Telecommunications ppt

ppt on telecommunications and universal mobile telecommunications system ppt
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Dr.DouglasPatton,United States,Teacher
Published Date:26-07-2017
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Fundamentals of telecommunications Friday, July 27, 2012 Will cover basic concepts of telecommunication systemsGoals To present the basics concepts of telecommunication systems with focus on digital and wireless, and the most important features of the propagation of telecommunication signals 2 Friday, July 27, 2012Basic Concepts Signal • Analog, Digital, Random Sampling • Bandwidth • Spectrum • Noise • Interference • Channel Capacity • BER • Modulation • Multiplexing • Duplexing • 3 Friday, July 27, 2012Telecommunication Signals Telecommunication signals are variation over time of voltages, currents or light levels that carry information. For analog signals, these variations are directly proportional to some physical variable like sound, light, temperature, wind speed, etc. The information can also be transmitted by digital signals, that will have only two values, a digital one and a digital zero. 4 Friday, July 27, 2012Telecommunication Signals: Features Amplitude is the maximum excursion from the zero value, and is generally measured in volts (V) or amps (A). For periodic signals, the number of repetitions of the signal in one second is called the frequency of the signal, measured in Hz and its multiples. The power of an electric signal is given by the product of its voltage and current and is measured in watts (W). The energy of the signal is give by the product power over the time considered and is measured in joules (J), and also in Wh, with its multiple, the kWh (kilo watt hour) most commonly used. 5 Friday, July 27, 2012Telecommunication Signals Any analog signal can be converted into a digital signal by appropriately sampling it. The sampling frequency must be at least twice the maximum frequency present in the signal in order to carry all the information contained in it. Random signal are the ones that are unpredictable and can be described only by statistical means. Noise is a typical random signal, described by its mean power and frequency distribution. 6 Friday, July 27, 2012 Examples of analog signals are voice and video, examples of digital signals are written text and the morse code used in telegraphy. Any analog signal can be converted to a digital one containing the same information. Digital signals are more robust and easier to store and transport, that is why nowadays digital signals prevailQuick review of unit prefixes - -12 12 10 1/ 1/1000000000000 1000000000000 p p pico pico- - -9 nano- 10 1/1000000000 n -6 micro- 10 1/1000000 µ -3 milli- 10 1/1000 m -2 centi- 10 1/100 c 3 kilo- 10 1 000 k 6 mega- 10 1 000 000 M 9 giga- 10 1 000 000 000 G 7 Friday, July 27, 2012 In physics, math, and engineering, we often express numbers by powers of ten. We will meet these terms again, e.g. in giga-Hertz (GHz), centi-meters (cm), micro-seconds (µs), and so on.Example of signals: Electromagnetic Waves Characteristic wavelength, frequency, and amplitude ‣ No need for a carrier medium ‣ Examples: light, X­rays and radio waves ‣ time: 1 second wavelength ( ) amplitude amplitude wavelength ( ) 8 Friday, July 27, 2012 The wavelength (sometimes referred to as lambda, λ) is the distance measured from a point on one wave to the equivalent part of the next, for example from the top of one peak to the next. The frequency is the number of whole waves that pass a fixed point in a period of time. Waves also have a property called amplitude. This is the distance from the center of the wave to the extreme of one of its peaks, and can be thought of as the “height” of a water wave. Unlike waves in water, electromagnetic waves require no medium to carry them through space. It may be said that the media that oscillates is the electromagnetic field.Phase The phase of a wave is the fraction of a cycle that the wave is offset from a reference point. It is a relative measurement that can be express in different ways (radians, cycles, degrees, percentage). Two waves that have the same frequency and different phases have a phase difference, and the waves are said to be out of phase with each other. 9 Friday, July 27, 2012 from Wikipedia A phase difference is analogous to two athletes running around a race track at the same speed and direction but starting at different positions on the track. They pass a point at different instants in time. But the time difference (phase difference) between them is a constant - same for every pass since they are at the same speed and in the same direction. If they were at different speeds (different frequencies), the phase difference is undefined and would only reflect different starting positions. Java applet for a demo: Interference (constructive and destructive) will be explained in the next slide using the concept of phase difference between the interfering waves.Wavelength and Frequency c = f λ c = speed (meters / second) f = frequency (cycles per second, or Hz) λ = wavelength (meters) If a wave on water travels at one meter per second, and it oscillates five times per second, then each wave will be twenty centimeters long: 1 meter/second = 5 cycles/second λ λ = 1 / 5 meters λ = 0.2 meters = 20 cm 10 Friday, July 27, 2012 A wave has a certain speed, frequency, and wavelength. These are connected by a simple relation: Speed = Frequency Wavelength The wavelength (sometimes referred to as lambda, λ) is the distance measured from a point on one wave to the equivalent part of the next, for example from the top of one peak to the next. The frequency is the number of whole waves that pass a fixed point in a period of time. Speed is measured in meters/second, frequency is measured in cycles per second (or Hertz, abbreviated Hz), and wavelength is measured in meters.Wavelength and Frequency 8 Since the speed of light is approximately 3 x 10 m/s, we can calculate the wavelength for a given frequency. Let us take the example of the frequency of 802.11b/g wireless networking: f = 2.4 GHz = 2,400,000,000 cycles / second wavelength (λ) = c / f 8 9 -1 = 3 10 m/s / 2.4 10 s -1 = 1.25 10 m = 12.5 cm Therefore, the wavelength of 802.11b/g WiFi is about 12.5 cm. 11 Friday, July 27, 2012 There are many more frequencies used in WiFi networking: one possible range spans over 85 MHz, starting at 2400 MHz and ending at 2485 MHz (but note that the ending value may be different in different countries). What is the wavelength of 5.3GHz 802.11a? 8 9 λ = 3 10 / 5.3 10 = 5.66 cmSinusoidal Signal A ⊖ time 0 v(t)= A cos(wt - ⊖) -A A = Amplitude, volts w = 2πf, angular frequency in radians f = frequency in Hz T = period in seconds, T= 1/f ⊖= Phase in degrees or radians 12 Friday, July 27, 2012 The sinusoidal signal is very important and can be expressed by a simple mathematical formula. It contains a single frequency. The phase is the offset from zero of the signal, when the offset is 90° we can also express the signal as v(t)=Asin (w t) Signals and Spectra 13 Friday, July 27, 2012 A signal can be characterized by its behavior over time or by its frequency components, which constitute its spectrum. Any periodic signal is composed of many sinusoidal components, all of them multiples of the fundamental frequency, which is the inverse of the period of the signal.Spectrum of a signal f 3 f 2 f 1 Oscilloscope Spectrum Analyzer 14 Friday, July 27, 2012 The graph shows that we can look at a signal from the perspective of its evolution over time, or we can look at it from the perspective of its frequency component, when we look at it from this perspective, we are dealing with the spectrum of the signal. The spectrum distribution relays very important information about a the signal and allows for the intuitive understanding of the concept of filtering electrical signals. In the example shown, the signal is formed by the superposition of 3 sinusoidal components of frequency f ,f and f 1 2 3. If pass this signal through a device that will remove f and f , the output is a pure sinusoidal with the f1 frequency. We call this operation “Low Pass filtering” because it removes the higher 2 3 frequencies. Conversely, we can apply the signal to a “High Pass Filter”, a device that will remove f and f leaving only a sinusoidal signal at the f frequency. 1 2 3 Other combinations are possible, giving rise to a variety of filters. No physical device can transmit all the infinite frequencies of the electromagnetic spectrum, so it will always perform some kind of filtering in the signal that goes through it. The bandwidth of a signal is the difference between the highest and the lowest frequency that it contains and is expressed in Hz.Electromagnetic Spectrum Approximate frequency in Hz 4 6 8 10 12 14 16 18 20 22 24 10 10 10 10 10 10 10 10 10 10 10 microwave visible light X rays ultraviolet radio gamma rays infrared 4 2 0 -2 -4 -6 -8 -10 -12 -14 -16 10 10 10 10 10 10 10 10 10 10 10 Approximate wavelength in meters Approximate range for WiFi 15 Friday, July 27, 2012 This picture represents the entire electromagnetic spectrum. It goes all the way from very low frequency radio waves on the left, to very high frequency X-rays and gamma rays on the right. In the middle, there's a very small region that represents visible light. In the scope of the entire electromagnetic spectrum, the range of frequencies that we can actually perceive with our eyes is very small. You can see on either side of visible light is infrared and ultraviolet. But the area that we are interested in is the very narrow range of frequencies used by WiFi equipment. That is the very thin sliver at the low end of the microwave range.Perspective wavelength town house man cat insect seed (meters) 1000 100 10 1 0,1 0,01 10000 0,001 4 5 6 7 8 9 10 11 (Hertz) 10 10 10 10 10 10 10 10 frequency AM radio microwaves FM radio telecom links GPS shortwaves WiFi mobile phones satellite TV radars the radio spectrum links with TV submarines radiohams 16 Friday, July 27, 2012 This picture represents some of the many different usages of the e.m. spectrum, from low frequency radio up to microwaves. E.m. communications with submarines are forced to use very low e.m. frequencies, because of the difficulties of propagation of higher frequency RF signals under water. Most of the other usages are concentrated on higher frequencies, because of the wider capacity available there (more channels and more data per channel). Examples are: shortwaves (international AM broadcast, maritime communications, radio amateurs HF bands, etc.): from 1 to 30 MHz FM radio: from 88 to 108 MHz TV broadcast: VHF channels in many bands from 40 to 250 MHz; UHF channels in many bands from 470 to 885 MHz (depending from the country) VHF and UHF radio ham bands: around 140-150 and 440-450 MHz, together with many other users (services, security, police, etc...) mobile phones: 850, 900, 1800, 1900 and 2100 MHz for GSM and CDMA cellular networks; GPS: 1227 and 1575 MHz WiFi: 2400-2485 MHz and 4915-5825 MHz (depending from the country). See for details. radars: common bands for radars are: L band (1–2 GHz), S band (2–4 GHz), C band (4–8 GHz), X band (8–12 GHz) but others are also used. satellite TV: C-band (4–8 GHz) and Ku-band (12–18 GHz) microwave telecom links: for example in the United States, the band 38.6 - 40.0 GHz is used for licensed high-speed microwave data links, and the 60 GHz band can be used for unlicensed short range data links with data throughputs up to 2.5 Gbit/s. The 71-76, 81-86 and 92–95 GHz bands are also used for point-to-point high-bandwidth communication links.WiFi frequencies and wavelengths Standard Frequency Wavelength 802.11 b/g/n 2.4 GHz 12.5 cm 802.11 a/n 5.x GHz 5 to 6 cm 2.4 GHz 5 GHz 17 Friday, July 27, 2012 This photo shows two Yagi antennas made from PC-board materials. The Yagi (sometimes referred also as Yagi-Uda, from the names of the two inventors) is one of the many designs for antennas. The antenna on the left is designed to work at 2.4 GHz, while the antenna on the right works for 5 GHz. The two antennas have similar characteristics and gain at their respective frequencies. You may notice that the ratio of the typical dimensions of the two antennas is the inverse ratio of the two frequencies: 5000:2400 = 12,5 : 6 = circa 2 It’s almost always true that antennas of comparable characteristics at 2.4 and 5 GHz have this same dimensional ratio of 2, i.e. a 5GHz antenna is half the size of a 2.4GHz antenna (with approx. the same gain).Communication System TX Channel RX 18 Friday, July 27, 2012 The basic communication system is formed by a transmitter TX, a communication channel and a receiver RX The Transmitter injects a signal into the channel that delivers it to the receiver. The receiver must recover the information contained in the receiver signal despite the limitations introduced by the channel. The channel can be a physical one, like a copper cable and an optical fiber, or simply air or even vacuum that transmits electromagnetic waves. Any channel is subject to some kind of electromagnetic “noise” and interference, will attenuate the signal and will change its shape (distorsion). Since it takes some time for the signal to traverse the channel, the received signal will have some latency with respect to the transmitted signal. This “latency” might change over time and contribute to “jitter” in the received signal. The signal might also reach the receiver by means of different trajectories, and in this case the different received versions will interact as a consequence of the “multipath”. Multipath can completely obliterate a signal but it can also used advantageously in some modern communications techniques.Attenuation Received Signal Transmitted Signal 19 Friday, July 27, 2012 Although the effect of attenuation can easily be overcome with an amplifier, the amplifier will also enhance any noise introduced by the channel and inevitably introduce some extra noise of its own.Noise in an analog Signal 20 Friday, July 27, 2012 Noise can completely masquerade the transmitted signal. Telecommunications engineers have strived for a century to find better ways to recover the information contained in the signal contaminated by noise.

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