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Articles by G. Senthilkumar
Total Records ( 3 ) for G. Senthilkumar
  G. Senthilkumar and R. Amutha
  The Multi-Carrier Code Division Multiple Access (MC-CDMA) is a powerful candidate for the current and next generation wireless systems. The adaptive interleaving techniques with limited feedback approach have been analyzed for breaking the interference limitation to further enhance the capacity of MCCDMA systems. When the channel is quantized for reducing the number of Channel State Information (CSI) bits and the processing load, the orthogonality of the user signals cannot be perfectly retained owing to inborn quantization error. This results in Multiple Access Interference (MAI). Hence, a novel codebook based adaptive chip interleaving technique is proposed to obtain the optimum interleaving patterns adaptively according to the propagation conditions for mitigating the MAI. As an alternate to the quantized CSI feedback, an algorithm for the codebook design is developed to create the address of the prestored interleaving patterns based on maximum signal to noise ratio criterion. The simulation result shows that the MCCDMA system using the proposed codebook based adaptive chip interleaving technique achieves significant performance improvement in terms of Bit Error Rate (BER) compared to the conventional MCCDMA system and existing chip interleaving techniques. It also shows that this reduces the quantization error and requires limited number of bits as codebook index for the feedback.
  G. Senthilkumar and R. Amutha
  The Multi-Carrier Code Division Multiple Access (MC-CDMA) is a strong candidate for the future wireless systems to provide high speed packet data and multimedia streaming services. The MCCDMA faces the problem from Multiple Access Interference (MAI) due to failure of orthogonality among the users under the frequency-selective fading channels and multipath effects. In this study, the MCCDMA system is developed by joining with Space-Time Block Coding (STBC) scheme and Multi Input Multi Output (MIMO) scheme for capacity enhancement. Along with STBC and MIMO schemes, Orthogonal Complete Complementary (OCC) spreading codes with suitable cross-correlation properties determine the interference-resist capability as well as spectral efficiency. Further, the mitigation of MAI in MCCDMA systems is approached in different way to minimize the error rates and to improve the spectral efficiency. The constellation movement scheme is proposed for Quadrature Amplitude Modulation (QAM) signal set where the constellation of one of the users is moved relative to the other by an angle chosen adaptively according to the channel conditions which causes MAI in order to satisfy minimum distance threshold at the detectors. The simulation result shows that the developed MCCDMA system achieves significant performance improvement in terms of Bit Error Rate (BER) and spectral efficiency compared to MCCDMA systems with Wash and Gold spreading codes. It also shows that the proposed constellation movement scheme combats MAI further and achieves a significant improvement in user capacity.
  S. Shanmughapriya , G. Senthilkumar , S. Arun , B.C. Das and K. Natarajaseenivasan
  A case-control study to identify the risk factors for ovarian carcinoma in Tiruchirapalli district, Tamilnadu, India a low incidence population was conducted. The invasive epithelial ovarian cancer case patients were 37. The control group consisted of 74 healthy women, matched according to age categories. Subjects were interviewed in person regarding socio demographic and reproductive characteristics. The unconditional logistic regression was performed and tests of statistical significance were based on difference in the log likelihoods and all p values were 2-sided. In logistic regression analysis, the risk of ovarian cancer was strongly related to the increased physical activity (OR: 3.227, 95% CI: 1.143, 9.108), intake of high fat (OR: 6.286, 95% CI: 0.779, 50.701) early age at menarche (OR: 6.389, 95% CI: 2.143, 19.047), post menopausal status (OR: 3.22, 95% CI: 1.417, 7.316). The use of contraceptive methods, tubal ligation, one birth, late menarche was found to be inversely associated with ovarian cancer risk. The risk of ovarian cancer decreased 80% by one birth event, 40% by use of contraceptives and tubal ligation and six times reduced risk for menarche at later age. The present study thus clearly typified this neoplasm as hormone dependent and it is possible to establish that "ovulation" mechanism determine the level of risk for ovarian cancer in this study population. In addition, the difference in the distribution of histologic subtypes in this population compared with high-incidence populations may point to further differences in risk factors.
 
 
 
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