KKW_ELTX_DCOM

                                                                                                                                           Name of Experiment :-Experimental Study of Basicline codes and Multilevel line codes. A  line code  is the code used for data transmission of a digital signal over a transmission line. This process of coding is chosen so as to avoid overlap and distortion of signal such as inter-symbol interference. Properties of Line Coding Following are the properties of line coding − As the coding is done to make more bits transmit on a single signal, the bandwidth used is much reduced. For a given bandwidth, the power is efficiently used. The probability of error is much reduced. Error detection is done and the bipolar too has a correction capability. Power density is much favorable. The timing content is adequate. Long strings of  1s  and  0s  is avoided to maintain transparency.               PRE TEST                                                           

                                                                                          Name of Experiment :- Experimental study of Delta Modulation and signal reconstruction The sampling rate of a signal should be higher than the Nyquist rate, to achieve better sampling. If this sampling interval in Differential PCM is reduced considerably, the sampleto-sample amplitude difference is very small, as if the difference is  1-bit quantization , then the step-size will be very small i.e.,  Δ   d e l t a d e l t a . Delta Modulation The type of modulation, where the sampling rate is much higher and in which the stepsize after quantization is of a smaller value  Δ , such a modulation is termed as  delta modulation . Delta Modulator The Delta Modulator comprises of a 1-bit quantizer and a delay circuit along with two summer circuits. Following is the block diagram of a delta modulator. The predictor circuit in DPCM is replaced by a simple delay circuit in DM. From the above diagram, we have

                                                                                                                                               Name of Experiment :-Experimental study of Quadrature Phase shift keying  The  Quadrature Phase Shift Keying  QPSK  is a variation of BPSK, and it is also a Double Side Band Suppressed Carrier  DSBSC  modulation scheme, which sends two bits of digital information at a time, called as  bigits . Instead of the conversion of digital bits into a series of digital stream, it converts them into bit pairs. This decreases the data bit rate to half, which allows space for the other users. QPSK Modulator The QPSK Modulator uses a bit-splitter, two multipliers with local oscillator, a 2-bit serial to parallel converter, and a summer circuit. Following is the block diagram for the same. At the modulator’s input, the message signal’s even bits (i.e., 2 nd  bit, 4 th  bit, 6 th  bit, etc.) and odd bits (i.e., 1st bit, 3 rd  bit, 5 th  bit, etc.) are separated

                                                                                                                                                  Name of Experiment :-Experimental study of generation and detection of Direct spread spectrum system(DSSS). A collective class of signaling techniques are employed before transmitting a signal to provide a secure communication, known as the  Spread Spectrum Modulation . The main advantage of spread spectrum communication technique is to prevent “interference” whether it is intentional or unintentional. The signals modulated with these techniques are hard to interfere and cannot be jammed. An intruder with no official access is never allowed to crack them. Hence, these techniques are used for military purposes. These spread spectrum signals transmit at low power density and has a wide spread of signals. Pseudo-Noise Sequence A coded sequence of  1s  and  0s  with certain auto-correlation properties, called as  Pseudo-Noise coding sequence  is

  Name of Experiment :-Implementation of Convolutional   Code Using MATLAB Convolutional Codes In convolutional codes, the message comprises of data streams of arbitrary length and a sequence of output bits are generated by the sliding application of Boolean functions to the data stream. In block codes, the data comprises of a block of data of a definite length. However, in convolutional codes, the input data bits are not divided into block but are instead fed as streams of data bits, which convolve to output bits based upon the logic function of the encoder. Also, unlike block codes, where the output codeword is dependent only on the present inputs, in convolutional codes, output stream depends not only the present input bits but also only previous input bits stored in memory. For generating a convolutional code, the information is passed sequentially through a linear finite-state shift register. The shift register comprises of (-bit) stages and Boolean function generators. A convolut