The modulation is accomplished by varying the sine and cosine inputs at a precise time. So the following su cient statistic is used for decision at the receiver. The signal is obtained by starting with a narrowband signal and directly modulating a high bandwidth signal. Pdf spread spectrum modulation techniques using matlab.
This chipping code is nothing but the spreading code which is multiplied with the original message and transmitted. Quaternary phase shift keying qpsk qpsk is the most common form of phaseshift keying. We handled phase difference between carriers of binary0 and bnary1 using nonreturntozero coding so we just multiplied dsss signal with a carrier that has 100 hz frequency. Thanks to the coding basis, ss can also be used as another method for implementing multiple access the real or apparent coexistence of.
Direct sequence spread spectrum is a form of transmission that looks very similar to white noise over the bandwidth of the transmission. The first step is differential encoding, a simple procedure that is used to remove any possible phase ambiguity between the transmitter of a bpsk modulated signal and the signal recipient. 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. At the receiver, the received spread spectrum signal is despreaded by correlating it with a local replica of the pn code. Qpsk modulation consists of two bpsk modulation on inphase and quadrature components of the signal. Direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions. The resulting signal occupies a bandwidth of 2b hz, and would typically override the noise occupying the same part of. Use of matched filter in direct sequence spread spectrum. Nov 11, 2016 direct sequence spread spectrum dsss is a transmission technology used in local area wireless network transmissions. The application of the heterodyne principle to modulation is shown schematically in figure 143. Direct sequence spread spectrum dsss for bpsk, qpsk and 16qam modulations version 2. As a result, the circuit design for the dsss products requires very good passband characteristics for the 22 mhz width. Direct sequence cdma is the most popular of cdma techniques. Qpsk bpsk dsss radio rf micro devices tx applications rf9958 or rf2658 with sx043 or sx041, bps to 1 mbps data rates bpsk or qpsk modulations notes for more information on ami dsss, 9898 3205 4 3 qpsk bpsk dsss radio rf micro devices tx applications rf2423 with sx043 or, 1 mbps data rates bpsk or qpsk modulations notes.
A text book conceptual block diagram of a dsss receiver is depicted in figure 2. Design of adtrdsssiruwb transmitter for bpsk modulation. Phaseshift keying psk is a digital modulation process which conveys data by changing modulating the phase of a constant frequency reference signal the carrier wave. This chipping code is nothing but the spreading code which is.
Digital data signal will be converted to analog tx iq signals through dac in bbp ic, tx iq pass through to low pass filter. The data is denoted by dt, the spreading signal is denoted by ct, and the spread waveform qt is fed to the bpsk modulator operating at a carrier frequency fc, and the transmitted signal is denoted by xt. Given a choice of 1 mhz versus 22 mhz, a 1mhz design is easier to design. In the transmitter stage, the baseband data signal mt is spread using pnsequence ct. The data is modulated using bpsk then sent through an awgn channel. 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. Interference at a specific frequency will only affect the signal during that short interval.
Then, the resultant spread signal st is applied to bpsk modulator. An introduction to spreadspectrum communications tutorial. May 01, 2018 this video explains the generation of binary phase shift keying modulation bpsk. However once received and processed with the correct descrambling codes, it is possible to extract the required data. There are several types available for modulation, viz. Direct sequence spread spectrum dsss for bpsk, qpsk and.
Consider the frequency translation of a baseband message of bandwidth b hz to a higher part of the spectrum, using dsbsc modulation. This design has a maximum process gain of 10log15 11. Types of spread spectrum n directsequence spread spectrum dsss n each information symbol is chipped into a pattern of smaller symbols n the pattern is called the spreadspectrum code or sequence n it is used in is95, wcdma, cdma2000 and ieee 802. The directsequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth. 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. Simulink model of a bpsk direct sequence spread spectrum. A subtype of fhss used in bluetooth wireless data transfer is. Performance analysis of dsss and fhss techniques over. Final step of dsss modulation at transmitter is multiplying dsss signal with carrier of bpsk. Two main spread spectrum modulation techniques are defined. One can, for example, use ss techniques to transmit a signal modulated via fsk or bpsk.
All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Spread spectrum dsss d2 127 dsss out clock prbs pseudonoise pn rf carrier bipolar message bpsk. Networks, undersea warfare, directsequence spreadspectrum, differential binary phaseshift keying, dsss, dbpsk, ds bpsk 16. Performance analysis of dsss and fhss techniques over awgn. After the despreading or removal of the directsequence modulation in the receiver, the information bandwidth is restored, while. Direct sequence spread spectrum with barker code and qpsk. Choose a web site to get translated content where available and see local events and offers.
The performance is evaluated in presence of awgn and rayleigh fading. This paper is intended to provide the basic concepts, without. Chip data rate of new channel kd zif k6 and code is a sequence of 1s and 1s f 1 bit a d d hi tt peter a. Block diagram for the generation production of bpsk has been given to clear the basics. Ber vs snr performance comparison of dsss cdma fpga based. Baseband processing bbp ic has dsss bpsk qpskcck and ofdm bpsk qpsk16qam64qam modulation function, it provides transmission data rate are 1, 2, 5. Direct sequence spread spectrum dsss a pseudonoise sequence pn t generated at the modulator, is used in conjunction with an mary psk modulation to shift the phase of the psk signal pseudorandomly, at the chipping rate r c 1t c a rate that is an integer multiple of the symbol rate r s 1t s.
Processing gain for direct sequence spread tm spectrum. Bpsk receiver simulation using spread spectrum techniques. The first step is differential encoding, a simple procedure that is used to remove any possible phase ambiguity between the transmitter of a bpsk. In this case the arrangement of figure 1 can be expanded to that of figure 2. Cck will also have similar spectrum due to spreading by high rate code words. In telecommunications, directsequence spread spectrum dsss is a spreadspectrum modulation technique primarily used to reduce overall signal interference. Break each bit into k chips userspecific fixed pattern.
In the transmitter, the input data stream is xored with the pn signal before transmission. The dscdma transmitter multiplies each of user signals by a distinct code waveform. Unlike frequencyhopping, a directsequence signal occupies the entire bandwidth continuously. It is widely used for wireless lans, rfid and bluetooth communication. It is widely used for wireless lans, rfid and bluetooth communication any digital modulation scheme uses a finite number of distinct. The dsss system two configurations are used for directsequence spreadspectrum evaluation hardware. Cesar vargas rosales, center for electronics and telecommunications dsss dsss uses pn sequences for spectrum spreading and phase modulation modulation is binary psk bpsk or quaternary psk qpsk bpsk 1 1 1 1 1 1 1 1 qpsk message 0 0 180 0 phase 1 1 bit bpsk 0 0 0 0 270 180 90 0 phase 1 1 1 11. Jun 23, 2003 this is a code for simulation of bpsk receiver using direct sequence spread spectrum. Data and phase waveforms for bpsk vi5 r l t 2 t cos 2. This experiment is concerned with demonstrating some of the principles of the first. The first uses a processing gain near the fcc minimum for part 15. In a direct sequence spread spectrum dsss communications system, the spreading of the information bits is performed by their modulation with a pseudonoise pn sequence before transmission.
Frequency hopping spread spectrum fhss and direct sequence spread spectrum dsss. When transmitting a dsss spread spectrum signal, the required data signal is multiplied. Security classification of abstract unclassified 20. On the receiver side we multiply with the same pn sequence and demodulate. The bercalculator block compares sent data with received data, and outputs a vector with count of symbols, errors, and the ber. The corresponding constellation is presented on gure 1. Note that spread spectrum is not a modulation scheme, and should not be confused with other types of modulation. 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. In this post, we are going to analyze the methodology for the the 16qam case, as it is the more complex and by understanding, we will easily apply the concepts to the bpsk and qpsk cases. Qpsk modulation and demodulation the signals of the qpsk modulation are defined in 1, where f. Using a digital modulation technique like bpsk or qpsk, a transmitter multiplies symbols with a pseudo random noise code.
The despreading operation spreads the jammer power psd and lowers its peak, and the bpf output shows the effect on the signal to jammer ratio. Chapter 5 digital bandpass modulation and demodulation techniques. Demodulator for bpsk the optimum receiver for bpsk in the presence of additive white gaussian noise is shown in figure vi3. Jul 05, 2016 in this post, we are going to analyze the methodology for the the 16qam case, as it is the more complex and by understanding, we will easily apply the concepts to the bpsk and qpsk cases. Fhss can, however, cause interference with adjacent directsequence spread spectrum dsss systems. Cck vs dsss vs ofdm difference between cck,dsss,ofdm. The spreading concept is same as used in cdma technique. The interference jammer is narrow, and has a highly peaked psd, while the psd of the ds is wide and low. 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. In direct sequence spread spectrum dsss, the transmitter and receiver contain identical psuedorandom sequence generators producing a pseudonoise pn signal. By transmitting the message energy over a bandwidth much wider than the minimum required, spread spectrum modulation techniques present two major advantages. Binary phase shift keying bpsk generation block diagrampsk.
By using phase shifts of 45, 5, 225, or 315 degrees, each modulated carrier pulse transmits 2 bits of information. Note that ss is not a modulation scheme, and should not be confused with other types of modulation. Figure 5 depicts a direct sequence spread spectrum sys tem where an msequence is used as the spreading code and bpsk as the modulation techniq ue. Drm d macleod ma phd mieee, in telecommunications engineers reference book, 1993. Direct sequence spread spectrum in a digital communication system in providing privacy and antijamming. Request pdf design of adtrdsssiruwb transmitter for bpsk modulation a novel scheme for ultra wideband uwb transceiver based on decision feedback using average differential transmitted. The basic building blocks of a ds cdma transmitter system are shown in figu c.
The simulation by matlab program simplifies the study, analysis and development of these techniques in modern digital communication networks. Security classification of this page unclassified 19. Directsequence spreadspectrum modulation in this lecture we consider directsequence spreadspectrum systems. Github mahmutaksakallidirectsequencespreadspectrum. Matlab program for frequency hopping spread spectrumfhss. Since bpsk is generally more robust with a somewhat lower implementation loss than qpsk, supporting spreading for only bpsk modulation does not in any way limit the use or functionality of the. Ber vs snr performance comparison of dsss cdma fpga. Dsss is a spreadspectrum modulation technique primarily used to reduce overall signal interference. In this design, qpsk modulation is used to modulate and transmit the spread signal 7. Hence, a selection of bpsk modulation is analogous to using qpsk with a spreading factor of 2. Dsss, the transmitter and receiver contain identical psuedorandom sequence generators producing a pseudonoise pn signal.
Thanks to the coding basis, spread spectrum can also be used as another method for. Using bpsk modulation and since the information are real, only the real part of the equation is of interest. The clock used to generate pn sequence should be same at the dsss transmitter and receiver. Based on your location, we recommend that you select. Jakes model has been used to obtained coefficients for rayleigh fading. Direct sequence spread spectrum an overview sciencedirect. Dsss transceiver a dsss transmitter is shown in figure 1. In this regard dsss gives a certain amount of security and to demodulate it, one must. Pdf performance evaluation of spread spectrum system. One can, for example, use spreadspectrum techniques to transmit a signal modulated by fsk or bpsk.
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