Data Transmission

International Journal of Advanced Research

The purpose of a Communication System is to transport an information bearing signal from a source to a user destination via a communication channel.

Communication has been one of the deepest needs of the human race throughout recorded history. It is essential to forming social unions, to educating the young, and to expressing a myriad of emotions and needs. Good communication is central to a civilized society.

Translation from the Polish language edition published by Wydawnictwa Komunikacji i Ł aczności Spółka z o.o.

Digital Signal Processing, 2011

We use the word modulation to mean the systematic alteration of one waveform, called the carrier, according to the characteristic of another waveform, the modulating signal or the message. In Continuous Wave (CW) modulation schemes, the carrier is a sinusoid. We use () c t and (), m t to denote the carrier and the message waveforms respectively. The three parameters of a sinusoidal carrier that can be varied are: amplitude, phase and frequency. A given modulation scheme can result in the variation of one or more of these parameters. Before we look into the details of various linear modulation schemes, let us understand the need for modulation.

electric pulses of varying amplitude. In digital technology, translation of information is into binary format (zero or one) where each bit is representative of two distinct amplitudes. Properties of Digital vs Analog signals Digital information has certain properties that distinguish it from analog communication methods. These include  Synchronizationdigital communication uses specific synchronization sequences for determining synchronization.  Languagedigital communications requires a language, which should be possess by both sender and receiver and should specify meaning of symbol sequences.  Errorsdisturbances in analog communication causes errors in actual intended communication but disturbances in digital communication does not cause errors enabling error free communication. Errors should be able to substitute, insert or delete symbols to be expressed.  Copyinganalog communication copies are quality wise not as good as their originals while due to error free digital communication, copies can be made indefinitely.  Granularityfor a continuously variable analog value to be represented in digital form there occur quantization error which is difference in actual analog value and digital representation and this property of digital communication is known as granularity. Differences in Usage in Equipment Many devices come with built in translation facilities from analog to digital. Microphones and speaker are perfect examples of analog devices. Analog technology is cheaper but there is a limitation of size of data that can be transmitted at a given time. Digital technology has revolutionized the way most of the equipment's work. Data is converted into binary code and then reassembled back into original form at reception point. Since these can be easily manipulated, it offers a wider range of options. Digital equipment is more expensive than analog equipment. Comparison of Analog vs Digital Quality Digital devices translate and reassemble data and in the process are more prone to loss of quality as compared to analog devices. Computer advancement has enabled use of error detection and error correction techniques to remove disturbances artificially from digital signals and improve quality. Differences in Applications Digital technology has been most efficient in cellular phone industry. Analog phones have become redundant even though sound clarity and quality was good. Analog technology comprises of natural signals like human speech. With digital technology, this human speech can be saved and stored in a computer. Thus, digital technology opens up the horizon for endless possible uses. Data Communication Terminology  Data Channel:-In this medium data carries from one point to another point.  Baud:-Each communication channel has certain capacity and it can carry information up to that extent only. This capacity measured in terms of Baud.  Bits per Second:-The speed at which data transferred between two points measured in terms of Bits per Second or bps.  bpsbits per second,  Bps-Bytes per second (Note capital B)  Bandwidth-The amount of data a communication system can transfer per unit time referred as Bandwidth of the system. Bandwidth simply indicates the data transfer rate. The more the data needed to be transmitted in the given unit time the more should be the bandwidth. Alternatively, it can be said that more the bandwidth of the communication system more will be the data transfer rate. Bandwidth measured in bps or Baud. Generally, a Baud is identical to bits per second. A rate of 100 Baud is equal to 100 bps.  In digital context, the level of bandwidth falls into three category:  Narrowband-Speed of narrowband varies between 45 to 300 Baud. Low speed devices use this narrowband channels.  Voice-band-Speed of voice-band channels ranges up to 9600 Baud. They are generally use in the ordinary telephone voice communication.  Broadband-The speed of broadband channels ranges up to 1 million Baud or more. High-speed devices use broadband for large volume of data transfer at high rate. Broadcast television, microwave and satellite uses broadband channel.  Data Transfer Rates:-The amount of data transferred per second by a communication channel is known as data transfer rate. It is measure in bits per second (bps). 1.3 Standard Organizations An association of organizations, governments, manufacturers and users form the standards organizations and are responsible for developing, coordinating and maintaining the standards .The purpose is that all data communications equipment are manufacturers and users comply with these standards. The primary standards organizations for data communication are: