Cooperative Spectrum Sharing For Cognitive Radio Networks:A Contract-based Approach

With the rapid development of wireless communication technologies,the existing fixed spectrum allocation strategy causes the shortage of available spectrum resources,and at the same time the allocated spectrum resources have low utilization rate.Because of the characteristics of relay cooperation and dynamic spectrum access,the cooperative spectrum sharing technology can better cope with the difficulties in wireless communication,and therefore has become a research hotspot in this field.Since there is a resource transaction between the primary user and the secondary user in the cooperative spectrum sharing,the content of the transaction is the spectrum resource of the primary user and the power resource of the secondary user.The traditional mathematical analysis tool is difficult to perform the resource exchange process.In order to analyze the resource exchange problem between the primary user and the secondary user,the cooperative relay model is mapped to the labor market model,in which the primary user and the secondary user respectively play the role of the employer and the employed in the labor market.Based on contract theory,this thesis studies the cooperative spectrum sharing between one primary user with one secondary user scenario,and multiple primary users with multiple secondary users scenario in cognitive radio networks.The main works are as following:(1)An Overlay-Underlay hybrid access mode cooperative spectrum sharing model based on channel statistics is proposed.In the model,one primary user and one secondary user perform cooperative communication,and the Overlay or Underlay cooperative spectrum sharing mode may be adopted according to the channel state cooperation mode.Based on this mode,an optimal contract design problem with the objective of maximizing the utility of the primary user is constructed.The constraint conditions are proposed to ensure that the secondary user can obtain non-negative utility,and a genetic algorithm is used to solve the optimization problem.Simulation results show that for the proposed Overlay-Underlay hybrid access mode cooperative spectrum sharing model,the optimal contract design can mobilize the enthusiasm ofcooperation between the primary and secondary users,therefore improving the spectrum utilization of the primary user and reducing energy consumption.It also provides secondary user with more opportunities to use the licensed spectrum to transmit information.(2)The proposed Overlay-Underlay hybrid cooperative spectrum sharing model is extended to multiple primary users and multiple secondary users scenario.Since multiple primary users and secondary users are randomly distributed in this scenario,the relative position and channel status of each primary user and each secondary user are different.Therefore,each primary user has different preferences for different secondary users,and it hopes to select the secondary user who can bring the maximum benefit as the relay.Meanwhile,each secondary user also has different preferences for different primary users,and it hopes to obtain more spectrum time.Based on this scenario,this thesis still aims to maximize the total utility of the primary users,and build the optimization problem of the optimal contract design in the complete information and incomplete information scenarios.In the complete information scenario,the Hungarian algorithm solves the relay selection problem between primary and secondary users because the statistical information of the channel is completely open,and the optimal contract design results under ideal conditions are obtained.In the incomplete information scenario,the generalized delay acceptance algorithm dynamically performs the contract design and achieves a stable market equilibrium,thereby obtaining optimal contract design results.Simulation results show that in the multiple primary users and multiple secondary users scenario,the average utility of the primary users in the incomplete information scenario is significantly increased by the proposed hybrid cooperative spectrum sharing strategy,which is close to the ideal value in the complete information scenario.