ABSTRACT In this letter, we aim to identify the optimal isotropic mother wavelet for a given spat... more ABSTRACT In this letter, we aim to identify the optimal isotropic mother wavelet for a given spatial dimension based on a localization criterion. Within the framework of the calculus of variations, we specify an Euler-Lagrange equation for this problem, and we find the unique analytic solutions. In the one- and two-dimensional cases, the derived wavelets are well known.
IEEE 10th INTERNATIONAL CONFERENCE ON SIGNAL PROCESSING PROCEEDINGS, 2010
... 10, pp. 2616-2627, Oct. 1994. [12] Saif al Zahir, Aimen El-Maleh, and Esam Khan, An efficien... more ... 10, pp. 2616-2627, Oct. 1994. [12] Saif al Zahir, Aimen El-Maleh, and Esam Khan, An efficient test vector compression technique based on geometric shapes, Proceedings of the 8th International Conference on Electronics, Circuits and Systems, ICECS 2001, vol. 3, no. 2-5, pp. ...
2010 IEEE International Conference on Communications, 2010
In this paper we propose a new model for the near-far effect in a CDMA system. We derive upper an... more In this paper we propose a new model for the near-far effect in a CDMA system. We derive upper and lower bounds for the maximum near-far effect for errorless transmission. Using these bounds, we propose some near-far resistant codes. Also a very low complexity ML decoder for a subclass of the proposed codes is suggested.
In CDMA systems, the received user powers vary due to moving distance of users. Thus, the CDMA re... more In CDMA systems, the received user powers vary due to moving distance of users. Thus, the CDMA receivers consist of two stages. The first stage is the power estimator and the second one is a Multi-User Detector (MUD). Conventional methods for estimating the user powers are suitable for underor fully-loaded cases (when the number of users is less than or
In this paper the existence of capacity achieving linear codes with arbitrarily sparse generator ... more In this paper the existence of capacity achieving linear codes with arbitrarily sparse generator matrices is proved. In particular, we show the existence of capacity achieving codes for which the density of ones in the generator matrix is arbitrarily low. The existing results on the existence of capacity achieving linear codes in the literature are limited to the codes whose
In this paper, we explore the mystery of synchronous CDMA as applied to wireless and optical comm... more In this paper, we explore the mystery of synchronous CDMA as applied to wireless and optical communication systems under very general settings for the user symbols and the signature matrix entries. The channel is modeled with real/complex additive noise of arbitrary distribution. Two problems are addressed. The first problem concerns whether overloaded error free codes exist in the absence of additive noise under these general settings, and if so whether there are any practical optimum decoding algorithms. The second one is about the bounds for the sum channel capacity when user data and signature codes employ any real or complex alphabets (finite or infinite). In response to the first problem, we have developed practical Maximum Likelihood (ML) decoding algorithms for overloaded CDMA systems for a large class of alphabets. In response to the second problem, a general theorem has been developed in which the sum capacity lower bounds with respect to the number of users and spreading ...
ABSTRACT We investigate a stochastic signal-processing framework for signals with sparse derivati... more ABSTRACT We investigate a stochastic signal-processing framework for signals with sparse derivatives, where the samples of a Lévy process are corrupted by noise. The proposed signal model covers the well-known Brownian motion and piecewise-constant Poisson process; moreover, the Lévy family also contains other interesting members exhibiting heavy-tail statistics that fulfill the requirements of compressibility. We characterize the maximum-a-posteriori probability (MAP) and minimum mean-square error (MMSE) estimators for such signals. Interestingly, some of the MAP estimators for the Lévy model coincide with popular signal-denoising algorithms (e.g., total-variation (TV) regularization). We propose a novel non-iterative implementation of the MMSE estimator based on the belief-propagation (BP) algorithm performed in the Fourier domain. Our algorithm takes advantage of the fact that the joint statistics of general Lévy processes are much easier to describe by their characteristic function, as the probability densities do not always admit closed-form expressions. We then use our new estimator as a benchmark to compare the performance of existing algorithms for the optimal recovery of gradient-sparse signals.
In this paper, we explore some of the fundamentals of synchronous Code Division Multiple Access (... more In this paper, we explore some of the fundamentals of synchronous Code Division Multiple Access (CDMA) as applied to wireless and optical communication systems under very general settings (of any size) for the user symbols and the signature matrix entries. The channel is modeled by real/complex additive noise of arbitrary distribution. Two problems are addressed. The first problem concerns whether
... The authors are with the Advanced Communication Research Institute (ACRI), Electrical Enginee... more ... The authors are with the Advanced Communication Research Institute (ACRI), Electrical Engineering Department, Sharif University of Tech-nology, Tehran, Iran (e-mail: {pedram pad, faraji}@ee.sharif.edu, mar-vasti ... [13] P. Pad, F. Marvasti, K. Alishahi, and S. Akbari, A class of ...
ABSTRACT In this letter, we aim to identify the optimal isotropic mother wavelet for a given spat... more ABSTRACT In this letter, we aim to identify the optimal isotropic mother wavelet for a given spatial dimension based on a localization criterion. Within the framework of the calculus of variations, we specify an Euler-Lagrange equation for this problem, and we find the unique analytic solutions. In the one- and two-dimensional cases, the derived wavelets are well known.
IEEE 10th INTERNATIONAL CONFERENCE ON SIGNAL PROCESSING PROCEEDINGS, 2010
... 10, pp. 2616-2627, Oct. 1994. [12] Saif al Zahir, Aimen El-Maleh, and Esam Khan, An efficien... more ... 10, pp. 2616-2627, Oct. 1994. [12] Saif al Zahir, Aimen El-Maleh, and Esam Khan, An efficient test vector compression technique based on geometric shapes, Proceedings of the 8th International Conference on Electronics, Circuits and Systems, ICECS 2001, vol. 3, no. 2-5, pp. ...
2010 IEEE International Conference on Communications, 2010
In this paper we propose a new model for the near-far effect in a CDMA system. We derive upper an... more In this paper we propose a new model for the near-far effect in a CDMA system. We derive upper and lower bounds for the maximum near-far effect for errorless transmission. Using these bounds, we propose some near-far resistant codes. Also a very low complexity ML decoder for a subclass of the proposed codes is suggested.
In CDMA systems, the received user powers vary due to moving distance of users. Thus, the CDMA re... more In CDMA systems, the received user powers vary due to moving distance of users. Thus, the CDMA receivers consist of two stages. The first stage is the power estimator and the second one is a Multi-User Detector (MUD). Conventional methods for estimating the user powers are suitable for underor fully-loaded cases (when the number of users is less than or
In this paper the existence of capacity achieving linear codes with arbitrarily sparse generator ... more In this paper the existence of capacity achieving linear codes with arbitrarily sparse generator matrices is proved. In particular, we show the existence of capacity achieving codes for which the density of ones in the generator matrix is arbitrarily low. The existing results on the existence of capacity achieving linear codes in the literature are limited to the codes whose
In this paper, we explore the mystery of synchronous CDMA as applied to wireless and optical comm... more In this paper, we explore the mystery of synchronous CDMA as applied to wireless and optical communication systems under very general settings for the user symbols and the signature matrix entries. The channel is modeled with real/complex additive noise of arbitrary distribution. Two problems are addressed. The first problem concerns whether overloaded error free codes exist in the absence of additive noise under these general settings, and if so whether there are any practical optimum decoding algorithms. The second one is about the bounds for the sum channel capacity when user data and signature codes employ any real or complex alphabets (finite or infinite). In response to the first problem, we have developed practical Maximum Likelihood (ML) decoding algorithms for overloaded CDMA systems for a large class of alphabets. In response to the second problem, a general theorem has been developed in which the sum capacity lower bounds with respect to the number of users and spreading ...
ABSTRACT We investigate a stochastic signal-processing framework for signals with sparse derivati... more ABSTRACT We investigate a stochastic signal-processing framework for signals with sparse derivatives, where the samples of a Lévy process are corrupted by noise. The proposed signal model covers the well-known Brownian motion and piecewise-constant Poisson process; moreover, the Lévy family also contains other interesting members exhibiting heavy-tail statistics that fulfill the requirements of compressibility. We characterize the maximum-a-posteriori probability (MAP) and minimum mean-square error (MMSE) estimators for such signals. Interestingly, some of the MAP estimators for the Lévy model coincide with popular signal-denoising algorithms (e.g., total-variation (TV) regularization). We propose a novel non-iterative implementation of the MMSE estimator based on the belief-propagation (BP) algorithm performed in the Fourier domain. Our algorithm takes advantage of the fact that the joint statistics of general Lévy processes are much easier to describe by their characteristic function, as the probability densities do not always admit closed-form expressions. We then use our new estimator as a benchmark to compare the performance of existing algorithms for the optimal recovery of gradient-sparse signals.
In this paper, we explore some of the fundamentals of synchronous Code Division Multiple Access (... more In this paper, we explore some of the fundamentals of synchronous Code Division Multiple Access (CDMA) as applied to wireless and optical communication systems under very general settings (of any size) for the user symbols and the signature matrix entries. The channel is modeled by real/complex additive noise of arbitrary distribution. Two problems are addressed. The first problem concerns whether
... The authors are with the Advanced Communication Research Institute (ACRI), Electrical Enginee... more ... The authors are with the Advanced Communication Research Institute (ACRI), Electrical Engineering Department, Sharif University of Tech-nology, Tehran, Iran (e-mail: {pedram pad, faraji}@ee.sharif.edu, mar-vasti ... [13] P. Pad, F. Marvasti, K. Alishahi, and S. Akbari, A class of ...
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