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135IMPLEMENTATION AND ANALYSIS BASED ON MIMO-OFDM IN TIME-VARYING CHANNELS USING IMAGE DENOISING: REVIEW
Uma Shankar Sharma
M.Tech (Digital Communication), RKDF College of Engineering, Bhopal Prof. Satyarth Tiwari
Dept. of Electronics Engineering, RKDF College of Engineering, Bhopal
Abstract - In the present correspondence world we are having uncommon changes in the organization identified with OFDM framework An OFDM framework manages various channels over which data are sent at various frequencies to gloat up transmission capacity effectiveness. In OFDM framework, a high-information rate channel can be isolated into number of N number of low information rate sub channels and every last sub direct can be balanced in various and differed sub-bearer. Those low information rate sub channels have band width not as much as that the lucidness transmission capacity of the channel. In an OFDM domain the info bit can be multiplexed into number of N image, every last with image time of T, and every image stream can be utilized to regulate the parallel sub bearers During correspondence an additional undesirable clam or signals run over with genuine flag because of any reason In this venture we have managed these commotion called AWGN in which at the recipient side Bit blunder rate is enhanced to recoup genuine picture that was sent from transmitter to beneficiary to accomplish this we have experienced different balance methods, for example, QAM BPSK QPSK and so forth These procedures were utilized for sound or video motions in OFDM however in this venture it has been accomplished for picture handling to recuperate unique picture Along with this IFFT and FFT channels are utilized at the transmitter and at the less than desirable end of OFDM framework.
1 INTRODUCTION
Remote correspondence norms which are being used and being worked on, receive or consider embracing orthogonal recurrence division multiplexing (OFDM) as new tweak strategy. OFDM has turned out to be conclusive adjustment conspire in future remote correspondence frameworks. For better methods for living has been instrumental in propelling human development. Correspondence administrations are accessible whenever and place free individuals from the restriction of being connected to specific gadgets. These days, on account of the advance in remote innovation, reasonable remote correspondence benefit has turned into a reality. Cell phones made individuals agreeable at whatever point and wherever they need. Advanced sound and video broadcasting gives buyers high- determination, better-quality and intuitive projects. The gadgets are thin, light, little and modest in their frame. keen cell phones are fit for media and broadband web get to are being appeared on the racks. Many tasks considering remote systems with variable degrees of scope are in the procedures. They will make remote access to web spine from, either inside or
outside and in country or metropolitan territories. In this, their development and future advance will be seen. The imperative part that the orthogonal recurrence division multiplexing (OFDM) procedure utilized as a part of remote correspondence frameworks will turn out to be clear. Presently, a great many people satisfy the requirement for data and stimulation through sound and video broadcasting. The introduction of AM radio can be seen to the mid twentieth century, while simple TV programs were first communicate in the Second World War. In center of twentieth century, FM radio projects were accessible. These innovation, were on simple correspondence, brought news, music, show, motion pictures and substantially more into our lives. To provide more programs, digital broadcasting techniques, such as digital audio broadcasting (DAB) and digital video broadcasting (DVB),, started to substitute the simple telecom innovations in the previous quite a long while.DAB is among the initial standards that use the OFDM technique. The DAB project began inmid- 1980 on OFDM, DAB has one benefit: a
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136 single-frequency network (SFN). In asingle frequency broadcasting network, one carrier frequency can be taken for all transmitters to broadcast the same radio program in the country without co- channel interference. But in the FM system, one out of approximately 15 possible frequencies can be utilized, resulting in an inefficient range off frequency-use factor of 15. A single- frequency network and a multi-frequency network. In the DAB system, it is not important to go for radio stations as with AM/FM radios. The programs of all radio stations are combined in multiplexes.
Multiplexes save maintenance cost of radio stations. On the other hand, variable bandwidths can be provided to each programmer, fulfilling their related demands for good quality. Music radio multiplexes can be transmitted at a rate which is up to the highest-quality192 Kbps, on the other hand mono talk and news programs use only 80 Kbps.
Moreover, the DAB system features better mobile receiving quality by OFDM technique.
1.1 Age of Modern Wireless Communications
Modern wireless communications is, the fastest growing part of the communications industry. It has gathered the attention of the media and the imagination of the people. Cellular mobile systems have seen outstanding progress over the last decade and there are now two billion users in the globe. Really, mobile phones have become a important trading tool and part of our life in most developed countries, and are supplanting antiquated wire line systems in developing countries. Modern wireless local area networks now replace wired networks in different houses, businesses, and campuses. Many modern applications, which have wireless sensor networks, automatic highways and industries, smart homes and appliances, and distanced telemedicine, are from research ideas to solid systems. Past of wireless communications the initial wireless networks were developed before-industrial age. These systems sent information over line-of-sight distances (later improved by telescopes) taking smoke signals, torch signaling, flashing mirrors, signal flares,
or semaphore flags etc. A set of signal combinations were developed to send complex messages along rudimentary form of signals. Different observation stations were set up on hilltops and along the roads to relay these messages over very large distances. These new communication networks were substituted first by the telegraph network (invented by Samuel Morse in 1838) and later by the telephone. After 1895, in a few decades the telephones were invented.
2 LITERATURE SURVEY
In [1] Patrick at.al. (2012). The different sources of errors in synchronizing an OFDM system have been proposed and their impact on the demodulated information symbol in the receiver has been investigated.
In [2] H. Meng, Y. L. Guan at.al coding Spreading, etc. an easy way is clipping but it provide degradation BER and distort the signal. Some more techniques are far better techniques than this but they need more information, so the transmission rate comes down. on reducing AWGN, other aspect like complexity, transmission rate, BER, error correction etc. also is taken into consideration.
In [3] G. Avril, M. Tlich, at.al have done lots of work and researches on efficient OFDM transmission and AWGN reduction. It is worth mentioning that understanding the impulsive noise characteristics of electrical devices individually is essential from the communication aspect. In this respect, some results on noise characteristics of different electrical appliances They have proposed, some of them established various techniques to reduce the AWGN.
Other uses various schemes to create efficient sequences to minimize the AWGN to minimum level with better error correction and reduced BER.
In [4] E.Yavuz, have performed a great work in the field of creating best Golay complementary sequences. Nothing in above has implemented the generated Golay sequences with MATLAB to give view of the actual performance of the OFDM system.
In [5] C. E. Shannon et.al. The fundamental problem of communication is that of reproducing at one point either
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137 exactly or approximately a messageselected at another point. Frequently the messages have meaning; that is they refer to or are correlated according to some system with certain physical or conceptual entities. These semantic aspects of communication are irrelevant to the engineering problem. The significant aspect is that the actual message is one selected from a set of possible messages. The system must be designed to operate for each possible selection, not just the one which will actually be chosen since this is unknown at the time of design. If the number of messages in the set is finite then this number or any monotonic function of this number can be regarded as a measure of the information produced when one message is chosen from the set, all choices being equally likely. As was pointed out by Hartley the most natural choice is the logarithmic function. In the case of a discrete source of information we were able to determine a definite rate of generating information, namely the entropy of the underlying stochastic process. With a continuous source the situation is considerably more involved. In the first place a continuously variable quantity can assume an infinite number of values and requires, therefore, an infinite number of binary digits for exact specification.
In [6] F. R. P. Cavalcanti and S.
Anderson digital communication systems has been greatly developed in the past few years and offers a high quality of transmission in both wired and wireless communication environments. Coupled with advances in new modulation techniques, Orthogonal Frequency Division Multiplexing (OFDM) is a well- known digital multicarrier communication technique and one of the best methods of digital data transmission over a limited bandwidth.
In [7] A.R.S. et al. proposed Communication involves splitting of the signal to give a number of signals over that frequency range. Each of these signals are individually modulated and transmitted over the channel. At the receiver end, these signals are demodulated and recombined to obtain the original signal.
In [8] J. Isabona, and M. E.
Ekpenyong OFDM is a method that permits the transmission of high data rates over extremely hostile channels at a comparable complexity. OFDM‟s spread spectrum technique distributes data over a large number of carriers that are spaced apart at precise frequencies. The spacing provides the “orthogonality” in this technique which prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM are high data link, resiliency to Radio Frequency (RF) interference and low multipath distortion. Throughput is a key measure of the quality of a wireless link.
It is defined as the data rate successfully received without error per second and we would naturally prefer that this quantity be as high as possible. OFDM is a promising technique that would satisfy the demands of the next generation of wireless data communication. This technique will improve the quality of data transmission link. This research studied the effect of the different parameters as they affect data quality during transmission with respect to the channel being used. A generic throughput model was also proposed for this technique.
In [9] M. Noh, and H. Park at.al and M. Ergen The LS estimation is the simplest channel estimation. This algorithm has lower complexity. However, it has larger mean square error (MSE) and easily influenced by noise and inters- carrier interference. Linear minimum mean square error (LMMSE) algorithm.
In [10] Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique, which divides the bandwidth into many carriers; each one is modulated by a low rate data stream. In term of multiple access technique, OFDM is similar to FDMA in that the multiple user access is achieved by subdividing the available bandwidth into multiple channels that are then allocated to users. However, OFDM uses the spectrum much more efficiently by spacing the channels much closer together. This is achieved by making all the carriers orthogonal to one another, preventing interference between the closely spaced carriers.
In [11]Yen. Dan Raphaeli at.al and L. Hanzo,e t.al established bounds on the
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138 region of desired triples (R, d, AWGN (C))where R is the code rate and (d) is the minimum Eucli dean distance of the code.
They proved a lower bound on AWGN in terms of R and (d) and show that there exist asymptotically good codes whose modulation (modification) is at most 8 log n. They show explicit constructions of error-correcting codes with minimum AWGN.
In [12] L. Hanzo, L-L.Yang, E- L.Kuan and K. Yen presented a flexible broadband mobile wireless communication system based on FH/MC DS-CDMA and reviewed a variety of existing as well as a range of forthcoming techniques, which might be required for developing broadband mobile wireless systems exhibiting a high flexibility and high communications efficiency. We argued that this broadband FH/MC DS- CDMA system exhibits a high grade of compatibility with the existing CDMA based systems, since it is capable of incorporating a wide range of techniques developed for the 2nd- and 3rd-generation mobile systems. At the time of writing research is well under way towards the SDR-based implementation of a range of existing systems. It is expected that these efforts will soon encompass a generic scheme not too different from the FH/MC DS-CDMA scheme advocated here.
In [13] T. Pollet.at.al discussed the following: the common technique of parallel transmission on many carriers;
the performance that can also be achieved on an undistorted channel; algorithms for gaining that performance; interacting with channel impairments; modification of the performance through coding; and methods of working section.
In [14] H. Nikola and R. Prasad the equalization of the received OFDM signal in frequency domain which is given gained by the assumption that the channel impulse response is changing in a linear fashion during a block period and compensate or fulfilled for the ICI terms that affect the bit-error rate (BER) performance.
In [15] Wei Chen, technique can be used in which SyQuest function is used to mitigate AWGN. Which has the probability conserves the peak power for the OFDM system. The coding may be adaptive in case there is unconsumed" guard interval
and peak power that exploits the samples in this region to mitigate additive noise and AWGN effect.
In [16] Chang R. W. theory for cancel the effect of AWGN. In PTS, one data symbol modulates onto the next sub carrier with predefined weighting coefficients. By doing so, the PAPR signals generated within a group can be each other and canceled out AWGN in.
In [17] OFDM spectrum the sub carriers consist of a main lobe followed by reducing amplitude side lobes. There is no interference among the sub carrier as long as orthogonally is maintained, because at the peak of every sub carrier there exist a spectral null. Frequency offset leads to loss of orthogonally because the spectral null does not coincide of the individual carrier‟s peak.
In [18]R. R. Mosier and R.G.
Clabaugh for reduction of AWGN,PAPR &
ICI power from OFDM system Coded OFDM was proposed in which the frequency separation between adjacent sub carriers is increases. In order to realize this goal firstly, two adjacent sub- carriers are paired as a group; then, jointly code data information in them.
After coding, only one of the two sub- carriers in that pair is transmit over each OFDM symbol interval. As in the coded OFDM system, only half sub-carriers are used for information transmission.
In [19] propose a 32-point FFT &
IFFT design for communication application like OFDM. The main objective of proposed architecture is to design efficient multiplication of FFT & IFFT using Vedic multiplication. It has numerous advantages such as: increase the speed, efficient timing, and better resource utilization parameter. In summary, speeds performance of our design easily satisfies most application requirements based on OFDM modulated wireless communication system.
2.1 Problem Formulation
In this thesis, I have generated the sequences to provide the effective code word for OFDM transmission by using the previous work done by various and used their work to reduce the AWGN to the minimum possible level at no cost of BER and system performance. Also the codes provide the good error correcting
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139 capability. I have shown the simulationresults of the scheme through MATLAB coding. The results show the significant reduction in AWGN with reduced BER and increased system performance.
Although OFDM has some advantages that make it suitable for fading channels, it presents a high AWGN, which is one of the main drawbacks of OFDM systems. A simple technique used to reduce the AWGN of OFDM signals is to clip the signal to a maximum allowed value, at the cost of BER degradation and out-of band radiation without degrading the BER but at the cost of adding extra information.
The goal of this thesis is to select the sequence. The sequences solves the notorious problem of power control in OFDM systems by maintaining a peak-to- mean envelope power ratio at minimum possible level while allowing simple encoding and decoding at high code rates for binary, quaternary or higher-phase signaling together with good error correction. The whole scheme is programmed with MATLAB R201a to show the Simulation Results. The graph generated after simulation shows the reduction in AWGN and Bit error rate in comparison to SNR.
2.2 Simulation Tool
MATLAB (Matrix Laboratory) is a numerical computing environment and fourth-generation programming language.
Developed by Math works, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages, including C, C++, Java, and FORTRAN.
MATLAB R2013a version is used for simulation purpose. The communication toolbox in MATLAB is used for calculating BER under deferent modulation schemes and optimization toolbox is used for maximize the function which is based on Trust-region algorithm.
Using MATLAB, simulation of OFDM was done with different modulation techniques using TSM technique. The digital modulation schemes such as QAM were selected to assess the performance of the designed OFDM system by finding their bit error rate (BER) for different values of signal to
noise ratio (SNR). In this project, I have focused on the problem of AWGN reduction with standard OFDM system.
Different modulation techniques are considered for PAPR reduction and compared with each other for their performances. I have also briefly discussed OFDM and its advantages and disadvantages.
2.3 Overview of This OFDM Simulation Project
When the simulation proceeds through the OFDM transmitter and communication channel, it pauses and waits for the user to trigger for proceeding to the receiver. The reason for using the last two *mat files is that as soon as the OFDM receiver proceeds, the program will clear all data/variables stored in MATLAB workspace.
Since MATLAB has a built-in function which performs Inverse Fast Fourier Transform, IFFT is opted for the development of this simulation. Six m- files are written to develop this MATLAB program of OFDM simulation. One of them is the main program script file, which is the only file that needs to be run, while other-files will be invoked accordingly. A 512-grayscale bitmap image is required as the source input.
Another bitmap image file will be generated at the end of the simulation as the output. Three MATLAB data storage files (errcalc. mat, OFDM parameters.
mat, and received.mat) are generated during the simulation.(err_calc.mat)is to archive the baseband data before the transmission, and be retrieved at the end of the simulation for the purpose of error calculations.
OFDM parameters matis to archive the parameters initialized at the beginning of the simulation and reserve them for the receiver to use later. In the reality, the receiver would always have these parameters; in this simulation, these parameters are configured by the user at the beginning, so they are passed to the receiver by of dmparameters.matas if being preset in the receiver. Received mat stores the time signal after it travels through the channel, and lets the receiver to read it directly. This is to simulate the real situation in which OFDM receivers have no knowledge of the data except for
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140 the received signal at the exit of thecommunication channel. Simulation runtime for both the transmitter and receiver are measured and shown on MATLAB command screen as a rough measurement of relative data rate.
3 CONCLUSION
This principle aim was achieved by setting and completing number of objectives. The first was to design a basic OFDM modem by using BPSK and the second was to design more comprehensive and decisive OFDM modem for the purpose of simulation. This was followed and taken by investigating the operation of the communication link with respect to the OFDM by utilizing Cyclic Prefix, with the aim of counteracting the effects of delay such as ISI and ICI. The performance related to OFDM modem was examined by taking the AWGN channel. An alternate comparative performance studies were taken by plotting the BER graphs for many simulations for different modulation types, different modulation orders and also different types of channel coding as considered. In addition to this additional analysis was done in order to examine the overall performance related to OFDM modem. It had been initially achieved by using AWGN and later with background noise. At last the complete functioning OFDM modem was examined through the transmission of an image. For this purpose, a high-level technical computing language called MATLAB was introduce for designing and implementing the outlined OFDM communication system.
Table contains the techniques and methods used in the current research, most important results were obtained, one of the best selected techniques and at last some advantages and disadvantages of these techniques. Outcome related to the comparison between different modulation orders to indicate that BPSK is the simplest modulation order to implement, because it offers lower data rates.
This simple modulation order gives out a very good performance in the communication system and it is more robust and resilient in presence of noise and interferences. After BPSK, 4-QAM in comparison to higher order QAM modulation, shown an excellent
performance. However it produced a very similar results to 4-PSK, but a better performance in the system was observed, due to its lower data rates and its robustness in presence of noise.
3.1 Future Work
In the current research, different modulation order and modulation type such as2PSK, 4PSK, 8PSK, 4FSK, 4QAM, 8QAM and 16-QAM were investigated and later compared. For future research, up to the type of data being transmitted, the modulation order and modulation type can dynamically be selected. This would help improving the overall performance, as the most suitable modulation technique for that particular data has been selected. Further research could also be done on the „coding and modulation for communication‟.
Applying the Artificial Neural Network (ANN) to an OFDM system with the aim of improving the performance of the system, have been observed in number of researches and studies This method can therefore be further implemented and applied to different components within the OFDM communication system to improve its performance.
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