What is the difference between the dsss or dsm and fhss or fasst 2. Understanding iq signals and quadrature modulation radio. The invention can be applied to any directsequence spread spectrum and differential modulation demodulation based communication systems. Direct sequence spreadspectrum modulation can be viewed as linear periodically. The dsss system two configurations are used for directsequence spreadspectrum evaluation hardware. Efficient demodulation scheme for dsss communication. An ss demodulation has been made on top of the normal demodulation operations above. The technique, referred to as the dominant mode despreading dmds algorithm, exploits the.
The term quadrature modulation refers to modulation that is based on the summation of two signals that are in quadrature. 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. Dsss is a very attractive modulation technique for. The changes in the carrier signal are chosen from a finite number of m alternative symbols the modulation alphabet. Multiplexing method of sharing a bandwidth with other independent data channels. Ee4512 analog and digital communications chapter 5 chapter 5 digital bandpass modulation and demodulation techniques binary amplitude shift keying. Pdf soft synchronization of direct sequence spread. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. Each channel sharing scheme a set of basis vectors.
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. 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. A modem is an equipment that performs both modulation and demodulation. A highspeed data stream is converted into multiple low. Dsss spreads data across a channel for redundancy, and the books say that bits are sent in parallel. Radio frequency rf modulation techniques basics dummies. 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. Cck vs dsss vs ofdm difference between cck,dsss,ofdm. This demodulator is more complex than most asynchronous demodulators. A demodulator for the dsss of figure 1 is shown in block form in figure 3. Direct sequence spread spectrum with barker code and qpsk international organization of scientific research 63 p a g e fig. Waste of bandwidth due to spreading is offset by multiple users. The first uses a processing gain near the fcc minimum for part 15. Direct sequence spread spectrum dsss is a spread spectrum technique whereby the original data signal is multiplied with a pseudo random noise spreading code.
As i understand it, both dsss and ofdm are intended to send many bits in parallel. The bandwidth of each is dependent on the message bit rate. Such a simplification will not be implemented in this experiment. 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. Chapter 5 digital bandpass modulation and demodulation techniques. Ee4512 analog and digital communications chapter 5 chapter 5 digital bandpass modulation and demodulation techniques binary amplitude shift keying pages 212219. Direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions. Introduction to iq demodulation of rfdata september 15, 1999 page 3 of 1 introduction 1. One can also demonstrate that signals added during the transmission such as an interferer.
An introduction to spreadspectrum communications tutorial. The dscdma transmitter multiplies each of user signals by a distinct code waveform. Dsss modulation the modulator inputs the m2 bit sequences and knows the full number of samples n to be used. The optimum receiver for binary directsequence spreadspectrum modulation and an additive white gaussian noise channel. Consider the frequency translation of a baseband message of bandwidth b hz to a higher part of the spectrum, using dsbsc modulation. 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. Mar 09, 1999 the invention is different from the conventional signal reception methods in that positive information is not discarded before the decision point. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Topics based on electronics, communication and computer are. In this regard dsss gives a certain amount of security and to demodulate it, one must. Fsk frequency shift keying d1 63 fsk in f 1 f 2 decision out figure 4.
A new technique for soft synchronization of directsequence spreadspectrum dsss signals is presented. This chapter describes the essential principles behind. The student is required to implement the mathematics of the modulator and demodulator to matlab code. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309. The student is required to implement the mathematics of the modulator and demodulator. The directsequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth. Chapter 5 digital bandpass modulation and demodulation.
For the sake of simplicity, ka 1 and ar ac have been chosen lowpass. The signal is obtained by starting with a narrowband signal and directly modulating a high bandwidth signal. Unlike frequencyhopping, a directsequence signal occupies the entire bandwidth continuously. Ss modulation is applied on top of a conventional modulation such as bpsk or direct conversion. Here a spreadspectrum demodulation has been made on top of the normal demodulation operations. Scribd is the worlds largest social reading and publishing site. 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.
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. A robust demodulator for oqpskdsss system request pdf. This is shown in block diagram form in figure 2 below. 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. Direct sequence spread spectrum an overview sciencedirect. Frequency hopping spread spectrum fhss and direct sequence spread spectrum dsss. Digital modulation methods can be considered as digitaltoanalog conversion and the corresponding demodulation or detection as analogtodigital conversion. 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. This experiment is concerned with demonstrating some of the principles of the first. There will be a minimum frequency separation required of the two tones. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation.
Pdf the directsequence spread spectrum modulation dsss is a very attractive modulation. Directsequence spreadspectrum modulation in this lecture we consider directsequence spreadspectrum systems. Modulation and demodulation medium, it would be dif. In this visualization the student only needs to submit their simulation. By transmitting the message energy over a bandwidth much wider than the minimum required, spread spectrum modulation techniques present two major advantages.
Download modulation damplitude demodulation damplitude book pdf free download link or read online here in pdf. This chipping code is nothing but the spreading code which is. 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. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Introduction to modulation and demodulation free download as powerpoint presentation. In practice, problems arise in baseband transmissions. 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. Direct sequence spread spectrum with barker code and qpsk. In all the detail on dsss and ofdm, i have missed which characterics of dsss and ofdm make these distinct technologies.
Notes for engineering in electronics, communications and computer science subjects are added. 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. Introduction to modulation and demodulation the purpose of a communication system is to transfer information from a source to a destination. Recall that our goal is to transmit data over a commu nication link, which we achieve by mapping the. Sequence spread specturm dsss modulation scheme is implemented with the. It is considered an ideal spreading code for its benefits in terms of large code resource quantity, nice correlation characteristics and high security. 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. Nov 11, 2016 direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. Introduction to modulation and demodulation modulation. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Demodulation of chaos phase modulation spread spectrum. 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. Typically, such communication systems can be found in wireless lans e.
Baseline parameter values are given and the modulation and demodulation technique is given mathematically. This design has a maximum process gain of 10log15 11. A modified directsequence spread spectrum modulation. One can also demonstrate that signals such as an interferer or jammer added during the transmission will be spread during the despreading operation. Modulation a mapping of the information on changes in the carrier phase, frequency or amplitude or combination. 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.
Chapter 7 spreadspectrum modulation spread spectrum technique simply consumes spectrum in excess of the minimum spectrum necessaryto send the data. An introduction to directsequence spreadspectrum communications. 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. Pdf digital modulator and demodulator ic for rfid tag. Multiplexing generally refers to independent signals, those produced by different sources.
In the transmitter, the input data stream is xored with the pn signal before transmission. The input multiplier performs the despreading of the received signal, and the second multiplier translates the modulated signal down to baseband. 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. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. Direct sequence cdma is the most popular of cdma techniques. One can also demonstrate that signals added during the transmission such as an interferer or jammer will be spread during the despreading operation. The easiest way of creating a dsss signal is to multiply one period of the spreading. Digital modulator and demodulator ic for rfid tag employing dsss and barker code article pdf available in journal of applied research and technology 106. The document is intended for users of the rf options on the system five. This spreading code has a higher chip rate this the bitrate of the code, which results in a wideband time continiuous scrambled signal. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors.
Ofdm is a combination of modulation and multiplexing. All books are in clear copy here, and all files are secure so dont worry about it. In telecommunications, directsequence spread spectrum dsss is a spreadspectrum modulation technique primarily used to reduce overall signal interference. Read online modulation damplitude demodulation damplitude book pdf free download link book now. 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. After the despreading or removal of the directsequence modulation in the receiver, the information bandwidth is restored, while. This chipping code is nothing but the spreading code which is multiplied with the original message and transmitted. In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation.