Saturday, March 2, 2019

Digital Modulation Techniques

LOVELY master key UNIVERSITY TERM PAPER Topic Digital Modulation Techniques Course commandment ELE102 Course title Electrical science-II Submitted toSubmitted by Subrahm anyam Tanala Sirvishwajeet kumar SecK1901 RollB57 table of contents INTRODUCTION 1 Aim 2 Analog passage methods 3 Digital prosody methods o 3. 1 Fundamental digital conversion methods o 3. 2 Modulator and detector principles of operation o 3. 3 name of cat valium digital conversion techniques 4 Digital baseband conversion or line coding 5 Pulse modulation methods 6 multifaceted modulation techniques 7 References INTRODUCTION In electronics, modulation is the process of variable cardinal or more properties of a gamy absolute frequency semiannual roll up radiation diagram, c distributivelyed the carrier argue, with respect to a modulating level. This is done in a like fashion as a musician may modulate a noise (a periodic quiverform) from a musical instrument by varying its volume, timing and pitch. The three key parameters of a periodic potherform atomic number 18 its bountifulness (volume), its contour (timing) and its frequency (pitch), all of which can be modified in accordance with a pitiable frequency luff to obtain the modulate type.Typically a high-frequency sinusoid vibrateform is used as carrier sharpening, just a squ ar wave pulse train may also occur. Aim The aim of digital modulation is to transfer a digital issue stream everywhere an analog passband channel, for example over the public switched telephone ne devilrk (where a bandpass filter limits the frequency range to between 300 and 3400 Hz), or over a limited radiocommunication frequency band. The aim of analog modulation is to transfer an analog baseband (or mildpass) signal, for example an audio signal or TV signal, over an analog passband channel, for example a limited radio frequency band or a cable TV ne 2rk channel. 2 Analog modulation methods In analog modulation, the mod ulation is applied in boundedly in response to the analog information signal. pic pic A low-frequency message signal (top) may be carried by an AM or FM radio wave. Common analog modulation techniques are Amplitude modulation (AM) (here the premium of the carrier signal is varied in accordance to the instantaneous bounty of the modulating signal) o Double-sideband modulation (DSB) ? Double-sideband modulation with carrier (DSB-WC) (used on the AM radio broadcasting band) ?Double-sideband suppressed-carrier transmission (DSB-SC) ? Double-sideband reduced carrier transmission (DSB-RC) o Single-sideband modulation (SSB, or SSB-AM), Angle modulation o Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) o conformation modulation (PM) (here the phase shift of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) The accompanying send off show s the results of (amplitude-)modulating a signal onto a carrier (both of which are sin waves).At any point along the y-axis, the amplitude of the spiel signal is equal to the score of the carrier signal and the modulating signal amplitudes. pic pic undecomposable example of amplitude modulation. 3 Digital modulation methods In digital modulation, an analog carrier signal is modulated by a digital bit stream. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet). pic pic Schematic of 4 baud (8 bps) data link.A simple example A telephone line is knowing for transferring audible sounds, for example tones, and not digital bits ( vigors and ones). Computers may however decease over a telephone line by means of modems, which are representing the digital bits by ton es, called symbols. If there are four alternative symbols (corresponding to a musical instrument that can gene pass judgment four different tones, one at a meter), the first symbol may represent the bit sequence 00, the second 01, the third 10 and the fourth 11. If the modem plays a descent consisting of 1000 tones per second, the symbol rate is 1000 symbols/second, or baud.Since each tone (i. e. , symbol) represents a message consisting of two digital bits in this example, the bit rate is twice the symbol rate, i. e. 2000 bits per second. This is similar to the technique used by dialup modems as opposed to DSL modems. . According to one definition of digital signal, the modulated signal is a digital signal, and agree to another definition, the modulation is a form of digital-to-analog conversion. Most textbooks would consider digital modulation schemes as a form of digital transmission, synonymous to data transmission very a few(prenominal) would consider it as analog transmiss ion. . 1 Fundamental digital modulation methods The most fundamental digital modulation techniques are based on keying In the fiber of PSK (phase-shift keying), a finite number of phases are used. In the cocktail dress of FSK (frequency-shift keying), a finite number of frequencies are used. In the case of conduct (amplitude-shift keying), a finite number of amplitudes are used. In the case of QAM (quadrature amplitude modulation), a finite number of at least two phases, and at least two amplitudes are used. FSK The two binary program states, logical system 0 (low) and 1 (high), are each represented by an line of latitude waveform.Logic 0 is represented by a wave at a specific frequency, and logic 1 is represented by a wave at a different frequency. Below shows the basic representation. picpic With binary FSK, the midriff or carrier frequency is shifted by the binary input data. gum olibanum the input and output rates of change are equal and therefrom the bit rate and ba ud rate equal. The frequency of the carrier is changed as a function of the modulating signal (data), which is existence transmissible. Amplitude remains unchanged. twain fixed-amplitude carriers are used, one for a binary zero, the other for a binary one. Uses of FSK.Today FSK Modems are used for short haul data communication over private lines or any dedicated wire pair. These are more used for communication between industrial applications like railroad signalling controls and wandering(a) robotic equipment. The short haul modem offers the following specs Speeds of up to 9600 bps Full-duplex or half duplex operation. Distance up to 9. 5 miles In the former(prenominal) FSK was used in the Bell 103 and Bell 202. These were the first data modem but due to their low bit rate there not being used any more. The Bell 103 had a data rate of exclusively 300 bauds. This modem was predominant until the early 1980s. material body tack Keying PSK Phase shift keying (PSK) is a metho d of transmitting and receiving digital signals in which the phase of a transmitted signal is varied to convey information. The simplest form of PSK has only two phases, 0 and 1. It is therefore a type of ASK with (t) taking the values -1 or 1, and its bandwidth is the analogous as that of ASK. The digital signal is broken up time wise into individual bits (binary digits). The state of each bit is determined according to the state of the preceding bit. If the phase of the wave does not change, then the signal state stays the similar (low or high).If the phase of the wave changes by 180 degrees, that is, if the phase reverses, then the signal state changes (from low to high or from high to low) If the phase of the wave changes by 180 degrees, that is, if the phase reverses, then the signal state changes (from low to high or from high to low). Because there are two attainable wave phases, this form of PSK is sometimes called bi-phase modulation. If two or more of the same logic lev el are received in secession the frequency will remain the same until the logic level changes. Variants of PSK. - binary Phase charge up Keying (BPSK) Use alternative sine wave phase to en inscribe bits Simple to implement, inefficient use of bandwidth Binary Phase Shift Keying (BPSK) demonstrates better act than ASK and FSK. PSK can be expanded to a M-array scheme, employing multiple phases and amplitudes as different states. Phase Shift Keying PSK Phase shift keying (PSK) is a method of transmitting and receiving digital signals in which the phase of a transmitted signal is varied to convey information. The simplest form of PSK has only two phases, 0 and 1. It is therefore a type of ASK with (t) taking the values -1 or 1, and its bandwidth is the same as that of ASK.The digital signal is broken up time wise into individual bits (binary digits). The state of each bit is determined according to the state of the preceding bit. If the phase of the wave does not change, then the si gnal state stays the same (low or high). If the phase of the wave changes by 180 degrees, that is, if the phase reverses, then the signal state changes (from low to high or from high to low) If the phase of the wave changes by 180 degrees, that is, if the phase reverses, then the signal state changes (from low to high or from high to low).Because there are two possible wave phases, this form of PSK is sometimes called bi-phase modulation. If two or more of the same logic level are received in secession the frequency will remain the same until the logic level changes. Variants of PSK. a)Binary Phase Shift Keying (BPSK) Use alternative sine wave phase to encode bits Simple to implement, inefficient use of bandwidth pic Binary Phase Shift Keying (BPSK) demonstrates better performance than ASK and FSK. PSK can be expanded to a M-array scheme, employing multiple phases and amplitudes as different states.Filtering can be employed to avoid spectral spreading. b)Quadrature Phase Shift Key ing (QPSK) Multilevel modulation technique 2 bits per symbol much spectrally efficient, more complex receiver picpicpic Quadrature Phase Shift Keying is effectively two independent BPSK systems (I and Q), and therefore exhibits the same performance but twice the bandwidth efficiency. railroad siding waveform is sum of modulated Cosine and Sine wave. Variants of QPSK pic Conventional QPSK has transitions by means of zero (i. e.. 180o phase transition). Highly linear amplifier required. In Offset QPSK, the transitions on the I and Q channels are staggered. Phase transitions are therefore limited to 90o ? /4-QPSK the set of constellation points are toggled each symbol, so transitions through zero cannot occur. This scheme produces the lowest envelope variations. Uses of PSK Binary Phase Shift Keying (BPSK) BPSK is generally used in deep space telemetry and also cable modems Quadrature Phase Shift Keying (QPSK) and it Variants Satellites CDMA, (Code-Division Multiple Access) refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications. TETRA, Terrestrial Trunked Radio) is a set of standards developed by the European Telecommunications Standardization Institute (ETSI) that describes a common winding radio communications infrastructure throughout Europe This infrastructure is targeted primarily at the mobile radio needs of public safety groups (such as police and enhance departments), utility companies, and other enterprises that provide voice and data communications services. LMDS, (Local Multipoint distribution System) is a system for broadband microwave wireless transmission pick out from a local antenna to homes and businesses within a line-of-sight radius, a rootage to the so-called last-mile technology problem of economically bringing high-bandwidth services to users. . 3. 3 List of common digital modulation techniques The most common digital modulation techniques are Phase-shi ft keying (PSK) o Binary PSK (BPSK), using M=2 symbols Quadrature PSK (QPSK), using M=4 symbols o 8PSK, using M=8 symbols o 16PSK, using M=16 symbols o Differential PSK (DPSK) o Differential QPSK (DQPSK) o Offset QPSK (OQPSK) o ? /4QPSK Frequency-shift keying (FSK) o audio recording frequency-shift keying (AFSK) o Multi-frequency shift keying (M-ary FSK or MFSK) o Dual-tone multi-frequency (DTMF) o Continuous-phase frequency-shift keying (CPFSK) Amplitude-shift keying (ASK) On-off keying (OOK), the most common ASK form M-ary vestigial sideband modulation, for example 8VSB Quadrature amplitude modulation (QAM) a combination of PSK and ASK o Polar modulation like QAM a combination of PSK and ASK. citation needed Continuous phase modulation (CPM) methods o Minimum-shift keying (MSK) o Gaussian minimum-shift keying (GMSK) Orthogonal frequency-division multiplexing (OFDM) modulation o discrete multitone (DMT) including adaptive modulation and bit-loading. riffle modulation Mis cellaneous modulation techniques The use of on-off keying to transmit Morse code at radio frequencies is known as continuous wave (CW) operation. reconciling modulation Space modulation A method whereby signals are modulated within airspace, such as that used in Instrument arrive systems. 7 REFRENCES J. R. Barry, E. A. Lee, D. G. Messerschmidt, Digital Communication, Kluwer Academic Publishers, 2004. www. wikipedia. org Communication systems (Simon Haykin), Wiley India

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