Safwan El Assad - Academia.edu (original) (raw)

Papers by Safwan El Assad

Advances in Electrical and Computer Engineering, 2021

International audiencePseudo-Random Number Generator of Chaotic Sequences (PRNG-CS) has caught th... more International audiencePseudo-Random Number Generator of Chaotic Sequences (PRNG-CS) has caught the attention in various security applications, especially for stream and block ciphering, steganography, and digital watermarking algorithms. Indeed, in all chaos-based cryptographic systems, the chaotic generator plays a vital role and exhibits appropriate cryptographic properties. Due to the technological outbreak, as well as the rapid growth of the Internet of Things (IoT) technology and their various use cases, PRNGs-CS software implementation remains an open issue to meet its service requirements. The hardware implementation is one of the most flagship technology used to implement PRNGs-CS with the aim is to provide high-performance requirements for such application security. Therefore, in this work, we propose a new PRNGs-SC-based architecture. The latter consists of three discrete chaotic maps weakly coupled, as well as, the Piecewise Linear Chaotic Map (PWLCM), the Skew Tent, and the Logistic map. The chaotic system is designed on Xilinx Spartan™-6 FPGA-board, using Very High-Speed Integrated Circuit Hardware Description Language (VHDL). Simulation results, performed over the ISE Design Suite environment, prove the effectiveness of our proposed architecture in terms of robustness against statistical attacks, throughput, and hardware cost. So, based on its architecture and the simulation results the proposed PRNG-SC can be used in cryptographic applications. © 2021. All Rights Reserved

Annales Des Télécommunications, 1996

Speckle appearing in synthetic aperture radar (SAR) images is generated by coherent processing of... more Speckle appearing in synthetic aperture radar (SAR) images is generated by coherent processing of radar signals. Basically the speckle has the nature of multiplicative noise. Recently, several methods have been proposed to remove speckle in SAR images, among them, Lee's methods, Frost's method and Zamperoni's method. In this paper, we propose an effective method for smoothing speckle-corrupted images. Digital processing is introduced, based on a contrast modification in a multiresolution pyramid image representation. The contrast modification is realized by a median filter or an adaptive order filter giving a reconstructed image. For assessing this new method, we realized a comparative study with several noise-smoothing algorithms.

2011 World Congress on Internet Security (WorldCIS-2011), 2011

This paper focuses on the security of Internet access over the third generation mobile telecommun... more This paper focuses on the security of Internet access over the third generation mobile telecommunication networks. We explore the characteristics of cryptographic attacks and the similarities between the exposures of different secret keys in cryptographic attacks and propose three measures that limit the exposure of the sensible secret key. These measures are the usage of a temporary key, TK, the protection of the messages that could be used by a cryptanalyst to recover the secret key and the increase of the size of the secret key.

Lecture Notes in Computer Science, 2008

Remarkable research efforts have been invested in recent years on the chaotic communications sche... more Remarkable research efforts have been invested in recent years on the chaotic communications schemes. In this paper we propose a modulation technique based on QAM-4 (Quadrature Amplitude Modulation). The data is split into I and Q channels. Each channel is spread by chaotic sequences generated over a fixed time interval by a specific digital chaotic system. There are two principal advantages of introducing the chaos in a communication scheme. The first is that it allows signals to be transmitted in a secure way, so that the signal could be perceived as a noise for a potential intruder. Secondly, the spread-spectrum characteristics of the signal improve the noise rejection propreties. A new coherent receiver structure is presented to synchronize each channel. Simulation results are presented to show the effectiveness of the proposed scheme.

International Journal of Internet Technology and Secured Transactions, 2014

A growing number of systems are highly connected and distributed over the internet. These systems... more A growing number of systems are highly connected and distributed over the internet. These systems require innovative software services and infrastructures in order to guarantee security and reliability. This issue has a particular relation to a wide range of topics such as real-time scheduling and encryption with quality of service constraints which are the main interests of this paper. The first contribution is a chaos-based cryptosystem which provides an acceptable level of security while executing at least 41 times faster than the AES algorithm. Secondly, we propose a scheduling scheme known as the deadline mechanism in order to guarantee an acceptable level of security even in computing overload situations. Dynamically choosing the best possible cryptosystem in dependance with processing availability is the basis of our mechanism.

SCS 2003. International Symposium on Signals, Circuits and Systems. Proceedings (Cat. No.03EX720), 2003

Abstract The use of chaotic spreading sequences is a new approach for DS-CDMA systems. Some chaot... more Abstract The use of chaotic spreading sequences is a new approach for DS-CDMA systems. Some chaotic PN spreading sequences show better correlation properties than conventional binary PN sequences, which are crucial for the BER performances. This paper is presenting a selection criterion for optimal sets of PN chaotic sequences, which are generated from periodic orbits of a particular class of chaotic dynamics. Finally, their BER performances in a synchronous DS-CDMA system are compared for two particular cases to show the ...

2014 10th International Conference on Communications (COMM), 2014

A variety of chaos-based cryptosystems have been investigated during the last decade. Most of the... more A variety of chaos-based cryptosystems have been investigated during the last decade. Most of them are based on the structure of Fridrich, which is based on the traditional confusiondiffusion architecture proposed by Shannon. Compared with traditional cryptosystems (DES, 3DES, AES, etc.), the chaosbased cryptosystems are more flexible, more modular and easier to be implemented, which make them more suitable for large scale-data encryption, such as images and videos. The heart of any chaos-based cryptosystem is the chaotic generator and so, a part of the efficiency (robustness, speed) of the system depends greatly on it. In this talk, we give an overview of the state of the art of chaos-based block ciphers and we describe some of our schemes already proposed. Also, we will focus on the essential characteristics of the digital chaotic generator that we published in October 2011 as a French patent and also we published in 2013 an extension of the patent in Europe, China, Japan, and USA. The needed performance of a chaos-based block cipher in terms of security level and speed of calculus depends on the considered application. There is a compromise between the security and the speed of the calculation. The security of these block ciphers will be analyzed.

Vlădeanu/Nonlinear Digital Encoders for Data Communications, 2014

Microwave Sensing and Synthetic Aperture Radar, 1996

ABSTRACT This paper presents a method for unsupervised segmentation of polarimetric SAR data into... more ABSTRACT This paper presents a method for unsupervised segmentation of polarimetric SAR data into classes of homogeneous microwave backscatter characteristics. Clustering of polarimetric backscatter are obtained either by the CMF-NSO or be SEM algorithm. These algorithms carry out the classification without a priori assumptions on the number of classes in the data set. Assessment of cluster validity is based on performance measures using hypervolume V or CS function criteria. The later measures the overall average compactness and separation of a fuzzy-partition. The CMF-NSO algorithm performs well in situations of large variability of cluster shapes and densities. Given the clusters of polarimetric backscatter, the entire image is segmented using a MAP estimation. Implementation of the MAP technique is accomplished by an ICM algorithm. Results, using fully polarimetric SAR forest data, obtained by the CMF-NSO following by the ICM algorithm with a K-distribution model are quite satisfactory.

SPIE Proceedings, 1996

ABSTRACT This paper deals with adaptive vector filtering of speckling in SAR images. The proposed... more ABSTRACT This paper deals with adaptive vector filtering of speckling in SAR images. The proposed method is based on the ordering of the vector data. The vector order is obtained by an Euclidean distance calculated from the center of a set of vectors. The local variation coefficient has been introduced for filter adaptivity. This coefficient is a reflection of the generalization of local scalar variation towards a case of a vectorial variation. For this purpose we use the fuzzy cluster analysis domain.In each large window, we decompose data into two groups using the fuzzy center mobile algorithm. The Euclidian distance between the two group centers provides good information about local variation in the window. In a homogeneous area this distance is minimal whereas it is considerable in the heterogeneous area. The global distribution of this distance coming from all windows of the image determine the threshold value. According to the local variation value, the vector will be treated in two different ways. If the local variation is less than the threshold value then we use a classic mean filtering. Otherwise, we replace the vector of interest by another ordered vector. Its choice depends on the local variation value.

Using chaotic sequences for spreading is a new approach for optimising the BER (Bit Error Rate) p... more Using chaotic sequences for spreading is a new approach for optimising the BER (Bit Error Rate) performances in the DS-CDMA (Direct Sequence - Code Division Multiple Access) systems. This paper presents the use of two very well known families of PWAM (Piece-Wise Affine Markov) maps, namely (n, t) - tailed shifts and (n, t) - broken identities maps, and their

In order to enable the coexistence of an everincreasing number of communication systems in a limi... more In order to enable the coexistence of an everincreasing number of communication systems in a limited amount of frequency, the tradi tional static frequency all ocation is not the best solution any longer. Cogni ti ve Radi o (CR) technolog y, based on a dynamic spectrum access, is a possible solution for improving the efficiency of spectrum usage. A first step in order to identify the frequency bands that are more suitable for opportunistic usage is to e valuate the degree in which licensed bands are currently used. Although some measurement campaigns have already been carried out, most of them were done in urban environments and only a few in other l ocations. This paper presents results of two measurement campaigns conducted in Romania both in urban and rural environments, covering the frequency range from 25 MHz up to 3.4 GHz. The results are confronted with the frequency allocati on table published by the national authority for radi o communicati ons and a comparison and anal ysis of the obtained data are being made.

2009 Fifth Advanced International Conference on Telecommunications, 2009

Abstract In this paper, nonlinear digital filters with finite precision are analyzed as recursive... more Abstract In this paper, nonlinear digital filters with finite precision are analyzed as recursive systematic convolutional (RSC) encoders. An infinite impulse response (IIR) digital filter with finite precision (wordlength of N bits) is a rate 1 RSC encoder over a Galois field GF (2 N). The Frey chaotic filter is analyzed for two different wordlengths N, and it is demonstrated that this encoder can be used for trellis-coded modulation (TCM) schemes. A definition for the encoding rate is provided in the context of the new structure. The Frey encoder scheme is ...

2012 16th IEEE Mediterranean Electrotechnical Conference, 2012

Secure IP multicast over satellite is very important for applications such as pay per view. These... more Secure IP multicast over satellite is very important for applications such as pay per view. These applications need a key management scheme to distribute a shared group key to all group members for encrypting the data. LKH has been proposed to distribute the group key in a way that scales efficiently for large group's size. However, the proposed schemes do

2009 International Conference for Internet Technology and Secured Transactions, (ICITST), 2009

Abstract The DVB-S (Digital Video Broadcasting-Satellite) was originally developed as a TV broadc... more Abstract The DVB-S (Digital Video Broadcasting-Satellite) was originally developed as a TV broadcasting protocol. Later on two encapsulation protocols were developed in order to allow network level TCP/IP encapsulation: Multi Protocol Encapsulation-MPE and ...

2010 3rd International Symposium on Electrical and Electronics Engineering (ISEEE), 2010

Abstract We notice a very strong “all IP” trend characterizing today's communication technol... more Abstract We notice a very strong “all IP” trend characterizing today's communication technology. There is a powerful IP backbone in place, but, in some cases, the “last mile problem” remains to be solved. One of the solutions for this problem is represented by IP ...

SPIE Proceedings, 1996

SAR data is a remote sensor which produces a high amount of data. Since the transmission of the c... more SAR data is a remote sensor which produces a high amount of data. Since the transmission of the corresponding raw signals requires extremely high data rates, on-board data compression is usually necessary. The approach presented in this paper use the statistic properties of the received signal in order to improve the compression performance.

AIP Conference Proceedings, 2010

The Digital Video Broadcasting—Satellite (DVB‐S) standard was originally conceived for TV and rad... more The Digital Video Broadcasting—Satellite (DVB‐S) standard was originally conceived for TV and radio broadcasting. Later, it became possible to send IP packets using encapsulation methods such as Multi Protocol Encapsulation, MPE, or Unidirectional Lightweight ...

Annales Des Télécommunications - AdT, 1995

High resolution radar imaging is used to perform target signature analysis. In this paper, we pre... more High resolution radar imaging is used to perform target signature analysis. In this paper, we present a comparative study of diverse 2- D imaging methods on spherical waves, such as sar processing and its modes, ssar and isar as well as holography, whose mathematical formulation is identical by using the spherical projection density function, although the measurement technique are quite different. We show that azimuth processing is unified, and under some conditions range processing can be unified. In order to reconstruct the fixed target side looking radar image, we have developed an idea based on the transformation of antenna lateral displacement as a function of equivalent angular displacement, and then the 1- D images coherent summation algorithm of classical holography can be used.

Signal Processing, 2010

In this paper, trellis coded modulation (TCM) schemes are designed using recursive encoders over ... more In this paper, trellis coded modulation (TCM) schemes are designed using recursive encoders over Galois field GF(2 N). These encoders are designed using the nonlinear left-circulate (LCIRC) function. The LCIRC function performs a bit left circulation over the representation word. Different encoding rates are obtained for these encoders when using different representation word lengths at the input and the output, denoted as N in and N, respectively. A generalized 1-delay GF(2 N) recursive encoder scheme using LCIRC is proposed for performance analysis and optimization, for any possible encoding rate, N in /N. Several TCM schemes using pulse amplitude modulation (PAM), and phase shift keying (PSK) are considered. The minimum Euclidian distance is estimated for all schemes and a general expression is found as a function of the word lengths N in and N. The symbol error rate (SER) is estimated by simulation for PSK-TCM transmissions over an additive white Gaussian noise (AWGN) channel.

Advances in Electrical and Computer Engineering, 2021

International audiencePseudo-Random Number Generator of Chaotic Sequences (PRNG-CS) has caught th... more International audiencePseudo-Random Number Generator of Chaotic Sequences (PRNG-CS) has caught the attention in various security applications, especially for stream and block ciphering, steganography, and digital watermarking algorithms. Indeed, in all chaos-based cryptographic systems, the chaotic generator plays a vital role and exhibits appropriate cryptographic properties. Due to the technological outbreak, as well as the rapid growth of the Internet of Things (IoT) technology and their various use cases, PRNGs-CS software implementation remains an open issue to meet its service requirements. The hardware implementation is one of the most flagship technology used to implement PRNGs-CS with the aim is to provide high-performance requirements for such application security. Therefore, in this work, we propose a new PRNGs-SC-based architecture. The latter consists of three discrete chaotic maps weakly coupled, as well as, the Piecewise Linear Chaotic Map (PWLCM), the Skew Tent, and the Logistic map. The chaotic system is designed on Xilinx Spartan™-6 FPGA-board, using Very High-Speed Integrated Circuit Hardware Description Language (VHDL). Simulation results, performed over the ISE Design Suite environment, prove the effectiveness of our proposed architecture in terms of robustness against statistical attacks, throughput, and hardware cost. So, based on its architecture and the simulation results the proposed PRNG-SC can be used in cryptographic applications. © 2021. All Rights Reserved

Annales Des Télécommunications, 1996

Speckle appearing in synthetic aperture radar (SAR) images is generated by coherent processing of... more Speckle appearing in synthetic aperture radar (SAR) images is generated by coherent processing of radar signals. Basically the speckle has the nature of multiplicative noise. Recently, several methods have been proposed to remove speckle in SAR images, among them, Lee's methods, Frost's method and Zamperoni's method. In this paper, we propose an effective method for smoothing speckle-corrupted images. Digital processing is introduced, based on a contrast modification in a multiresolution pyramid image representation. The contrast modification is realized by a median filter or an adaptive order filter giving a reconstructed image. For assessing this new method, we realized a comparative study with several noise-smoothing algorithms.

2011 World Congress on Internet Security (WorldCIS-2011), 2011

This paper focuses on the security of Internet access over the third generation mobile telecommun... more This paper focuses on the security of Internet access over the third generation mobile telecommunication networks. We explore the characteristics of cryptographic attacks and the similarities between the exposures of different secret keys in cryptographic attacks and propose three measures that limit the exposure of the sensible secret key. These measures are the usage of a temporary key, TK, the protection of the messages that could be used by a cryptanalyst to recover the secret key and the increase of the size of the secret key.

Lecture Notes in Computer Science, 2008

Remarkable research efforts have been invested in recent years on the chaotic communications sche... more Remarkable research efforts have been invested in recent years on the chaotic communications schemes. In this paper we propose a modulation technique based on QAM-4 (Quadrature Amplitude Modulation). The data is split into I and Q channels. Each channel is spread by chaotic sequences generated over a fixed time interval by a specific digital chaotic system. There are two principal advantages of introducing the chaos in a communication scheme. The first is that it allows signals to be transmitted in a secure way, so that the signal could be perceived as a noise for a potential intruder. Secondly, the spread-spectrum characteristics of the signal improve the noise rejection propreties. A new coherent receiver structure is presented to synchronize each channel. Simulation results are presented to show the effectiveness of the proposed scheme.

International Journal of Internet Technology and Secured Transactions, 2014

A growing number of systems are highly connected and distributed over the internet. These systems... more A growing number of systems are highly connected and distributed over the internet. These systems require innovative software services and infrastructures in order to guarantee security and reliability. This issue has a particular relation to a wide range of topics such as real-time scheduling and encryption with quality of service constraints which are the main interests of this paper. The first contribution is a chaos-based cryptosystem which provides an acceptable level of security while executing at least 41 times faster than the AES algorithm. Secondly, we propose a scheduling scheme known as the deadline mechanism in order to guarantee an acceptable level of security even in computing overload situations. Dynamically choosing the best possible cryptosystem in dependance with processing availability is the basis of our mechanism.

SCS 2003. International Symposium on Signals, Circuits and Systems. Proceedings (Cat. No.03EX720), 2003

Abstract The use of chaotic spreading sequences is a new approach for DS-CDMA systems. Some chaot... more Abstract The use of chaotic spreading sequences is a new approach for DS-CDMA systems. Some chaotic PN spreading sequences show better correlation properties than conventional binary PN sequences, which are crucial for the BER performances. This paper is presenting a selection criterion for optimal sets of PN chaotic sequences, which are generated from periodic orbits of a particular class of chaotic dynamics. Finally, their BER performances in a synchronous DS-CDMA system are compared for two particular cases to show the ...

2014 10th International Conference on Communications (COMM), 2014

A variety of chaos-based cryptosystems have been investigated during the last decade. Most of the... more A variety of chaos-based cryptosystems have been investigated during the last decade. Most of them are based on the structure of Fridrich, which is based on the traditional confusiondiffusion architecture proposed by Shannon. Compared with traditional cryptosystems (DES, 3DES, AES, etc.), the chaosbased cryptosystems are more flexible, more modular and easier to be implemented, which make them more suitable for large scale-data encryption, such as images and videos. The heart of any chaos-based cryptosystem is the chaotic generator and so, a part of the efficiency (robustness, speed) of the system depends greatly on it. In this talk, we give an overview of the state of the art of chaos-based block ciphers and we describe some of our schemes already proposed. Also, we will focus on the essential characteristics of the digital chaotic generator that we published in October 2011 as a French patent and also we published in 2013 an extension of the patent in Europe, China, Japan, and USA. The needed performance of a chaos-based block cipher in terms of security level and speed of calculus depends on the considered application. There is a compromise between the security and the speed of the calculation. The security of these block ciphers will be analyzed.

Vlădeanu/Nonlinear Digital Encoders for Data Communications, 2014

Microwave Sensing and Synthetic Aperture Radar, 1996

ABSTRACT This paper presents a method for unsupervised segmentation of polarimetric SAR data into... more ABSTRACT This paper presents a method for unsupervised segmentation of polarimetric SAR data into classes of homogeneous microwave backscatter characteristics. Clustering of polarimetric backscatter are obtained either by the CMF-NSO or be SEM algorithm. These algorithms carry out the classification without a priori assumptions on the number of classes in the data set. Assessment of cluster validity is based on performance measures using hypervolume V or CS function criteria. The later measures the overall average compactness and separation of a fuzzy-partition. The CMF-NSO algorithm performs well in situations of large variability of cluster shapes and densities. Given the clusters of polarimetric backscatter, the entire image is segmented using a MAP estimation. Implementation of the MAP technique is accomplished by an ICM algorithm. Results, using fully polarimetric SAR forest data, obtained by the CMF-NSO following by the ICM algorithm with a K-distribution model are quite satisfactory.

SPIE Proceedings, 1996

ABSTRACT This paper deals with adaptive vector filtering of speckling in SAR images. The proposed... more ABSTRACT This paper deals with adaptive vector filtering of speckling in SAR images. The proposed method is based on the ordering of the vector data. The vector order is obtained by an Euclidean distance calculated from the center of a set of vectors. The local variation coefficient has been introduced for filter adaptivity. This coefficient is a reflection of the generalization of local scalar variation towards a case of a vectorial variation. For this purpose we use the fuzzy cluster analysis domain.In each large window, we decompose data into two groups using the fuzzy center mobile algorithm. The Euclidian distance between the two group centers provides good information about local variation in the window. In a homogeneous area this distance is minimal whereas it is considerable in the heterogeneous area. The global distribution of this distance coming from all windows of the image determine the threshold value. According to the local variation value, the vector will be treated in two different ways. If the local variation is less than the threshold value then we use a classic mean filtering. Otherwise, we replace the vector of interest by another ordered vector. Its choice depends on the local variation value.

Using chaotic sequences for spreading is a new approach for optimising the BER (Bit Error Rate) p... more Using chaotic sequences for spreading is a new approach for optimising the BER (Bit Error Rate) performances in the DS-CDMA (Direct Sequence - Code Division Multiple Access) systems. This paper presents the use of two very well known families of PWAM (Piece-Wise Affine Markov) maps, namely (n, t) - tailed shifts and (n, t) - broken identities maps, and their

In order to enable the coexistence of an everincreasing number of communication systems in a limi... more In order to enable the coexistence of an everincreasing number of communication systems in a limited amount of frequency, the tradi tional static frequency all ocation is not the best solution any longer. Cogni ti ve Radi o (CR) technolog y, based on a dynamic spectrum access, is a possible solution for improving the efficiency of spectrum usage. A first step in order to identify the frequency bands that are more suitable for opportunistic usage is to e valuate the degree in which licensed bands are currently used. Although some measurement campaigns have already been carried out, most of them were done in urban environments and only a few in other l ocations. This paper presents results of two measurement campaigns conducted in Romania both in urban and rural environments, covering the frequency range from 25 MHz up to 3.4 GHz. The results are confronted with the frequency allocati on table published by the national authority for radi o communicati ons and a comparison and anal ysis of the obtained data are being made.

2009 Fifth Advanced International Conference on Telecommunications, 2009

Abstract In this paper, nonlinear digital filters with finite precision are analyzed as recursive... more Abstract In this paper, nonlinear digital filters with finite precision are analyzed as recursive systematic convolutional (RSC) encoders. An infinite impulse response (IIR) digital filter with finite precision (wordlength of N bits) is a rate 1 RSC encoder over a Galois field GF (2 N). The Frey chaotic filter is analyzed for two different wordlengths N, and it is demonstrated that this encoder can be used for trellis-coded modulation (TCM) schemes. A definition for the encoding rate is provided in the context of the new structure. The Frey encoder scheme is ...

2012 16th IEEE Mediterranean Electrotechnical Conference, 2012

Secure IP multicast over satellite is very important for applications such as pay per view. These... more Secure IP multicast over satellite is very important for applications such as pay per view. These applications need a key management scheme to distribute a shared group key to all group members for encrypting the data. LKH has been proposed to distribute the group key in a way that scales efficiently for large group's size. However, the proposed schemes do

2009 International Conference for Internet Technology and Secured Transactions, (ICITST), 2009

Abstract The DVB-S (Digital Video Broadcasting-Satellite) was originally developed as a TV broadc... more Abstract The DVB-S (Digital Video Broadcasting-Satellite) was originally developed as a TV broadcasting protocol. Later on two encapsulation protocols were developed in order to allow network level TCP/IP encapsulation: Multi Protocol Encapsulation-MPE and ...

2010 3rd International Symposium on Electrical and Electronics Engineering (ISEEE), 2010

Abstract We notice a very strong “all IP” trend characterizing today's communication technol... more Abstract We notice a very strong “all IP” trend characterizing today's communication technology. There is a powerful IP backbone in place, but, in some cases, the “last mile problem” remains to be solved. One of the solutions for this problem is represented by IP ...

SPIE Proceedings, 1996

SAR data is a remote sensor which produces a high amount of data. Since the transmission of the c... more SAR data is a remote sensor which produces a high amount of data. Since the transmission of the corresponding raw signals requires extremely high data rates, on-board data compression is usually necessary. The approach presented in this paper use the statistic properties of the received signal in order to improve the compression performance.

AIP Conference Proceedings, 2010

The Digital Video Broadcasting—Satellite (DVB‐S) standard was originally conceived for TV and rad... more The Digital Video Broadcasting—Satellite (DVB‐S) standard was originally conceived for TV and radio broadcasting. Later, it became possible to send IP packets using encapsulation methods such as Multi Protocol Encapsulation, MPE, or Unidirectional Lightweight ...

Annales Des Télécommunications - AdT, 1995

High resolution radar imaging is used to perform target signature analysis. In this paper, we pre... more High resolution radar imaging is used to perform target signature analysis. In this paper, we present a comparative study of diverse 2- D imaging methods on spherical waves, such as sar processing and its modes, ssar and isar as well as holography, whose mathematical formulation is identical by using the spherical projection density function, although the measurement technique are quite different. We show that azimuth processing is unified, and under some conditions range processing can be unified. In order to reconstruct the fixed target side looking radar image, we have developed an idea based on the transformation of antenna lateral displacement as a function of equivalent angular displacement, and then the 1- D images coherent summation algorithm of classical holography can be used.

Signal Processing, 2010

In this paper, trellis coded modulation (TCM) schemes are designed using recursive encoders over ... more In this paper, trellis coded modulation (TCM) schemes are designed using recursive encoders over Galois field GF(2 N). These encoders are designed using the nonlinear left-circulate (LCIRC) function. The LCIRC function performs a bit left circulation over the representation word. Different encoding rates are obtained for these encoders when using different representation word lengths at the input and the output, denoted as N in and N, respectively. A generalized 1-delay GF(2 N) recursive encoder scheme using LCIRC is proposed for performance analysis and optimization, for any possible encoding rate, N in /N. Several TCM schemes using pulse amplitude modulation (PAM), and phase shift keying (PSK) are considered. The minimum Euclidian distance is estimated for all schemes and a general expression is found as a function of the word lengths N in and N. The symbol error rate (SER) is estimated by simulation for PSK-TCM transmissions over an additive white Gaussian noise (AWGN) channel.