ABSTRACT
To satisfy the growing spectrum demands of emerging wireless applications, cognitive radios have been considered as a viable option. It enables dynamic spectrum access opportunistically using wideband spectrum sensing (WSS) methods to discover the temporarily free frequency bands. WSS requires a high-speed analog-to-digital converter (ADC), which has high power consumption and hardware complexity. Improving the power consumption and hardware complexity of the ADC is one of the existing challenges in energy-constrained applications. To alleviate this problem, we propose compressive sensing (CS) in maximum-minimum subband energy detection method to sense the wideband spectrum by utilizing the sparse nature of spectrum occupancy with the minimal possible number of measurements. The CS method uses Fourier Transform and chaotic sequence in designing the measurement matrix to achieve both determinacy and randomness. The Bayesian method is used to reconstruct the signal from the available measurements. From the reconstructed signal, the maximum-minimum subband energy detection (ED) method is used to decide whether the primary user (PU) is absent or present in a particular frequency band. The simulation results show that the proposed CS-based maximum-minimum subband energy detection approach improves the probability of detection by 7.5% compared to the conventional maximum-minimum subband energy detection method of spectrum sensing. The proposed spectrum sensing method is simple and robust to noise uncertainty and signal strength variations.
ABSTRACT
BACKGROUND: Craniopagus parasiticus is rare with an incidence of approximately four to six cases in 10,000,000 births. In our case, the head of the parasitic twin protruded from the temporal area of the normal twin's cranium. The parasitic twin had two deformed lower limbs, of which one was rudimentary, and long bones of the bilateral lower limbs and some pelvic bone. Dissection of the mass of the parasitic twin's body revealed the intestine but no chest organs or abdominal organs. There was a rudimentary labium but no vaginal opening. In resource-limited countries, maternal age or nutritional factors may play a role in craniopagus parasiticus. CASE PRESENTATION: A 38-year-old multigravida (gravida V para IV) woman of Amhara ethnicity was referred from a rural health center to our hospital due to prolonged second stage of labor at 42+1 weeks. On her arrival at our hospital, an obstetrician decided to do a caesarean section because she was unable to deliver vaginally. A live baby girl weighing 4200 g was delivered. The placenta was single and normal. Her Appearance, Pulse, Grimace, Activity, and Respiration scores were 7 and 9 at 1 and 5 minutes, respectively. She appeared to be grossly normal except for the parasitic co-twin attached to her cranium. After a week of extensive counselling and investigation, a successful separation operation was done. Postoperation, she comfortably suckled on the breast and had no neurological deficit. Two weeks after separation she was discharged in a good healthy condition with an arrangement for postnatal follow up. CONCLUSIONS: The causes of craniopagus parasiticus are still unknown due to a rarity of cases and a limited number of studies on it. There have been only nine to ten cases of craniopagus parasiticus, of which only three survived past birth and were documented in the literature. Genetic scientists and researchers continue to investigate this case because they might find explanations for the birth defect, and provide answers to improve the prognosis and the life chances of twins with craniopagus parasiticus.