UNIT 2 DIGITAL MODULATION

Springer eBooks, 1992

2004

Complex modulation may be achieved by imposing multiple modulation techniques on a single carrier, as in quadriture phase shift key amplitude modulation (QPSKAM) and the use of the FM carrier for both the FM modulation and the subsidiary communication authorization (SCA) modulation, or by using a succession of modulated carriers to modulate a higher level carrier, as in Bell System frequency domain multiplexing (FDM). Unintentional complex modulation is also frequently the result of poor filtering and unintended feedback loops.

After studying this chapter, you should be able to:

2012

The concept of modulation is a key factor in commun ication, because without an appropriate modulation method or scheme, getting an expected th roug put in such a communication effort would be impossible to achieve. Communication engineers and researchers have not relented in trying to find the best modulation methods aimed at achieving an expected t hroughput, bandwidth/power efficiency, low error performance, etc in digital communication networks. Digital modulation is preferred to the analogue mo dulation due to their error-free capability.Moreso, this cho i e of digital modulation is dependent on the type of communication network that is to be established. Ho wever, trade-offs must be made between the bandwidt h efficiency, power efficiency and the cost of implem ntation of such a network. This paper focuses onsome methods usually employed in the process of modulation in digital communicati on networks. Specifically, binary phase shift keying, quadrature phase shift keying, eigh...

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:

Studying the process of analogue and digital modulation, 2017

The study of communication systems is largely based on signals and systems theory. An important objective in modulation is to produce a signal whose frequency range is suitable for transmission over the communication channel to be used. This paper presents an approach for studying the process of the main types of modulations of low and higher order. By using of computer simulations in MATLAB environment different types of modulation can be deep analyzed. It can be used for educational purposes in engineering education.

IEEE Transactions on Information Theory, 1998

The principle of coding in the signal space follows directly from Shannon's analysis of waveform Gaussian channels subject to an input constraint. The early design of communication systems focused separately on modulation, namely signal design and detection, and error correcting codes, which deal with errors introduced at the demodulator of the underlying waveform channel. The correct perspective of signalspace coding, although never out of sight of information theorists, was brought back into the focus of coding theorists and system designers by Imai's and Ungerböck's pioneering work on coded modulation. More recently, powerful families of binary codes with a good tradeoff between performance and decoding complexity have been (re-) discovered. Bit-Interleaved Coded Modulation (BICM) is a pragmatic approach combining the best out of both worlds: it takes advantage of the signal-space coding perspective, whilst allowing for the use of powerful families of binary codes with virtually any modulation format.