Reserch On Energy Efficient Technology With Imperfect Spectrum Sensing In Cognitive Radio Networks

With the rapid increasing demanding of the wireless services and applications in4G, wireless communication system needs more and more spectrum resource, which leads to the spectrum resource becomes more and more scarcity. Fortunately, cognitive radio technology is regarded as a promising technology to effectively resolve the contradiction between the low utilization of the rare spectrum resource and increasing demanding of wireless communication applications. In cognitive radio networks, the cognitive users sense the spectrum and find any access opportunity to use the spectrum, as long as the interference to primary users is lower than the specified threshold.Moreover, energy and environment is the world’s problem and more and more attentions have been paid on the green communications. Although the cognitive radio can make decisions intelligently, it needs more energy on spectrum sensing and spectrum decisions. Hence, the research on energy efficiency in cognitive radio networks is becoming more and more important and brings great challenge to experts and scholars. Besides, with the spectrum sensing errors, the cognitive may make wrong decision on idle spectrum and busy spectrum, which will lead to miss spectrum access chance or make interference to primary users. So taking spectrum sensing errors into consideration, the research on cognitive radio networks is actual requirement.With imperfect spectrum sensing, this paper investigates the energy efficient sensing/transmission duration and transmission power in cognitive radio networks. Based on k-out-of-N fusion rule, we formulate the energy efficiency function in terms of sensing time, transmission time and transmission power, subject to the total power constraint and interference constraint. Firstly, it is derived that for a given fusion rule threshold, the objective function is unimodal with one optimization parameter varying while other parameters are fixed. Furthermore, we provide the corresponding closed-form expressions of the optimal data transmission duration and transmission power. Finally, the globally unimodal property is proven, and hence, the globally optimal point can be easily found with the proposed algorithm based on the alternating direction method (ADM). Numerical simulation results show that our proposed scheme is much better than the existing ones.Furthermore, we research the energy efficient power allocation with imperfect spectrum sensing based on OFDM in cognitive radio networks. Firstly, the energy efficiency module is formulated, subject to the total power allocation constraint and the interference constraint, with the consideration of the imperfect spectrum sensing. Because of the joint optimization of the sensing time and the power allocation among the subcarriers, we give the two steps solution to solve the optimization problems. One step is searching the sensing time from zero to the frame duration, last step is solving the optimal power allocation with the fixed sensing time. With the Lagrange deposition algorithm, we propose one low complexity power allocation algorithm. Simulation results show that the above method is right and has better trade-off between capacity and energy consumption than the others.