On the Performance of MRC Receiver with Unknown Timing Mismatch-A Large Scale Analysis

There has been extensive research on large scale multi-user multiple-input multiple-output (MU-MIMO) systems recently. Researchers have shown that there are great opportunities in this area, however, there are many obstacles in the way to achieve full potential of using large number of receive antennas. One of the main issues, which will be investigated thoroughly in this paper, is timing asynchrony among signals of different users. Most of the works in the literature, assume that received signals are perfectly aligned which is not practical. We show that, neglecting the asynchrony can significantly degrade the performance of existing designs, particularly maximum ratio combining (MRC). We quantify the uplink achievable rates obtained by MRC receiver with perfect channel state information (CSI) and imperfect CSI while the system is impaired by unknown time delays among received signals. We then use these results to design new algorithms in order to alleviate the effects of timing mismatch. We also analyze the performance of introduced receiver design, which is called MRC-ZF, with perfect and imperfect CSI. For performing MRC-ZF, the only required information is the distribution of timing mismatch which circumvents the necessity of time delay acquisition or synchronization. To verify our analytical results, we present extensive simulation results which thoroughly investigate the performance of the traditional MRC receiver and the introduced MRC-ZF receiver

Improving NOMA Multi-Carrier Systems with Intentional Frequency Offsets

In this letter, we investigate the possible benefits of asynchrony in the frequency domain for the non-orthogonal multiple access (NOMA) schemes. Despite the common perspective that asynchrony in transmission or reception of multi-stream signals is harmful, we demonstrate the advantages of adding intentional frequency offset to the conventional power domain-NOMA (P-NOMA). We introduce two methods which add artificial frequency offsets between different sets of sub-carriers destined for different users. The first one uses the same successive interference cancellation (SIC) method as the conventional P-NOMA except that it enjoys reduced inter-user interference (IUI) between interfering sub-carriers. The second scheme adopts a precoding at the base station and a linear preprocessing scheme at the receiving user. It decomposes the broadcast channel into parallel channels circumventing the need for SIC. As a result, it fully exploits the advantages provided by the frequency asynchrony and enables the interference-free transmission to the users. The numerical results show that both methods can outperform the conventional P-NOMA

Effect of metformin on the spatial memory in aged rats

Background: Aging process is often accompanied with some degree of decline in all the abilities, including learning and memory. One of the attracting research fields has been devoted to finding antiaging drugs. Metformin has shown some memory-enhancing features in aged humans and laboratory animals. Aims and Objective: To evaluate the effects of 50, 75, and 100 mg/kg of metformin on the spatial memory performance of aged rats in the Morris water maze. Materials and Methods: Thirty-two male 24-month-old rats were divided randomly into four groups (n = 8) including control group and 50-, 75-, and 100-mg/kg metformin groups. After 36 days of treatment, the learning process was assessed by the reference memory task in the Morris water maze. All the rats received water maze training (four trials/day for 5 days) to assess the hippocampal-dependent spatial learning and, then, received a 60-s probe trial test of spatial memory retention 24 h after the twentieth trial. Result: Over 5 days of training, metformin (50, 75, and 100 mg/kg/day) treatment significantly reduced the latency and path length to find the escape platform (P < 0.01). In probe trials (without platform), on the last day of training, the metformin-treated groups spent significantly longer time in the platform quadrant when compared with the control group. Among the treated groups, 100 mg/kg dosage of metformin induced the best rehearsals memory (P < 0.05). Conclusion: These results showed that, in the old rats, 36-day orally administered metformin showed a positive influence on the spatial memory performance in the Morris water maze. © 2015 Farzaneh Ganji

Effect of short time captopril administration on spatial memory in aging rats

Introduction: The brain renin-angiotensin system (RAS) has been reported having a pathological role in age-related impairment in learning and memory. Therefore, angiotensin converting enzyme inhibitors (ACEi) are expected to have positive ef fects on memory. Longtime treatment with captopril (an angiotensin converting enzyme inhibitor) significantly attenuates the age-related impairment in learning and memory. Materials and Methods: In the present study, 24 month old male Wistar rats were divided into four experimental groups (n=8). Captopril treated groups received daily ip injections of captopril at doses of 5, 10, 15 mg/kg/day for one week, the forth group served as control and remained untreated. Learning process was assessed by the reference memory task in the Morris water maze. All rats received water maze training (4 trials/day for 5 days) to assess hippocampal dependent spatial learning and then received a 60-s probe test of spatial memory retention 24 h after the 20th trial. Results: Over 5 days of training, captopril 5, 10, 15 mg/kg/day treatment signi ficantly reduced the latency and path length to finding the escape platform. In probe trails (without platform), on the last day of training, the captopril -treated group spent significantly longer time in the platform quadrant than control animals. Among treated group, 10 /mg/Kg dosage of captopril induced the best rehearsals memory. Conclusion: These results confirm the previous studies that ACEi have a positive influence on memory and it was noticeable that even short time treatment by captopril can improve spatial memory in the aged rats. © 2015, Iranian Society of Physiology and Pharmacology. All rights reserved

Effect of vitamin C and quercetin treatment on the liver histopathologic profile in congenital lead exposed male rat pups

Introduction: Lead is one of the most important environmental pollutants due to its vast use in various industries. Lead accumulation in different organs, especially the brain, liver and kidneys can cause serious health problems. Lead exposure is more dangerous during fetal period and childhood. Materials and Methods: Timed pregnant female rats divided into 6 groups. Group 1served as control group and received tap water, group 2 received 500 mg/liter lead acetate in the drinking water from 5th day of gestation up to 25th day post-partum, group 3 received the same dose of lead acetate along with daily IP injection of 40mg/kg quercetin, Group 4 received the same dose of lead acetate along with 2g/liter vitamin C, groups 5 and 6 received vitamin C and quercetin respectively like groups 2 and 3 but without lead acetate. On the 25th day postpartum, 6 male pups in each group were deeply anesthetized by chloroform; livers were removed and processed for Hematoxyline- Eosin staining. The microscopic slides were photographed and liver tissue morphological characteristics were evaluated. Results: Lead exposure caused extensive histopathologic changes in liver tissue including hepatocyte degradation, cell nucleus bifurcation and inflammation around hepatic veins. Quercetin and vitamin C treatment could prevent these pathologic changes to a considerable extent. Conclusion: Vitamin C in drinking water and quercetin via IP injection could protect the liver tissue against lead hepatotoxic effects. © 2015, Iranian Society of Physiology and Pharmacology. All rights reserved