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DIGITAL DATA TRANSMISSION - I

Digital Modulation Techniques There are three ways in which the bandwidth of the channel carrier may be altered simply. It is worth emphasizing that these methods are chosen because they are practically simple, not because they are theoretically desirable. These are the altering of the amplitude, frequency and phase of the carrier sine wave. These techniques give rise to amplitude-shiftkeying (ASK), frequency-shift-keying (FSK) and phase-shift-keying (PSK), respectively. ASK describes the technique the carrier wave is multiplied by the digital signal f(t) | EE-458 LAB REPORT EXPERIMENT 5 DIGITAL DATA TRANSMISSION - I 1 27 2010 Purpose The objectives of this laboratory are 1. To implement baseband amplitude shift keying and phase reversal keying for binary communication systems. 2. To investigate the operation of these systems. 3. To measure the effects of noise on the probability of error in the received data. Equipment List 1. PC with Matlab and Simulink Page 2 Digital Modulation Techniques There are three ways in which the bandwidth of the channel carrier may be altered simply. It is worth emphasizing that these methods are chosen because they are practically simple not because they are theoretically desirable. These are the altering of the amplitude frequency and phase of the carrier sine wave. These techniques give rise to amplitude-shiftkeying ASK frequency-shift-keying FSK and phase-shift-keying PSK respectively. ASK describes the technique the carrier wave is multiplied by the digital signal f t . Mathematically the modulated carrier signal is s t ft ft ii 3rfct 4 Figure Amplitude shift keying Figure Amplitude shift keying -- frequency domain The pulses representing the sample values of a PCM waveform can be transmitted on a RF carrier by use of amplitude phase or frequency modulation. For digital amplitude modulation it is known as Amplitude Shift Keying. Here the carrier amplitude is determined by the data bit for that interval. We note that the transmitter for such a system simply consists of an oscillator that is gated on and off accordingly ASK is often referred to as on-off keying. The oscillator runs continuously as the on-off gating is carried out. The circuit is connected according to the schematic shown. A silicon diode and a 50-ohm terminator are also used. The VCO generates a 20 kHz carrier signal and receiver reference. The summer and variable power supply changes the threshold of the decision circuit. Threshold Adjustment Page