Design of a Digital Transmission System Using ASAK for the Transmission and Reception of Text Messages Using LABVIEW

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1 Design of a Digital Transmission System Using ASAK for the Transmission and Reception of Text Messages Using LABVIEW K. Ravi Babu 1, M.Srinivas 2 1 Asst. Prof, Dept of ECE, PBR VITS 2 Asst. Prof, Dept of ECE, VR Siddardha Engg College Abstract :Amplitude-Shift Keying (PSK) is a digital modulation scheme in which data is expressed by modulating the carrier signal Amplitude. It uses limited number of amplitudes and each represents particular pattern of binary data. Each bit pattern forms symbol that is represented by amplitude. The demodulator designed for symbol set used by modulator determines the amplitude of extracted signal and maps to symbol thus recovering original data. This is a coherent receiver. In this paper text messages are transmitted after modulating and demodulated and extracted original data using labview. Keywords: Phase Shift Keying, Modulator, Demodulator I. INTRODUCTION A. Modulation If the carrier signal [8] characteristic varies with the message signal amplitude, then it is known as modulation. There are three types of modulation. 1.Amplitude modulation 2.Frequency modulation 3.Phase modulation B. Phase Modulation If the phase of the carrier signal varies with amplitude [9] of the message signal, then it is known as Phase Modulation. The Basic Digital formats are. 1.Amplitude Shift Keying or Abundancy Shift Keying (ASK) 2.Frequency Shift Keying or Recurrence Shift Keying (FSK) 3.Phase shift Keying or Stage movement Keying (PSK). 1.1 ASK Modulation and Demodulation: ASK is known as the amplitude shift keying it is defined as The amplitude of an analog carrier signal varies in accordance with the digital (modulating signal), keeping frequency and phase constant The level of amplitude can be used to represent binary logic 0s and 1s we can think of a carrier signal as an ON or OFF switch In the modulated signal, logic 0 is represented by the absence of a carrier and logic 1 is represented by the presence of carrier thus giving OFF/ON keying. Amplitude modulation is often associated with the modulation method of AM radio. When the carrier wave is C(t) and the modulating signal is m(t), the modulated wave is as shown fig1.5. ASK/OOK modulation, a modulator is used to shift the amplitude of the carrier wave proportionally to the amplitude of the modulating signal (digital signal). In the case of a digital signal, the modulating signal applied to the modulator is called digital modulation. The modulator is the same as for analog modulation. With an ASK modulating signal, the digital signal value is either -1 or +1, and when it is changed to 0 and +1 it is called OOK. With OOK, the amplitude direction of the modulated wave is indicated by the presence or absence of a carrier wave. DOI: /IJRTER H6JWC 371

2 In other words, when the signal is 0, there is no carrier wave and when it is 1, there is a carrier wave. The spectrum of the ASK modulated wave is centered on the carrier frequency and the square wave spectrum which is the modulating signal takes a spread-out form. Fig1.Generation Of Ask Signal 1.2 ASK demodulation: The ASK demodulator, which is designed specifically for the symbol-set used by the modulator, determines the amplitude of the received signal and maps it back to the symbol it represents, thus recovering the original data. Frequency and phase of the carrier are kept constant.there are two methods to design the ASK demodulator, which are 1. Asynchronous Detector 2. Synchronous Detector Asynchronous ASK Detector: Asynchronous detection is also called as Non-coherent detection in this detection process does not need receiver carrier to be phase locked with transmitter carrier. The advantage of this type of system is that the system become simple. But there is also having one disadvantage of this type of system that is having high Error probability. Asynchronous detection having different blocks and they are arranged as shown in block All Rights Reserved 372

3 Synchronous ASK Detector : Synchronous diction is also called as coherent detection. This detection is done by correlating received noisy signal and locally generated carrier Coherent detection consists of a product modulator followed by an integrator and a decision making device. Fig :2 Synchronous Detection Incoming ASK signal was applied to one input of the product modulator and another input of the product modulator is supplied with a sinusoidal carrier and then product modulator multiplies the both the signals and it given to the integrator A transducer is a device which converts one form of energy into another form.the message from the information source may or may not be electrical in nature. In a case when the message produced by the information source is not electrical in nature, an input transducer is used to convert it into a timevarying electrical signal./> Transmitter : The function of the transmitter is to process the electrical signal from different aspects. Modulation is the main function of the transmitter. In modulation, the message signal is superimposed upon the high-frequency carrier signal. In short, we can say that inside the transmitter, signal processing such as restriction of range of audio frequencies, amplification and modulation of are achieved. All these processing of the message signal are done just to ease the transmission of the signal through the channel. The Channel and the Noise: The term channel means the medium through which the message travels from the transmitter to the receiver. In other words, we can say that the function of the channel is to provide a physical connection between the transmitter and the receiver. There are two types of channels, namely pointto-point channels and broadcast channels. Examples of point-to-point channels are wire lines, microwave links and optical fibers. On the other hand, the broadcast channel provides a capability where several receiving stations can be reached simultaneously from a single transmitter. An example of a broadcast channel is a satellite in geostationary orbit, which covers about one third of the earth s surface. During the process of transmission and reception the signal gets distorted due to noise introduced in the system. Noise is an unwanted signal which tends to interfere with the required signal. Noise signal is always random in character. Noise may interfere with signal at any point in a communication system. However, the noise has its greatest effect on the signal in the channel. Receiver : The main function of the receiver is to reproduce the message signal in electrical form from the distorted received signal. This reproduction of the original signal is accomplished by a All Rights Reserved 373

4 known as the demodulation or detection. Demodulation is the reverse process of modulation carried out in transmitter. Destination : Destination is the final stage which is used to convert an electrical message signal into its original form.for example in radio broadcasting, the destination is a loudspeaker which works as a transducer i.e. converts the electrical signal in the form of original sound All Rights Reserved 374

5 II. TEXT MESSAGING USING DIGITAL ASK MODULATION OF AUDIO USING NI MYDAQ Block diagram: Lab view implementation: 2.1Transmitter: Algorithm: First, Enter a text message of 10 characters Wait until a user presses 'Send' to do anything Convert the message to ASCII 8 bit integers Add 255 to the beginning of the set of integers (which will translate to , or a long high signal to trigger off ) Convert the integers to bits (symbols) Each time a bit = 1, Generate a sine wave pattern Each time a bit = 0, Generate a DC value of zero The output signal is given to audio in 2.2 Receiver 2.2.1Algorithm: Acquire an input audio signal. Using an old technique for decoding AM analog radio, apply a full rectifier to the signal (i.e., absolute value) and filter the signal with a low pass filter. Trigger off of the initial bits Once a known length of data is collected (based on expected number of characters), translate the bits. Decode the signal left back into bits (1 s and 0 s) based on the known data rate (samples per symbols) Convert the bits into integer numbers. Convert the integer numbers back into ASCII text. It is commonly used to transmit digital data over optical All Rights Reserved 375

7 International Journal of Recent Trends in Engineering & Research (IJRTER) IV. CONCLUSION In this project we have transferred text message between two computers using wired channel. In future, this wired channel can be replaced with speaker and microphone which can be separated up to some distance. Some channel redundancy coding and advanced modulation technique can also be incorporated. REFERENCES [1] [Online] Available: Txt-File-to-ASCII-to Txt to-binary-matlabequivalent/tdp/ c. [2] [Online] Available: binary-phase-shift-keying-bpsk.html. binary bpsk.html. [3] [Online] Available: sgallery.com/2013/03/ PSK-matlab-code.html. PSK [4] [Online] Available: ref/textread.htmlh. Poor, An Introduction to Signal Detection and Estimation; New York: Springer-Verlag, Springer 1985, ch. 4. [5] [Online] Available: Devices/Basic-BPSK-Modulator Modulator-in-Labview/ tdp/ [6] [Online] Available: digital-waveform-array-into-boolean/td-p/ /page/3 digital p/ /page/3. [7] [Online] Available: DOC DOC [8] [Online] Available: modulation [9] [Online] Available: modulation [10] [Online] Available: Paper-Solution-CTNC P

Chapter-15. Communication systems -1 mark Questions

Chapter-15. Communication systems -1 mark Questions Chapter-15 Communication systems -1 mark Questions 1) What are the three main units of a Communication System? 2) What is meant by Bandwidth of transmission? 3) What is a transducer? Give an example. 4)