Abstract:

The different risks and hazards that may affect human life due to the destruction of the means of communication with the outside world, have a great challenge in the development of communication technology that has a high demand in terms of spectrum resources. So to solve this problem, you need a good spectrum management and therefore a more efficient use of it. Solution around an embedded radio equipment, multifunction and multi-standard to access to all the radio resources available in the near environment, could solve this problem with its ability to access any network that environment can contain. The cognitive radio (CR) has a better solution to adapt to varying conditions of the radio spectrum. In cognitive radio systems, secondary users (SU) need to optimize the decision-making cognition cycle to reach an optimal solution that meets the requested QoS. In this paper we propose genetic algorithms (GA) as a better intelligence engine, more specifically, the GA used for solving the optimization problem of radio parameters.

Abstract:

In underlay cognitive networks, secondary users operating with primary user are adhering to stringent interference constraint which limits their transmission power and coverage area. Therefore, it is very likely that the underlay networks will make use of relays to transmit signals to the distant secondary users. The retransmitting relay will be selected among the available secondary users; hence, relay selection becomes more challenging due to strict interference limits. In this paper, we propose a secondary relay selection scheme which maximizes the end-to-end signal to noise ratio (SNR) for the secondary link while keeping the interference levels to the primary network below a certain threshold. We derive closed form expressions of the probability density function (PDF) of the SNR at the secondary destination, the outage probability, the average bit error probability and the ergodic capacity. Analytical results are validated by simulations and they provide comparative analysis of the relay selection scheme proposed herein.