40120140503001 2-3

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40120140503001 2-3

  1. 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME 1 PERFORMANCE EVALUATION AND IMAGE TRANSMISSION OVER OFDM SYSTEM Nasheet Fatima Sukanya A Kulkarni EXTC Department, EXTC Department, Sardar Patel Institute of Technology, Sardar Patel Institute of Technology, Andheri West, Mumbai Andheri West, Mumbai ABSTRACT In this paper a scheme is proposed for image transmission over Orthogonal Frequency Division Multiplexing (OFDM) systems using LDPC.As High PAPR overcomes the advantages of OFDM so Trigonometric transforms are used in this scheme for improving the performance of the OFDM systems by reducing the Peak to Average Power Ratio (PAPR) of OFDM signal. SPIHT is used for source coding of images to be transmitted. Then, the transmitted data of each parallel subchannel is modulated by Binary phase Shift Keying (BPSK) modulation because it provides high throughput and best performance when combined with the OFDM. Finally, the modulated data are fed into an IFFT circuit, such that the OFDM signal is generated.In the proposed scheme the transmit data sequence of the OFDM signal after Inverse Fast Fourier Transform (lFFT) is grouped into in- phase and in-quadrature components, then each component is transformed using either the Discrete Cosine Transform (DCT) or the Discrete Sine Transform (DST). The simulation results show that adding the DST to the system reduces the PAPR of OFDM signal more than the DCT. which The simulation results show that adding the DST to the system improves the visual quality of reconstructed image. Keywords: OFDM, PAPR, SPIHT, Trignometric Transforms. 1. INTRODUCTION 1.1 OFDM Orthogonal frequency division Multiplexing (OFDM) has a promising future as a new modulation scheme in many next generation wireless communication systems due to its several significant advantages [2]: INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2014): 7.2836 (Calculated by GISI) www.jifactor.com IJECET © I A E M E
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME 2 1. Robust to multipath fading, intersymbol interference, cochannel interference and impulsive parasitic noise. 2. Lower implementation complexity than the single carrier solution. 3. High bandwidth efficiency The main disadvantage of OFDM is its large PAPR. When N signals are added with the same phase they produce a peak power which is N times the average power. The large peaks at the transmitter occasionally force its amplifier into saturation and result in signal distortion and hence lead to degradation in the system performance. High PAPR requires [4] a linear High Power Amplifier otherwise nonlinear signal distortion occurs and leads to high adjacent channel interference and poor system performance. HPA requires large back off from the peak power to reduce the distortion caused by the nonlinearity of HPA and these results in low power efficiency. High PAPR also causes sophistication of analog to digital converter (ADC) and digital to analog converter (DAC).Thus reduction of PAPR is very crucial in OFDM systems. 1.1.1 PAPR In OFDM systems, total bandwidth is divided into many overlapping orthogonal sub channels, which are transmitted in parallel synchronously[2]. Let A=[A0 A1…..AN-1]T denote an input symbol vector in frequency domain, where Ak is complex data of the kth subcarrier and N is the number of subcarriers. The OFDM signal is generated by summing all the N modulated subcarrriers each of which is separated by 1/NTs in the frequency domain. Here Ts is OFDM symbol duration. A continuous time OFDM signal is represented as (1) A Discrete time OFDM signal obtained by sampling above signal at Nyquist rate is represented as (2) However, the main concept of orthogonality comes from the linear relationship between IFFT and FFT which have been implemented in transmitter and receiver, respectively. Jones goes on to say, "By the use of the Fast Fourier Transform (FFT) algorithm, it can be better because it allows precise control of all those multiple simultaneous frequencies (carriers) used to simultaneously carry many data bits in parallel on different frequencies." 1.1.2 APPLICATIONS OFDM is a promising modulation technique that is considered for adoption by 4G community to provide 10-20 Mbps and at least 2 Mbps in the moving vehicles. Presently OFDM is applied in Digital Television Broadcasting, European digital audio Broadcasting (DAB) and Digital Video Broadcasting (DVB-T), the European telecommunications standard (ETSI) HIPERLAN/2 standard, the IEEE 802.11 a standard for wireless local area networks (WLANs) and IEEE 802.16 standard for wireless metropolitan area networks (WMANs).[2]
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME 3 1.2 SPIHT The SPIHT algorithm has been introduced by Said and Pearlman [7]. It is algorithm based on the wavelet Transform and restricts the necessity of random access to the whole image to small sub images. The success of this algorithm in compression efficiency and simplicity makes it well known as a benchmark for embedded Wavelet image coding. SPIHT displays exceptional characteristics over several properties all at once including: Good image quality with a high PSNR (Peak Signal to Noise Ratio), fast coding and decoding, a fully progressive bit-stream, can be used for lossless compression, may be combined with error protection ability to code for exact bit rate or PSNR, flexibility of code rate and simplicity. 1.3 LDPC Codes LDPC codes have attracted much attention particularly in the field of coding theory. LDPC codes are a class of linear block codes which provide a reliable transmission for coding performance that is very close to the Shannon's limit. A (N, K) LDPC code can be represented by a very sparse parity-check matrix having M rows, N columns and code rate R=K/N, where K=N-M. It was originally invented by Gallager in 1963 [8] and rediscovered by Mackay and Neal recently [9]. LDPC has been adopted as the DVB-S2 standard. The rest of this paper is organized as follows: the system description, the simulation results and finally, the conclusions followed by the relevant references. 2. SYSTEM DESCRIPTION The paper concentrates on two targets reducing the PAPR of the OFDM signal and improving the quality of the reconstructed images. It considers the trigonometric transforms as a way for reducing the PAPR by using the character of the DCT/DST energy focused in the low component. The data of OFDM signal is modulated by IFFT then using DCT/DST, which can reduce the PAPR. At the same time, the proposed method reduces the PAPR greatly and the system has character of low complexity hardware. Fig.1 Image Transmission and Reception System SPIHT Encoding LDPC Encoder S/P Replacement and Inverse Transform Transform and replacement IFFT BPSK Mapping LDPC Decoder BPSK Demapping P/S FFT SPIHT Decoding Add CP Remove CP AWGN Channel
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME 4 2.1 Image Transmission 1. The SPIHT divides the image stream into several layers. 2. Then the image stream is converted to a binary format. 3. Afterwards the information bits are LDPC encoded at the LDPC encoder. 4. The baseband data is BPSK modulated 5. Then, the transmitted data of each parallel sub channel is modulated by Binary phase shift keying (BPSK) modulation because it provides high throughput and best performance when combined with the OFDM. 6. Finally, the modulated data are fed into an IFFT circuit, such that the OFDM signal is generated. This is SystemI. 7. In SystemII and System III the output of IFFT is split into two components in-phase and in- quadrature. And then DCT (SystemII) or DST (SystemIII) is applied. 2.2 AWGN Channel Additive white Gaussian noise (AWGN) is a basic noise model used in information theory to mimic the effect of many random processes that occur in nature. The modifiers denote specific characteristics: • 'Additive' because it is added to any noise that might be intrinsic to the information system. • 'White' refers to idea that it has uniform power across the frequency band for the information system. It is an analogy to the color white which has uniform emissions at all frequencies in the visible spectrum. • 'Gaussian' because it has a normal distribution in the time domain with an average time domain value of zero. 2.3 Image Reception 1. The replacement and inverse transform are then applied to the received samples. 2. OFDM subchannel demodulation is implemented by using a (FFT) then the Parallel-to-Serial (P/S) conversion is implemented. 3. This received OFDM symbols are demodulated at the demodulator. 4. The demodulated bits are decoded with each LDPC encoded block and data bits are restored. These data are converted into image format, such that SPIHT decoding can be performed 2.4 Trigonometric Transformation process The output of IFFT is split into two components in-phase and in-quadrature. And then DCT (SystemII) or DST (SystemIII) is applied to both components, separately. The first half of samples of the in-phase component after the transform (Li) is concatenated with the first half of samples of the in-quadrature component after the transform (Lq) to form the new in-phase component. Similarly, the second half of samples of the in-phase component after the transform (Hi) is concatenated with the second half of samples of the in-quadrature component after the transform (Hq) to form the new in-quadrature component. Finally, the new components are added to produce the OFDM signal. 2.5 Proposed Schemes SystemI: The system which consists of coded OFDM SystemII: The system I with the DCT transforms for the transmitted signal. SystemIII: The system I with the DST transform for the transmitted signal.
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME 5 3. SIMULATION RESULTS 3.1. Performance of OFDM system in terms of PAPR In this section, simulation experiments are carried out to study the transmission of SPIHT coded images on COFDM modified by Trigonometric transforms over AWGN channel. PAPR is given by equation (1). Here x(t) is the OFDM signal and E[.] is the average power [2]. (3) The parameters used in the simulation are: the number of subcarriers of a coded OFDM system (N) is considered to be 1024, and Cyclic Prefix is taken 25% and rate is 0.2.Results are shown in Table1,Table 2 and Table3. Table 1: PAPR with Cyclic Prefix Image Size System1 System2 System3 Lena.bmp (256×256) 13.8344 9.5581 7.6563 Cameraman. Tif (256×256) 13.7139 9.6206 7.8575 Girl.bmp (225×225) 13.7303 8.6907 7.3878 Lighthouse.jpg (768×1024×3) 13.7229 10.2994 7.5498 Table 2: PAPR without Cyclic Prefix Image Size System1 System2 System3 Lena.bmp (256×256) 33.0747 15.2667 13.2011 Cameraman.tif (256×256) 35.3386 15.4356 12.8199 Girl.bmp (225×225) 31.4924 12.1586 11.1857 Lighthouse.jpg (768×1024×3) 36.8342 16.6390 13.7040 3.2 Performance for Image Transmission in terms of PSNR The fidelity of image transmission is measured by the Peak Signal-to-Noise Ratio (PSNR), which is usually expressed in terms of the logarithmic scale. It can be defined as follows: PSNR=101og1o (PEAK2 /MSE) (4) Where, MSE is the mean squared error between the original and the reconstructed image, and Peak is the maximum possible magnitude for a pixel inside the image. The peak value is 255 for an 8 bits/pixel of original Image. Here N is taken as 256.
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME 6 Table 3: PAPR (with Cyclic Prefix) for different values of N Image Size System N=512 N=1024 Lena.bmp (256×256) System1 11.0578 13.8344 System2 5.5279 9.5581 System3 5.1909 7.6563 Cameraman.tif (256×256) System1 11.1146 13.7139 System2 6.2039 9.6206 System3 5.0711 7.8575 Girl.bmp (225×225) System1 11.0761 13.7303 System2 5.7373 8.6907 System3 5.1558 7.3878 Lighthouse.jpg (768×1024×3) System1 11.1163 13.7229 System2 5.9984 10.2994 System3 5.5561 7.5498 Table 4: PSNR for rate=0.2 Image Size System1 System2 System3 Lena.bmp (256×256) 27.6882 27.6882 37.8743 Cameraman.tif (256×256) 26.0853 26.0853 35.4933 Girl.bmp (225×225) 29.4518 29.4518 40.8864 Lighthouse.jpg (768×1024×3) 29.0779 29.0779 38.0979 Linux_256.jpg (256×256×3) 28.1374 28.1374 45.3756 Birds.jpg (800×554×3) 27.8079 27.8079 37.0346 Table 5: PSNR for rate=0.5 Image Size System1 System2 System3 Lena.bmp (256×256) 32.4240 32.4240 37.8743 Cameraman.tif (256×256) 30.4284 30.4284 35.4933 Girl.bmp (225×225) 35.0725 35.0725 40.8864 Lighthouse.jpg (768×1024×3) 33.3792 33.3792 38.0979 Linux_256.jpg (256×256×3) 35.7595 35.7595 45.3756 Birds.jpg (800×554×3) 32.0202 32.0202 37.0346
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 01-07 © IAEME 7 4. CONCLUSION Simulation results are obtained using MATLAB. The results show that PAPR reduction can be achieved by using Cyclic Prefix. Also System II and System III have less PAPR as compared to System I (From Table1 and Table2).Also for high values of N PAPR increases (Table 3). System III is best in terms of PAPR reduction. For SystemI and SystemII PSNR increases with increase in rate. System III gives best PSNR at all rates (refer Table4 and Table5). 5. REFERENCES [1] Naglaa F. Soliman, Abd Alhamid, A. Shaalan, Mohammed M. Fouad.B, “Robust Image Transmission with OFDM over an AWGN channel”, National Radio Science Conference, April, 2011. [2] Dae-Woon Lim, Seok-Joong Heo, and Jong-Seon No, “An Overview of Peak-to-Average Power Ratio Reduction Schemes for OFDM Signals”, Journal of Communications And Networks, Vol. 11, No. 3, pp. 229-239, June 2009. [3] J. Kim and Y. Shin, “An Effective Clipped Companding scheme for PAPR Reduction of OFDM Signals”, Proceedings of the IEEE ICC08, pp. 668-672, 2008. [4] T. Jiang and G. Zhu, “Complement Block Coding for Reduction in Peak-to-Average Power Ratio of OFDM Signals”, IEEE Communications Magazine, Vol. 43, no.9, pp. S17 - S22, Sept. 2005. [5] L. Guan, T. Jiang, D. Qu and Y. Zhou, “Joint Channel Estimation and PTS to Reduce Peak- to-Average Power Ratio in OFDM Systems without Side Information”, IEEE Signal Processing Letters, Vol. 17, No.10, pp. 883-886, October 2010. [6] A.Rushdi and J. Tuqan, “Peak reduction in Trigonometric Based OFDM System", Proceedings in ACSSC 2007, pp. 1747 - 1751, 2007. [7] Said and W. A. Pearlman, “A New, Fast, and Efficient Image Codec Based on Set Partitioning in Hierarchical Trees”, IEEE Transactions on Circuits and systems for video technology, Vol.6, No.3, pp.243-250, June 1996. [8] R.G. Gallager, “Low Density Parity check codes”, IEEE Transactions on Information Theory, Vol. IT-8, pp. 21-28,Jan. 1962. [9] Yuan Yang, Mong-Kai Ku, “LDPC coded OFDM modulation for high spectral efficiency transmission”, Proceedings in ECCSC 2008, pp. 280- 284, July 2008. [10] S.D. Giri and Prof. A.R. Salunke, “OFDM Based Wireless Lan Transmitter”, International Journal of Electronics and Communication Engineering &Technology (IJECET), Volume 4, Issue 2, 2013, pp. 469 - 476, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. [11] K.Muralibabu, Dr. K.Ramanaidu, Dr. S.Padmanabhan and Dr. T.K.Shanthi, “A Novel PAPR Reduction Scheme using Discrete Cosine Transform Based on Subcarrier Grouping in OFDM System”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 3, Issue 3, 2012, pp. 251 - 257, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. [12] Ashok Kumar Kajla, Rupesh Sharma, Yash Walia and Sukoon Mishra, “Improve Peak To Average Power Ratio (PAPR) Reduction Techniques in OFDM System”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 4, Issue 7, 2013, pp. 28 - 35, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

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