Power Allocation And Spatial Interference Detection In Wireless Spectrum-sharing Systems

With the rapid deployment of wireless networks, a growing demand for wireless radio spectrum has been witnessed during the last decade. However, a great portion of the licensed spectrum is severely under-utilized under the fixed spectrum assignment policy. The concept of cognitive radio is proposed to improve the spectrum efficiency and has been receiving an increasing attention in recent years, since it equips wireless users the capability to optimally adapt their operating parameters according to the interactions with the surrounding radio environment. There have been many significant developments in the past few years on cognitive radios. This paper selects two application scenarios of the spectrum sharing cognitive radio to discuss.The first case is Device-to-Device(D2D) communications in the LTE-Advanced Networks. D2 D can increase the spectrum efficiency and extend the coverage of the cellular network. Therefore, D2 D communication is a key way to improve the performance of the future LTE-Advanced cellular networks. However, the power allocation of D2 D communications calls for the careful design to overcome the increasing energy consumption of user device and to protect the cellular user from the interference when D2 D users reuse the same spectrum. In this paper, we propose an approach of power allocation of D2 D users that underlay in a cell with one base station(BS) and multiple cellular users by minimizing the energy consumption per bit per second with limited interference impact on the corresponding cellular receiver. To obtain a solution, we transform the original problem formulated as the ratio of two functions into another parametric formulation. An algorithm is developed by using the monotonicity of the parametric formulation and the relationship between the two formulations. Finally, we verify the proposed scheme by numerical simulations.The second case is the underlay Multiple Input Multiple Output(MIMO) cognitive radio networks. The emergence MIMO communication provides cognitive radio networks with new directions and possibilities. This paper proposes a blind technique that enables a MIMO cognitive radio Secondary User(SU) to transmit in the same band with a Primary User(PU) simultaneously by utilizing separate spatial dimensions than the PU. Specifically, The SU learns the null space of the interference channel to the PU without burdening the PU with any explicit cooperation. The only condition required is that during the learning period, the SU is allowed to inflict “non-harmful” interference to the PU. The SU measures a monotonic function of this interference in order to learn the null space. Specifically, during the learning interval, the SU learns the null space by iteratively modifying the spatial orientation of its transmitted signal and measures the effect of this modification on the monotonic function that it observes. We provide simulation results demonstrating that the algorithm converges rapidly.