Research On Cognitive Relay Networks With Wireless Energy Harvesting And Information Transfer

Due to the shortage of wireless spectrum resources and the demand of green economy,the spectrum efficiency and energy efficiency have become the important design indexes of modern wireless communication systems.Therefore,how to improve the efficiency of spectrum utilization while improving the energy efficiency becomes the difficult problem of the current research.Cognitive relay communication technology achieves the sharing of spectrum resources with low-cost consuming,which effectively improves the spectrum utilization.At the same time,the wireless energy conversion technology which harvests energy from the radio achieves a significant breakthrough.Therefore,it is an effective technology to improve the energy efficiency.This paper studies the wireless energy harvesting and information transfer technology which is applied to cognitive relay networks.Based on the theoretical modeling,convex optimization and biconvex optimization,we develop a series of resource allocation algorithms in cognitive relay networks with the wireless energy conversion protocol.The main achievements of this paper include:1.We propose the energy harvesting and information transfer protocol for one-way cognitive relay networks.The transmission can be divided into two phases.In the first phase,based on the power splitting method,the secondary user transmitter obtains the primary user's signals and harvests energy from the radio sent by the primary user at the same time.Besides,the secondary user receiver also harvests energy form the primary user's signals.In the second phase,the secondary user transmitter transmits the acquired primary user's signals to the primary user receiver while superimposing its own secondary user's signal with the harvested energy.Based on the above-mentioned transfer protocol,we derive the theoretical expressions of the outage probability for the primary and secondary network users.The results show that,with the proper power allocation method,the outage performance of the network under this protocol is better than the situation with no spectrum sharing.In addition,we further analyze the rate-energy trade-offs between secondary users maximizing ergodic capacity and maximizing harvested energy.The energy efficiency of the system is also studied under different transmitting power and power splitting ratios.Moreover,simulation results show that this protocol can guarantee the transmission quality of the primary users and the secondary users,and this is based on not consuming the secondary user's own energy.2.Based on the proposed protocol,in order to further improve the spectral efficiency and energy efficiency,this paper consider and solve the following three joint optimization problems: a)to maximize the sum data rate of the primary and secondary users,b)to maximize the data rate of the primary user while the data rate of the secondary user exceeds the given threshold,c)to maximize the secondary user's data rate while the primary user's data rate is not lower than the threshold and the amount of energy harvested by the secondary user is not below the target value.Obviously,the above three problems are non-convex.We theoretically prove that the above three optimization problems can be converted to the classical biconvex optimization problems.Besides,we propose two different iterative optimization algorithms.Through the numerical simulation,we can see that the proposed algorithm can effectively and significantly improve the sum data rates,the primary user's data rate and the secondary user's data rate,which proves the effectiveness of the algorithms in the different scenarios.3.To further improve the spectral efficiency,we propose the energy harvesting and information transfer protocol for two-way cognitive relay networks.Unlike the one-way cognitive relay network protocol,this protocol enables the primary users to communicate in both directions at the same time.Besides,it makes the secondary user share the primary users' spectrum to communicate.Interestingly,it does not consume the secondary user's own energy and improves the spectrum efficiency.Under this protocol,we present the theoretical outage probability expressions for the primary users.For the secondary users,we can not give the accurately theoretical expression.However,we give the theoretical lower and upper bounds.In addition,we also study the relationship between the overall system energy efficiency and transmitting power along with the power splitting ratio.The study shows that the two coefficients need to be controlled in a certain range,which can achieve the optimal system energy efficiency.Besides,the numerical simulation results show that our proposed two-way cognitive relay network protocol can effectively guarantee the twoway communication of the primary users and the unidirectional data communication of the secondary users.Under the appropriate power allocation coefficient situation,the protocol can outperform the non-spectrum sharing situation,and this is based on the case that not consuming the secondary user's own energy.