International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-7 Issue-2, December 2017 Techniques of Modulation: Pulse Amplitude Modulation, Pulse Width Modulation, Pulse Position Modulation Diouba Sacko, Alpha Amadou Kéïta Abstract: The modulation technique aims at adapting the It is the case of broadcasting, television, and the satellite frequency band of the informative signal to that of the communication. According to the nature of the useful signal transmission channel. This avoids a great attenuation of certain (analogical or numerical) and that of the carrier signal frequencies on the transmission channel and also reduces the effects of the noise. In addition, the modulation technique, which (analogical or numerical), we distinguish the following requires a transposition of the low frequencies towards the high types of modulation: AM, FM, PM, ASK, FSK, PSK, PAM, frequencies, is used during the transmission of the informative PWM and PPM. In base band transmission, i.e. on short signal (or useful signal) on long distances: the narrow band distances, no need for transposition of frequency. This type transmission. There are several types of modulation according to of transmission utilizes the copper wire, the coaxial cable, the nature of the informative signal (analogical or digital) and the twisted pair or optical fiber as transmission channel. that of carrier signal (analogical or digital). In fact, the type of modulation to choose depends of practical application. In the In this article, we will study PAM, PWM and PPM transmission in baseband, i.e. on short distances, any frequency modulations. In these types of modulation, the useful signal transposition is needed. This type of transmission utilizes copper is of analogical form while the carrier signal is a pulse wire, coaxial cable, the twisted pair or optical fiber as physical resulting from a clock. These two signals (useful and support; to transport pulse trains. In this article, we consider the carrier) arrive in a modulator who will give at its output the narrow band transmission. We choose an informative signal of modulated signal (PAM, PWM or PPM). low frequency analogical nature (for example the human voice) and a carrier signal of high frequency digital nature (for example The analysis of the simulation results allows us to the clock signal). For frequency transposition, we use modulator determine the advantages, the disadvantages and the with adapted sensitivity. Indeed, we simulate signals modulated in applicability of the various types of modulation. Let us amplitude (PAM, Pulse Amplitude Modulation), in width (PWM, mention that obtained results from simulation are little Pulse Width Modulation) and in position (PPM, Pulse Position different from those of the real world because of the Modulation). On an illustrative basis, we simulated the case of an performance of the used software and other environmental audio informative signal. We analyze obtained results from simulation and recall advantages, disadvantages and applicability parameters. PAM, PWM and PPM modulations are used for of each type of modulation. The modulation software used is ISIS the analogical transmissions of the signals over optical from proteus. Let us mention that obtained results from fibers, in the remote control IRE or telemetry. simulation are little different from those of the real world and that because of the performance of the utilized software and II. STRUCTURE OF PAPER other environmental parameters. PAM, PWM and PPM modulations are particularly employed for the analogical The work is subdivided in seven chapters. The first chapter transmissions of the signals on optical fibers, in remote control gives us the general information on the analogical IRE or telemetry. modulation. In the chapters two, three, and four, we study Keywords: Modulation, PAM, PWM, PPM, Simulation theoretically PAM, PWM and PPM modulations; respectively. In the fifth chapter, we use ISIS software of I. INTRODUCTION proteus to simulate these modulations. The sixth chapter simulates the case of an audio useful signal by using the The modulation technique aims at adapting the frequency same software. The last chapter discusses about the band of the useful signal to that of the transmission channel. advantages, disadvantages and applicability of PAM, PWM This avoids a great attenuation of certain frequencies on the and PPM modulations. transmission channel and also reduces the effects of the noise. The technique of modulation, which requires a III. GENERAL INFORMATION ON THE transposition of the low frequencies towards the high ANALOGICAL MODULATION frequencies, is employed during the transmission on long With the development of the telecommunication devices, it distances: It is the narrow band transmission. To transmit a was necessary to code information to be transmitted in order useful signal which is generally low frequency on long to adapt it to the transmission channel such as optical fiber, distances we use another signal called carrier signal to coaxial cable, radio-transmit by relay of the systems. Coding transpose its frequency towards high frequencies. is also necessary when we must simultaneously transmit several signals on a single channel. Nowadays coding is Revised Version Manuscript Received on December 04, 2017. subject of research and calibration. The frequency Dr. Diouba Sacko, Département de Génie Informatique et de Télécommunications, Ecole Nationale d’Ingénieurs- Abderhamane Baba transposition (modulation) is an example of coding Touré, Bamako, République du Mali. information. Dr. Alpha Amadou Keïta, Département des Sciences Fondamentales, Ecole Nationale d’Ingénieurs- Abderhamane Baba Touré, Bamako, République du Mali. Published By: Blue Eyes Intelligence Engineering & Sciences Publication Pvt. Ltd. 100 Techniques of Modulation: Pulse Amplitude Modulation, Pulse Width Modulation, Pulse Position Modulation We distinguish two types of analogical modulations: We consider: • Continuous analogical modulations s (t) = A(t)cos ((2 πf0)t+ φ(t)), the expression of the signal to Amplitude modulation (AM); be transmitted Frequency modulation (FM); In FM, the instantaneous phase is written: Phase modulation (P.M) θi (t) = ((2 πfo) t + φ(t)) and the instantaneous frequency: • Analogical modulations by pulses Pulse Amplitude Modulation (PAM); 1dθ i ( t ) 1dϕ ( t ) Fi (t) = = f o + Pulse Width Modulation (PWM); 2π dt 2π dt Pulse Position Modulation (PPM). f + K *x(t) According to the useful signal (low frequency), the = 0 f modulation consists at the variation of one of the The modulated signal s (t)) can be written in the form: characteristics (amplitude, frequency, phase, width or S(t) = A(t)cos ((2πfo) t + ϕ(t)) = A(t)cos ( θi(t)) position) of the carrier signal (high frequency). A modulator The maximum excursion in frequency: ∆f = K *A generally has two inputs and one output. By applying the f m We consider: useful and carrier signals at the inputs, it gives to its output π the modulated signal which will be propagated in the S (t) = A (t) cos ((2 f0) t + φ (t)), the expression of the transmission channel. signal to be transmitted In PM: 3.1. Principle of the Modulation φ(t) = Kp*x(t) The transmission of a telecommunications signal (radio, Kp = 2πKf; with Kp-index multiplier (in PM) and K f- index T.V…) is done in the form of electromagnetic wave. It is of frequency multiplier (in FM) propagated with the celerity of the light (C = 3.108 m/s). Modulations FM and PM are called angular modulations . The useful signal x (t) is low frequency and can be produced 3.3. Modulation of a Linear Tension by a microphone, a walkman or CD reader. The carrier signal p (t) is high frequency, and is produced by a local Table below gives us a comparison between AM, FM and oscillator. AM (image) signals in terms of bandwidth and power. In addition, it gives us the corresponding frequency bands for carrier signals. Table 1: Comparison of the Continuous Analogical Modulations Type of Band- Carrier Power modulation width [150 [1 Radio long 4,5 KHz; MW ; waves AM KHz 285 2 (amplitude) Fig 1: Modulator Block kHz] MW] 3.2. Characteristics of the Signals [88 [1 Local radio 15 KHz ; MW ; We consider FM (frequency) kHz 108 2 x(t) = A cos ((2πf ) t) and m m kHz] MW] p(t) = Apcos ((2π f ) t) P [470 the expressions of useful and carrier signals; respectively. [10 Television AM MHz ; A , Ap _ amplitudes of the useful and carrier signals; 6 MHz W; m (phase) (image) 860 50W] fm , f P _ frequencies of the useful and carrier signals. MHz] The modulated signal in amplitude is written: S(t) = (1 + K x(t))* p(t); IV. PULSE AMPLITUDE MODULATION: PAM With: K*Am the modulation coefficient and K the index of multiplier (modulator) In modulated signal (PAM), the width and position of pulses In a traditional modulation: k ≤100% are constant while the amplitude of pulses varies There is overmodulation when k = m > 100 % proportionally with the amplitude of analogical useful Amax− A min signal. Carrier signal is from a clock. It is shown that: k= = m Amax+ A min 4.1. Principle The modulator transforms the analogical useful signal into a succession of rectangles. These rectangles are formed following the action of the sampler-blocker. Indeed, the taken samples, with regular intervals of time, on the useful signal are maintained for certain duration. Fig -2: Modulation rate Published By: Blue Eyes Intelligence Engineering 101 & Sciences Publication Pvt. Ltd. International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-7 Issue-2, December 2017 The rectangle amplitudes vary proportionally with those of filter, whose cut-off frequency will be judiciously chosen, in the useful signal. order to extract at the output the average value representing demodulated signal (or useful signal). VI. PULSE POSITION MODULATION: PPM In modulated signal (PPM), the amplitude and width of pulses are constant while the position of pulses varies proportionally with the amplitude of analogical useful signal.