Application backgroundoqpsk, also known as the offset four phase shift keying offsetqpsk, is an improved qpsk. For efficient radiation, the antenna from which the signal is being. Request pdf a robust demodulator for oqpskdsss system ieee802. Performance of oqpsk as a modulation scheme using awgn channel for. It has the same phase relationship with qpsk, and is also divided into two channels, and then the orthogonal modulation. Qpsk vs oqpsk vs pi4qpskdifference between qpsk,oqpsk,pi4qpsk. Dec 18, 2005 hi all, i have to demodulate an oqpsk signal. A demodulator for offset quaternary phase shift keyed oqpsk signals modulated with two words. Description of 4 qpsk modulation scheme a study of various modulation schemes like qpsk, oqpsk, gmsk, and tfm have been made, and attention, demodulation has certain advantages in the cellular systems, and 4shifted qpsk allows the flexibility to use, modulation and demodulation modulator the theory behind signal mapping and baseband. A synchronous demodulator would be sensitive to these phase reversals. Qpsk modulationquadrature phase shift keying modulation. Demodulator for bpsk the optimum receiver for bpsk in the presence of additive white gaussian noise is shown in figure vi3.
Design and implement of oqpsk modulator based on fpga. Here is what i understood from the explanation of the block diagram, and would like to confirm from this platform if my understanding is right. Then, the second stage will be the implementation of qpsk using usrp hardware. They are configured for framebased processing with bit signal inputs. Digital modulation techniques this month, well take a necessarily brief look in another direction of digital data. Bpsk and qpsk modulation and demodulation with simulink chapter pdf available february 2018 with 10,743 reads. The computational expense of this approach depends upon the particular modulation format and demodulation algorithm being implemented. For information about delays incurred by modulatordemodulator pair processing, see modulation delays. Differential quadrature phaseshiftkeying dqpsk format provides a promising alternative as it, like qpsk, transmits 2 bits per symbol and hence the symbol. Offset qpsk minimizes power variations between symbols by delaying the i to q timing so the carrier trajectory. The output is a baseband representation of the modulated signal. The simulation involves, generating random message bits, modulating them using qpsk modulation, addition of awgn channel noise corresponding to the given signaltonoise ratio and demodulating the noisy signal using a.
Keywordsqpsk, oqpsk, raised cosine filter, root raised cosine filter. Oqpsk and pi4 qpsk are variants of the basic qpsk modulation schemes. The performance analysis of cdma system using qpsk and oqpsk modulation techniques has attracted considerable. This page explain these modulation types and explain difference between qpsk. Qpsk, oqpsk, cpm probability of error for awgn and flat. Comparison of performance metrics for qpsk and oqpsk. Comparison of receiver blue line and transmitter green line power spectrum for 32psk d. It is widely used for wireless lans, rfid and bluetooth communication any digital modulation scheme uses a finite number of distinct. Phase ambiguity resolution for offset qpsk modulation systems.
The staggering restricts the phase changes to 90 as. Offset qpsk oqpsk oqpsk is a modified form of qpsk where the bit waveforms on i and q channels are offset or shifted in phase from each other by onehalf of a bit time. Al though its possible to just push bits into a transmitter, alittle effort and thought can make the process. The simulation involves, generating random message bits, modulating them using qpsk modulation, addition of awgn channel noise corresponding to the given signaltonoise ratio and demodulating the noisy signal using a coherent qpsk receiver. Introduction qpsk and oqpsk are regarded as successful modulation formats in is95 cdma, cdma2000 and wcdma mobile communication systems 1. Pass the recovered carrier phase into the demodulator model where it can be used directly as the reference phase. Modulation qpsk cours pdf bits coding mega rate stan or per. The appearance of a bpsk signal in the time domain is shown in figure 2 lower trace. The oqpsk modulation is a psk modulation, using 2 bits per symbol and a delay of one bit in the in quadrature signal refer to optisystem component library, oqpsk pulse generator.
For qpsk demodulator, a coherent demodulator is taken as an example. A robust demodulator for oqpskdsss system request pdf. Jul, 2017 qpsk modulation and demodulation in matlab awgn channel. In qpsk, modulation is symbol based,where one symbol contains 2 bits. The oqpsk modulator baseband block modulates the input signal using the offset quadrature phase shift keying oqpsk method and applies pulse shape filtering to the waveform. I found out the quadrature qpsk demodulation technique which seems very straight forward. Qpsk modulation and demodulation with matlab and python. Qpsk can produce the phase ambiguity in carrier recovery process. Im following several articles trying to set up to receive lrpt signals from the m2 satellite. By reverting to a lower order modulation scheme the link can be made more reliable with fewer. Then we will use quantization, qpsk modulation, qpsk demodulation and dequantization. Phase shift keying of oqpsk modulation in four phase shift keying. For bpsk this is just a rectangular pulse of duration t. The drawbacks are the increased snr required and the increase in the complexity of the system.
Waveform simulation technique and the complex equivalent baseband simulation model will be provided on a casebycase basis. Demodulation using oqpsk method simulink mathworks espana. I conducted a research on how to implement a qpsk demodulator. This example shows the oqpsk modulator baseband and oqpsk demodulator baseband blocks connected with no channel or impairments distorting the signal between them. Following link covers qpsk matlab code and provide matlab codes for other modulation types.
Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Once locked, however, an oqpsk demodulator is essentially a qpsk demodulator that shifts one channel a halfsymbol somewhere before the slicer. In high amplifiers and for certain satellite applications, oqpsk offers better performance digital modulation schemes oqpsk 4 7 6. Demodulation does not require any external filters, coherent carriers, or. Al though its possible to just push bits into a transmitter, alittle effort and thought can make the process much more efficient. As for the topics concerned, only the basic techniques of modulation and demodulation of various digital modulation techniques are covered.
The simple way, if you have a lot of time, is to sweep the frequency very slowly. Performance simulations of well known digital modulation techniques are also. The gaussian noise is created from the boxmuller algotithm, easy to implement. The modulation is accomplished by varying the sine and cosine inputs at a precise time.
Power spectrum for 32psk modulation was shown in figure. It is widely used for wireless lans, rfid and bluetooth communication. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. The input is a baseband representation of the modulated signal. This page explain these modulation types and explain difference between qpsk vs oqpsk vs pi4qpsk. By using phase shifts of 45, 5, 225, or 315 degrees, each modulated carrier pulse transmits 2 bits of information. Pdf digital modulation is a process that impresses a digital symbol on to a signal. The bcm38 is a universal headend advanced tdma physical layer qpsk qam burst receiver docsiseurodocsisbased, ieee 802. Qpsk, oqpsk, dqpsk modulator and demodulator trainer kit. The oqpsk demodulator baseband block applies pulse shape filtering to the input waveform and demodulates it using the offset quadrature phase shift keying oqpsk method. Qpsk modulation in qpsk modulation, each symbol was mapped in the data string clustering diagrams to be expressed with 2 bits.
Dec 10, 2014 digital modulation schemes oqpsk 3 7 5. Dpsk is an alternative form of digital modulation where the binary input information is contained in the difference between two successive signaling. The block diagram of an oqpsk modulator is shown in fig. This can be achieved by using a pll phase lock loop at the receiver. Performance analysis and simulation of both qpsk and oqpsk. The complete waveform simulation for the aforementioned qpsk modulation and demodulation is given next.
A robust demodulator for oqpskdsss system springerlink. Oqpsk modulation techniques has attracted considerable attention in research area 24. Higher order phase modulation schemes are less complex and signals can be recovered without implementing any channel. The transition from analog communication to digital has advanced the use of qpsk. Definition quadrature phase shift keying qpsk is a form of phase shift keying in which two bits are modulated at once, selecting one of four possible carrier phase shifts 0, 90, 180, or 270 degrees. For each of a plurality of candidate values for the initial phase, the correlation coefficient between a signal whose clock delay has been estimated and compensated and an ideal signal generated based on the signal is computed, and the. Modulation is achieved by varying the phase of the basis functions depending on the message symbols. As usual in this kind of modulation, symbols chips have an halfsine shape, and the q channel has a 90 degree half simbol offset with respect to the i channel. In this lab, you will observe the quadrature phase shift keying qpsk modulation and demodulation building simulink simulation. 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. Modulation and demodulation medium, it would be dif.
Learn integrator and comparator at the demodulator. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Higher order phase modulation schemes are less complex and signals can. The first thing i have to do and perhaps the most difficult is removing the frequency offset from the received i and q signals. Bpsk binary phase shift keying d1 71 the information about the bit stream is contained in the changes of phase of the transmitted signal.
Study and analysis of oqpsk modulation and demodulation with variable bit pattern and frequency. The only real trick is how to get it into a locked condition, and there are many ways to do that. Qpsk modulation and demodulation in matlab awgn channel. Offset quadrature phase shift keying modulation and demodulation objectives.
The offset qpsk modulation analytic system capable of estimating the initial phase of an offset qpsk modulated signal is disclosed. Ask, fsk, psk, and qam are all forms of digital modulation. For information about delays incurred by modulator demodulator pair processing, see modulation delays. Readers are presented with stepbystep derivations showing the operation of qpsk modulation and demodulation. It covers qpsk, oqpsk and pi4qpsk modulation techniques. Drawback of qpsk modulation application 180 phase changes cause abrupt changes in the signal, resulting in large spectral side lobes. The performance of conventional differential demodulator is not satisfactory.
Phase modulation schemes have been extensively used in the mobile environment. Quaternary phase shift keying qpsk qpsk is the most common form of phaseshift keying. They are widely used based on their unique individual phase transition functionalities compare to one another. In coherent detection technique the knowledge of the carrier frequency and phase must be known to the receiver. When a digitally modulated signal stream input to a power amplifier passes from one symbol through zero towards another symbol, it is like turning it off and on, again and again. Modulation using oqpsk method simulink mathworks espana. The following equation outlines qpsk modulation technique. Demodulation using oqpsk method matlab mathworks italia.
1045 1330 1229 959 561 1472 1453 417 1340 1022 1493 287 840 324 460 1487 1294 1018 969 296 163 1236 357 468 45 208 888 892 1120 1443 165 1182 1169