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Ijecet 06 10_006

Ijecet 06 10_006

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Ijecet 06 10_006

  1. 1. http://www.iaeme.com/IJECET/index.asp 53 editor@iaeme.com International Journal of Electronics and Communication Engineering & Technology (IJECET) Volume 6, Issue 10, Oct 2015, pp. 53-65, Article ID: IJECET_06_10_006 Available online at http://www.iaeme.com/IJECETissues.asp?JType=IJECET&VType=6&IType=10 ISSN Print: 0976-6464 and ISSN Online: 0976-6472 © IAEME Publication A COMPARATIVE SURVEY ON PAPR REDUCTION TECHNIQUES FOR OFDM PERFORMANCE IMPROVEMENT Rimpi Datta Dept. of Electronics and Communication, Narula Institute of Technology, India Anirban Bhar Dept. of Information Technology, Narula Institute of Technology, India Arpita Barman Santra Dept. of Electronics and Communication, Narula Institute of Technology, India Sohan Ghorai Dept. of Electronics and Communication, Narula Institute of Technology, India ABSTRACT The Orthogonal Frequency Division Multiplexing is one of the modulation techniques widely used in the broadband wireless technology. One of the main problems of this technology is the high peak-to-average power ratio of transmission signal due to the superposition of many subcarriers. This paper presents a comparative studies of peak-to-average power ratio reduction technique, which compares among the selective mapping method, clipping method and Tone reservation techniques for PAPR reduction. The paper presents the performance of these different PAPR reduction techniques and compares it with unreduced PAPR. Key words: PAPR, OFDM, Selective Mapping Algorithm, Clipping, Tone Reservation. Cite this Article: Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai. A Comparative Survey on PAPR Reduction Techniques for OFDM Performance Improvement, International Journal of Electronics and Communication Engineering & Technology, 6(10), 2015, pp. 53-65. http://www.iaeme.com/IJECET/issues.asp?JType=IJECET&VType=6&IType= 10 1. INTRODUCTION Orthogonal Frequency Division Multiplexing (OFDM) scheme is a popular standard for next generation mobile radio communication system [2]. In OFDM system, serial
  2. 2. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai http://www.iaeme.com/IJECET/index.asp 54 editor@iaeme.com data stream is multiplexed into a large number of orthogonal sub-channels producing a bandwidth efficient signal spectrum. As it is robust against multipath fading, the orthogonal frequency division multiplexing system can transmit high-speed data using a number of orthogonal sub-carriers [4]. Various studies show that when OFDM sub- carriers are added with the same phase [4], it produces a high peak to average power ratio (PAPR). PAPR is the ratio between the maximum power of a sample OFDM signal and the average power of that OFDM symbol. High PAPR introduces signal distortion in the nonlinear region of power amplifier and the signal distortion introduces the degradation of bit error rate [2]. Major study has been carried out on effect of PAPR in OFDM and study shows that PAPR depends on the SNR for Channel with signal and noise. The effect has been tested with introducing a Gaussian noise in OFDM system. 1.1. OFDM System OFDM has been developed as the modulation method in the new wireless technologies. It mitigates the serious problem of multipath propagation, which causes massive data errors, and loss of signal in the microwave and UHF spectrum. OFDM is a broadband multicarrier modulation technique that gives very good performance and it is very beneficial over single-carrier modulation methods as it fits better with today’s high-speed data requirements and operation in the UHF and microwave spectrum [1]. The main Features of OFDM systems are processing on the source data, the symbols are modulated onto orthogonal sub-carriers, orthogonally is maintained during channel transmission, Synchronization, Demodulation of the received signal by using FFT, Channel equalization, Decoding and de-interleaving. In the OFDM system, Inverse Fast Fourier Transform/Fast Fourier Transform (IFFT /FFT) algorithms are used in the modulation and demodulation of the signal [6, 3]. The length of the IFFT/FFT vector determines the resistance of the system to errors caused by the multipath channel [6]. OFDM is generated by firstly choosing the spectrum required, based on the input data and modulation scheme used. Each carrier to be produced is assigned some data to transmit. The required amplitude and phase of the carrier is then calculated based on the 3 modulation scheme (typically differential BPSK, QPSK, or QAM) [6, 1]. Then, the IFFT converts this spectrum into a time domain signal. The FFT transforms a cyclic time domain signal into its equivalent frequency spectrum. Finding the equivalent waveform, generated by a sum of orthogonal sinusoidal components, does this. The amplitude and phase of the sinusoidal components represent the frequency spectrum of the time domain signal. OFDM signal has high peak-to-average-power ratio (PAPR) value. Figure 1 OFDM Spectrum
  3. 3. A Comparative Survey on PAPR Reduction Techniques For OFDM Performance Improvement http://www.iaeme.com/IJECET/index.asp 55 editor@iaeme.com 1.2. Peak to Average Power Ratio (PAPR) Let us consider a data block of length N as a vector where N denotes the number of sub-carriers. The duration of a symbol in X is T. Each symbol in X modulates one of a set of subcarriers where { }. The modulation scheme taken either quadrature amplitude modulation (QAM) or quadrature phase shift keying (QPSK) by definition. The subcarriers are orthogonal to each other, that is, , where and NT is the duration of OFDM [8] data block X. The complex envelop of the OFDM signal is expressed as , (1) PAPR is defined as the ratio of the maximum divided by the average power of the signal [4]. Now the PAPR of the signal expressed in (6) can be defined as (2) The effects of PAPR need to be studied for a continuous time OFDM signals, as the cost and power dissipation of the analog components dominated by this factor. Reducing the value of PAPR dramatically increases the performance of OFDM system and reduces the cost of system. However, most existing PAPR tuning methods can only be implemented on discrete time OFDM signals [9]. For better calculation of true PAPR, the OFDM signal samples are obtained by oversampling equation (6) by a factor of L to approximate the PAPR of the true OFDM signals better [9]. The L- times oversampled time domain samples can be obtained by an LN-point inverse discrete fourier transform (IDFT) of the data block with zero padding [8]. It was shown in [7] that is sufficient to get . Therefore, I have considered for my numerical calculation in this paper [9]. One of the major drawbacks of the OFDM system. Drawback is high PAPR (PeakTo Average Power ratio). PAPR means randomly sinusoidal leads occurred during transmission of the OFDM signal. So in this chapter we discuss basics of PAPR, why it is created & what the proposed solution are for reduce it. So as per the introduction of PAPR we can judge that to reduce the PAPR is most important point in the OFDM system. Because of when we are talking about the high speed data communication in real life like video calling, high speed internet access, and also main point is that high speed data access up to 2mbps while moving on the vehicle at 100km/h, digital video broadcasting (DVB), Microwave terrestrial television, Digital audio broadcasting (DAB), 4G system, hyper LAN. So this most type of communication systems required high data rate. But problem occurs like PAPR in OFDM system prevent these types of facilities in the real life. So to reduce it is most important. Various studies show that when OFDM sub-carriers are added with the same phase [2], it produces a high peak to average power ratio (PAPR). PAPR is the ratio between the maximum power of a sample OFDM signal and the average power of that OFDM symbol. High PAPR introduces signal distortion in the nonlinear region of power amplifier and the signal distortion introduces the breakdown of bit error rate [4]. Extensive study has been carried out on effect of PAPR in OFDM system and it shows that PAPR depends on the SNR for Channel with signal and noise. The effects of PAPR need to be studied for a continuous time OFDM signals, as the cost and power dissipation of the analog components dominated by this factor. Reducing the value of PAPR dramatically increases the performance of OFDM
  4. 4. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai http://www.iaeme.com/IJECET/index.asp 56 editor@iaeme.com system and reduces the cost of system. So we want to reduce the PAPR in the OFDM system by using different reduction technique algorithms for PAPR in the OFDM systems and make a comparative analysis of these techniques and want to get OFDM signal with improved higher bit error rate. MATLAB based simulation results are included. 1.3. PAPR Reduction Techniques Researchers have been proposed several PAPR reduction Techniques. These techniques can be divided into two groups. There are signal scrambling techniques and signal distortion techniques. Block coding techniques selected mapping (SLM), partial transmit sequence (PTS) etc. are signal scrambling techniques. Signal distortion techniques are peak windowing, envelope scaling, peak reduction carrier and clipping and filtering. In this paper we discuss about the techniques signal scrambling techniques and signal distortion techniques. 2. LITERATURE REVIEW 2.1. Selective Mapping The SLM technique is developed from the idea of symbol scrambling. In this technique, a set of candidate signals are generated to represent the same information, the signal with lowest PAPR is selected and transmitted. The information about the selection of these candidate signals need to be explicitly transmitted along with the selected signal as side information. Selected mapping needs to transmit the information to the receiver, about the selected signal, as side in formation. If there is an error in the received side information, then it is very difficult for the receiver to recover the information from the transmitted selected signal. That is the reason why a strong protection against transmission errors is needed regarding side information. Once the receiver has these side information then the decoding process is very simple. SLM can be employed for larger number of sub carriers with moderate complexity. The technique uses codes only for PAPR reduction and does not include error correction capabilities of codes. The complexity is increased due to the multiple numbers of IFFT operations. The need for transfer of side information to the receiver without any margin for transmission errors is very crucial under the fading channels. Under such noisy channels, the side information is distorted to result in BER degradation in the OFDM systems. Hence, the side information affected the system performance and its bandwidth efficiency. Figure 2 Transmitter Block Diagram with SLM technique The transmitter side [10] of an OFDM system with SLM technique is shown in figure 1. In the SLM technique, a set of U different, distinct sequences-
  5. 5. A Comparative Survey on PAPR Reduction Techniques For OFDM Performance Improvement http://www.iaeme.com/IJECET/index.asp 57 editor@iaeme.com (0,2π), n=0,1,………N-1, u=1,2,……….U must be defined. At first, the input information is divided into OFDM data block X, which consists of N symbols, by the serial-to parallel (S/P) conversion and then data block X is multiplied carrier wise with each one of the U different phase sequences P(u), resulting in a set of U different OFDM data blocks n=0,1,……..N-1, u=1,2……..U Then all U alternative data blocks are transformed into time domain to get transmit OFDM symbol- The sequence with minimum PAPR is selected for transmission. The receiver block diagram is shown in fig.3. Figure 3 Receiver Block Diagram To recover the data sequence X at the receiver, SLM needs to transmit the information on the selected phase sequence as side information , which results in some loss of transmission efficiency. If each phase sequence is –P(u) n generated as the cyclically shifted version of the previoussequence, the information needed to transmit will be less to reconstruct the data. The BER performance will not be affected due to the presence of this technique because the original information is transformed into a different sequenceand we can rebuild the information from the selected phase sequence itself. 2.2. Clipping The simplest approach for reducing the PAPR of OFDM signals is clipping [11,12]. But this technique comes under the distortion based category. In this technique, the high amplitude peaks of the signal are clipped to a predetermined threshold value which limits the peak envelope of the input signal. Since the clipping is done on the actual information itself, there is a possibility to loose the data. So there will be a trade-off between the clipping and the BER performance. Let x[n] denote the pass band signal and x˛[n] denote the clipped version of x[n],which can be expressed as (3)
  6. 6. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai http://www.iaeme.com/IJECET/index.asp 58 editor@iaeme.com Where A is the pre-specified clipping level. This technique has some drawbacks which causes in band signal distortion, resulting in Bit Error Rate performance degradation. It also causes out-of-band radiation, which imposes out-of-band interference signals to adjacent channels. This out-of-band radiation can be reduced by filtering. This filtering of the clipped signal leads to the peakregrowth. That means the signal after filtering operation may exceed the clipping level specified for the clipping operation. 2.3. Tone Reservation Tone Reservation (TR) is one of the well-known methods for PAPR reduction of Orthogonal Frequency Division Multiplexing (OFDM) systems. In this method some sub carriers are reserved for PAPR reduction and the symbols in these sub carriers are selected such that the PAPR of the OFDM frame is minimized. This technique contains some set of reservation of tones. By using this technique reserved tones can be used to minimize the PAPR. This method is used for multicarrier transmission and also shows the reserving tones to reduce the PAPR. This technique is depend on amount of complexity. When there is number of tones is small reduction in PAPR may represent non negligible samples of available bandwidth. Advantage of this tone reservation is very positive that no process is needed at receiver end. And also do not need to transmit the side information along with the transmitted signal. in this data block is added to the time domain signal to reduce the peak leads. 3. SIMULATION RESULTS Simulation has been performed using MATLAB and compared with various algorithm. 3.1. Selective mapping algorithm Simulation has been performed using MATLAB In selective mapping algorithm as reduction technique for PAPR in OFDM systems, here we consider 16 subcarriers. Here we use phase rotation by multiplying all the subcarriers in the sum by different phases to create a new data vector, not only that but also as we don't know the optimum phases to give the best PAPR we now create more than one vector and then select the optimum value. Now the selector should test the PAPR for the data vectors and select the one with the least PAPR to use in transmission. Here we can see the Performance analysis using selective mapping. Table 1Selective PAPR Comparison Chart for Different PAPR Selection Selective PAPR PAPR Values PAPR 29.2900 PAPR1 22.0610 PAPR2 31.2678 PAPR3 31.3918
  7. 7. A Comparative Survey on PAPR Reduction Techniques For OFDM Performance Improvement http://www.iaeme.com/IJECET/index.asp 59 editor@iaeme.com Figure 4 'PAPR against different phase shifts' 3.2. Clipping and Filtering as a PAPR reduction techniques when OFDM signal pass through power amplifier system the signal distort. The effects of the nonlinear distortions introduced by a High Power Amplifier (HPA) on the system performance are evaluated in terms of the Bit Error Rate (BER). So a need of technique which reduces PAPR and amplitude clipping is one of the techniques used to reduce PAPR .In amplitude clipping, a threshold value of the amplitude set and any subcarrier having the amplitude more than that value is clipped or that subcarrier is filtered to bring out a lower PAPR values. By using this techniques we can investigates the effects of high power amplifier and the channel noise on the OFDM signals and then introduces clipping as a PAPR reduction method to reduce the PAPR effect. Firstly select parameters- QPSK signal constellation having 128 data points, size of each OFDM block-8 and assigns the length of cyclic prefix. Then Generate 1 x 128 vector of random data points, Perform QPSK modulation then perform IFFT for each block. Make the serial stream a matrix where each column represents a pre-OFDM block). Firstly we have to find out the number of columns that will exist after reshaping then secondly Create empty matrix to put the IFFT's data next Operate column wise .After that Compute and append Cyclic Prefix. Append the CP to the existing block to create the actual OFDM block then Convert to serial stream for transmission. Now we get actual OFDM signal. Now by using clipping techniques reduce the PAPR. To show the effect of the PAPR simply we add random complex noise when the power exceeds the avg. value, otherwise it add nothing.
  8. 8. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai http://www.iaeme.com/IJECET/index.asp 60 editor@iaeme.com Figure 5.1 x 128 vector of random data points Figure 6 Transmitted data and phase representation Figure 7 OFDM signal representation
  9. 9. A Comparative Survey on PAPR Reduction Techniques For OFDM Performance Improvement http://www.iaeme.com/IJECET/index.asp 61 editor@iaeme.com Figure 8 Clipped Signal Representation Figure 9 OFDM Signal after High Power Amplifier (HPA) Figure 10 clipped Signal after High Power Amplifier (HPA)
  10. 10. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai http://www.iaeme.com/IJECET/index.asp 62 editor@iaeme.com Figure 11 Received data phase representation Figure 12 Received Data clipped representation 3.3. Tone reservation as PAPR techniques There we use the 12 information subcarriers (BPSK modulated). Now consider the 4 reduction carriers we will map different combinations from them by changing the reduction subcarrier case (positive or negative). Let us dedicate r1,r2,r3 and r4 as peak reduction carriers and transmit on x1:x12 so when x1:x12 summation creates a peak, a combination from r1,r2,r3 and r4 creates an anti-peak but not the exact anti-peak or the output would be a flat signal from which data can be retrieved. Then the total sum should have less peaks, but we have noted that even if it has less peaks but sometimes the value of these peaks are twice the original peaks. So that we must take both criteria into consideration the number of peaks and its values. Now calculate the PAPR.
  11. 11. A Comparative Survey on PAPR Reduction Techniques For OFDM Performance Improvement http://www.iaeme.com/IJECET/index.asp 63 editor@iaeme.com Table 2 Tone Reservation Performance Tone Reservation PAPR PAPR Values PAPR 26.6393 PAPR1 29.2900 PAPR2 25.8413 PAPR3 25.4080 PAPR4 21.6240 PAPR5 21.7348 PAPR6 25.4585 PAPR7 24.3934 PAPR8 23.6455 PAPR9 24.5452 PAPR10 22.8342 PAPR11 26.3100 PAPR12 25.7989 PAPR13 26.0764 PAPR14 23.2783 PAPR15 22.1395 PAPR16 23.4401 Figure 13 Representation of sum with no peak reduction carriers (PRC)
  12. 12. Rimpi Datta, Anirban Bhar, Arpita Barman Santra and Sohan Ghorai http://www.iaeme.com/IJECET/index.asp 64 editor@iaeme.com Figure 14 Sums with no peak Figure 15 Sum with no peak Reduction carriers (PRC) Reduction carriers (PRC) Figure 16 Sum with no Peak reduction Carriers (PRC) 4. CONCLUSION The evaluation of PAPR performance is done by CCDF parameters. In this literature several PAPR reduction technique has been discussed. I found that tone reservation is a good technique for PAPR reduction but it needs side information to receiver to recover original data block that increases algorithmic complexity. Also the above.
  13. 13. A Comparative Survey on PAPR Reduction Techniques For OFDM Performance Improvement http://www.iaeme.com/IJECET/index.asp 65 editor@iaeme.com Also they are less immune to dynamic noise. In future a pre-coder will be combined with a neuro-fuzzy algorithm to reduce time complexity and increase performance. REFERENCES [1] Jiang Tao, Yang Yang, ong Yong-Hua,: Exponential Companding Technique for PAPR Reduction in OFDM Systems, IEEE Transaction on Broadcasting, Vol. 51, No. 2, June 2005, pp 244-248 [2] Yoo Seungsoo, Yoon Seokho, Kim Sun Yong, Song Iickho,: A Novel PAPR Reduction Scheme for OFDM Systems Selective Mapping of Partial Tones (SMOPT), IEEE Transaction on Consumer Electronics, Vol. 52, No. 1, Feb. 2006, pp 40-43 [3] Lim, Dae-Woon., No, Jong-Seon., Lim, Chi-Woo.: A New SLM OFDM Scheme With Low Complexity for PAPR Reduction, IEEE Signal Processing Letters, Vol. 12, No. 2, February 2005, pp 93-96 [4] Lim, Dae-Woon., Heo, Seok-Joong., No, Jong-Seno., Chung, H. : A new PTS OFDM with Low Complexity for PAPR Reduction [5] Kaur Parneet, Singh Ravinder,: Complementary Cumulative Distribution Function for Performance Analysis of OFDM Signals, IOSR Journal of Electronics and Communication Engineering, Vol. 2, No. 5, Oct. 2012, pp 851- 854 [6] Wulich, D.: Definition of Efficient PAPR in OFDM, IEEE Communication Letters, Vol. 9, No. 9, Sept. 2005, pp 832-834 [7] Tellado, J: Peak to Average Ratio Reduction for Multicarrier Modulation, Ph.D. Dissertation, University of Stanford, 1999. [8] Han Seung Hee, Lee Jae Hong,: PAPR Reduction of OFDM Signals Using a Reduced Complexity PTS Technique, IEEE Signal Processing Letters, Vol. 11, No. 11, Nov. 2004, pp 887-890 [9] Jiang Tao, Xiang Weidong, Richardson Paul C, Guo Jinhua, Zhu Guangxi,: PAPR Reduction of OFDM Signals Using Partial Transmit Sequences With Low Computational Complexity, IEEE Transaction on Broadcasting, Vol. 53, No. 3, Sept. 2007, pp 719-724 [10] Wen-Xiang Lin, Jia-Chin Lin, and Yu-Ting Sun, “Modified selective mapping technique for papr reduction in OFDM systems,” 12th International Conference on ITS Telecommunications (ITST), pp. 764–768, 2012 [11] Y.-C.Wang and Z.-Q. Luo, “Optimized iterative clipping and filtering for papr reduction of ofdm signals,” IEEE Transactions on Communications, vol. 59, no. 1, 2011. [12] Wang and C. Tellambura, “A simplified clipping and filtering technique for par reduction in OFDM systems,” IEEE Signal Process. Lett, vol. 12, no. 6, pp. 453– 456, 2005. [11] J. Armstrong, “Peak-to average power reduction for OFDM by repeated clipping and frequency domain filtering”, Electron. Lett, vol. 38, no. 5, pp. 246–247, 2002. [13] Ms. Shraddha R. Waghmare and Prof. Dr. Shripad P. Mohani. A New Approach In Distortionless Techniques For PAPR Reduction In Multicarrier Transmission Systems, International Journal of Electronics and Communication Engineering & Technology, 4(5), 2013, pp. 207 – 213. [14] Ashok Kumar Kajla, Rupesh Sharma, Yash Walia, and Sukoon Mishra. Improve Peak To Average Power Ratio (PAPR) Reduction Techniques In OFDM Systems, International Journal of Electronics and Communication Engineering & Technology, 4(5), 2013, pp. 207 – 213.

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