Can Punctured Rate-1/2 Turbo Codes Achieve a Lower Error Floor than their Rate-1/3 Parent Codes?

In this paper we concentrate on rate-1/3 systematic parallel concatenated convolutional codes and their rate-1/2 punctured child codes. Assuming maximum-likelihood decoding over an additive white Gaussian channel, we demonstrate that a rate-1/2 non-systematic child code can exhibit a lower error floor than that of its rate-1/3 parent code, if a particular condition is met. However, assuming iterative decoding, convergence of the non-systematic code towards low bit-error rates is problematic. To alleviate this problem, we propose rate-1/2 partially-systematic codes that can still achieve a lower error floor than that of their rate-1/3 parent codes. Results obtained from extrinsic information transfer charts and simulations support our conclusion.Comment: 5 pages, 7 figures, Proceedings of the 2006 IEEE Information Theory Workshop, Chengdu, China, October 22-26, 200

Infeção fetal não primária por citomegalovírus

Cytomegalovirus (CMV) is the most common congenital viral infection, causing hearing, visual and psychomotor impairment. Preexisting maternal CMV immunity substantially reduces, but not eliminates, the risk of fetal infection and affectation. This article is about a case of nonprimary maternal CMV infection during pregnancy, with vertical transmission, resulting in severe fetal affectation. Preconceptional analysis indicated maternal CMV past infection. Pregnancy progressed uneventfully until the 20th week ultrasound (US), which revealed cerebral abnormalities: thin and hyperechogenic cerebral cortex with prominent lateral ventricles, bilateral periventricular hyperechogenicities, cerebellar vermis hypoplasia and absent corpus callosum. The MRI suggested these findings were compatible with congenital infection rather than primary brain malformation.The fetal karyotype was normal. The title of CMV's IgG antibodies almost tripled. Since the first semester, analysis of the polymerase chain reaction (PCR) for CMV DNA in the amniotic fluid was negative. The pregnancy was terminated at 23 weeks. Neuropathological findings at autopsy showed severe brain lesions associated with CMV infection.O citomegalovírus (CMV) é a infeção viral congénita que mais comumente causa deficiência auditiva, visual e psicomotora. A preexistência de imunidade materna reduz substancialmente, mas não elimina, o risco de infeção e afetação fetal. Trata-se de um caso de infeção materna não primária por CMV durante a gravidez, com transmissão vertical, resultando em afetação fetal severa. As análises preconcepção indicavam infecção passada por CMV. A gravidez decorreu sem intercorrências até a ecografia efetuada na 20ª semana, que revelou alterações cerebrais: córtex cerebral fino e hiperecogénico com ventrículos laterais proeminentes, hiperecogenecidades periventriculares bilaterais, hipoplasia do vérmis cerebeloso e ausência de corpo caloso. A ressonância magnética sugeriu que estes achados eram mais favoráveis a uma infeção congénita do que com uma malformação cerebral primária. O cariótipo fetal era normal. O título de anticorpos IgG para CMV havia triplicado desde a dosagem do primeiro trimestre. O PCR para o DNA do CMV no líquido amniótico foi negativo. A gravidez foi interrompida na 23ª semana. Os achados neuropatológicos na autópsia mostraram lesões cerebrais severas associadas a infeção por CMV.info:eu-repo/semantics/publishedVersio