Digital Signal Processing

S. K. Padmanabhan ¹, T. Jayachandra Prasad ²

Affiliations
1 Sathyabama University, Chennai, IN
2 Rajeev Gandhi Memorial College of Engineering and Technology, Andhra Pradesh, IN

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) has emerged as very popular wireless transmission technique in which digital data bits are transmitted at a high speed in a radio environment. But the high peak-to-average power ratio (PAPR) is the major setback for OFDM systems demanding expensive linear amplifiers with wide dynamic range. In this article, we introduce adaptive Signal clipping has been suggested as an effective peak-to-average power ratio (PAPR) reduction scheme for orthogonal frequency-division multiplexing (OFDM).In this paper we use fast average algorithm for adaptive clipping. There are several schemes to reduce PAPR, in our architecture we introduce an adaptive clipping method. In adaptive clipping block, the threshold is dynamically fixed from the average values of the peaks. The computational tradeoff is leveraged by using fast average algorithm. Our architecture also includes a LDPC encoder which also contributes in reduction of PAPR. The architecture is implemented using Simulink. The measured results of the architecture shows an exponential decrease in PAPR.

Keywords

OFDM, PAPR.

Full Text

     

B. D. Venkatramana Reddy ¹, T. Jayachandra Prasad ²

Affiliations
1 Department of Electronics and Communication Engineering, Madanapalle Institute of Technology & Science, Madanapalle-517325, A.P, IN
2 Department of Electronics and Communication Engineering, RGM College of Engineering & Technology, Nandyal-518501, A.P, IN

Abstract

Watermarks can be embedded in the pixel domain or a transform domain. Discrete Fourier Transform (DFT), Discrete Cosine Transform (DCT), Discrete Wavelet Transform (DWT) and Singular Value Decomposition (SVD) have been used as mathematical tools for embedding data into an image. In this paper, we present a new robust hybrid watermarking scheme for colour images based on Quaternion Fourier Transform (QFT) and Quaternion Singular Value Decomposition (QSVD). After applying the QFT to the cover image, we map the QFT coefficients into four quadrants, and apply the QSVD to each quadrant. The singular values in each quadrant are then modified by the singular values of the QFT-transformed visual watermark. The quality of the watermarked image and extracted watermark is measured using peak signal to noise ratio (PSNR) and normalized correlation (NC) respectively. Robustness of proposed algorithm is tested for various attacks. We assume that the size of the visual watermark is one quarter of the size of the image.

Keywords

Quaternion Fourier Transform, Quaternion Singular Value Decomposition, Singular Values, Watermark Embedding.

Full Text