Cooperation and Underlay Mode Selection in Cognitive Radio Network

In this research, we proposes a new method for cooperation and underlay mode selection in cognitive radio networks. We characterize the maximum achievable throughput of our proposed method of hybrid spectrum sharing. Hybrid spectrum sharing is assumed where the Secondary User (SU) can access the Primary User (PU) channel in two modes, underlay mode or cooperative mode with admission control. In addition to access the channel in the overlay mode, secondary user is allowed to occupy the channel currently occupied by the primary user but with small transmission power. Adding the underlay access modes attains more opportunities to the secondary user to transmit data. It is proposed that the secondary user can only exploits the underlay access when the channel of the primary user direct link is good or predicted to be in non-outage state. Therefore, the secondary user could switch between underlay spectrum sharing and cooperation with the primary user. Hybrid access is regulated through monitoring the state of the primary link. By observing the simulation results, the proposed model attains noticeable improvement in the system performance in terms of maximum secondary user throughput than the conventional cooperation and non-cooperation schemes

Multibody approach for railway dynamic analysis

In the work presented, a computational tool used for the dynamic simulation of railway vehicle systems was developed using multibody systems formulations. The model based on the multibody techniques developed by Shabana. With respect to other exciting methodologies the proposed one make use of a combined frame of references that permit the use of independent coordinates, with out the possibility to have singularity configurations depending on the rotation sequence. The combined frame of references used as a base for the formulation and modeling of wheel-rail contact problem with high precision. The program was designed for considering with a flexible form the different configuration of railway vehicles. The main structure of the program has the ability of making changes for enhancement of the wheel-rail contact model or the implementation of dynamic structure of the track, which considered to be future aspects for a PHD dissertation. The model used was applied to make a simulation for single bogie , also for a complete vehicle with two bogies. The obtained results of the dynamic response for a defined track composed of, tangent segment, transition curve which take the form of a clothoid curve, and finally circular curve with constant radius. The calculations were made for different velocities, lower than the critical in which the vehicle responded in stable form, and higher than the critical at which the instability of the vehicle was studied.Elsayed Abdel Hameed Amer Shaltout, R. (2010). Multibody approach for railway dynamic analysis. http://hdl.handle.net/10251/13763Archivo delegad