This chapter describes the essential principles behind. The dscdma transmitter multiplies each of user signals by a distinct code waveform. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. This experiment is concerned with demonstrating some of the principles of the first. This demodulator is more complex than most asynchronous demodulators. Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. Introduction to iq demodulation of rfdata september 15, 1999 page 3 of 1 introduction 1.
Directsequence spreadspectrum modulation in this lecture we consider directsequence spreadspectrum systems. The signal is obtained by starting with a narrowband signal and directly modulating a high bandwidth signal. Direct sequence spread spectrum dsss or often just spread spectrum is a variation of the dsbsc modulation scheme with a pulse train called a pseudonoise sequence or just pn sequence for the carrier instead of a simple sinewave. Multiplexing generally refers to independent signals, those produced by different sources. A modem is an equipment that performs both modulation and demodulation. There will be a minimum frequency separation required of the two tones. An ss demodulation has been made on top of the normal demodulation operations above. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309. The directsequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth.
This design has a maximum process gain of 10log15 11. Well use qpsk as an example of how quadrature modulation works, and in the process well see how amplitude modulation of iq signals can produce phase shifts. Demodulation of chaos phase modulation spread spectrum. This is shown in block diagram form in figure 2 below. Each channel sharing scheme a set of basis vectors. Dec 01, 2018 the chaos phase modulation sequences consist of complex sequences with a constant envelope, which has recently been used for directsequence spread spectrum underwater acoustic communication. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Multiplexing method of sharing a bandwidth with other independent data channels. Introduction to modulation and demodulation free download as powerpoint presentation. Digital modulator and demodulator ic for rfid tag employing dsss and barker code article pdf available in journal of applied research and technology 106.
Ofdm is a combination of modulation and multiplexing. We can calculate the sensitivity if we know the sn at the input of the demodulator and the noise floor and the noise figuire of the receiver like this. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. Such a simplification will not be implemented in this experiment. In preparation for managing your wireless networks, you should know something about the different radio frequency rf modulation techniques that are implemented in ieee 802. Cck vs dsss vs ofdm difference between cck,dsss,ofdm. In this technology, a data signal at the sending station is combined with a high data rate bit sequence, which divides user data based on a spreading ratio. Dsss spreads data across a channel for redundancy, and the books say that bits are sent in parallel. One can also demonstrate that signals added during the transmission such as an interferer or jammer will be spread during the despreading operation. Quadrature amplitude modulation qam is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. The input multiplier performs the despreading of the received signal, and the second multiplier translates the modulated signal down to baseband. Two main spread spectrum modulation techniques are defined.
In the transmitter, the input data stream is xored with the pn signal before transmission. A robust demodulator for oqpskdsss system request pdf. In direct sequence spread spectrum dsss, the transmitter and receiver contain identical psuedorandom sequence generators producing a pseudonoise pn signal. Modulation and demodulation medium, it would be dif. One can also demonstrate that signals such as an interferer or jammer added during the transmission will be spread during the despreading operation. Read online modulation damplitude demodulation damplitude book pdf free download link book now. Pdf soft synchronization of direct sequence spread. The optimum receiver for binary directsequence spreadspectrum modulation and an additive white gaussian noise channel. Ss modulation is applied on top of a conventional modulation such as bpsk or direct conversion. By transmitting the message energy over a bandwidth much wider than the minimum required, spread spectrum modulation techniques present two major advantages. The easiest way of creating a dsss signal is to multiply one period of the spreading. In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal.
Notes for engineering in electronics, communications and computer science subjects are added. Understanding iq signals and quadrature modulation radio. This spreading code has a higher chip rate this the bitrate of the code, which results in a wideband time continiuous scrambled signal. Unlike frequencyhopping, a directsequence signal occupies the entire bandwidth continuously. Dsss is a very attractive modulation technique for. A modified directsequence spread spectrum modulation. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. The dsss system two configurations are used for directsequence spreadspectrum evaluation hardware.
Download modulation damplitude demodulation damplitude book pdf free download link or read online here in pdf. I think the orthogonality properties of dssscodes holds for bpsk modulation how does the psk demodulator differentiates one carrier from the other in cdma, but if we use other digital modulation we will probably lose the orthogonality properties for most of them dbpsk, 256qam. Waste of bandwidth due to spreading is offset by multiple users. Modulation a mapping of the information on changes in the carrier phase, frequency or amplitude or combination. The invention can be applied to any directsequence spread spectrum and differential modulation demodulation based communication systems. In this regard dsss gives a certain amount of security and to demodulate it, one must. The directsequence spreadspectrum dsss receiver program is a multifaceted contribution to defence wireless communications capability it provides an alternative modulation scheme for specialpurpose link scenarios as well as an advanced, reconfigurable, wideband signal processing engine that lends itself to multiple. Ee4512 analog and digital communications chapter 5 chapter 5 digital bandpass modulation and demodulation techniques binary amplitude shift keying pages 212219. Chapter 5 digital bandpass modulation and demodulation techniques. Recall that our goal is to transmit data over a commu nication link, which we achieve by mapping the. Nov 11, 2016 direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions. Direct sequence spread spectrum with barker code and qpsk international organization of scientific research 63 p a g e fig.
Direct sequence spread spectrum technique, which also known as direct sequence code division multiple access dscdma, is one of the two approaches to spread spectrum modulation for digital signal transmission. The bandwidth of each is dependent on the message bit rate. After the despreading or removal of the directsequence modulation in the. The first uses a processing gain near the fcc minimum for part 15. Direct sequence spread spectrum an overview sciencedirect. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. The technique, referred to as the dominant mode despreading dmds algorithm, exploits the. Oct 26, 2005 we can calculate the sensitivity if we know the sn at the input of the demodulator and the noise floor and the noise figuire of the receiver like this. Scribd is the worlds largest social reading and publishing site. It is considered an ideal spreading code for its benefits in terms of large code resource quantity, nice correlation characteristics and high security. Digital modulation methods can be considered as digitaltoanalog conversion and the corresponding demodulation or detection as analogtodigital conversion.
For the sake of simplicity, ka 1 and ar ac have been chosen lowpass. This chipping code is nothing but the spreading code which is. In telecommunications, directsequence spread spectrum dsss is a spreadspectrum modulation technique primarily used to reduce overall signal interference. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. After the despreading or removal of the directsequence modulation in the receiver, the information bandwidth is restored, while. If the received carrier phase is assumed to be constant, each of the seven reference values will have to be shifted only once at the beginning of the simulation. This chipping code is nothing but the spreading code which is multiplied with the original message and transmitted. Radio frequency rf modulation techniques basics dummies.
An introduction to spreadspectrum communications tutorial. Chapter 7 spreadspectrum modulation spread spectrum technique simply consumes spectrum in excess of the minimum spectrum necessaryto send the data. The document is intended for users of the rf options on the system five. The student is required to implement the mathematics of the modulator and demodulator to matlab code. In practice, problems arise in baseband transmissions.
As i understand it, both dsss and ofdm are intended to send many bits in parallel. All books are in clear copy here, and all files are secure so dont worry about it. Introduction to modulation and demodulation modulation. Topics based on electronics, communication and computer are. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. A demodulator for the dsss of figure 1 is shown in block form in figure 3. Direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions. Ee4512 analog and digital communications chapter 5 chapter 5 digital bandpass modulation and demodulation techniques binary amplitude shift keying. A highspeed data stream is converted into multiple low. In this visualization the student only needs to submit their simulation. Direct sequence spread spectrum dsss whenever a user wants to send data using this dsss technique, each and every bit of the user data is multiplied by a secret code, called as chipping code. Chapter 5 digital bandpass modulation and demodulation.
This page compares cck vs dsss vs ofdm and describes difference between cck, dsss and ofdm modulation techniques there are various versions of wlan standard developed to address different data rate and coverage requirements. Pdf the directsequence spread spectrum modulation dsss is a very attractive modulation. The psdu data modulation format is manually specified. Pdf digital modulator and demodulator ic for rfid tag. Here a spreadspectrum demodulation has been made on top of the normal demodulation operations. In all the detail on dsss and ofdm, i have missed which characterics of dsss and ofdm make these distinct technologies. An introduction to directsequence spreadspectrum communications. Fsk frequency shift keying d1 63 fsk in f 1 f 2 decision out figure 4. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a.
What is the difference between the dsss or dsm and fhss or fasst 2. Direct sequence spread spectrum dsss is a spread spectrum technique whereby the original data signal is multiplied with a pseudo random noise spreading code. It conveys two analog message signals, or two digital bit streams, by changing modulating the amplitudes of two carrier waves, using the amplitudeshift keying ask digital modulation. Sequence spread specturm dsss modulation scheme is implemented with the. The student is required to implement the mathematics of the modulator and demodulator. Direct sequence cdma is the most popular of cdma techniques. Mar 09, 1999 the invention is different from the conventional signal reception methods in that positive information is not discarded before the decision point. The changes in the carrier signal are chosen from a finite number of m alternative symbols the modulation alphabet. Efficient demodulation scheme for dsss communication. Frequency hopping spread spectrum fhss and direct sequence spread spectrum dsss.
A new technique for soft synchronization of directsequence spreadspectrum dsss signals is presented. The term quadrature modulation refers to modulation that is based on the summation of two signals that are in quadrature. Introduction to modulation and demodulation the purpose of a communication system is to transfer information from a source to a destination. Dsss modulation the modulator inputs the m2 bit sequences and knows the full number of samples n to be used. Fsk frequency shift keying d1 61 conceptually, and in fact, the transmitter could consist of two oscillators on frequencies f1 and f2, with only one being connected to the output at any one time. Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier. Typically, such communication systems can be found in wireless lans e. Direct sequence spreadspectrum modulation can be viewed as linear periodically. In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation. Consider the frequency translation of a baseband message of bandwidth b hz to a higher part of the spectrum, using dsbsc modulation. Direct sequence spread spectrum with barker code and qpsk.
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