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Adaptive notch filters (ANF) are a special case of IIR adaptive filters that are able to track and cancel a time-varying sinusoid or a narrow band interference signal from a broad band signal. These filters update zeros and poles of the notch filters based on an objective function that minimizes the output signal energy. An ANF algorithm can only be used in practical applications if the underlying adaptive algorithm is inherently stable. QR-decomposition algorithms are known for their stability in finite precision environment. A QR-decomposition based adaptive notch filter is introduced and derived which is capable of estimating and canceling multiple narrow band interferers or sinusoids. The simulation results show that the convergence speed of the proposed method is equivalent to the recursive prediction-error (RPE) algorithm. more...

With the widespread use of wireless communication systems, efforts are directed to reduce the human exposure to RF radiation. Multiobjective optimization is becoming essential to achieve satisfactory antenna performance whilst minimizing the radiation level in the human body. A technique based on the genetic algorithm is proposed to optimize a multiobjective function involving weighted goals related to the antenna performance and the near-field radiation pattern inside the human body. Electromagnetic simulation based on FDTD formulation is performed using SEMCAD X. Dispersive material characteristic is chosen for the human head phantom. Results illustrate the enhancement introduced by this technique of antenna design that could be used in multifunction communication systems. more...

This paper presents the realization of the forward automatic censored cell averaging detector (F-ACCAD), a novel CFAR algorithm for detecting targets in log-normal distribution clutter recently published in [1]. The algorithm is realized through an FPGA-based parallel architecture. The timing constraints of high resolution radar applications are considered and satisfied in the system. The sequential nature of the algorithm has been parallelized to achieve the desired processing delay. The intensive statistical calculations and the complexity of the algorithm have been significantly reduced by using lookup tables (LUTs). Batcher's sort, a parallel sorting algorithm, is adopted in this work. The hardware synthesis results and timing analysis are reported at the end. more...

Today, the buzzword is high-data rate wireless connectivity without mobility constraints. The provision of high rates to users, anytime and everywhere is challenged by the time- varying wireless medium and dynamic nature of interference. Primarily, this challenge is directly related to the limited radio resources, spectrum in particular, and energy (i.e., power) to a certain extend. Therefore, a practical resource management method, in the form of power control, that can address system interference and thus improve spectrum utilization is presented. The proposed scheme is tested in a wireless network that employs Orthogonal Frequency Division Multiple Access (OFDMA) tech- nique. The simulated results reveal that a significant improvement in capacity is obtained on top of the conventional water-filling algorithm. Our study is informed by the fact that most current and future wireless networks (e.g., WiMAX, LTE, LTE-advanced) are based on OFDMA technology. more...

In many problems of digital signal processing, it is required to determine a model matching the statistics of a given observation of a generally non-Gaussian random process. Because of the wide range of systems that can be represented by Volterra series and Wiener expansions, the discrete nonlinear second-order Wiener filter (NSWF) driven by white Gaussian noise has been used in this study to match the statistics of a discrete zero-mean stationary non-Gaussian random process. First, we derive the autocorrelation function and show that it does not provide sufficient information necessary for estimating the parameters of the proposed model. Next, we derive the third-order moment sequence and show that it provides additional information that can be used in conjunction with the autocorrelation function to solve the problem. The power spectrum and bispectrum of the discrete NSWF have been also derived. more...

A challenging problem in radar signal processing is to achieve reliable target detection in the presence of interferences. In this paper, we propose a novel algorithm for automatic censoring of radar interfering targets in log-normal clutter. The proposed algorithm, termed the forward automatic censored cell averaging detector (F-ACCAD), consists of two steps: removing the corrupted reference cells (censoring) and the actual detection. Both steps are performed dynamically by using a suitable set of ranked cells to estimate the unknown background level and set the adaptive thresholds accordingly. The F-ACCAD algorithm does not require any prior information about the clutter parameters nor does it require the number of interfering targets. The effectiveness of the F-ACCAD algorithm is assessed by computing, using Monte Carlo simulations, the probability of censoring and the probability of detection in different background environments. more...

In this paper we present hardware realization of a novel Automatic Censored Cell Averaging (ACCA) Constant False Alarm Rate (CFAR) detection algorithm based on Ordered Data Variability (ODV) using Field Programmable Gate Array (FPGA). This algorithm has been recently proposed in the literature for radar target detection in non-homogeneous environments. The unknown background level can be estimated by dynamically selecting a suitable set of ranked reference window cells and by doing successive hypothesis tests. The ACCA-ODV based CFAR detector does not require any prior information about the background environment and uses the variability index statistic as a shape parameter to reject or accept the ordered cells under investigation. Recent advancements in modern FPGAs and availability of sophisticated electronic design tools have made it possible to realize the ACCA-ODV CFAR detector in a cost-effective way. The designed hardware is modular and has been physically realized in Altera Stratix II FPGA device. more...

A computationally efficient procedure for the reconstruction of the impulse response of a (minimum- or nonminimum-phase) linear time-invariant system from its bispectrum is presented. This method is based on computing cepstrum of the impulse response sequence from the omega /sub 1/= omega /sub 2/ slice of the bispectrum. The algorithm can be implemented by using only the one-dimensional fast Fourier transform algorithm. > more...

Fourth-order cross moments are used in modern digital signal processing as a powerful analytical tool for the synthesis and analysis of signals and systems. Computing fourth-order cross moments from incoming time-series data is computationally intensive process and requires fast computing systems and parallel processing techniques to meet the real time processing requirement. An algorithm based on matrix-matrix product formulation is adopted in this paper. This paper presents an FPGA based design for high-speed computation of fourth-order cross moments. The proposed design is coded in VHDL and functionally verified by implementing it on Xilinx Virtex-II Pro FPGA chip. FPGA implementation results are presented. The proposed design operates at a maximum frequency of 101.812 MHz. more...

Higher-order Statistics (HOS), also known as cumulants, cross moments and their frequency domain counterparts have emerged as a powerful signal processing tool for the synthesis and analysis of signals and systems. The computation of higher-order cross moments is a necessary step towards the estimation of other statistics such as the higher-order cumulants and Wigner Spectra. In this paper, we present FPGA based design for the computation of third-order cross moments. The proposed design is coded in VHSIC Hardware Description Language (VHDL) and functionally verified by synthesizing it on Xilinx Spartan-3 XC3S2000FG900-4 FPGA chip. FPGA implementation results are presented. The proposed design operates at a maximum frequency of 86.618 MHz. more...

This paper proposes an adaptive pseudonoise (PN) code acquisition system that adopts smart antennas and a cell averaging constant false alarm rate (CA-CFAR) processor to achieve reliable PN code acquisition in the presence of fading and interference. Hence, the decision threshold is adjusted according to the varying environment in order to improve the detection performance. The performance of the proposed system has been assessed theoretically by deriving closed form expressions for the probability of detection and probability of false alarm. The mean acquisition time is also obtained, and simulation results have been presented to verify the derived theoretical analysis. more...

This paper presents a novel design for real-time histogram equalization based on field programmable gate arrays (FPGAs). The design is implemented using non-conventional schemes to compute the histogram statistics and equalization in parallel. Counters are used in conjunction with a dedicated decoder specially designed for this purpose. The hardware is fast, simple, and flexible with reasonable development cost. The proposed system is implemented using Stratix II family chip type EP2S15F484C3. The maximum clock frequency can reach up to 250 MHz. In this case, the total time required to perform histogram equalization for an image of size 256 /spl times/ 256 is 0.262 ms. more...

This paper introduces a new method to estimating the parameters of a noncausal AR model. This method is based on a new formulation that relates the unknown AR parameters to both second- and higher-order cumulants. A genetic algorithm has been used to solve for the unknown AR parameters by minimizing a nonlinear cost function that is defined in terms of model's output cumulants. more...

Date of Conference: 7-9 June 1993 Conference Name: IEEE Signal Processing Workshop on Higher-Order Statistics, HOST 1993 In this paper, ''least squares'' and recursive methods for simultaneous identification of four nonminimum phase linear, time-invariant FIR systems are presented. The methods utilize the second- and fourth-order cumulants of outputs of the four FIR systems of which the common input is an independent, identically distributed (i.i.d.) non-Gaussian process. The new methods can be extended to the general problem of simultaneous identification of three or more FIR systems by choosing the order of the utilized cumulants to be equal to the number of systems. To illustrate the effectiveness of our methods, two simulation examples are included. more...

In many problems of digital signal processing, it is required to estimate higher-order cumulants of a given process. We present a fast, inexpensive, and unbiased cumulant estimator. This estimator is based on, a polarity scheme. Unbiasedness is achieved by the addition of statistically independent auxiliary noise sources to the input signals. This scheme has the advantage of being computationally efficient in comparison to conventional estimation methods. more...

It has been shown that the narrowband (NB) interference suppression capability of a direct sequence (DS) spread spectrum system can be enhanced considerably by processing the received signal via a subspace based prediction error filter. In this paper, a new interference-suppression method utilizing a subspace-based interpolation error filter is presented. The performance of DS spread spectrum communication systems in the presence of NB interference is studied when linear interpolation filters are employed for the estimation and subsequent suppression of the interference. The advantages of linear interpolation filters over linear prediction filters with an identical number of taps are examined. more...

Decision feedback sequence estimation (DFSE) is a reduced state alternative to maximum likelihood sequence estimation (MLSE). In this paper, we examine the performance of a system composed of a linear pre-filter in conjunction with a DFSE. In addition, we present a new optimization approach for the linear pre-filter. This approach has an advantage over MSE-based approaches in that it takes into account the effects of noise correlation and error distance variations. The performance of the proposed optimization approach is evaluated and compared with several existing optimization techniques. more...

Recently, a new approach to the problem of data detection for communications over band-limited channels with unknown channel-impulse response is proposed (Vaidis and Weber, IEEE Trans. Commun. 46 (February 1998) 232). This approach utilizes the Viterbi algorithm (VA) for maximum-likelihood sequence estimation (MLSE) in a block adaptive technique for simultaneous channel and data estimation. In this paper, a novel computationally efficient modified VA is developed for MLSE in direct sequence (DS) spread spectrum system. The new modified VA is employed in the approach of Vaidis and Weber (1998) for recovering DS spread spectrum signals in the presence of channel distortion and additive Gaussian noise. The simulation results show that the approach of Vaidis and Weber (1998) implemented with the new modified VA achieves lower probability of error and higher speed of convergence. more...

Combined linear-Viterbi equalization (CLVE) is a technique that employs a linear pre-filter in conjunction with the Viterbi algorithm (VA) to mitigate the effects of intersymbol interference. The aim of the linear pre-filter is to shape the original channel impulse response to some shorter desired impulse response (DIR) in order to reduce the complexity of the VA. In this paper, we present a new MSE based approach for optimizing CLVEs. This approach takes advantage of the modifications to the VA which are suitable for channels having coarsely located coefficients. Specifically, the new approach has the flexibility in choosing the positions and optimizing the values of nonzero coefficients of DIR. As a result, it includes the conventional MSE-based approaches as a special case. Simulation results have been presented to illustrate the performance of proposed method. more...

Higher-order statistics or cumulants, and their associated Fourier transforms, have been established as powerful analytical tools in modern signal processing. To achieve real-time performance in estimating cumulants directly from the incoming time-series data, it is necessary to design a VLSI implementable parallel architecture that speeds up the estimation process. This paper presents a computationally efficient VLSI architecture for computing third-order cumulants for two-dimensional signals. Specifically, the third-order cumulants estimation algorithm is first reformulated so that any redundancy due to symmetry properties is eliminated, and the inherently available parallelism is revealed and exploited by a suitable architecture. It is based on a systolic array implementation and exploits parallelism, pipelining, and regular cell structures. The system architecture consists of (3q/sup 2/+9q+2) processing elements (PEs), where q is the maximum lag of third-order cumulant sequence. Performance in terms of speedup and efficiency is evaluated. more...

Cumulants or higher-order statistics have been established as powerful analytical tools in modern signal processing. To estimate cumulants directly from the incoming time-series data in real-time, it is necessary to design a parallel architecture that speeds up the estimation process. This paper describes an efficient VLSI systolic array architecture for computing third-order cumulants for two-dimensional signals. The cumulants estimation algorithm is first reformulated so that any redundancy due to symmetry properties is eliminated. The architecture exploits parallelism, pipelining, and regular cell structures. The architecture, designed with 1.0 /spl mu/ CMOS process, is capable of operating at a speed of 13 MHz. Performance results, in terms of speedup and efficiency, are presented. more...

Next generation elastic optical networks will very likely require dual polarization (DP) optical transmitter with inherent flexibility to dynamically change its baud rate and/or modulation format. We develop a prototype of compact flexible DP M-ary quadrature amplitude modulation (MQAM) optical transmitter and demonstrate its reconfigurability to accommodate baud rates ranging from 8 to 32 Gbaud/s using the same hardware. The prototype has another advantage in that the modulation format can also be dynamically changed from binary phase shift keying up to 64 quadrature amplitude modulation (QAM) for single and DPs, all over a single optical carrier. This allows the generation of variable data rate up to 384-Gb/s over a single wavelength. Experimental results show that for the most challenging setting of DP-64 QAM/32 Gbaud, the worst case values of error vector magnitude and bit error rate are 6.7 and 3×10 −2 , respectively. For less stringent settings, i.e., lower baud rate and/or lower modulation format, forward error correction limit error free transmission is easily obtained. Further results are also reported to demonstrate transmitter flexibility and software definability, by measuring symbol streams showing instantaneous swapping between modulation schemes with a swapping time less than 10 symbols duration, i.e., 0.3 ns. more...

Low earth orbit (LEO) satellite systems allow a broad range of services to be provided using small, lightweight, cellular-like portable telephones. Exploiting LEO satellites to support distress signals for aircrafts, ships and international travelers is explored in the current paper. A multi-service priority-oriented algorithm is proposed for handling voice, data and emergency signals over LEO satellites. The emergency signal is privileged with service priority so that rescue operation can be carried out as soon as possible. The priority mechanism includes channel reservation as well as joining a queue if no free channel is available as long as the request is roaming in the handover area. In addition, a simplified but efficient approach is suggested for locating the object of an imminent danger situation. As LEO satellites are non-geostationary, the visible period of each spot-beam is small. Consequently, a teletraffic model, that accommodates the mobility of spot-beams as well as the resulting handover rate, is developed in order to gauge the performance of the proposed algorithm. Numerical results for access denying and service-dropping rates are presented for nominal system parameters. more...

The utilization of adaptive equalization in the design of atmospheric laser link transceiver architectures that can be used for television and broadcast signal interconnect between the external place of event and the master control room is suggested. At the transmitter side of the proposed transceiver; an array of atmospheric laser sources, digital signal processing, and optical radiators are used to send light waves in free space. At the receiver side, an adaptive finite impulse response least mean square (LMS) equalizer with activity detection guidance (ADG) and tap decoupling (TD) is used to mitigate the effect of channel impairments. The performance of the suggested adaptive equalizer is compared with that of the conventional adaptive equalizer based only on the standard LMS algorithm. The simulation results revealed that the adaptive LMS equalizer with ADG and TD is a promising solution for the inter-symbol interference problem in optical wireless communication systems. more...

Cataloged from PDF version of article. In this paper, recursive and least squares methods for identification of nonminimum phase linear time-invariant (NMP-LTI) FIR systems are developed. The methods utilize the second- and third-order cumulants of the output of the FIR system whose input is an independent, identically distributed (i.i.d.) non-Gaussian process. Since knowledge of the system order is of utmost importance to many system identification algorithms, new procedures for determining the order of an FIR system using only the output cumulants are also presented. To illustrate the effectiveness of our methods, various simulation examples are presented. more...

This paper presents a new adaptive technique for the identification of a linear system driven by white non-Gaussian noise. The system can be a non-minimum phase system. The adaptive identification technique is a least mean-square (LMS) type algorithm and it is obtained by using the higher order correlations of the system output. © 1991 IEEE more...

The problem of modeling of nonGaussian processes generated by linear systems driven by a white nonGaussian process, and nonlinear systems driven by a white Gaussian process is addressed using the Volterra representation of systems. Cumulant-based approaches are developed for identifying the parameters of the proposed model when only a finite sample of received observations is available. It is shown that by using a partial set of the output cumulant samples, the computational complexity required in determining the kernels of the model is considerably reduced. The analysis is not restricted to special forms of the second-order Volterra system. > more...

The authors present a method for reconstruction of the impulse response of a nonminimum phase, linear, time-invariant (NMP-LTI) system from the second- and third-order statistics of the output sequence. The method is based on computing the complex cepstrum of the unknown impulse response from the power spectrum and a one-dimensional (1D) slice of the bispectrum. This method has the advantages of being independent of the type of the system (MA, AR, ARMA) and its computational complexity is also independent of the order of the utilized spectrum. > more...

Quality generation of 30 GHz MMW beat-tone utilizing extended L-band InAs/InP quantum-dash laser source exploiting self-injection locking scheme is reported along with the successful transmission of 2 Gbps QPSK signal over a hybrid 20km-fiber-5m-FSO-2m-wireless channel. more...

Millimeter-wave (MMW) technology has been envisioned as a promising front haul access solution for fifth-generation (5G) networks and beyond, thanks to its seamless integration with the existing optical fiber network infrastructure (i.e., radio-over-fiber or MMW-over-fiber), to address the rising demand of high end-user data rates [1] . Moreover, photonic generation of high-quality MMWs carrier beat-tones for optimum transmission performance and optical sources satisfying the requirements of next-generation optical networks is of paramount importance. For instance, operation in extended L-band wavelengths is under consideration for future optical networks [2] . However, to our knowledge, only C-band optical sources are reported in the literature for MMW technology [3] . Hence, we report a high-quality photonic generation of 33 GHz MMW beat-tone using injection locking technique on InAs/InP quantum-dash laser diode (QD-LD) operating in mid-L-band ~1610 nm, and first demonstration of 4 m wireless (WL) transmission of 2 Gbit/s quadrature-phase-shift keying (QPSK) signal over 28 GHz MMW beat-tone carrier. more...