Incentive Mechanism for Cooperative Scalable Video Coding (SVC) Multicast Based on Contract Theory

In scalable video coding (SVC) multicast, videos are encoded into several layers that represent multiple quality levels. Mobile users with different wireless channel conditions can obtain different numbers of layers and have different quality of experience (QoE). To enhance the QoE of the users that suffer from the worse channel quality, it is beneficial to stimulate users' cooperation in relaying enhancement layers. However, potential relays may be unwilling to truthfully cooperate with receivers, which results in the asymmetric information problem in relay selecting. In this paper, we model the video relaying selection as a market with multiple receivers (principals) and relays (agents), and solve the problem according to the contract theory. The proposed solution is divided into following two steps: first, contract design and item preselection, and second, matching between each principal and agent. We propose a contract parameter determination method termed as the Matching-Aware strategy. Different from traditional strategies, the proposed Matching-Aware strategy makes the contract competitive in principal-agent matching without knowing the probability distribution of relays' types. The matching step is undertaken by the base station with the purpose of maximizing the social welfare. Numerical results corroborate that the contract-based video relaying scheme can tackle the asymmetric information problem. Besides, compared with other two baseline strategies, the proposed Matching-Aware strategy achieves higher QoE.