Channel assignment scheme in clustered multichannel cognitive radio networks with outdated CSI over Rayleigh fading channels

This work investigates channel assignment for cooperative spectrum sensing in multichannel cognitive radio networks, where the heterogeneity of primary user (PU) activity and the effect of varying channel condition on the received signal‐to‐noise ratio during cluster formation are considered. With the objective to minimize interference to the PU while enhancing multiple spectrum utilization of the secondary user (SU), an overlapping cluster‐based assignment is formulated into a nonlinear integer optimization problem. To obtain an efficient solution, the nonlinear integer problem is transformed into a mixed integer linear problem, based on which, this paper proposes an exact solution and then two new heuristic algorithms for suboptimal solutions, respectively. Furthermore, a comparative study of four different cluster head selection schemes with respect to their performance in cooperative spectrum sensing, under cluster's heterogeneity in terms of SUs distribution relative to PU transmitter location is presented. Based on the study, a robust cluster head selection scheme is proposed. Simulation results show that good sensing performance and increased opportunistic spectrum utilization in multichannel cognitive radio networks are two sides of a coin that depend on the ratio of the SUs to the number of PU channels. How far away the PU is from the cluster center is also seen to be key in the optimal selection of cluster heads in cooperative spectrum sensing.     

The role of the house fly (Musca domestica) in the dissemination of hookworm

The effect of cooling rate, warming rate, and duration of phase transition upon survival of frozen canine kidneys was investigated. In the present study, 11 kidneys out of 14 rapidly cooled (2--4degreesC/min) to --22degreesC and thawed (70--110degreesC/min) were viable following contralateral nephrectomy. The serum creatinine and BUN levels rose to a maximum of 8.4 and 30 mg%, respectively, on the eighth day post-contralateral nephrectomy. Average survival time was 10 days; however, two of the dogs in this group were allowed to survive, one for 3 months and one for over 2 years. Eight kidneys out of 16 slowly cooled (0.25-1.0degreesC/min) and either rapidly or slowly warmed (20-30degreesC/min) had function to produce small amounts of urine; however, they did not survive more than 5 days after contralateral nephrectomy. Cooling rates of 0.1 and 10degreesC/min were too harmful to the kidney to have renal function after reimplantation. The minimum renal cell damage as assessed by LDH and GOT in the post-freeze perfusate was found in the 2-4degreesC/min cooling rate following rapid warming (70degrees-110degreesC/min). Correlation of the duration of phase transition time to renal cell damage was linear for LDH and GOT (r=0.93). This result suggests that the duration of phase transition time also is an important factor during the freezing process, affecting post-thaw survival of canine kidneys.     

Analysing wear behaviour of Al–CaCO3 composites using ANN and Sugeno-type fuzzy inference systems

Neural Computing and Applications - Design of experiment for the development of stir cast calcium carbonate-reinforced aluminium composite is a search for optimum combination of material and...     

Improved Soft Iterative Channel Estimation for Turbo Equalization of Time Varying Frequency Selective Channels

In this paper, we present computationally efficient iterative channel estimation algorithms for Turbo equalizer-based communication receiver. Least Mean Square (LMS) and Recursive least Square (RLS) algorithms have been widely used for updating of various filters used in communication systems. However, LMS algorithm, though very simple, suffers from a relatively slow and data dependent convergence behaviour; while RLS algorithm, with its fast convergence rate, finds little application in practical systems due to its computational complexity. Variants of LMS algorithm, Variable Step Size Normalized LMS (VSSNLMS) and Multiple Variable Step Size Normalized LMS algorithms, are employed through simulation for updating of channel estimates for turbo equalization in this paper. Results based on the combination of turbo equalizer with convolutional code as well as with turbo codes alongside with iterative channel estimation algorithms are presented. The simulation results for different normalized fade rates show how the proposed channel estimation based-algorithms outperformed the LMS algorithm and performed closely to the well known Recursive least square (RLS)-based channel estimation algorithm.