Jean-Yves Chouinard

Estimation of Gilbert's and Fritchman's models parameters using the gradient method for digital mobile radio channels

A series of error sequence measurements in a typical mobile radio channel has been conducted to study the time distribution of transmission errors. E.N. Gilberts (1960) and B.D. Fritchmans (1967) digital communication channel models are shown to describe adequately the observed error bursts occurring in the mobile radio channel. An estimation method based on the gradient algorithm is proposed for computing the parameters values of both models from the experimentally derived error distributions. A digital mobile radio channel simulator based on Gilberts and Fritchmans models with the parameter values as estimated using the gradient technique is presented. >

A secure image encryption algorithm based on Rubik's cube principle

In the past few years, several encryption algorithms based on chaotic systems have been proposed as means to protect digital images against cryptographic attacks. These encryption algorithms typically use relatively small key spaces and thus offer limited security, especially if they are one-dimensional. In this paper, we proposed a novel image encryption algorithm based on Rubiks cube principle. The original image is scrambled using the principle of Rubiks cube. Then, XOR operator is applied to rows and columns of the scrambled image using two secret keys. Finally, the experimental results and security analysis show that the proposed image encryption scheme not only can achieve good encryption and perfect hiding ability but also can resist exhaustive attack, statistical attack, and differential attack.

On the design and performance analysis of multisymbol encapsulated OFDM systems

A new multicarrier system, termed multisymbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM), is proposed, in which one cyclic prefix (CP) is used for multiple OFDM symbols. The original motivation for the MSE-OFDM proposal is to reduce the redundancy due to the CP in static-channel environments. The authors then found that an alternative implementation of the system can be used to improve the robustness to frequency offset and reduce the peak-to-average power ratio (PAPR). Equalization and demodulation algorithms for the MSE-OFDM system are proposed. A new preamble and the corresponding frequency-offset and channel estimation techniques are studied for the MSE-OFDM system. Using the proposed MSE-OFDM preamble, the joint maximum likelihood (ML) estimation of the frequency offset and the channel impulse response (CIR) is investigated in this paper. Possible ways to reduce the joint estimation complexity, including exploitation of the preamble structure, approximation of the joint ML estimator, and fast Fourier transform (FFT) pruning, are discussed. The performance of the proposed MSE-OFDM systems and channel estimators are analyzed and verified through numerical simulations. An analysis on the bandwidth efficiency, the performance with frequency offset, and the PAPR of the MSE-OFDM system are also presented

Statistical modeling of the received signal envelope in a mobile radio channel

Propagation loss measurements taken in the Ottawa region in the 900-MHz frequency band are reported and discussed. Significant statistical parameters for a mobile radio channel, such as the mean, the standard deviation of the signals, the level crossing rates and the fading distance, are presented. The signal is first transformed from a time scale to a distance scale; it is then separated into slow and rapid variation components, a low-pass filter with a cutoff point corresponding to 0.125 cycle per wavelength being used to estimate the slow variation component. The statistical analysis of the rapid variation is related to the Rice probability law and to a direct-component-to-multipath-component ratio. For the medium-density urban area under consideration, this ratio is shown to change from around 5 dB to around 9 dB as one moves from medium-density urban to the surrounding open areas. >

Efficient Non-Pilot-Aided Channel Length Estimation for Digital Broadcasting Receivers

Channel estimation and equalization techniques are crucial for the ubiquitous broadcasting systems. Conventional receivers for most broadcasting or wireless standards preset the channel length to the maximal expected duration of the channel impulse response for the adopted channel estimation and equalization algorithms. The excessive channel length often significantly increases the implementational complexity of the wireless receivers and leads to the redundant information which would induce the additional estimation errors. Moreover, such a scheme does not allow the dynamic memory allocation for variable channel lengths. This could further increase the power consumption and reduce the battery life of a mobile device. The knowledge of the actual channel length would, in principle, help the system designers decrease the complexity of the channel estimators using maximum likelihood (ML) and minimum-mean-square-error (MMSE) algorithms. In this paper, we address this important channel length estimation problem and propose a novel autocorrelation-based algorithm to estimate the channel length without the need of pilots or training sequence. The associated threshold for the channel length estimation depends on the sample size, the signal-to-noise ratio and the leading/last channel coefficients. In addition, we provide the mean-square analysis on the effectiveness of the proposed non-pilot-aided channel length estimator through Monte Carlo simulations.

Robust data transmission using the transmitter identification sequences in ATSC DTV signals

Transmitter identification (TxID, or transmitter fingerprinting) technique is used to detect, diagnose and classify the operating status of radio transmitters. Due to an ever-increasing number of transmitters, the need for transmitter identification is becoming an urgent issue, since it enables the broadcast authorities and operators to identify the source of interference. As a result, transmitter identification has been recognized as an important feature in the ATSC synchronization standard for distributed transmission. A new robust data transmission technique using the transmitter identification (TxID) sequences in the digital TV (DTV) signals is proposed in this paper. The major advantage of this low data transmission system is its robustness and extremely large coverage. The principle of the proposed data transmission system is presented. The modulation technique and throughput of the data transmission system is also evaluated.

A new position location system using DTV transmitter identification watermark signals

A new position location technique using the transmitter identification (TxID) RF watermark in the digital TV (DTV) signals is proposed in this paper. Conventional global positioning system (GPS) usually does not work well inside buildings due to the high frequency and weak field strength of the signal. In contrast to the GPS, the DTV signals are received from transmitters at relatively short distance, while the broadcast transmitters operate at levels up to the megawatts effective radiated power (ERP). Also the RF frequency of the DTV signal is much lower than the GPS, which makes it easier for the signal to penetrate buildings and other objects. The proposed position location system based on DTV TxID signal is presented in this paper. Practical receiver implementation issues including nonideal correlation and synchronization are analyzed and discussed. Performance of the proposed technique is evaluated through Monte Carlo simulations and compared with other existing position location systems. Possible ways to improve the accuracy of the new position location system is discussed.

Eigendecomposition of the multi-channel covariance matrix with applications to SAR-GMTI

This paper investigates ground moving target indication using a multiaperture synthetic aperture radar. Target detectors based on an eigendecomposition of the multi-channel covariance matrix are presented. Comparisons of the proposed detectors with classical methods, such as displaced phase centre antenna, or along track interferometry, show increased capability in heterogeneous terrain. By decomposing the complex Wishart probability distribution of the sample covariance matrix into probability distributions of the eigenvalues and eigenvectors, we calculate the probability of moving target detection vs. the signal to clutter plus noise ratio for a fixed false alarm rate in homogeneous and heterogeneous terrain. The probability distributions allow implementation of a constant false alarm rate detector. The complete analysis is presented for a two-channel system.

Noncoherent diversity reception over Nakagami-fading channels

A method for computing the average bit-error probability of binary differential phase-shift keying (DPSK) and frequency shift-keying (FSK) signals transmitted over Nakagami asymptotically slow fading channels with postdetection diversity reception is presented to extend previously published results. The previously published results apply only for maximum ratio combining, i.e., with predetection combining, where phase coherency is necessary. The results for postdetection combining are derived with the explicit expressions for the most practical cases of independent channels and particular cases of correlated channels.

Physical Layer Authentication for Mobile Systems with Time-Varying Carrier Frequency Offsets

A novel physical layer authentication scheme is proposed in this paper by exploiting the time-varying carrier frequency offset (CFO) associated with each pair of wireless communications devices. In realistic scenarios, radio frequency oscillators in each transmitter-and-receiver pair always present device-dependent biases to the nominal oscillating frequency. The combination of these biases and mobility-induced Doppler shift, characterized as a time-varying CFO, can be used as a radiometric signature for wireless device authentication. In the proposed authentication scheme, the variable CFO values at different communication times are first estimated. Kalman filtering is then employed to predict the current value by tracking the past CFO variation, which is modeled as an autoregressive random process. To achieve the proposed authentication, the current CFO estimate is compared with the Kalman predicted CFO using hypothesis testing to determine whether the signal has followed a consistent CFO pattern. An adaptive CFO variation threshold is derived for device discrimination according to the signal-to-noise ratio and the Kalman prediction error. In addition, a software-defined radio (SDR) based prototype platform has been developed to validate the feasibility of using CFO for authentication. Simulation results further confirm the effectiveness of the proposed scheme in multipath fading channels.