K. Deergha Rao

Mitigation of UWB Signals Spectral Leakage to the GPS L1 Band via Filtering After Clipping in the UWB Transmitter

Abstract Ultra-wideband (UWB) has recently attracted much attention as an indoor short-range high-speed wireless communication. However, the high peak-to-average power ratio (PAPR) limits its capacity due to distortion caused by nonlinear components such as high-power amplifiers. Hence it is necessary to reduce the PAPR of UWB signals. Deliberate clipping is a simple technique for PAPR reduction. But PAPR reduction of UWB signals by clipping may cause spectral leakage. The spectral power leakage to outside frequency bands causes interference with the other systems operating in the vicinity of UWB. Global Positioning System (GPS) has a pivotal role in so many critical systems upon which the public depends for its safety and well-being, and thus it is necessary to assess the interference to the GPS band due to UWB signals spectral leakage. Therefore, in this paper, the interference to the GPS caused by spectral leakage of clipped direct-sequence UWB (DS-UWB) signals and multiband orthogonal frequency division multiplexing UWB (MB-OFDM UWB) signals is assessed, and the effect of filtering after clipping on the spectral leakage is evaluated using power spectral density (PSD) and bit-error rate (BER) as performance measures.

HYPERCHAOS BASED IMAGE ENCRYPTION

Chaos based encryption may offer new quality in secure data transmission. A recently proposed Chaotic-Key Based Algorithm (CKBA) has been shown to be unavoidably susceptible to chosen/known-plaintext attacks and ciphertext-only attacks. In this paper, Hyper Chaotic-Key Based Algorithm (HCKBA) using hyper chaos is proposed to enhance the security of CKBA. The enhanced security of the proposed algorithm is analyzed through cryptanalysis. Further, VLSI architecture of the proposed algorithm is designed. The VLSI architecture is implemented on an image using XILINXs ModelSim to demonstrate the effectiveness of the proposed scheme.

Effect of PAPR Reduction Techniques on the Performance of MB-OFDM UWB in Wireless Communications

Abstract Multiband orthogonal frequency division multiplexing (MB-OFDM) is an efficient approach for ultra-wideband (UWB) wireless communication applications. One major difficulty of MB-OFDM UWB signal is its large peak-to-average power Ratio (PAPR). The high PAPR limits its capacity due to the distortion caused by the nonlinear characteristics of both the analog-to-digital converter (ADC) and high-power amplifier (HPA). Hence, it is necessary to reduce the PAPR of MB-OFDM UWB signals. Several techniques have been reported in the literature for PAPR reduction in OFDM. These techniques can also be extended for PAPR reduction in MB-OFDM UWB signals. However, comparative performance evaluation of these techniques for PAPR reduction in MB-OFDM UWB signals is lacking in the literature. Hence, in this paper, four techniques, namely, filtering after clipping, turbo coding of clipped signals, tunable predistorter, and active constellation extension are extended for PAPR reduction of MB-OFDM UWB signals and their performance is evaluated and compared through computer simulations. In this evaluation, the bit-error rate (BER) is used as the performance measure.

A New and Secure Cryptosystem for Image Encryption and Decryption

Abstract Illegal data access has become prevalent in wireless and general communication networks. Recently, the use of chaotic signals for secure data transmission has shown significant growth in developing chaotic encryption and decryption algorithms. The application of the Brahmagupta–Bhãskara (BB) equation for encryption is reported in a very recent article. However, a number of chaos-based algorithms are proved to be insecure in the literature. It is also shown in the literature that the BB equation based algorithm can be broken by a low complexity known plaintext attack. Hence, in this paper, a new secure cryptosystem based on the BB equation and chaos is proposed for image encryption and decryption. Cryptanalysis of the proposed cryptosystem is also provided. The efficacy of the proposed cryptosystem is illustrated through implementation results on two images.

Robust Multiuser Detection in Chaotic Communication Systems over Non-gaussian Fading Channels

Abstract In this article, we deal with the problem of robust code division multiple access (CDMA) signal detection in a chaotic communication system transmitting across a Non-gaussian fading channel. Since the performance of robust multiuser detector depends on the selection of M-estimator and the spreading sequences, a new influence function is used to derive an improved robust detector for the problem of data detection in CDMA impulsive fading channels using chaotic spreading. Numerical results show that the proposed robustification offers improved performance over Huber’s minimax detector and outperforms the DPSK decorrelating detector, particularly when the channel is highly impulsive.

Integration of GPS and Baro-Inertial Loop Aided Strapdown INS and Radar Altimeter

This paper presents development of a Kalman filter for optimal combination of GPS, baro-inertial loop aided strapdown INS and radar altimeter data. Simulation results are provided to show the improvement in performance that occurs with an optimal combination of navigation data provided by GPS, INS and radar altimeter.

FPGA implementation of complex multiplier using minimum delay Vedic real multiplier architecture

Complex numbers multiplication is a key arithmetic operation to be performed with high speed and less consumption of power in high performance systems such as wireless communications. Hence, in this paper, two possible architectures are proposed for a Vedic real multiplier based on the URDHVA TIRYAKBHYAM (Vertically and cross wise) sutra of Indian Vedic mathematics and an expression for path delay of an N×N Vedic real multiplier with minimum path delay architecture is developed. Then, architectures of four Vedic real multipliers solution, three Vedic real multipliers solution of complex multiplier are presented. The architecture of Vedic real multiplier with minimum path delay is used in the implementation of complex multiplier. The architectures for the four multiplier solution and three multiplier solution of complex multiplier for 32 × 32 bit complex numbers multiplication are coded in VHDL and implemented through Xilinx ISE 13.4 navigator and Modelsim 5.6. Finally, the results are compared with that of the four and three real multipliers solutions using the conventional Booth and Array multipliers.

A REAL TIME COMPLEX EKF LEARNING ALGORITHM FOR MULTILAYERED NEURAL NETWORKS

The complex backpropagation (BP) algorithm to train the neural networks for complex signals is available in the literature. However, the convergence speed of complex BP is slow. Hence, in this paper, a real time complex extended Kalman filtering (EKF) algorithm which has faster convergence speed than the complex BP algorithm is obtained. An approach using a two step recursion procedure for updating the weights of the complex EKF algorithm has been suggested. Illustrative simulation results are promising and confirm the efficacy of the algorithm.

Improving Performance of an Adaptive Equalizer using EKF Trained Multilayered Neural Networks

In this paper, the Extended Kalman Filtering (EKF) based learning algorithm which has much faster convergence speed than the backpropagation algorithm has been extended for training the neural network used for Adaptive Equalization of communication channel. Further, it has been shown that the bit error rate obtained using the EKF algorithm is much superior to that was obtained with the backpropagation algorithm. But due to its computational intensity, parallel processing of the EKF based learning algorithm is indispensable for real time implementation. Hence, parallel implementation of the EKF based learning algorithm on a network of three transputers has been developed.

Ridge Regression based EKF for GPS Navigation under Bad GDOP Conditions

In this paper, ridge regression based extended Kalman filter (EKF) for accurate GPS navigation solution under bad GDOP conditions (ie high GDOP values) is obtained. The effectiveness of the ridge regression based EKF for GPS navigation solution under bad GDOP conditions is illustrated in respect of a typical simulated trajectory.