Focusing on the characteristics of selfishness of relay users and asymmetric network information in cognitive radio networks, a multi-user cooperative communication mechanism was proposed. Firstly, by modeling the cooperative communication as a labor market, a modeling method for the multi-user contract-based relay selection framework was investigated under the symmetric network information scenario. Then, to avoid the adverse selection problem due to the hidden-information of Secondary User (SU) before contract assignment, a contract-based relay selection model was proposed to incentivize the contribution of secondary users for ensuring cooperative communication. The experimental results show that, by hiring the secondary users with better channel condition or less relay cost, Primary User (PU) can obtain much more cooperative communication utility. The proposed multi-user contract-based cooperative communication framework can put forward new ideas for efficient utilization of spectrum resource.

To alleviate the shortage of licensed spectrum resource, a method to design and implement the multi-user Cooperative Spectrum Sharing (CSS) mechanism was proposed based on the characteristics of asymmetric network information and selfishness of communication users. First, by modeling the CSS as a labor market, a modeling method for the multi-user contract-based CSS framework was investigated under the symmetric network information scenario. Then, to avoid the moral hazard problem due to the hidden-action of Secondary Users (SUs) after contract assignment, a contract-based CSS model was proposed to incentivize the contribution of SUs for ensuring spectrum sharing. The experimental results show that, when the direct transmission rate of Primary User (PU) is less than 0.2 b/s, in comparison with the case of non-cooperative spectrum sharing, the capacity of network is more than 3 times larger. The proposed multi-user contract-based CSS framework will put forward new ideas for efficient sharing and utilization of spectrum resource.

According to the diversity, dynamics and correlation of product design knowledge, this paper put forward a knowledge representation method for product design based on ontology, established a knowledge unit with the core of object, concept set, property set, proposition set and function set, and designed the links between them. On this basis, this paper introduced input and output modules to enhance the comprehensiveness and flexibility of product design knowledge representation. Finally, the paper took cylindrical spiral spring design as an example and verified the effectiveness of the proposed method.