International Journal of Electronics andJOURNAL OF ELECTRONICS(IJECET), ISSN            INTERNATIONAL Communication Engine...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
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Cooperative partial transmit sequence for papr reduction in space frequency block code mimo ofdm signal

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Cooperative partial transmit sequence for papr reduction in space frequency block code mimo ofdm signal

  1. 1. International Journal of Electronics andJOURNAL OF ELECTRONICS(IJECET), ISSN INTERNATIONAL Communication Engineering & Technology AND0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)ISSN 0976 – 6464(Print)ISSN 0976 – 6472(Online)Volume 3, Issue 2, July- September (2012), pp. 321-327 IJECET© IAEME: www.iaeme.com/ijecet.htmlJournal Impact Factor (2012): 3.5930 (Calculated by GISI) ©IAEMEwww.jifactor.com COOPERATIVE PARTIAL TRANSMIT SEQUENCE FOR PAPR REDUCTION IN SPACE FREQUENCY BLOCK CODE MIMO-OFDM SIGNAL 1 Bharti Rani, 2 Mrs Garima Saini 1 Scholar, M.E, NITTTR, Chandigarh 2 Assistant Prof. ECE, NITTTR, Chandigarh Email id erbharti2@gmail.comABSTRACTOrthogonal frequency division multiplexing (OFDM) is a popular method for high data ratewireless transmission. OFDM is combined with antenna to increase the diversity gain toenhance the system capacity on time-variant and frequency-selective channels, resulting in amultiple-input multiple-output (MIMO) configuration. To better handle fading channel,Space frequency block code (SFBC) MIMO-OFDM is preferred. In this paper spacefrequency block code (SFBC) is used for reducing PAPR using Co-operative partial transmitsequence (Co-PTS).Index Terms: Space frequency block code (SFBC), Multiple-input multiple-output (MIMO),Orthogonal frequency division multiplexing (OFDM), peak-to-average power ratio (PAPR)INTRODUCTIONWith the constant demand of high spectral efficiency and high transmission speed for audio,video and internet applications, MIMO-OFDM has become the most promising technologycombination for present and future wireless communications [1]. MIMO offers spatialdiversity and therefore increase the capacity while OFDM allow systems to work in timevarying or frequency selective environment. Recently, Multiple input multiple output(MIMO) Orthogonal frequency division multiplexing (OFDM) with space frequency blockcode (SFBC) has attracted increasing attention because it is robust to time selective fadingchannels [2]. However, SFBC MIMO-OFDM signal also inherit disadvantages from OFDMtechniques e.g sensitivity to synchronization errors and high peak-to-average power ratio(PAPR).Therefore many PAPR reduction methods have been introduced. 321
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEMEEspecially, the signal scrambling methods such as partial transmit sequence(PTS), selectivemapping, ploy phase interleaving and inversion(PII) ,cross-antenna translation and partialshift sequence method [3,4,5,6,7] .All the PAPR reductions methods have some drawbackssuch as increase in transmit power, high computational complexity, high bit error rate(BER),, reduction in bit transmission rate of the system and high peak-to-average power ratio. In thispaper, a co-operative partial transmit sequence (Co-PTS) is proposed for SFBC MIMO-OFDM signal [8]. In Co-PTS, alternate optimization and spatial sub block circularpermutation are combined. The use of alternate optimization results improvement inperformance for PAPR reduction.OFDM and PAPRIn OFDM modulation, a block of N symbols Xn (n=0,1,2,…N-1) is transmitted in parallel,and each of them modulates a group of N subcarriers fn(n=0,1,2…,N-1). The subcarriers areorthogonal to each other, and fn = n∆f, where ∆f= 1/T and T is the symbol period. Theresulting baseband OFDM signal x(t) can be written as: x(t) = ∑ேିଵ ܺ݊ ݁ ௝ଶగ௡∆௙௧ ௡ୀ଴ 0≤ ‫ݏܶ < ݐ‬ (1)In real implementation, the digital transmission signal may be generated by the Inverse FastFourier Transform (IFFT) in the transmitter and restored by Fast Fourier Transform (FFT) inthe receiver. The PAPR of the OFDM signal can be defined as: ୫ୟ୶ ଴ஸ௡ஸேିଵ{ூ௑௡ூ మ} PAPR(X) =10 ா{ூ௑௡ூ మ } (2)Where E{.} denotes the expectation operation. Because independent phases of subcarriersmay align with each other, OFDM signals often exhibit a high PAPR, and the PAPRincreases proportionally with the number of subcarriers. The complementary cumulativedistribution function (CCDF) is often used to characterize the probability that PAPR of anOFDM signal exceeds a given threshold (PAPR0), which can be expressed asCCDF = Pr(PAPR>PAPR0) (3)SFBC MIMO-OFDM SystemThe SFBC MIMO-OFDM system that employs Alamouti scheme, although is an extension tomore than two transmits antennas [7, 9]. A block diagram of such scheme is shown in Fig 1.A data symbol vector X = [X0, X1, . . . , XN−1] is encoded with space-frequency encoder intotwo vectors X1 and X2, 322
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME TX1 IFFT & CP X S/P Space freq TX2 Encoder IFFT & CP Y ^X P/S Space freq PR & FFT Decoder Fig 1. Block Diagram of SFBC MIMO-OFDM SystemX1 = [X0, -X1*…... XN−2,-X*N-1]X2 = [X1, X0*…... XN−1,-X*N-2] (4)Which are fed to the IFFT Cyclic Prefix (CP) blocks and sent simultaneously from antennasTX1 and TX2, respectively. The demodulated signal at the receiver is then given byY = Λ1X1 + Λ2X2 + Z, (5)After decoding the Y signal we get the signal ^XProposed Co-PTS SchemesIn this paper, a cooperative partial transmit sequence (co-PTS) is proposed with SFBCMIMO-OFDM signal [8, 10]. In cooperative partial transmit sequence (Co-PTS) , alternateoptimisation and spatial sub block circular permutation are combined, where the use ofalternate optimisation results in reducing computational complexity and the use of spatial subblock circular permutation across all the transmitting antenna is able to increase the numberof candidate sequences, which equivalently improves the performance for PAPR reduction. TX1 D/S S/P SFBC SSCP IFFT TX2Fig 2. Proposed Co-PTS with SFBC MIMO-OFDMThe proposed design is shown in Fig 2. Firstly the input sequence is modulated by QPSKmodulation and converting into parallel form. The modulated signal X is coded into twovectors X1(n) and X2(n) by space frequency encoder block and a factor spatial sub-blockcircular permutation (SSCP) & alternate partial transmit sequence are introduced to achievethe modulate PAPR reduction performance.Algorithm:- Step1:- The modulated signal X, X(n) = [X1, X2, X3,………….. XN-1] the frequency domainsequence of OFDM system with N subcarriers 323
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEMEStep2:- The data symbol vector Xv (n) is coded into two vectors X1(n) and X2(n) by spacefrequency encoder block asX1 (n) = [X0(n), −X1*(n),…….., XN−2(n),-X*N-1(n)]X2 (n) = [X1(n), X0*(n),…….., XN−1 (n),-X*N-2(n)]Step3:- To achieve the minimum PAPR, a factor for spatial sub-block circular permutation(SSCP) and alternate optimisation are used.Step4:- All SSCP data block are transformed into time domain to get transmitted symbol orsimply take IFFT of that sequence, Finally, the one signal with the minimum PAPR isselected for transmissionSIMULATIONS AND RESULTSThe complementary cumulative distribution function (CCDF) of the PAPR of OFDM signalswith 128 subcarriers, 4 & 8 sub block and phase weighting factors (±j) & (±1) are used toevaluate the PAPR reduction performance of Co-PTS compared with original OFDM andSFBC MIMO-OFDM Signal. In the following results, 105 random QPSK modulated OFDMsignals are generated for simulation and the oversampling factor L is four. 0 10 co-pts sfbc mimo ofdm sfbc mimo ofdm orignal -1 10 ccdf -2 10 -3 10 -4 10 2 4 6 8 10 12 14 papr(dB) Fig 3. PAPR performance of SFBC MIMO-OFDM signal in case 128 subcarriers, 4 sub block and phase weighting factor ±1 0 10 co-pts sfbc mimo ofdm sfbc mimo ofdm orignal -1 10 ccdf -2 10 -3 10 -4 10 2 4 6 8 10 12 14 papr(dB) Fig 4. PAPR performance of SFBC MIMO-OFDM signal in case 128 subcarriers, 8 sub block and phase weighting factor ±1 324
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME 0 10 co-pts sfbc mimo ofdm sfbc mimo ofdm orignal -1 10 ccdf -2 10 -3 10 -4 10 2 4 6 8 10 12 14 papr(dB) Fig 5. PAPR performance of SFBC MIMO-OFDM signal in case 128 subcarriers, 4 sub block and phase weighting factor ±j 0 10 co-pts sfbc mimo ofdm sfbc mimo ofdm orignal -1 10 ccdf -2 10 -3 10 -4 10 2 4 6 8 10 12 14 papr(dB) Fig 6. PAPR performance of SFBC MIMO-OFDM signal in case 128 subcarriers, 8 sub block and phase weighting factor ±j Table1. Proposed PAPR values of 128 subcarrier for SFBC MIMO-OFDM with Co-PTS Technique S.no Subcarrier Subblock Modulation PAPR 1 128 4 QPSK 4.7dB 2 128 8 QPSK 4.3dB 3 128 4 QPSK 5.8dB 4 128 8 QPSK 6.0dB 325
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME Table 2. Comparison between the various techniques Techniques Parameter Modulation PAPR Type PTS for Subcarrier-128 QAM 6.4dB MIMO-OFDM Sub block-8 PII for SFBC MIMO- Subcarrier-128 QAM 8.2dB OFDM Sub block-16 CAT for SFBC MIMO- Subcarrier-256 QAM 7.5dB OFDM Sub block-4 Partial Shift Sequence Subcarrier-128 QPSK 8.5dB for SFBC MIMO- Sub block-4 OFDM Co-PTS for MIMO- Subcarrier-128 QPSK 7.4dB OFDM Sub block-8 SLM for MIMO-OFDM Subcarrier-128 QPSK 8.6dB Sub block-2It is observed form table 2 that the PAPR ratio in reference literature [3,4,5,6,7] for MIMO-OFDM & SFBC MIMO-OFDM was found large as compared to the proposed table 1. WithSFBC MIMO-OFDM by using Co-PTS technique. Hence, this proposed technique givesbetter result of PAPR approximately 4.7dB with 8 subblock compared to previous techniques.CONCLUSIONThe proposed Co-PTS technique with SFBC MIMO-OFDM signal makes use of alternateoptimisation to reduce peak to average power ratio. At the same time, the number ofcandidate sequences is increased by employing spatial sub block circular permutation, whichimproves PAPR reduction performance equivalently.REFERENCES[1] Helmut Bolcskei, Eth Zurich, “MIMO-OFDM Wireless Systems: Basic, Perspectives, andChallenges”, IEEE transaction on wireless communication, Vol 13, pp31-37, Aug, 2006[2] Sen-Hung Wang; Chih-Peng Li, “A Low-Complexity PAPR Reduction Scheme for SFBCMIMO-OFDM Systems” IEEE transaction on signal processing letters, Vol.16, No.11,pp941-944, 2009.[3] Phetsomphou, D.; Yoshizawa, S.; Miyanaga, Y, “A partial transmit sequence techniquefor papr reduction in MIMO -OFDM Systems” IEEE Conferences on communications andinformation technologies, pp672-676, 2010 , ,[4] Gao Jing Wang Jinkuan Xie Zhibin, “A New concurrent SLM algorithm for STBCMIMO-OFDM System” IEEE Conferences on Intelligent Signal Processing andCommunication Systems, pp132-135, Nov.28-Dec.1, 2007 326
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME [5] Zoran Latinovi´c, Student Member, IEEE, and Yeheskel Bar-Ness, Fellow, IEEE,“SFBC MIMO-OFDM Peak-to-Average Power Ratio Reduction by Polyphase Interleavingand Inversion” IEEE, Communications Letters, Vol.10, No.4, pp266-268, April, 2006[6] Yuan Ouyang, “Peak-to-Average Power Ratio Reduction by Cross-Antenna Translationfor SFBC MIMO-OFDM Systems”IEEE Conference on vehicular technology, Vol.9, No.7,pp592-594, July 2009.[7] Jae Wook Kwon, Sang Kyu Park, “Peak-to-average power ratio reduction by the partialshift sequence methods for space frequency block code ofdm systems” IEEE InternationalConferences on Network Infrastructure and Digital Content,pp890-893, 2009.[8] L. Wang and J. Liu, “Cooperative PTS for PAPR reduction in MIMO-OFDM” IEEEElectronics Letters, Vol. 47, No. 5, pp472-474, March 2011[9] King F. Lee and Douglas B. Williams “A Space-Frequency Transmitter DiversityTechnique for OFDM Systems” IEEE Conferences on Global Telecommunications, Vol.3, pp1473-1477, 2000 [10] A. D. S. Jayalath, C. Tellambura and H. Wu “Reduced complexity PTS and new phasesequence for SLM to reduce PAPR of an OFDM signal” IEEE Conferences on VehicularTechnology,Vol.3,pp 1914 – 1917,2000 327

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