. The Electromagnetic Spectrum 5. Bandwidth and Information Capacity 6. Challenges...

Module No.1: Introduction to Communication Systems Theory (ECE 21118: Communication Systems Theory) Outline 1. Historical Background 2. Electronic Communication Systems 3. Modulation and Multiplexing 4. The Electromagnetic Spectrum 5. Bandwidth and Information Capacity 6. Challenges in Communication Systems 3 Historical Background Communication Systems Theory Introduction Communication is the process of exchanging information. Two main barriers of human communications: a. Language b. Distance Breakthrough in communications started in the late 19th century when electricity and its applications were explored. Electronic communication have increased our ability to share information, such as the telephone, radio, television, and the Internet. 5 Significant Historical Events in Electronics Communications DATES EVENTS 1830 American scientist and professor Joseph Henry transmitted the first practical electrical signal. 1837 Samuel Finley Breeze Morse invented the Telegraph and patented it in 1844. 1843 Alexander Bain invented the facsimile. 1847 James Clerk Maxwell postulated the Electromagnetic Radiation Theory. 1860 Johann Philipp Reis, a German who produces a device called Telephone that could transmit a musical tone over a wire to a distant point but incapable of reproducing it. 1864 James Clerk Maxwell, a Scottish physicist established the Theory of Radio or Electromagnetism which held the rapidly oscillating electromagnetic waves exist and travel at through space with the speed of light. 6 Significant Historical Events in Electronics Communications DATES EVENTS 1875 Thomas Alba Edison invented Quadruplex telegraph, doubling existing line qualities. J. M. Emile Baudot invented the first practical Multiplex Telegraph and another type of telegraphy codes which consisted of pre – arranged 5 - unit dot pulse. A. C. Cowper introduced the first Facsimile Machine or writing telegraph using a stylus. 1876 Alexander Graham Bell and Thomas A. Watson invented the Telephone capable of transmitting voice signals (March 10). 1877 Thomas Edison invented the Phonograph. 1878 Francis Blake invented the Microphone Transmitter using platinum point bearing against a hard carbon surface. 1882 Nikola Tesla outlined the basic principles of radio transmission and reception. 1887 Heinrich Hertz detected electromagnetic waves with an oscillating circuit and establishes the existence of radio waves. 7 Significant Historical Events in Electronics Communications DATES EVENTS 1889 Hertz discovered the progressive propagation of electromagnetic action through space using a spark – gap wave generator, to measure the length and velocity of electromagnetic waves and their direct relation to light and heat as their vibration, reflection, refraction and polarization. 1890 Almon Strowger introduced the dial – switching system transmitting the desired telephone number electrically without the assistance of a human telephone operator. 1895 Marchese Guglielmo Marconi discovered ground – wave radio signals. 1898 Guglielmo Marconi established the first radio link between England and France. 1901 Reginald A. Fessenden transmits the world’s first radio broadcast using continuous waves. Marconi transmits telegraphic radio messages from Cornwall, England to Newfoundland, first successful transatlantic transmission of radio signals. 1904 John Ambrose Fleming invented the Vacuum Tube Diode. 8 Significant Historical Events in Electronics Communications DATES EVENTS 1906 Reginald Fessenden invented Amplitude Modulation (AM). Lee De Forest added a grid to the diode and produced triode. Ernst F. W. Alexanderson invented the Tuned Radio Frequency Receiver (TRF) an HF Alternator producing AC, contributing better voice broadcasting. 1907 Reginald Fessenden developed the Heterodyne Receiver. 1918 Edwin H. Armstrong invented the Superheterodyne Receiver. 1923 J. L. Baird and C. F. Jenkins demonstrated the transmission of Black and White Silhouettes in motion. Vladymir Zworykin and Philo Farnsworth developed television cameras, the Iconoscope and the Image Detector. The first practical television was invented in 1928. 1931 Edwin Armstrong invented the Frequency Modulation, greatly improving the quality of the signals. 1937 Alec Reeves invented Pulse Code Modulation for digital encoding of signals. 1945 Arthur C. Clarke proposed the use of satellites for long distance radio transmissions. 9 Significant Historical Events in Electronics Communications DATES EVENTS 1962 AT&T launched Telstar I, the first satellite to received and transmit simultaneously. A year later, Telstar II was launched and used for telephone, TV fax and data transmission. 1965 COMSAT and INTELSAT launched the first communications satellite code name Early Bird at approximately 34000 km above sea level. 1967 K. C. Kao and G. A. Bockam of Standard Telecommunications Laboratories in England proposed the use of cladded fiber cables as new transmission medium. 1977 First commercial use of optical fiber cables 1983 Cellular telephone networks introduced. 1991 Tim Berners – Lee developed World Wide Web (WWW). 11 Historical Background Telegraph Samuel Morse invented the telegraph in 1844. The telegraph is considered as the forerunner in digital communications. It is a variable-length code using an alphabet of 4 symbols: a dot, a dash, a letter space, and a word space. Notice that short sequences represent frequent letters. 12 Historical Background Radio James Clerk Maxwell formulated the electromagnetic theory of light and predicted the existence of radio waves in 1864. Heinrich Hertz experimentally confirmed the existence of radio waves by in 1887. Guglielmo Marconi demonstrated wireless communications over long distances using radio waves in 1887. Reginald Fessenden invented the first radio broadcast using amplitude modulation in 1906. Edwin Armstrong invented the superheterodyne radio receiver in 1918 and frequency modulation in 1933. 13 Historical Background Telephone Alexander Graham Bell invented the first telephone in 1875. The telephone made real-time transmission of speech by electrical encoding and replication of sound a practical reality. Electronics In 1904, John Ambrose Fleming invented the vacuum-tube diode, which paved the way for the invention of the vacuum-tube triode by Lee de Forest in 1906. The transistor was invented in 1948 by Walter H. Brattain, John Bardeen, and William Shockley at Bell Laboratories. The first silicon integrated circuit (IC) was produced by Robert Noyce in 1958. 14 Historical Background 5G Evolution Wireless communications Figure 1-1: IEEE Communications Society 15 Electronic Communication Communication Systems Theory Electronic Communication Systems The fundamental purpose of an electronic communications system is to transfer information from one place to another. All electronic communication systems have a transmitter, a communication channel or medium, and a receiver. Figure 1-2: Basic Components of Electronic Communication System 17 Information Source In electronic communication systems, the message is referred to as information, or an intelligence signal. The source of information could either be in analog form such as human voice and music, or in digital form such as binary-coded numbers or alphanumeric codes. Analog signals are time-varying voltages or currents that are continuously changing. Digital signals are voltages or currents that change in discrete steps or levels. 1 0 1 1 0 0 1 1 1 0 1 Analog Digital 18 Transmitter The first step in sending a message is to convert it into electronic form suitable for transmission. Transducers are used to convert physical characteristics (temperature, pressure, light intensity, and so on) into electrical signals. Examples: 1. Voice messages – microphone converts acoustic energy into an electric audio signal 2. Television – camera sensor converts light information into video signals 3. Computer systems – input devices (mouse, keyboard, etc.) converts mechanical energy into binary codes 19 Transmitter (Tx) The transmitter is a collection of electronic components and circuits designed to convert the electrical signal to a signal suitable for transmission over a given communication medium. Transmitters are made up of oscillators, amplifiers, tuned circuits, filters, modulators, frequency mixers, frequency synthesizers, and other circuits. 20 Communication Channel or Transmission Media The communication channel is the medium by which the electronic signal is sent from one place to another. It can either be a guided channel by using wire conductors, fiber- optic cable, or waveguides, or unguided channel when signals are transmitted over free space. Guided channels are also called wireline channels, while unguided channels are called wireless channels. 21 Communication Channel Wireline Channel Electronic conductors – examples include coaxial cables for TV, twisted-pair cables used in a local area network (LAN) Optical media - fiber-optic cable or light pipe that carries the message on a light wave Wireless Channel Free space – when free space is the medium, the resulting system is known as radio. Acoustic – underwater communication Optical – through infrared such as remote control. 22 Receiver (Rx) A receiver is a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back to a form understandable by humans. Receivers contain amplifiers, oscillators, mixers, tuned circuits, filters, and demodulator that recovers the original intelligence signal from the modulated carrier. The main objective is to retrieve the transmitted signal at the receiver end. 23 Noise Noise refers to unwanted signals that tend to disturb the quality of the received signal in a communication system. The sources of noise may be internal or external to the system. The measure of noise is usually expressed in terms of the signal-to- noise ratio (SNR), which is the signal power divided by the noise power and can be stated numerically as Unitless: 𝑃𝑆 PS → Signal Power 𝑃𝑁 PN → Noise Power in decibel: 𝑃𝑆 𝑆𝑁𝑅(𝑑𝐵) = 10 log 𝑃𝑁 24 Types of Electronic Communication Electronic communications are classified according to whether they are: 1. One-way (simplex) or two-way (half duplex or full duplex) transmissions 2. Analog or digital signals 3. Baseband or Modulated Signals Types of Electronic Communication ONE WAY VS. TWO WAY One-way: Simplex The simplest method of electronic communication is referred to as simplex. This type of communication is one-way. Examples are: AM and FM Radio broadcasting TV broadcasting Beeper (personal receiver) Types of Electronic Communication ONE WAY VS. TWO WAY Two-Way or Duplex: Half Duplex The form of two-way communication in which only one party transmits at a time is known as half duplex. Examples are: Police, military, etc. radio transmissions Citizen band (CB) Amateur radio Two-Way or Duplex: Full Duplex When people can talk and listen simultaneously, it is called full duplex. The telephone is an example of this type of communication.  Types of Electronic Communication ANALOG SIGNALS VS. DIGITAL SIGNALS ANALOG SIGNALS: An analog signal is a smoothly and continuously varying voltage or current. Examples are: Figure 1-3: Analog signals (a) Sine wave “tone” (b) Voice (c) Video (TV) signal Types of Electronic Communication ANALOG SIGNALS VS. DIGITAL SIGNALS DIGITAL SIGNALS: Digital signals change in steps or in discrete increments. Most digital signals use binary or two-state codes. Examples are: Telegraph (Morse code) Continuous wave (CW) code Serial binary code (used in computers)  Types of Electronic Communication ANALOG SIGNALS VS. DIGITAL SIGNALS DIGITAL SIGNALS: Figure 1-4: Digital signals (a) Telegraph (Morse code) (b) Continuous-wave (CW) code (c) Serial binary code. Types of Electronic Communication ANALOG SIGNALS VS. DIGITAL SIGNALS DIGITAL SIGNALS: Many transmissions are of signals that originate in digital form but must be converted to analog form to match the transmission medium. Digital data over the telephone network. Analog signals. They are first digitized with an analog-to-digital (A/D) converter. The data can then be transmitted and processed by computers and other digital circuits. Types of Electronic Communication BASEBAND SIGNALS VS. MODULATED SIGNALS BASEBAND SIGNALS: Baseband signal refers to the information signal, regardless of whether it is analog or digital. MODULATED SIGNALS: To transmit baseband signals by radio, modulation technique must be used. A radio-frequency (RF) wave, or radio wave, is an electromagnetic signal that is able to travel long distances through space. Modulation is the process of having a baseband voice, video or digital signal modify another, high-frequency signal called the carrier. Modulation and Multiplexing Baseband Transmission Baseband information can be sent directly and unmodified over the medium or can be used to modulate a carrier for transmission over the medium. In telephone or intercom systems, the voice is placed on the wires and transmitted. In some computer networks, the digital signals are applied directly to coaxial or twisted-pair cables for transmission. Modulation and Multiplexing Broadband Transmission A broadband transmission takes place when a carrier signal is modulated, amplified, and sent to the antenna for transmission. The two most common methods of modulation are: Amplitude Modulation (AM) Frequency Modulation (FM) Another method is called phase modulation (PM), in which the phase angle of the sine wave is varied. 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. Figure 1-5: Modulation at the Transmitter 37 Modulation 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 mathematically expressed as: 𝑣 = 𝑉𝑝 sin 2𝜋𝑓𝑡 + 𝜃 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. Antenna It is extremely difficult to radiate low frequency signals from an antenna in the form of electromagnetic energy. 39  Types of Modulation Modulation Continuous-wave Pulse Modulation Modulation Considered as Considered as Analog Digital Analog Digital ASK PWM PCM AM Angular FSK PPM Delta Modulation FM PM PSK PAM 40 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. (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) 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. 43 Types of Modulation 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). Figure 1-8: Example of Digital Modulation Scheme 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. 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. 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. Figure 1-20: Example of demultiplexing at the Receiver 47  Types of Multiplexing There are three basic types of multiplexing: frequency division, time division, and code division. 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. Signal 1 Signal 2 Frequency Signal 3 Frequency Frequency Figure 1-21: FDM technique 48 Types of Multiplexing Time Division Multiplexing (TDM) In TDM, the multiple intelligence signals are sequentially sampled, and a small piece of each is used to modulate the carrier 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) 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. 51 Types of Multiplexing Code Division Multiplexing (CDM) 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. 51 Electromagnetic Spectrum Communication Systems Theory Electromagnetic Spectrum 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. 53 Figure 1-24: The Electromagnetic Spectrum Electromagnetic Spectrum 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. 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. The International Telecommunications Union (ITU) is an international agency in control of allocating frequencies and services 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) 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. 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 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. 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. 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). Light wavelengths are usually expressed in terms of Angstroms (Å). 61 Figure 1-27: The Visible Spectrum The Optical Spectrum 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. 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 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 𝜆= 𝑓 64 EXAMPLE#1: Determine the wavelength in meters for following frequencies: (a) 1 kHz, (b) 100 kHz, and (c) 10 MHz. 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 Bandwidth and Channel Bandwidth 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. 68 Bandwidth 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 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. 70 Information Theory Information theory is a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems. 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 Information Capacity 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. 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 signal. Television channels, where the available channel bandwidth is limited by regulatory agencies. 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) 2. Small bandwidth (measured in Hz) 3. Large data rate (measured in bps) 4. Low distortion (measured in SNR or BER) 5. Low cost (complex systems with low cost) 80 Some Research Areas 6G Systems Figure 1-30: Requirements for 6-G Wireless Technology 81 Some Research Areas mmWave MIMO Systems 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 References A. Bruce Carlson, et. al. Communication Systems: An Introduction to Signals and Noise in Electrical Communication, 5th Edition. McGraw Hill Companies Inc., 2010. Louis Frenzel Jr. Principles of Electronic Communication Systems, 4th Edition. McGraw-Hill Education, 2016. Simon Haykin and Michael Moher. An Introduction to Analog and Digital Communications. Wiley Textbooks, 2012. Simon Haykin. Communication Systems, 4th Edition. Wiley Textbooks, 2001. Wayne Tomasi. Electronic Communication Systems, 5th Edition. Singapore: Pearson Education South Asia Pte. Ltd, 2004. 84