Joint Blocklength and Power Optimization in High-Speed Railway Relay Communication Systems

For a high-speed railway relay downlink communication system based on short-packet transmission, the problem of maximizing the minimum user throughput by jointly optimizing the transmission packet length and the transmission power control of the relay device is investigated in this paper. The optimization problem is a nonconvex and mixed-integer one that is difficult to obtain an optimal solution, and a low-complexity algorithm is proposed to obtain the solution to the joint optimization problem. First, a closed-form expression of the optimal blocklength is derived by fixing the transmission power; Secondly, in the case of fixed blocklength, the non-convex optimization subproblem of transmission power is transformed into a convex problem by introducing auxiliary variables and using the successive convex approximation method. Finally, the feasibility and effectiveness of the proposed algorithm in this paper are verified by simulation.