Outage capacity regions of multicarrier DF relaying in underwater acoustic channels

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this paper, we investigate the information theoretical limits on the performance of cooperative multicarrier underwater acoustic (UWA) communication systems. We assume decode-and-forward (DF) relaying and consider non-orthogonal half-duplex cooperation. Under the assumptions of sparse and frequency-selective Rician fading channel and correlated Gaussian ambient noise, we derive the maximum achievable sum-rate and common/individual outage capacity regions for the cooperation protocol under consideration. We further investigate the effect of several parameters such as underwater temperature, carrier frequency, etc. on the outage capacity regions.TÜBİTA

Outage capacity regions of multicarrier DF relaying in underwater acoustic channels

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this paper, we investigate the information theoretical limits on the performance of cooperative multicarrier underwater acoustic (UWA) communication systems. We assume decode-and-forward (DF) relaying and consider non-orthogonal half-duplex cooperation. Under the assumptions of sparse and frequency-selective Rician fading channel and correlated Gaussian ambient noise, we derive the maximum achievable sum-rate and common/individual outage capacity regions for the cooperation protocol under consideration. We further investigate the effect of several parameters such as underwater temperature, carrier frequency, etc. on the outage capacity regions.TÜBİTA

Information theoretic performance of cooperative underwater acoustic communications

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Cooperative communication is considered as a major enabling technique to meet the demanding performance requirements of future underwater acoustic (UWA) communication systems. In this paper, we investigate the information theoretic performance of a cooperative UWA system to provide insight into the fundamental performance limits imposed by underwater acoustic channels. We first propose an approximate statistical model for the non-stationary ambient noise. The proposed model allows mathematical tractability and is a good fit for most operating frequencies in practical systems. Based on this ambient noise model, we investigate the outage performance of a precoded cooperative multicarrier UWA system with amplify-and-forward (AF) relaying. Our numerical results for cooperative UWA systems demonstrate significant performance gains over point-to-point systems. The impact of several system and environmental parameters on the performance is further demonstrated.Qatar National Research Fun

Error probability of DF relaying with pilot-assisted channel estimation over time-varying fading channels

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this paper, we investigate the error rate performance of a cooperative network with adaptive decode-and-forward (DF) relaying over time-selective frequency-flat Rayleigh-fading channels. We assume pilot-symbol-assisted modulation (PSAM) for the estimation of time-varying fading channel coefficients. For the system under consideration, we derive an exact closed-form expression for the average bit/symbol error rate, which is further validated through Monte Carlo simulations. Such closed-form solutions are highly desirable because they allow for rapid and efficient performance evaluation. Through the derived expression, we also demonstrate the effect of various system parameters such as the number of relays, Doppler values, and filter length on system performance

Performance of multicarrier cooperative communication systems over underwater acoustic channels

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Multicarrier transmission in the form of orthogonal frequency division multiplexing (OFDM) is an efficient method to handle inter-symbol interference resulting from the frequency selectivity of the underwater acoustic (UWA) channels. OFDM can be further combined with cooperative transmission to benefit from the spatial diversity advantages and improve the performance over conventional point-to-point UWA communication systems. In this study, the authors consider a cooperative OFDM UWA communication system and investigate the outage performance for both amplify-and-forward relaying and decode-and-forward (DF) relaying. They derive expressions for bounds on outage probability and outage capacity. Monte Carlo simulations corroborate and quantify the enhanced performance of cooperative OFDM UWA communication compared with direct transmission systems. Through numerical simulations, they investigate the impact of geometry on outage probability and signal-to-noise ratio requirements in cooperative OFDM UWA communication with DF relaying. Furthermore, the authors analyse the effects of relay location and carrier frequency on the outage probability for both relaying schemes.King Fahd University of Petroleum & Minerals (KFUPM

Exact closed-form error probability expression for cooperative diversity networks with channel estimation errors in time selective Rayleigh fading channels

Due to copyright restrictions, the access to the full text of this article is only available via subscription.In this paper, we investigate the performance of a cooperative network with adaptive decode-and-forward (DF) relaying over time-selective frequency-flat Rayleigh fading channels. In adaptive DF relaying, only a subset of the available relays with "good" channels are allowed to participate in the relaying phase. The destination combines the direct and the relayed signals using maximal ratio combining technique. Pilot-symbol-assisted modulation (PSAM) is used for the estimation of time-varying fading channel coefficients. For the system under consideration, we derive an exact closed-form expression for the average bit error rate. Such closed form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. We further present computer simulations to validate our analytical results

Cooperative underwater acoustic communications

Due to copyright restrictions, the access to the full text of this article is only available via subscription.This article presents a contemporary overview of underwater acoustic communication (UWAC) and investigates physical layer aspects on cooperative transmission techniques for future UWAC systems. Taking advantage of the broadcast nature of wireless transmission, cooperative communication realizes spatial diversity advantages in a distributed manner. The current literature on cooperative communication focuses on terrestrial wireless systems at radio frequencies with sporadic results on cooperative UWAC. In this article, we summarize initial results on cooperative UWAC and investigate the performance of a multicarrier cooperative UWAC considering the inherent unique characteristics of the underwater channel. Our simulation results demonstrate the superiority of cooperative UWAC systems over their point-to-point counterparts

Radiographic evaluation of dental age maturity in 3–17-years-old saudi children as an indicator of chronological age

Objective: This study was aimed to evaluate the dental age in Saudi children from panoramic radiographs using the Demirjian method to estimate their chronological age. Materials And Methods: This retrospective cross-sectional study consisted of 1902 panoramic radiographs of 955 boys and 947 girls between the ages of 3–17 years. All children were placed in the age group closest to their chronological age. The dental age was scored on all seven left mandibular teeth by calibrated examiners. Bivariate analyses using the t-test and Pearson correlation were performed. Results: There was significant difference in both boys and girls in all the age groups between their chronological age and dental age. Even though there was a slight overestimation in boys in some age groups and slight underestimation in girls in some groups, correlation analysis showed that there was a highly significant correlation between the chronological age and dental age for both boys (r2 = 0.96, P < 0.001) and girls (r2 = 0.98, P < 0.001). Moreover, correlation analyses for each age group showed a significant correlation between the chronological age and the dental age, using the Demirjian method, in most age groups (P < 0.01). When comparing the maturation score between boys and girls, the Student's t-test showed that there were no statistical differences between boys and girls in most age groups. Conclusion: Saudi boys and girls living in the western region of Saudi Arabia exhibited similar pattern of dental development when compared to the Demirjian method. Hence, the Demirjian method could be used as reference in children from the western region of Saudi Arabia

Influence of Curing Light Type and Staining Medium on the Discoloring Stability of Dental Restorative Composite

Discoloration kinetics of 4 commercial nano-filled resin composites polymerized with LED and QTH source types in 4 different staining media held at 37°C are investigated. Quartz Tungsten Halogen (QTH) and Light Emitting Diode (LED) were used. Dental composites color change was monitored with a digital spectrophotometer at one, two and four weeks for quantitative comparison. The kinetics and intensities of the color change in accelerated aging tests in staining media were monitored and discussed. Discoloring followed diffusive driven kinetics. The four composites polymerized with QTH light showed higher differences in color change intensities compared to LED cured ones. All the QTH cured samples have shown significant higher variations of color changes intensities compared to LED samples (p<0.05). LED cured composite showed comparatively more stable initial shade persistence than QTH cured ones, which may be explained in terms of higher level of polymerization and surface hardness reached by the LED light cure resinous composite matrix