Cdma spread spectrum communications activexperts software. The main difference is in how they spread the data into the wider bandwidth. Frequency hopping code division multiple access fhcdma is a basic modulation technique used in spread spectrum signal transmission. Employing a modulation that is digital likebpsk or qpsk, a transmitter multiplies symbols by having a pseudo noise rule that is random. For a technical example of dsss technology, see cdma. Wifi, bluetooth, basically all modern rf communications processing gain jam resistant cdma. Difference between fhss and dsss difference between. These programmes are not heavily commented but infact are very simple and intutive to understand. Cdma is a form of direct sequence spread spectrum communications. Fhss can, however, cause interference with adjacent directsequence spread spectrum dsss systems. Introduction the increasing interest and applications of direct sequence spreadspectrumdsss technologystemfrom itsrobustness to fading, its antiinterference capability, and. Fh cdma is the repetitive switching of frequency at the time of radio transmission. Against the backcloth of the explosive expansion of the internet and the continued dramatic increase in demand for highspeed multimedia wireless services, there is an urging demand for flexible, broadband transceivers. An introduction to directsequence spreadspectrum communications, maxim app note 1890.
Fhss is used to avoid interference, to prevent eavesdropping, and to enable codedivision multiple access cdma communications. Spectral plots illustrate directsequence spreadspectrum dsss and frequency hopping spreadspectrum fhss methods. Slow frequencyhopping multicarrier dscdma for transmission. The pseudorandom sequence is referred to as the spreading code or a pseudonoise sequence. Performance comparison of frequency hopping and direct sequence spread spectrum systems in the 2. A dsss transmitter converts an inbound information bit stream directly into a phrase flow. Index terms directsequence, frequencyselective fading, multicarrier, multipath, narrowband interference, periodic autocorrelation function, spread spectrum. Cdma signal spreading the very basics of how its done duration. The problems of obtaining phase and timing references for directsequence spreadspectrum communication systems are discussed in reference 26. Frequency hopping spread spectrum, direct sequence spread spectrum and cdma 1. Frequencyhopping spread spectrum fhss is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. Performance of ds cdma systems is usually,better and more reliable.
Cdma can be implemented in several ways, two of which are frequency hopping and direct sequencing. The changes are controlled by a code known to both transmitter and receiver. Direct sequence contrasts with the other spread spectrum process, known as frequency hopping spread spectrum. Direct sequence ds direct sequence code division multiple access ds cdma is a technique to multiplex users by different codes. Direct sequence spread spectrum with example explained in hindi duration. The duration of an element in the code is called the chip time. From the beginning it was designed to be resistant to noise, interference, jamming, and unauthorized detection. Software rad io technology in fhmc dscdma communication system. Frequencyhopping spread spectrum wikimili, the best. Direct sequence spread spectrum techniques spread spectrum technology was first introduced about 50 years ago by the military as a way of sending secure communications.
A versatile broadband multiple access scheme, combining frequencyhopping fh with multicarrier dscdma fhmc dscdma is proposed and investigated. In the baseband frequency hopping the trxs operates at fixed frequencies. The ratio between the user symbol time and the chip time is called the spread factor. Digital multicarrier spread spectrum versus direct. I have made two files for frequency hopping, one of them is not showing 6 proper impulsive peaks but other programme is infact showing them, in dsss i have generated 20 bits and each bit is 6 units long and then it is xored with another pseudorandom. As nearby hopping interferers are unlikely to continuously transmit in the same frequency slot as the reference user, the nearfar problem is less severe than in direct sequence ds cdma. The most frequent practices are direct sequence spread spectrum and frequency hopping spread spectrum. Frequency hopping code division multiple access fh cdma is a basic modulation technique used in spread spectrum signal transmission. Dscdma transmitter c is the frequency of the carrier and 0 and 5.
The code is generated pseudorandomly, the receiver knows how to generate the same code, and correlates the received signal with that code to extract the data. Interference at a specific frequency will only affect the signal during that short interval. The performance of directsequence spread spectrum with various forms of rfi is considered in references 24, 25, and 36 through 38. After the despreading or removal of the directsequence modulation in the receiver, the information bandwidth is restored, while. That is, each user symbol is carried over multiple parallel subcarriers, but it is phaseshifted typically 0 or 180. This helps to reduce the strength of electronic warfare, that is, the. Psd of a random binary signal mt consider a random binary sequence of 0s and 1s. These programmes are not heavily commented but infact are very simple and intutive to understand the frequency hopping and related tasks. Construction of optimal sets of frequency hopping sequences. The digital data is directly coded at a much higher frequency. Directsequence and frequencyhopping spread spectrum 1 21 unlike dsss, frequencyhopped channels can, in principle, be over lapped, adjacent, or spaced. Particularly for wireless lans, where terminals can be located anywhere, this advantage made sfh popular. Fhss and dsss, which stand for frequency hopping spread spectrum and direct sequence spread spectrum, are two spread spectrum techniques.
In 1985, the fcc allocated three frequency bands to spread spectrum communications. In this paper, based on the simulink platform of matlab software with the technologies of directsequence spreadspectrum dsss 4 and frequency hopping. International journal of recent technology and engineering. Spread spectrum frequency hopping spread spectrum fhss direct sequence spread spectrum dsss dsss. Softwarebased implementation of a frequency hopping twoway. Frequency hopping code division multiple access fhcdma, in which a broad slice of the bandwidth spectrum is divided into many possible broadcast frequencies. Frequency hopping spread spectrum, direct sequence spread. Frequency hopping spread spectrum is defined in the 2. Free spectrum software, best spectrum download page 1 at. A slow frequency hopping, multicarrier directsequence, codedivision multipleaccess sfhmc dscdma scheme is proposed and investigated, which has the potential of providing a joint framework for 2ndgeneration narrowband cdma, 3rdgeneration wideband cdma and highrate broadband access networks. Fhcdma is the repetitive switching of frequency at the time of radio transmission. Frequency hopping spread spectrum, direct sequence spread spectrum and cdma. The worlds most comprehensive professionally edited abbreviations and acronyms database all trademarksservice marks referenced on this site are properties of their respective owners. Frequency hopping spread spectrum, direct sequence spread spectrum and cdma a very simplified method for elaboration of frequency hopping techniques.
Frequencyhopping spread spectrum fhss is a method of transmitting radio signals by. Qpsk modulation for dssscdma transmitter and receiver using fpga susan kuriakose 1, ms. Both fhss and directsequence spreadspectrum dsss systems can transmit at 1 watt, a thousandfold increase from the 1 milliwatt limit on. A novel multiple access scheme based on slow frequency hopping multicarrier directsequence code division multiple access sfhmc dscdma is proposed and investigated, which can be rendered. In telecommunications, directsequence spread spectrum dsss is a spreadspectrum modulation technique primarily used to reduce overall signal interference. In frequency hopping systems, the transmitter changes the carrier frequency according to a. In this paper, a construction of optimal sets of frequency hopping sequences is presented. Direct sequence sss psdf of a random pulse signal example. Frequency hopping spread spectrum and direct sequence spread spectrum are two main spread coding technologies. The following matlab project contains the source code and matlab examples used for frequency hopping spread spectrum, direct sequence spread spectrum and cdma. Abcs of spread spectrum a technology introduction and. Introduction to spread spectrum, by michael hendry. A comparison of frequency hopping and direct sequence. Frequency hopping spread spectrum fhss is a method of transmitting radio signals by shifting carriers across numerous channels with pseudorandom sequence which is already known to the sender and receiver.
This binary sequence is transmitted as random signal mt with 1s and 0s being sent using the pulses shown below. Directsequence and frequencyhopping spread spectrum. Multirate transmission in frequencyhopping multicarrier. Blind softdetection of the sfhmc dscdma signals is investigated.
Software implementation for frequency hopping synchronization is discussed and a method for direct sequence and frequencyhopping united acquisition is also introduced. In direct sequence spread spectrum transmission, the user data signal is multiplied by a code sequence. The most popular forms of spread spectrum include frequency hopping multiple access fhma and code division multiple access cdma. Digital modulation direct sequence, code division multiple access dscdma, frequency hopping code division multiple access fhcdma, time division multiple access tdma, frequency division multiple access fdma, pdf file. Carrier interferometry ci provides wideband transmission protocols with frequencyband selectivity to improve interference rejection, reduce multipath fading, and enable operati. The energy of the signal is equally divided among di erent frequencies. Systm,generate wideband signals controlled by commanding the carrier frequency, frequency hopping syestem,generate wideband signals controlled by the code is direct carrier,modeulation direct sequence frequency hopping,devices,use,less,power,and,are,cheaper. The construction is based on the settheoretic characterization of an optimal set of fh sequences. Scpc, directsequence scpc, frequency hopping and cdma network mode scpc based on iess 308309 and stanag 4486 frequency hopping waveform based on stanag 4606 fully automated dama network wide range of user data rates. A subtype of fhss used in bluetooth wireless data transfer is. Miji jacob 2 1, 2ece, sngce, kadayiruppu, india abstract direct sequence spread spectrum technique, which also known as direct sequence code division multiple access.
Multicarrier codedivision multiple access mccdma is a multiple access scheme used in ofdmbased telecommunication systems, allowing the system to support multiple users at the same time over same frequency band mccdma spreads each user symbol in the frequency domain. For nonoverlapping channels the total spread of the fh signal is at least the channel bandwidth times the number of hops. Evaluation of direct sequence and frequency hopping shows that both of. Moreover, specifically the security of the frequency hopping code division multiple access fhcdma system mainly relies on the longcode generator that consists of a 42bit longcode mask generated by a 42bit lfsrs. The current solutions are baseband frequency hopping bb fh and synthesized frequency hopping rf fh. Frequency hopping is generated by switching consecutive bursts in each time slot through different trxs according to the assigned hopping sequence. A comparison of frequency hopping and direct sequence spread spectrum modulation for ieee 802. Digital modulation techniques, qpsk, fdma, tdma, pcm. In this technique, the same bandwidth is used by different users. Fhma is an access technology where mobile radios may share radio channels by transmitting for brief periods of time on a single radio channel and then hopping to other radio channels to continue transmission. Channelcoded timehopping and directsequence ultrawideband. Design and implementation of a frequencyhopping tdma system.
Multicarrier sublayer for direct sequence channel and. The directsequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth. Code division multiple access or cdma has its roots in wwii era spread spectrum technology. Frequency hopping spread spectrum signal on 24 mhz duration. Multicarrier codedivision multiple access wikipedia. Following are the two types of spread spectrum techniques. Directsequence spreadspectrum communications for multipath. Fhss utilizes frequency hopping while dsss utilizes pseudo noise to modify the phase of the signal. What is frequency hopping code division multiple access. Matlab program for frequency hopping spread spectrumfhss.
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