DIGITAL MODULATION AS A REMEDIATION OF ANALOG COMMUNICATION

QUESTION

Answer ONE of the following questions.

1. Since its arrival in the middle of the nineteenth century, photography has been
haunted by the ambivalence of, on the one hand, its “evidential force” as a
technology of truth, and on the other, as a medium of artistic expression that
undermines any claims to truth the medium might hold. Analyse photography’s
ambivalent status with reference to at least two photography commentators on the
course, and demonstrate your points with reference to specific photographic
contexts.

2. What is technological determinism? Analyse the claims of a technologically
determinist approach with reference to examples of a particular communication
technology studied in this course (i.e. sound technology, photography or print).

3. David Bolter adopts the word “remediation” to express the way in which the
remediation of one medium is seen in contemporary culture as improving on
another medium. With reference to the shift from analogue to digital
communication practices, analyse the assumption that remediation is an
improvement of one medium on another. Demonstrate your points with reference to
specific contexts in either print technology or photography.

4. Susan Sontag has suggested that photographs are “an ethics of seeing” (Sontag
1977). Analyse the implications of this claim with reference to specific
photographic contexts. For example, you might wish to analyse the scandal over the
publication of the Abu Graib photographs or the Bill Henson controversy.

5. Discuss the idea of the phonograph as a technology that writes sound. What
intentions did inventors have for the technology? What claims were made about the
technology? How has the technology actually been used?

6.  R Murray Schafer argues that sound reproduction technologies such as the

phonograph create ‘sound walls’ around listeners (Schafer 1994, p.95-96). Analyse
the use of portable music players such as iPods using his theory.

7. Analyse the role of digitisation in the proliferation of free culture. What impact has
the increased availability of a wide range of media on the Internet had on ‘amateurs’
and ‘professionals’ respectively? What role do intellectual property laws play?

SOLUTION

1 Executive Summary:

The chapter describes about the basics of communication .What is modulation and how it is used is explained in the chapter. Modulation is the process in which the signal which is to be transmitted is superimposed over the signal of more strength so that it can cover long distance communication. Why and how modulation and its techniques are used in communication process is explained with proper example. There are two types of modulation techniques, continuous and pulse modulation. It is further divided into analog and digital communication. In analog communication the signal to be transmitted is continuous in nature where as in digital communication it is discrete in nature. How digital communication is basically a remediation of analog communication is explained in the chapter with proper examples on photography.

<2> Communication:

Communication is an important part of our life. Communication is exchange of information between two mediums. The equipments required for the exchange of information are known as communication equipments. These equipments together form a communication system. Communication system is the medium through which the transmission of information takes place.

Radio broadcasting, mobile communication, point to point communication, television broadcasting and computer communication, all are the examples of communication. Among Communication system the oldest system for communication is line telegraphy, originated in 1840s. Later on, after few decades, line telephony arrived. With the arrival of satellites and fiber optics, the spectrum of communication is widely increased. (Haykin,1994 and Lathi 1988)

As we know various equipments or elements of communication, when assembled together form a communication system. Communication system is used to transfer information from a source to a user destination. Various equipments that constitute a communication system are as follows:

2.1   Information Source:

Information source is the point of origin of message signal. Message signal originates from this source of information.

Message signals can be in the form of words, codes or signals. The desired message signal is produced by information source, which is transmitted further.

2.2   Input Transducer:

Input transducer is used to convert one form of energy into another form of energy. Sometimes message generated from an information source is not in the form of electrical signal such as sound waves and radio waves etc. In such a case transducer is used to convert this message signal into an electrical signal. Microphone is an example of transducer, which converts a sound or a message signal into an electrical signal.

2.3   Transmitter:

In transmitter electrical signal generated by transducer is amplified and modulated to be transmitted to a channel. Now the question arises what is modulation. Modulation is the process in which a weak signal is superimposed on a signal of higher frequency for long distance communication. Modulation of signal can takes place in various forms such as amplitude modulation, frequency modulation and analog modulation. Amplitude, frequency and angle of a wave is varied in accordance with time in these modulation techniques.

2.4   Channel:

The signal to be transmitted is passed the channel from a transmitter to a receiver.

2.5   Receiver:

The purpose of the receiver is to obtain the original signal by demodulating the modulated electric signal. This process of recovering original signal is known as detection or demodulation.

2.6   Output transducer:

Output transducer is used to convert the electrical signal into original signal, for transmission of information to its final destination.

Block Diagram of Communication System:

3 Analog and Digital Signals:

Analog signal is a continuous, time varying signal which varies continuously with time. Majority of signals around us are analog signals. Analog signals are continuous for the given time interval and are defined for each value of time. Speech is an example of analog signal as its amplitude varies over a continuous range.  Whereas signals which are represented with a sequence of numbers with each number representing magnitude of the signal at a given instant of time. Such types of signals are known as digital signals. Printed language is an example of digital signals consisting of 10 numbers, 26 letters, space and many other punctuation symbols. In binary number system digital signal is represented by only two values that is 1 or 0.In binary system we can take either zero or one (Haykin, 1998 and chakrabarti, 2003). These two numbers also represents the voltage levels (High and Low voltage levels).

4 Modulation:

Modulation is a process in which a weak signal such as voice signal is superimposed on a signal of higher frequency and is sent to the desired destination. Weak signals are message signals or signals which carries the information and signals of higher frequency on which the message signal is superimposed is known as carrier signal. Now the question is why we need modulation (Singh and Sapre, 2007).Weak signals such as voice signals are not capable of covering long range for communication. For this we require signals of higher frequency which are capable of covering long range of distances. Therefore for long distance communication weak signals are superimposed on signals of higher frequency and are sent to the required destination. Modulation is achieved at the transmitter within a communication system from where it is transmitted via channel .At receiving original signal is recovered by the receiver (Sharma,2007 and Haykin , 1995). Modulation is of two types:

4.1   Continuous Wave Modulation:

In continuous modulation the carrier signal is continuous in nature and the process of modulation is known as continuous wave modulation. Continuous wave modulation is of three types:

• Amplitude modulation: In which the amplitude of the carrier signal is varied in accordance with the message signal.
• Frequency Modulation: In which the frequency of the carrier signal is varied in accordance with the message signal.
• Angle modulation: In which the angle of the wave is varied.

4.2   Pulse Modulation:

In pulse modulation, the carrier wave is in pulse form. The carrier wave consists of rectangular pulses which are periodic in nature. The pulse modulation is of following types.

• Pulse Amplitude Modulation
• Pulse Duration Modulation
• Pulse Position Modulation

5 Analog and Digital Communication:

Depending on the nature of the signal communication is divided into analog and digital communication.

6 Analog Modulation:

If the message signal to be transmitted is analog in nature than the process of communication is known as analog communication. The examples of analog signals are speech, video etc.

In analog modulation, the carrier wave is modulated by a message signal to produce a modulated signal. This modulation process is carried out in the transmitter of the communication system. This modulated signal is passed through the channel .At receiver end this signal is demodulated and is sent to the output transducer for the recovery of original signal.

7 Digital Modulation:

On the other hand, in digital communication the message signal to be transmitted is digital in nature. Digital communication involves the transmission of information in digital form (Kanefsky, 1987 and Lathi ,1993). The process of digital communication is as follows:

7.1   Discrete Information Source:

In digital communication system discrete information source produces non-continuous time varying signal, which consists of discrete symbols.

7.2   Source Encoder:      

This signal is passed to source encoder which assigns these symbols some particular binary value such as 1 or 0 to convert them to digital signal. Collection of these binary numbers is known as codeword. Each symbol is assigned with unique codeword such as 4, 16, 8 bits length. Here 256 symbols cab be represented by 8 bits and 65536 symbols by 16 bits .

7.3   Channel:

After the conversion of signal in to digital format, it is passed through a channel. This in turn passes it to modulator.

7.4   Modulator:

Modulator as we know is used to modulate the signals. Here digital modulation techniques are used to modulate the signal. Various digital modulation techniques are, amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK), differential phase shift keying (DPSK) and minimum shift keying (MSK)( J. Das , S.K Mullick and P.k . Chatterjee, 1986).

From here the signal is again passed through the channel to demodulator, which demodulates the signal. From here the signal is passed to channel decoder, than to source decoder, which is used to decode the encoded signal. From decoder the signal is finally passed to its destination.

Digital modulation is a remediation of analog modulation in many ways as stated below:

• More information capacity
• High data security
• High quality of communication
• Faster system availability

Let’s take an example of Analog and digital photography:

Analog and digital photography:

The difference between analog and digital camera is that silver halide based film used to capture an image is not used in digital cameras. In digital camera the light reflected off an image is exposed to a charge coupled device. This device is covered green, blue n red semiconductors which are thousands in number. Each and every element of CCD is excited by photons of light, which in turn converts photons to electrical signals. This electrical signal is then transformed to digital signal and is stored in hard disk. Digital camera has the advantages of massive storage of photographs, higher operating speed, better night modes and more clear pictures.

References:

Kanefsky, M. (1987) Communication Techniques for Digital and Analog Signal , New York: John Wiley and Sons

Haykin, S. (1994), An introduction to Analog & Digital Communications, Singapore: John Wiley & Sons

Haykin, S. (1983), Communication Systems, 2nd edition, New Delhi: Wiley Eastern Limited

Lathi, B.P. (1988), Communication Systems, New Delhi: Wiley Eastern Limited

Haykin, S. (1995), Communication Systems, 3^rd edition, Singapore: John Wiley & Sons

Das, J, Mullick, S.K and Chatterjee, P.K.(1986), Principles of Digital Communication, New Delhi: Wiley Eastern Limited

Lathi, B.P. (1993), Modern Digital and Analog Communication System, 2nd edition, New Delhi: Oxford University Press

Sharma, S. (2007), Principles of Communication, 6th edition, New Delhi:  S.K Kataria &Sons.

Singh, R.P and Sapre ,S.D.(2007),Communication System, New Delhi: McGraw Hill

Chakrabarti, P. (2003), Principle of Digital Communication, New Delhi: Dhanpat Rai & Co.

GG66

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