Introduction to Communication Systems 222 CNET 3 Academic

Introduction to Communication Systems (222 CNET - 3) Academic Year 1439 -40(Second Semester) CHAPTER - 5 DIGITAL MODULATION TECHNIQUES Mohammed Rizwan Shaik

Chapter Contents Digital Modulation Techniques 5. 1 Introduction 5. 2 Modulation Schemes : ASK , FSK and PSK 5. 3 M-ARY Schemes : FSK and PSK

Objectives of this chapter Upon completion of this chapter student able to Ø Define ASK, FSK, PSK. Ø Describe generation and demodulation of ASK, FSK and PSK. Ø Define M-ary FSK and M-ary PSK.

Introduction • Need for Digital Modulation: Ø AM, FM, PM will help to translating the analog message from low frequency or baseband range to high frequency or passband range. Ø The Pulse modulation techniques deal with representing the message at discrete instants of time. Ø Discrete transmission of such message over long distance via high frequency channels is not possible. Ø As in such case analog and digital message needs to be translated to the high frequency range.

Types of Modulation Schemes Ø The digital modulation techniques are based on the analog modulation techniques. Ø Basic Digital Modulation Techniques: 1. Amplitude Shift Keying 2. Frequency Shift Keying 3. Phase Shift Keying Ø The variants of basic modulation techniques termed as M-ARY include 1. M-ary PSK 2. M-ary FSK

Categories

Definitions • The digitized message with sequence of 0’s and 1’s called as digital or binary message. • ASK is a digital modulation technique defined as the process of shifting the amplitude of the carrier signal between two levels, depending on whether 1 or 0 is to be transmitted. • FSK is a digital modulation technique defined as the process of shifting the frequency of the carrier signal between two levels, depending on whether 1 or 0 is to be transmitted. • PSK is a digital modulation technique defined as the process of shifting the phase of the carrier signal between two levels, depending on whether 1 or 0 is to be transmitted.

Generation of ASK signal

Waveforms ASK waveforms

Generation of FSK ﺟﻴﻞ ﻣﻦ

Phase Shift Keying Vc 1 = VC COS ωCt and Vc 2 = -VC COS ωCt

Definition of M-ARY Scheme • This is the type of digital modulation technique used for data transmission in which two or more bits are transmitted at a time. • The channel bandwidth is reduced because more number of bits can be transmitted on a single signal. • M – is denoted as Multiple bits or number of conditions/levels. Types of M-ARY Schemes: 1. M-ARY PSK 2. M-ARY FSK M-ARY PSK : • This is called as M-ary Phase Shift Keying (M-ary PSK). • The phase of the carrier signal, takes on M different levels.

Generation of M-ARY PSK

M-ARY PSK

Generation of M-ARY FSK • This is called as M-ary Frequency Shift Keying (M-ary FSK). • The frequency of the carrier signal, takes on M different levels. ﻣﺨﺘﻠﻔﺔ ﻣﺴﺘﻮﻳﺎﺕ ﻋﻠﻰ ﻳﺄﺨﺬ ، ﺍﻟﻨﺎﻗﻞ ﺇﺷﺎﺭﺓ ﺗﺮﺩﺩ M.

M-ARY FSK Waveforms

M-ary Equation • N is the number of bits necessary(message signal) N ( ﺍﻟﺮﺳﺎﻟﺔ )ﺇﺷﺎﺭﺓ ﺍﻟﻼﺯﻣﺔ ﺍﻟﺒﺘﺎﺕ ﻋﺪﺩ ﻫﻮ • M is the number of conditions, levels, or (carrier signals) combinations possible with N bits. M ﻫﻮ ( ﺍﻟﺤﺎﻣﻠﺔ ﺍﻟﻤﻮﺟﺔ )ﺇﺷﺎﺭﺍﺕ ﺗﻮﻟﻴﻔﺎﺕ ﺃﻮ ﺍﻟﻤﺴﺘﻮﻳﺎﺕ ﺃﻮ ﺍﻟﺸﺮﻭﻁ ﻋﺪﺩ ﺑﺘﺎﺕ ﻣﻊ ﺍﻟﻤﻤﻜﻨﺔ N. 2 N= M • For example, with two bits, 22 = 4 conditions are possible.

Problems

Problems

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