Clustered NOMA-based downlink adaptive relay coordinated transmission scheme for future 6G cell-free edge network

With the emergence of new mobile network applications (augmented reality, virtual reality and internet of vehicles), users' requirements for network service become higher. However, poor channel quality of direct link, and limit backhaul capacity of the network make some users cannot obtain their requested contents from direct link or core network, and even lead to network congestion, which become the bottleneck of the 6th generation mobile networks (6G). Therefore, this paper study clustered non-orthogonal multiple access (NOMA)-based downlink adaptive relay coordinated transmission scheme for future 6G cell-free edge network to improve the sum data rate of users in the NOMA cluster. Firstly, the system model includes the network model considering the 6G cell-free edge network architecture, and the content request and caching strategy are given. Then, the adaptive relay coordinated transmission scheme, and sum data rate maximization problem considering the maximum transmit power optimization of small cell base stations (SBSs) and relays, and the way that users obtain their requested contents is formulated. Finally, the continuous convex optimization approximation based iterative power optimization (CCOA-IPO) algorithm is proposed to solve the formulated sum data rate maximization problem. Numerical results show that the proposed scheme can provide higher sum data rate for users than the direct transmit scheme, relay decode-and-forward (DF) scheme, and relay amplify-and-forward (AF) scheme.