A Ebrahimi

Publications (5)6.83 Total impact

• Conference Proceeding: Estimation of channel parameters in a multipath environment via optimizing highly oscillatory error functions using a genetic algorithm

  A. Ebrahimi, A. Rahimian
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  ABSTRACT: Channel estimation is of crucial importance for tomorrow's wireless mobile communication systems. This paper focuses on the solution of channel parameters estimation problem in a scenario involving multiple paths in the presence of additive white Gaussian noise. We assumed that number of paths in the multipath environment is known and the transmitted signal consists of attenuated and delayed replicas of a known transient signal. In order to determine the maximum likelihood estimates one has to solve a complicated optimization problem. Genetic algorithms (GA) are well known for their robustness in solving complex optimization problems. A GA is considered to extract channel parameters to minimize the derived error-function. The solution is based on the maximum-likelihood estimation of the channel parameters. Simulation results also demonstrate GA's robustness to channel parameters estimation errors.
  Software, Telecommunications and Computer Networks, 2007. SoftCOM 2007. 15th International Conference on; 10/2007
• Conference Proceeding: Solving Multi-path Time Delay Estimation Problem in the Presence of Additive White Gaussian Noise Using a Genetic-Algorithm

  A. Ebrahimi, V. Tabatabavakili
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  ABSTRACT: In practical world, there always exist problems of multi-path time delay estimation (MTDE) and it is an important problem in the fields of sonar, radar, digital communication and geophysics. We consider the problem of estimating the arrival times of overlapping ocean-acoustic signals from a noisy received waveform that consists of attenuated and delayed replicas of a known transient signal. We assume that the transmitted signal and the number of paths in the multipath environment are known. Many existing time-delay estimation algorithms perform poorly due to converging to local optimum points. In this paper, an efficient genetic-algorithm (GA) is applied to deal with the above problem. To the best of our knowledge this study is the first attempt to solve time delay estimation (TDE) using an evolutionary technique, genetic-algorithms. The performance of generic-algorithm is examined for different signal-noise scenarios. Our simulation results show that the time delays are estimated well based on the genetic-algorithm.
  Wireless and Optical Communications Networks, 2007. WOCN '07. IFIP International Conference on; 08/2007
• Article: Association of the dopamine transporter gene (DAT1) core promoter polymorphism -67T variant with schizophrenia.

  N Khodayari, M Garshasbi, F Fadai, A Rahimi, L Hafizi, A Ebrahimi, H Najmabadi, Mina Ohadi
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  ABSTRACT: Dysfunction of the central dopaminergic neurotransmission has been suggested to play an important role in the etiology of schizophrenia. The dopamine transporter (DAT1) mediates the active reuptake of dopamine from the synapses and thereby plays a key role in the regulation of the dopaminergic neurotransmission. In this study, we sought to determine the possible association of the DAT1 gene core promoter polymorphism -67A/T with schizophrenia in a case/control study. The allele and genotype frequencies of the polymorphism were studied in 100 patients and 100 controls, which were matched on the basis of sex, age, and ethnicity. The genotype frequencies in the patients group were as follows: AA 29%; AT 59%; TT 12% versus the genotype frequencies in the control group: AA 57%; AT 38%; TT 5% [chi2 = 16.54, df = 2, OR = 2.25 (95% CI 1.46-3.45, P < or = 0.0003]. For the first time, these findings provide tentative evidence for the contribution of the DAT1 gene core promoter polymorphism to the etiopathophysiology of schizophrenia at least in the Iranian male population that we studied. Replication studies of independent samples and family-based association studies are necessary to further evaluate the significance of our findings.
  American Journal of Medical Genetics Part B Neuropsychiatric Genetics 08/2004; 129B(1):10-2. · 3.70 Impact Factor
• Article: The frequency of GJB2 mutations and the Delta (GJB6-D13S1830) deletion as a cause of autosomal recessive non-syndromic deafness in the Kurdish population.

  N Mahdieh, C Nishimura, K Ali-Madadi, Y Riazalhosseini, H Yazdan, S Arzhangi, K Jalalvand, A Ebrahimi, S Kazemi, R J H Smith, H Najmabadi
  Clinical Genetics 07/2004; 65(6):506-8. · 3.13 Impact Factor
• Source

  Available from: who.int

  Article: Caesarean section rates in teaching hospitals of Tehran: 1999-2003.

  A Moini, K Riazi, A Ebrahimi, N Ostovan
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  ABSTRACT: To determine the trends of caesarean section in teaching hospitals of Tehran University of Medical Sciences, a retrospective analysis was performed on the obstetric data from 3 hospitals in a 5-year period. The caesarean section rate increased from 35.4% of deliveries in 1999 to 42.3% in 2003. The data showed that there was a steady increase in elective operations that might explain the rise in overall caesarean section rate.
  Eastern Mediterranean health journal = La revue de santé de la Méditerranée orientale = al-Majallah al-ṣiḥḥīyah li-sharq al-mutawassiṭ 13(2):457-60.