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`APPLICATION OFAPPLICATION OFAPPLICATION OF APPLICATION OF
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`VISUAL SIMULATION IN VISUAL SIMULATION IN VISUAL SIMULATION IN VISUAL SIMULATION IN
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`COMMUNICATION SYSTEMSCOMMUNICATION SYSTEMS
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`COMMUNICATION SYSTEMSCOMMUNICATION SYSTEMS
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`A Project Report
`
`Submitted in partial fulfillment of the requirements for the award of the degree
`of
`
`BACHELOR OF TECHNOLOGY
`
`IN
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`ELECTRONICS AND INSTRUMENTATION ENGINEERING
`
`By
`
`Ranjeet Mohapatra(10407016)
`
`Sameer Ranjan Behera(10407006)
`
`Under the guidance of
`
`Prof. S.K.Patra
`
`
`Department of Electronics & Instrumentation Engineering
`
`National Institute of Technology
`
`Rourkela,769008 (2007-2008)
`
`
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 1
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`APPLICATION OFAPPLICATION OFAPPLICATION OF APPLICATION OF
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`VISUAL SIMULATION IN VISUAL SIMULATION IN VISUAL SIMULATION IN VISUAL SIMULATION IN
`
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`COMMUNICATION SYSTEMSCOMMUNICATION SYSTEMS
`
`COMMUNICATION SYSTEMSCOMMUNICATION SYSTEMS
`
`A Project Report
`
`Submitted in partial fulfillment of the requirements for the award of the degree
`of
`
`BACHELOR OF TECHNOLOGY
`
`IN
`
`ELECTRONICS AND INSTRUMENTATION ENGINEERING
`
`By
`
`Ranjeet Mohapatra(10407016)
`
`Sameer Ranjan Behera(10407006)
`
`Under the guidance of
`
`Prof. S.K.Patra
`
`
`Department of Electronics & Instrumentation Engineering
`
`National Institute of Technology
`
`Rourkela,769008 (2007-2008)
`
`
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 2
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`National Institute of Technology
`
`Rourkela
`
`
`
`CERTIFICATE
`
`This is to certify that the thesis entitled, “Application of Visual Simulation in communication
`systems” submitted by Sri Sameer Ranjan Behera and Sri Ranjeet Mohapatra in partial
`fulfillments for the requirements for the award of Bachelor of Technology Degree in
`Electronics & Instrumentation Engineering at National Institute of Technology, Rourkela
`(Deemed University) is an authentic work carried out by him under my supervision and
`guidance.
`
`To the best of my knowledge, the matter embodied in the thesis has not been submitted to
`any other University / Institute for the award of any Degree or Diploma.
`
`
`Date:
`
`
`
`Prof. S. K. PATRA
`
`Dept. of Electronics & Instrumentation Engg
`
`National Institute of Technology
`
`Rourkela - 769008
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 3
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`ACKNOWLEDGEMENT
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`We place on record and warmly acknowledge the continuous
`
`encouragement, invaluable supervision, timely suggestions and inspired guidance offered by
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`our guide Prof. S.K.Patra, Professor, Department of Electronics and instrumentation
`
`Engineering, National Institute of Technology, Rourkela, in bringing this report to a successful
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`completion.
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`We are grateful to Prof. G.Panda, Head of the Department of Electronics
`
`and instrumentation Engineering, for permitting us to make use of the facilities available
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`in the department to carry out the project successfully. Last but not the least we express our
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`sincere thanks to all of our friends who have patiently extended all sorts of help for
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`accomplishing this undertaking.
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`Finally we extend our gratefulness to one and all who are directly or
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`indirectly involved in the successful completion of this project work.
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` Ranjeet Mohapatra(10407016)
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`Sameer Ranjan Behera (10407006)
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 4
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`CONTENTS
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`PAGE NO
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`List of figures
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`Abstract
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`CHAPTER 1
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`GENERAL INTRODUCTION
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`CHAPTER 2
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`ANALOG MODULATION
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`i.
`ii.
`iii.
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`Amplitude Modulation
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`Frequency Modulation
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`Combination of AM & FM
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`DIGITAL CIRCUITS
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`ii
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`iv
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`1-4
`5-12
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`6
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`9
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`11
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`13-21
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`CHAPTER 3
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`i.
`ii.
`iii.
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`Counters
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`Multiplexers
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`Flip-flops
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`CHAPTER 4
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`FILTERS AND EQUALIZERS
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`i.
`ii.
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`Equalizers
`Filters
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`CHAPTER 5
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`COMMUNICATION
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`i.
`ii.
`iii.
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`Channel Simulation
`Transmission Techniques
`Turbo Codes
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`REFERENCES
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 5
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`
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`LIST OF FIGURES
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`Figure-2.1
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`Figure-2.2
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`Figure-2.3
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`Figure-2.4
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`Figure-3.1
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`Figure-3.2
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`Figure-3.3
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`Figure-3.4
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`Figure-3.5
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`Figure-3.6
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`Figure-4.1
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`Figure-4.2
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`Figure-4.3
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`Figure-4.4
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`Figure-4.5
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`ii
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`Amplitude Modulation:
`Input Signal
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`Amplitude Modulation &
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`Demodulation
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`Frequency Modulation
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`Amplitude Modulation Vs
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`Frequency Modulation
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`Binary Counters
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`Multiplexers
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`Demultiplexers
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`Multiplexer Simulation
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`JK-Flipflops
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`D-Flipflops
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`Equalizers
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`Equalization of Channel
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`Distortion
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`Simple IIR Filter
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`Simple FIR Filter
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`FIR Filter Parameters
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 6
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`FIR Filter Simulation
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`IIR Filter Simulation
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`Multipath Propagation
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`Propagation Loss
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`Mobile Channel Fading
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`Block Interleaver
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`Gray Encoding & Decoding
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`Convolution Coding
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`Reed-Solomon Coding
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`Turbo Encoder
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`Turbo Decoder
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`Turbo Codes
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`Figure-4.6
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`Figure-4.7
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`Figure-5.1
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`Figure-5.2
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`Figure-5.3
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`Figure-5.4
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`Figure-5.5
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`Figure-5.6
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`Figure-5.7
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`Figure-5.8
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`Figure-5.9
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`Figure-5.10
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`iii
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 7
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`ABSTRACT
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`
`
`
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`A communications system is a collection of individual communications networks, transmission
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`systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of
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`interconnection and interoperation to form an integrated whole. The components of a
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`communications system serve a common purpose, are technically compatible, use common
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`procedures, respond to controls, and operate in unison. A typical communication link includes, at
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`a minimum, three key elements: a transmitter, a communication medium (or channel), and a
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`receiver. The ability to simulate all three of these elements is required in order to successfully
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`model any end-to-end communication system. In order to achieve this target we have used a
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`simulation software “VisSim” ,or Visual Simulator ,that allows us to use a graphical approach to
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`simulation and modeling.
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` With graphical programming, the diagram is the source code, depicted as an arrangement of
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`nodes connected by wires. Each piece of data flows through the wires, to be consumed by nodes
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`that transform the data mathematically or perform some action such as I/O. The visual simulator
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`allows us to model end-to-end communication systems at the signal or physical level. We use
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`VisSim/ Comm to build both transmitter and receiver models, filters and equalizers, as well as
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`channel models and coding techniques from a first principles perspective, by selecting and
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`connecting predefined blocks. In this project work we simulate a variety of models including
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`analog, digital and mixed mode designs, and quickly simulate their behavior using the VisSim/
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`Comm software and graphical programming.
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`iv
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 8
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`CHAPTER 1
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`
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`
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`GENERAL INTRODUCTION
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`COMMUNICATION SYSTEMS
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`AND “VisSim”
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`1
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 9
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`1. COMMUNICATIONS SYSTEMS AND VisSim
`
` A
`
` communications system is a collection of individual communications networks, transmission
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`systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of
`
`interconnection and interoperation to form an integrated whole.The components of a
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`communications system serve a common purpose, are technically compatible, use common
`
`procedures, respond to controls, and operate in unison.As such any communications system
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`consists of subsystems which work together to achieve a common link ,through achieving its
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`own functionality.
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`A typical communication link includes, at a minimum, three key elements: a transmitter, a
`
`communication medium (or channel), and a receiver. The ability to simulate all three of these
`
`elements is required in order to successfully model any end-to-end communication system. The
`
`transmitter and receiver elements can in turn be further subdivided into sub-systems.These
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`include a data source (analog or digital), an optional data encoder, a modulator, a demodulator,
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`an optional data decoder, and a signal sink. To understand the process of such a communication
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`we need to visualize or simulate such a link ,so as to have a better understanding of the process
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`involved.We have used a simulation software “VisSim” ,or Visual Simulator ,that allows us to
`
`use a graphical approach to simulation and modeling.
`
` With graphical programming, the diagram is the source code, depicted as an arrangement of
`
`nodes connected by wires. Each piece of data flows through the wires, to be consumed by nodes
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`that transform the data mathematically or perform some action such as I/O.
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`The concept of a dataflow diagram (which, unlike a flowchart, shows the motion of data rather
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`than the motion of logic) is nothing new. In fact, even the idea of letting a dataflow diagram be
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`the sole input to a compiler or interpreter has been put into practice for years. A number of
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`graphical programming tools are available today, each tailored to a particular industry.The tool
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`in use, ”VisSim” ,has a special communication module that allows us to create accurate
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`simulation environment of the communication system involved. It is a software program for
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`modeling end-to-end communication systems at the signal or physical level. Execution is
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`determined by the structure of a graphical block diagram on which the programmer connects
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`2
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 10
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`different function-nodes by drawing wires. These wires propagate signals and any subsystem
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`can execute as soon as all its input data become available. Since this might be the case for
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`multiple subsystems simultaneously, we are capable of parallel execution.
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`Simulation of communication channel and evaluating the performance requires
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`accurate reconstruction of the channel and its subsystems. We have used
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`graphical programming to create a visual simulation of communication systems
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`using VisSim.The essential advantages in visual simulation are due to ease of
`modeling of:
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`Transmitter and Receiver Models
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`Communication system design can be divided into two categories: transmitter design and
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`receiver design. VisSim/ Comm lets us build build both transmitter and receiver models, from a
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`first principles perspective, by simply selecting and connecting predefined blocks. We simulate a
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`variety of models including analog, digital and mixed mode designs, and quickly simulate their
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`behavior. The VisSim/Comm block set provides a variety of modulators and demodulators,
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`including standard analog, PSK, QAM and differential formats. .
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`Channel Models
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`VisSim/Comm includes a variety of predefined channel models supporting both fixed and mobile
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`service scenarios. Included are fading, multipath, bandlimited, and gaussian noise models.
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`Further all VisSim/Comm blocks, can modify model parameters to suit their specific needs.
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`Filter and Equalizer Design
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`VisSim/Comm supports a wide range of customizable filters, including FIR, IIR, gaussian, raised
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`cosine and root raised cosine filters. Additional blocks, such as the complex FFT block, make it
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`easy to view gain and phase responses of any filter. Furthermore, for designs that require
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`adaptive filters, fractionally-spaced LMS equalizer blocks are included.
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`Predicting System Performance
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`Once designed, a transmitter or receiver model can be simulated to determine its performance
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`under a variety of operating conditions. VisSim/Comm highly interactive interface makes it easy
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`to perform ‘what if’ simulations and carry out performance trade-offs. For example, in analog
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`modulation we can keep amplitude modulation and frequency modulation side by side and
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`evaluate their envelope shapes , simultaneously.
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`3
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 11
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` However like any other approach to coding, graphical programming is not a panacea that meets
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`all software needs. Besides the obviously more expensive hardware required to create and view
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`dataflow diagrams, there are far fewer cheap or free software tools available. Despite their ability
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`to be compiled, graphical programs still rely on hefty runtime libraries that may slow
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`performance. Additionally, the dataflow model proves unsettling and unproductive for some
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`coders and inappropriate for some jobs.
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`Thus the graphical programming approach used in Vissim eases the simulation by creating a
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`platform for visual implementation of such communication systems .The visual presentation of
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`their ideas is direct and refreshing. The ability to prototype rapidly and call on a wide range of
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`industry-specific libraries leads to productivity increase for certain tasks.
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`
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`4
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`CHAPTER 2
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`ANALOG MODULATION
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`AMPLITUDE MODULATION
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`FREQUENCY MODULATION
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`COMBINATION OF AM AND FM
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`5
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 13
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`2.ANALOG MODULATION
`
`2.1Amplitude modulation (AM)
`
`Amplitude modulation is a technique used in electronic communication, most commonly for
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`transmitting information via a radio carrier wave. AM works by varying the strength of the
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`transmitted signal in relation to the information being sent. For example, changes in the signal
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`strength can be used to reflect the sounds to be reproduced by a speaker, or to specify the light
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`intensity of television pixels. In its basic form, amplitude modulation produces a signal with
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`power concentrated at the carrier frequency and in two adjacent sidebands. Each sideband is
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`equal in bandwidth to that of the modulating signal and is a mirror image of the other. Amplitude
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`modulation that results in two sidebands and a carrier is often called double sideband amplitude
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`modulation (DSB-AM). Amplitude modulation is inefficient in terms of power usage and much
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`of it is wasted. At least two-thirds of the power is concentrated in the carrier signal, which carries
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`no useful information (beyond the fact that a signal is present); the remaining power is split
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`between two identical sidebands, though only one of these is needed since they contain identical
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`information.
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`Carrier Wave:
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`
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`Waveform to be transmitted:
`
`
`
`
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`Hence ,the net amplitude modulated wave is of the form
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`Modulation Index : As with other modulation indices, in AM, this quantity, also called
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`modulation depth, indicates by how much the modulated variable varies around its 'original'
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`level. For AM, it relates to the variations in the carrier amplitude and is defined as:
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`
`
`6
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 14
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`Now we will simulate the amplitude modulation using VisSim. The main parameters that are
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`
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`needed here are:
`
`1. Input Signal(which is a combination of many sine waves )
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`2. AM Modulator (which modulates the input signal)
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`3. Complex to Real (converts the complex quantity into real & imaginary part)
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`The Input Signal consists of a no. of sine waves where we can change the amplitudes of the sine
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`waves by the following method:
`
`Fig 2.1
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`7
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 15
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`
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`The AM Modulator has the following parameters (that can also be changed according to our
`
`wish):
`
`1. Carrier frequency
`2. Amplitude
`3. Initial Phase
`4. Modulation Factor
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`Here there are basically two types of Phase Output Modes:
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`1. Wrapped[0,2pi]
`2. Unwrapped
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`Fig-2.2 AM modulation and demodulation
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`8
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 16
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`The outputs that we get here are basically:
`
`1. AM Modulated Signal and Envelope
`2. Synchronous detector Output
`3. Peak Rectifier Output and Filtered Output
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`2.2 FREQUENCY MODULATION
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`In telecommunications, frequency modulation (FM) conveys information over a carrier wave
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`by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the
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`carrier is varied while its frequency remains constant). In analog applications, the instantaneous
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`frequency of the carrier is directly proportional to the instantaneous value of the input signal.
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`Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a
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`technique known as frequency-shift keying.
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`Suppose the baseband data signal to be transmitted is
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`
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`and is restricted in amplitude to be
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`
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`and the sinusoidal carrier is
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`
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`where fc is the carrier's base frequency and A is an arbitrary amplitude. The modulator combines
`the carrier with the baseband data signal to get the transmitted signal,
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`
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`where
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`
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`Modulation Index :As with other modulation indices, in FM this quantity indicates by how much
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`the modulated variable varies around its unmodulated level. For FM, it relates to the variations in
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`the frequency of the carrier signal where fm is the highest modulating frequency of xm(t). If , the
`modulation is called narrowband FM, and its bandwidth is approximately 2fm. If , the
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`
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`9
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 17
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`modulation is called wideband FM and its bandwidth is approximately 2f∆. While wideband FM
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`uses more bandwidth, it can improve signal-to-noise ratio significantly.
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`Now we will simulate the amplitude modulation using VisSim. The main parameters that are
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`needed here are:
`
`1. Source or the Input Signal(which is a combination of many sine waves )
`2. FM Modulator (which modulates the input signal)
`3. FM Demodulator
`4. Complex to Real (converts the complex quantity into real & imaginary part)
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`
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`Here also we can change the values of the parameters according to our requirement.
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`FM modulation
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`Fig 2.3
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`10
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`HTC Corp., HTC America, Inc. - Ex. 1026, Page 18
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`The outputs that we get here are basically:
`
`1. Baseband Information Signal
`2. FM Modulated Signal
`3. Recovered Information Signal
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`
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`2.3 Combination of AM and FM:
`
`The major advantage that we can have with VisSim is that we can plot the Input Signal, The AM
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`Modulated Signal and the FM Modulated signal simultaneously which helps us in comparing the
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`two outputs with a single source
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`Here the basic components that are involved:
`1. Input Signal(which is a combination of many sine waves )
`2. AM Modulator (which modulates the input signal w.r.t. Amplitude)
`3. FM Modulator(which modulates the input signal w.r.t. Frequency)
`4. Complex to Real (converts the complex quantity into real & imaginary part)
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`The outputs that we achieve here are:
`1. AM Modulated Signal and Envelope
`2. FM Modulated Signal
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`AM Vs FM
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`Fig 2.4
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`CHAPTER 3
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`DIGITAL CIRCUITS
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`COUNTERS
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`MULTIPLEXERS
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`FLIP FLOPS
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`3. DIGITAL CIRCUITS
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`3.1COUNTERS
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`In digital logic and computing, a counter is a device which stores (and sometimes displays) the
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`number of times a particular event or process has occurred, often in relationship to a clock signal.
`In practice, there are two main types of counters:
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`• up counters which increase (increment) in value
`• down counters which decrease (decrement) in value
`A few major designs of counters are
`• Asynchronous (ripple) counters
`• Synchronous counters
`• Decade counters
`• Up-Down counters
`• Ring counters
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`3.1.1 Asynchronous (ripple) counters
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`The simplest counter circuit is a single D-type flip flop, with its D (data) input fed from its own
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`inverted output. This circuit can store one bit, and hence can count from zero to one before it
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`overflows (starts over from 0). This counter will increment once for every clock cycle and takes
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`two clock cycles to overflow, so every cycle it will alternate between a transition from 0 to 1 and
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`a transition from 1 to 0. Notice that this creates a new clock with a 50% duty cycle at exactly half
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`the frequency of the input clock. If this output is then used as the clock signal for a similarly
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`arranged D flip flop (remembering to invert the output to the input), you will get another 1 bit
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`counter that counts half as fast. Putting them together yields a two bit counter:
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`cycle Q1 Q0 (Q1:Q0)dec
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`0 0 0
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`0 1 1
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`0
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`1
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`3.1.2 Synchronous counters
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`Where a stable count value is important across several bits, which is the case in most counter
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`systems, synchronous counters are used. These also use flip-flops, either the D-type or the more
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`complex J-K type, but here, each stage is clocked simultaneously by a common clock signal.
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`Logic gates between each stage of the circuit control data flow from stage to stage so that the
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`desired count behaviour is realised. Synchronous counters can be designed to count up or down,
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`or both according to a direction input, and may be presettable via a set of parallel "jam" inputs.
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`Most types of hardware-based counter are of this type.
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`3.1.3 Decade counters
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`Decade counters are a kind of counter that counts in tens rather than having a binary
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`representation. Each output will go high in turn, starting over after ten outputs have occurred.
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`This type of circuit finds applications in multiplexers and demultiplexers, or wherever a scanning
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`type of behaviour is useful. Similar counters with different numbers of outputs are also common.
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`3.1.4 Up-Down Counters
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`It is a combination of up counter and down counter, counting in straight binary sequence. There
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`is an up-down selector. If this value is kept high, counter increments binary value and if the
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`value is low, then counter starts decrementing the count. The Down counters are made by using
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`the complemented output to act as the clock for the next flip-flop in the case of Asynchronous
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`counters.
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`3.1.5 Ring Counters
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`A ring counter is a counter that counts up and when it reaches the last number that is designed to
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`count up to, it will reset itself back to the first number. For example, a ring counter that is
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`designed using 3 JK Flip Flops will count starting from 001 to 010 to 100 and back to 001. It will
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`repeat itself in a 'Ring' shape and thus the name Ring Counter is given.
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`Here we will now simulate the counter with the help of VisSim. The example that we take into
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`consideration is the Binary Counter. In a Binary Counter each bit represent either ‘0’ or ‘1’. If it
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`is a 4 bit Binary Counter then it can calculate upto 15 and as soon as it counts 15 the counters
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`again resets to ‘0’.Like in a decade counter we can count from 0-9. The basic components that
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`we need here are:
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`•
`Input data stream
`• 4-bit counter(which can counts up to 15)
`The output that we will get here are the:
`• Counter output
`• Carry Flag
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`Binary counter
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`Fig 3.1
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`3.2 MULTIPLEXER
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`In electronics, a multiplexer or mux (occasionally the term muldex is also found, for a
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`combination multiplexer-demultiplexer) is a device that performs multiplexing; it selects one of
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`many analog or digital input signals and outputs that into a single line. An electronic multiplexer
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`makes it possible for several signals to share one expensive device or other resource, for example
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`one A/D converter or one communication line, instead of having one device per input signal.
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`In electronics, a demultiplexer (or demux) is a device taking a single input signal and selecting
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`one of many data-output-lines, which is connected to the single input. A multiplexer is often
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`used with a complementary demultiplexer on the receiving end. An electronic multiplexer can be
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`considered as a multiple-input, single-output switch, and a demultiplexer as a single-input,
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`multiple-output switch.
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`Multiplexer
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`Fig 3.2
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`Demultiplexer
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`Fig 3.3
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`Multiplexer simulation
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`Fig 3.4
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`3.3 FLIP FLOPS
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`In digital circuits, a flip-flop is a kind of bistable multivibrator, an electronic circuit which has
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`two stable states and thereby is capable of serving as one bit of memory. Today, the term flip-
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`flop has come to generally denote non-transparent (clocked or edge-triggered) devices, while the
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`simpler transparent ones are often referred to as latches.
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`A flip-flop is controlled by (usually) one or two control signals and/or a gate or clock signal. The
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`output often includes the complement as well as the normal output. As flip-flops are
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`implemented electronically, they require power and ground connections. Flip-flops can be either
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`simple (transparent) or clocked. Simple flip-flops can be built by two cross-coupled inverting
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`elements – transistors, or NAND, or NOR-gates – perhaps augmented by some enable/disable
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`(gating) mechanism. Clocked devices are specially designed for synchronous (time-discrete)
`systems and therefore one such device ignores its inputs except at the transition of a dedicated
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`clock signal (known as clocking, pulsing, or strobing). This causes the flip-flop to either change
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`or retain its output signal based upon the values of the input signals at the transition. Some flip-
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`flops change output on the rising edge of the clock, others on the falling edge.
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`3.3.1 JK Flip Flop:
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`The JK flip-flop augments the behavior of the SR flip-flop by interpreting the S = R = 1
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`condition as a "flip" or toggle command. Specifically, the combination J = 1, K = 0 is a
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`command to set the flip-flop; the combination J = 0, K = 1 is a command to reset the flip-flop;
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`and the combination J = K = 1 is a command to toggle the flip-flop, i.e., change its output to the
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`logical complement of its current value. Setting J = K = 0 does NOT result in a D flip-flop, but
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`rather, will hold the current state. To synthesize a D flip-flop, simply set K equal to the
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`complement of J. The JK flip-flop is therefore a universal flip-flop, because it can be configured
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`to work as an SR flip-flop, a D flip-flop, or a T flip-flop.
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`JK flip flop
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`Fig 3.5
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`3.3.2 D flip-flop
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`The Q output always takes on the state of the D input at the moment of a rising clock edge, and
`never at any other time. It is called the D flip-flop for this reason, since the output takes the value
`of the D input or Data input, and Delays it by one clock count. The D flip-flop can be interpreted
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`as a primitive memory cell, zero-order hold, or delay line.
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`Truth table of D flip flop
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`Clock
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`D Q Qprev
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`Rising edge
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`Rising edge
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`0 0 X
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`1 1 X
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` Table 3.1
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`D flip flop
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`Fig 3.6
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`CHAPTER 4
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`FILTERS AND EQUALIZERS
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`EQUALIZERS
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`FILTERS
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`4. FILTERS AND EQUALIZERS
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`4.1 Equalizers
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`In a communication system, the transmitter sends the information over an RF channel. The
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`channel distorts the transmitted signal befores it reaches the receiver. The receiver ”task” is to
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`figure out what signal was transmitted and turn the received signal in understandable
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`information. Equalization is a technique to improve received signal quality and link performance
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`over a noisy communication channel. Equalization compensates for intersymbol interference
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`created by multipath due to time dispersive channels. An equalizer within a receiver compensates
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`for the average range of channel amplitude and phase characteristics. Equalizers must be
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`adaptive since the channel is unknown and time varying generally. An adaptive equalizer is a
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`filter that adaptively updates its coefficients in order to track a time-varying communication
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`channel. It is frequently used with coherent modulations such as phase shift keying in wireless
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`communications, mitigating the effects of multipath propagation and Doppler spreading. The
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`channel equalizer models the impulse response of the radio channel and based on the estimate
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`removes unwanted phenomena (for example echo) from the signal.
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`An equalization (EQ) filter, or an equalizer is a filter, usually adjustable, chiefly meant to
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`compensate for the unequal frequency response of some other signal processing circuit or
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`system.An EQ filter typically allows the user to adjust one or more parameters that determine the
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`overall shape of the filter's transfer function. It is generally used to improve the fidelity of sound,
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`to emphasize certain instruments, to remove undesired noises.Equalizers may be designed with
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`peaking filters, shelving filters, bandpass filters, plop filters or high-pass and low-pass filters.
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`Shown below is the block diagram of a 5 tap adaptive filter that takes in input as well as error to
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`adaptively equalize the channel.Further channel equalization of a QAM link has been simulated
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`using VisSim.
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`Equalizer
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`Fig :4.1
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`Fig-4.2Equalization of channel distortions
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`4.2 FILTERS
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`In electronics, a digital filter is any electronic filter that works by performing digital
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`mathematical operations on an intermediate form of a signal. This is in contrast to older analog
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`filters which work entirely in the analog realm and must rely on physical networks of electronic
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`components (such as resistors, capacitors, transistors, etc.) to achieve the desired filtering effect.
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`Digital filters are implemented according two one of two basic principles, according to how they
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`respond to an impulse:
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`•
`Infinite impulse response (IIR)
`• Finite impulse response (FIR)
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`4.2.1 Infinite impuls