Varun Jeoti

PAPR Reduction in OFDM Systems: Zadoff-Chu Matrix Transform Based Pre/Post-Coding Techniques

High Peak to Average Power Ratio (PAPR) is one of the major drawbacks in Orthogonal Frequency Division Multiplexing (OFDM). The high PAPR increases the complexity of Analogue to Digital (A/D) and Digital to Analogue (D/A) converters and also reduces the efficiency of RF High Power Amplifier (HPA). In this paper, we propose two novel PAPR reduction techniques for OFDM systems, Zadoff-Chu matrix Transform (ZCT) precoding based PAPR reduction technique and ZCT postcoding based PAPR reduction technique. Simulation results show that, at clip rate of 10-1, the PAPR of our both proposed systems reduced to 0dB, 3dB, 4.1dB and 4.3dB for M-QAM (where M = 4, 16, 64, 256). Both ZCT precoding and postcoding based OFDM systems are shown better PAPR gain and Bit Error Rate (BER) performance than Walsh Hadamard Transform precoded OFDM (WHT-OFDM) and OFDM conventional.

On Image Encryption: Comparison between AES and a Novel Chaotic Encryption Scheme

In this paper, a novel chaotic image encryption scheme based on multiple chaotic systems, a 2D cat map and S-box, is proposed. The two stages of masking based on multiple PLCMs (m-PLCMs) are performed-once before and once after the substitution by S-Box. The proposed chaotic encryption scheme (CES) is less computationally intensive compared to AES, and is expected to provide the same level of security. The simulation and analysis results show that the chaotic signals are greatly sensitive to the key and the algorithm has a large space of keys. At the same time, the algorithm exhibits good encryption speed (less computations), and better security performance

Front-end estimation of Noise Power and SNR in OFDM systems

In this paper a front-end noise power and SNR estimation method based on one OFDM preamble is proposed and compared with previously published SNR estimators - none of which are front-end estimator. The estimator makes use of two identical halves property of time synchronization preamble used in OFDM systems and relies on autocorrelation of the same. The current estimator is compared with two existing SNR estimators, the Reddy estimator and Subspace based estimator in terms of normalized mean square error (NMSE) and estimated SNR. It is observed that current estimator gives SNR estimates better than Reddy and subspace estimators. The estimator performs SNR estimation at front-end of the receiver unlike all other estimators which perform SNR estimation at back-end of the receiver.

Hybrid chaotic image encryption scheme based on S-box and ciphertext feedback

Multimedia security has become serious issue due to prevalence of multimedia technology and, at the same time, rapid progress and wide acceptance of Internet in our society today. In this paper an image encryption scheme is proposed based on generalized logistic map, AES S-box, ciphertext feedback, piecewise linear chaotic maps. The cryptosystem is based on AES S-box, generalized logistic map and ciphertext feedback. A bank of piecewise linear chaotic maps is used to extract the secret chaotic key stream that is used for masking purpose. The proposed image encryption scheme is less computationally intensive. At the same time, it far excels in security compared to the representative multimedia encryption schemes. The proposed scheme is shown to be secure against differential and linear cryptanalysis.

Cyclostationary feature based multiresolution spectrum sensing approach for DVB-T and wireless microphone signals

The demand for wireless communication has grown remarkably in the last year, consequently raising the problem of spectrum scarcity. In this context, cognitive radio is an emerging technology that aims to overcome that scarcity which is one of the most challenging problems in modern wireless communication. Among its fundamental function, the most important is the spectrum sensing which require precise accuracy and low complexity. Thus, various signal detection methods have been proposed for multiresolution spectrum sensing (MRSS). None of these techniques have been used in a wavelet based cyclostationary feature detector. To achieve that we suggest a cyclostationary feature based MRSS in the context of IEEE 802.22 Wireless Regional Area Network (WRAN) for cognitive radio to classify and identify the primary signal either Digital Video Broadcasting- Terrestrial (DVB-T) or wireless microphone signal. This knowledge of identifying primary signals can help cognitive radio to use fraction of TV band when only a wireless microphone signal is present in the channel. The performance of the proposed scheme is evaluated by probability of correct classification. The result indicates that better performance can be achieved by the proposed scheme especially in a low SNR environment.

On secure OFDM system: Chaos based constellation scrambling

Of late, chaos based cryptography has attracted significant attraction of the researchers due to their simplicity of implementation, complex behavior and extreme sensitivity to initial conditions. In this paper an efficient technique to introduce security at physical (PHY) layer is proposed in 802.11i design to provide security in medium access control. Since it does not emphasize on availability, several denial of service (DoS) attacks are possible. The DoS attacks are easy to mount because management and control frames are unprotected and so are MAC headers. This paper proposes a security scheme at PHY layer by scrambling OFDM constellation symbols to encrypt data transmission to resist against these malicious attacks. The scrambling matrix is based on a key derived from a one dimensional chaotic nonlinear dynamical system using logistc map. The initial condition of the map acting as the derived key is dependent on the external key. The scrambling is completely reversible with the use of appropriate key. However, use of a wrong initial condition even at 4th decimal point produces entirely different sequence resulting in erroneous constellations with equal probability.

Reader to reader anticollision protocols in dense and passive RFID environment

A dense radio frequency identification network, consists of several readers located in close proximity to improve coverage and read rate. In such environment, reader to reader collision (RRC) is a common and inevitable problem. Although a number of algorithms has been proposed to mitigate these collisions, most of them require extra hardware, do not make an effective use of the network resources or they are incompatible with the current standards and regulations. This paper reviews the significant proposals for anti-collision of RFID readers, coordination in passive and dense reader environment (DRE). The short comings and incompatibilities with the state of the art standards like EPCglobal Class-1 Gen-2 are also discussed. Finally, research directions to improve the current RRC approaches are presented.

A Novel Zadoff-Chu Matrix Transform Precoded Interleaved-OFDMA Uplink System for 4G Cellular Systems: Peak to Average Power Ratio Performance

Abstract High Peak to Average Power Ratio (PAPR) is one of the major drawbacks in the Orthogonal Frequency Division Multiple Access (OFDMA) systems. In this paper, we present a novel Zadoff-Chu Matrix Transform (ZCMT) precoding based Interleaved-OFDMA uplink system with improved PAPR for the upcoming 4G cellular systems. The proposed system is based on the precoding of constellation symbols with ZCMT precoder in such a way that the system becomes Constant Envelope OFDMA (CE-OFDMA). The CE-OFDMA signal allows the Radio-Frequency (RF) high power amplifier to operate near its saturation levels, thus maximize the power efficiency. However, even 0 db PAPR or CE-OFDMA systems must contend with pulse shaping to keep out of band radiation low and to meet the transmission spectrum mask requirement. Hence, the PAPR is analyzed with Root Raised Cosine pulse shaping. Simulation results show that proposed system has better PAPR gain than the walsh-hadamard transform (WHT) precoded Interleaved-OFDMA uplink systems and the conventional Interleaved-OFDMA uplink systems.

Cyclostationarity-Based Spectrum Sensing for Analog TV and Wireless Microphone Signals

Spectrum sensing is a vital signal processing task in the cognitive radio systems in order to detect and identify the primary users signals (the licensees). In this paper, we study the performance of cyclostationary features detector as a spectrum sensing technique for IEEE 802.22 Wireless Regional Area Network (WRAN). We propose two algorithms based on cyclostationary features to detect the presence of TV-PAL and wireless microphone signals. These algorithms are evaluated in comparison with energy detector. The results show that the performance of cyclostationarity-based algorithms is superior to energy detector performance especially in the case of noise uncertainty.

Wireless backhaul for broadband communication over Sea

A comprehensive survey of different possible solutions to provide wireless backhaul PTP links for broadband communication over Sea is presented. The main purpose of wireless backhaul network is to provide LongDistance Point-To-Point (PTP) broadband communication. Wireless Backhaul gives a low cost solution for access to remote areas with difficult terrain to install any wired link. Long-range backhaul network with high capacity and reliability is limited to line-of-sight (LOS) distances requiring high antenna towers for further increase in range. A mirror image of WiMax-like system used on land can be envisaged on Sea to provide similar services at even non line-of-sight (NLOS) distances. Satellite communication can also provide large distance coverage for communication over Sea. Tropospheric propagation using evaporation ducts over Sea is also explored for long-range wireless communication over Sea to achieve Trans-horizon NLOS distances. Current work and future challenges regarding backhaul broadband communication over Sea with some proposed solutions are discussed at the end.