Performance comparison of frequency hopping and direct sequence spread spectrum systems in the 2. The problems of obtaining phase and timing references for directsequence spreadspectrum communication systems are discussed in reference 26. Fhss and dsss, which stand for frequency hopping spread spectrum and direct sequence spread spectrum, are two spread spectrum techniques. The construction is based on the settheoretic characterization of an optimal set of fh sequences. Software implementation for frequency hopping synchronization is discussed and a method for direct sequence and frequencyhopping united acquisition is also introduced. Code division multiple access or cdma has its roots in wwii era spread spectrum technology. 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. Frequency hopping spread spectrum, direct sequence spread spectrum and cdma. Difference between fhss and dsss difference between. Frequencyhopping spread spectrum fhss is a method of transmitting radio signals by. Employing a modulation that is digital likebpsk or qpsk, a transmitter multiplies symbols by having a pseudo noise rule that is random.
Psd of a random binary signal mt consider a random binary sequence of 0s and 1s. Dscdma transmitter c is the frequency of the carrier and 0 and 5. Cdma spread spectrum communications activexperts software. Frequency hopping spread spectrum and direct sequence spread spectrum are two main spread coding technologies. Design and implementation of a frequencyhopping tdma system. 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. Softwarebased implementation of a frequency hopping twoway. Multicarrier sublayer for direct sequence channel and. In this paper, a construction of optimal sets of frequency hopping sequences is presented. Fh cdma is the repetitive switching of frequency at the time of radio transmission. The pseudorandom sequence is referred to as the spreading code or a pseudonoise sequence.
Index terms directsequence, frequencyselective fading, multicarrier, multipath, narrowband interference, periodic autocorrelation function, spread spectrum. Wifi, bluetooth, basically all modern rf communications processing gain jam resistant cdma. Cdma can be implemented in several ways, two of which are frequency hopping and direct sequencing. Slow frequencyhopping multicarrier dscdma for transmission. For instance a random binary sequencewaveform could be. Abcs of spread spectrum a technology introduction and. In telecommunications, directsequence spread spectrum dsss is a spreadspectrum modulation technique primarily used to reduce overall signal interference. 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 data. Spectral plots illustrate directsequence spreadspectrum dsss and frequency hopping spreadspectrum fhss methods. 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. Frequency hopping is generated by switching consecutive bursts in each time slot through different trxs according to the assigned hopping sequence. The following matlab project contains the source code and matlab examples used for frequency hopping spread spectrum, direct sequence spread spectrum and cdma.
The main difference is in how they spread the data into the wider bandwidth. A dsss transmitter converts an inbound information bit stream directly into a phrase flow. Fhss is used to avoid interference, to prevent eavesdropping, and to enable codedivision multiple access cdma communications. Direct sequence contrasts with the other spread spectrum process, known as frequency hopping spread spectrum. The current solutions are baseband frequency hopping bb fh and synthesized frequency hopping rf fh. What is frequency hopping code division multiple access. An introduction to directsequence spreadspectrum communications, maxim app note 1890. Multicarrier codedivision multiple access wikipedia. In this paper, based on the simulink platform of matlab software with the technologies of directsequence spreadspectrum dsss 4 and frequency hopping. Performance of ds cdma systems is usually,better and more reliable. Fhss can, however, cause interference with adjacent directsequence spread spectrum dsss systems.
These programmes are not heavily commented but infact are very simple and intutive to understand. The duration of an element in the code is called the chip time. 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. 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. Carrier interferometry ci provides wideband transmission protocols with frequencyband selectivity to improve interference rejection, reduce multipath fading, and enable operati.
Cdma signal spreading the very basics of how its done duration. 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. A versatile broadband multiple access scheme, combining frequencyhopping fh with multicarrier dscdma fhmc dscdma is proposed and investigated. In this technique, the same bandwidth is used by different users. Frequency hopping spread spectrum, direct sequence spread spectrum and cdma a very simplified method for elaboration of frequency hopping techniques. A subtype of fhss used in bluetooth wireless data transfer is. The most frequent practices are direct sequence spread spectrum and frequency hopping spread spectrum. That is, each user symbol is carried over multiple parallel subcarriers, but it is phaseshifted typically 0 or 180. For nonoverlapping channels the total spread of the fh signal is at least the channel bandwidth times the number of hops. This binary sequence is transmitted as random signal mt with 1s and 0s being sent using the pulses shown below.
These programmes are not heavily commented but infact are very simple and intutive to understand the frequency hopping and related tasks. Frequency hopping code division multiple access fhcdma, in which a broad slice of the bandwidth spectrum is divided into many possible broadcast frequencies. 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. 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. Miji jacob 2 1, 2ece, sngce, kadayiruppu, india abstract direct sequence spread spectrum technique, which also known as direct sequence code division multiple access. Interference at a specific frequency will only affect the signal during that short interval. 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. In direct sequence spread spectrum transmission, the user data signal is multiplied by a code sequence. Introduction to spread spectrum, by michael hendry. The most popular forms of spread spectrum include frequency hopping multiple access fhma and code division multiple access cdma.
Cdma is a form of direct sequence spread spectrum communications. The ratio between the user symbol time and the chip time is called the spread factor. In 1985, the fcc allocated three frequency bands to spread spectrum communications. Fhss utilizes frequency hopping while dsss utilizes pseudo noise to modify the phase of the signal. Frequency hopping spread spectrum, direct sequence spread. Frequency hopping spread spectrum signal on 24 mhz duration.
Frequencyhopping spread spectrum wikimili, the best. The performance of directsequence spread spectrum with various forms of rfi is considered in references 24, 25, and 36 through 38. A comparison of frequency hopping and direct sequence. Frequency hopping spread spectrum, direct sequence spread spectrum and cdma 1. From the beginning it was designed to be resistant to noise, interference, jamming, and unauthorized detection. 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. Software rad io technology in fhmc dscdma communication system. For a technical example of dsss technology, see cdma. Directsequence and frequencyhopping spread spectrum. Directsequence spreadspectrum communications for multipath. 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. Channelcoded timehopping and directsequence ultrawideband. Spread spectrum frequency hopping spread spectrum fhss direct sequence spread spectrum dsss dsss. Frequency hopping spread spectrum is defined in the 2.
Free spectrum software, best spectrum download page 1 at. The energy of the signal is equally divided among di erent frequencies. The worlds most comprehensive professionally edited abbreviations and acronyms database all trademarksservice marks referenced on this site are properties of their respective owners. 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. In the baseband frequency hopping the trxs operates at fixed frequencies. Fhcdma is the repetitive switching of frequency at the time of radio transmission. Qpsk modulation for dssscdma transmitter and receiver using fpga susan kuriakose 1, ms. 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. Frequency hopping code division multiple access fhcdma is a basic modulation technique used in spread spectrum signal transmission. A comparison of frequency hopping and direct sequence spread spectrum modulation for ieee 802. 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.
This helps to reduce the strength of electronic warfare, that is, the. After the despreading or removal of the directsequence modulation in the receiver, the information bandwidth is restored, while. Particularly for wireless lans, where terminals can be located anywhere, this advantage made sfh popular. Following are the two types of spread spectrum techniques. Frequency hopping code division multiple access fh cdma is a basic modulation technique used in spread spectrum signal transmission. In techniques such as direct sequence spread spectrum, the modulated signal is spread over a frequency range which must be continuous. Digital modulation techniques, qpsk, fdma, tdma, pcm. Direct sequence sss psdf of a random pulse signal example.
International journal of recent technology and engineering. Multirate transmission in frequencyhopping multicarrier. Differentiate between frequency hopping and direct. Evaluation of direct sequence and frequency hopping shows that both of. Construction of optimal sets of frequency hopping sequences. Matlab program for frequency hopping spread spectrumfhss. In frequency hopping systems, the transmitter changes the carrier frequency according to a. The directsequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth. Introduction the increasing interest and applications of direct sequence spreadspectrumdsss technologystemfrom itsrobustness to fading, its antiinterference capability, and. The changes are controlled by a code known to both transmitter and receiver. Directsequence and frequencyhopping spread spectrum 1 21 unlike dsss, frequencyhopped channels can, in principle, be over lapped, adjacent, or spaced. Frequency hopping sequences are needed in fhcdma systems. 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.
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