Vikram Karwal

Independently updating the DCT and DST for shifting windowed data

Abstract When processing a signal or an image using the Discrete Cosine Transform (DCT) or Discrete Sine Transform (DST), a typical approach is to extract a portion of the signal by windowing and then form the DCT or DST of the window contents. By shifting the window point by point over the signal, the entire signal may be processed. In this paper we develop algorithms to “update” the DCT and DST to reflect the modified window contents using less computation than by directly evaluating the modified transform via standard Fast Transform algorithms. Our algorithms constitute an improvement over previous DCT/ DST update algorithms because our approach establishes independence between the DCT and the DST: the algorithm for DCT makes use only of DCT terms, and similarly for DST. Algorithms are derived for use without windowing and with split-triangular, Hanning, Hamming and Blackman windows.

Improved Algorithm for ODCT Computation of a Running Data Sequence

Fast windowed update algorithms capable of independently updating the odd discrete cosine transform (ODCT) and odd discrete sine transform (ODST) of a running data sequence are analytically developed. In this algorithm, to compute the ODCT coefficients of a real-time sequence, we do not require the ODST coefficients. Similarly, the ODST coefficients of the shifted sequence can be calculated without using ODCT coefficients. The running input data sequence is sampled using a rectangular window. However, this idea can be easily extended for other windows. The update algorithm derived herein can be used to compute the transform coefficients of the shifted sequence as new data points are available. The complexity of developed algorithm is . The validity of algorithm is tested by MATLAB simulations.

A new windowing function to reduce ICI in OFDM systems

A new transmitter side windowing function to reduce inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems with carrier frequency offset is proposed in this paper. The results show that the proposed method outperforms all the recently proposed windowing functions in the literature in terms of average signal power to average ICI power ratio (SIR), bit error rate (BER) and peak to average power ratio (PAPR).

Joint Overlay-Underlay Optimal Power Allocation in Cognitive Radio

In this paper a novel cognitive radio system model is proposed in which secondary user transmitter (SU-Tx) operates under two modes underlay and overlay, based on the channel sensing information it receives. This is an effort to maximize transmission data rate based on the threshold which decides the mode of operation. In this paper, the resources are utilized efficiently by making them operate in both the modes. It provides the optimal power allocation to the CR user in a way that it should not provide interference to its neighbouring users, specifically the most prioritized primary/licensed users. The performance of each mode is analyzed with attainable ergodic and outage capacity.

Fast windowed update algorithm for ODCT computation

In this paper algorithms capable for independent updating the type-II Odd Discrete Cosine Transform (ODCT-II) and type-II Odd Discrete Sine Transform (ODST-II) coefficients of a real-time windowed data sequence are proposed. The update algorithm is developed for split-triangular windowed input data. This windowing function reduces ringing effect encountered in rectangular windowing function. The computational complexity of developed algorithm is O(N). Proposed algorithm will further reduce the memory requirements significantly as we do not need to compute ODST coefficients while updating ODCT coefficients. These set of algorithms will be useful in applications where we need only the ODCT coefficients or only ODST coefficients. The analytically developed algorithms have been tested by Matlab implementation.

Free space optical communications with distributed switch-and-stay combining

The authors study the performance of an amplify-and-forward dual-hop, switch-and-stay combining receiver, used in free space optical communications over non-identical fading channels. One path is characterised by the generalised Malaga (or M distribution), whereas the other is influenced by the combined effects of Gamma–Gamma distributed atmospheric turbulence, pointing error and path loss. Novel closed-form expressions for the end-to-end moment generating function, probability density function, and cumulative distribution function are derived in terms of Meijers G function. Furthermore, the performance of the system is analysed, and closed-form expressions are presented for the end-to-end outage probability and channel capacity.