Joint Uplink and Downlink Transmission Design for URLLC Using Finite Blocklength Codes

This paper considers a joint uplink (UL) and downlink (DL) transmission design problem for achieving ultra-reliable and low-latency communications (URLLC) in a two-hop wireless network. Specifically, we assume that a sensor node sends information signals to a base station (BS) and then the BS sends some processed signals to some mobile terminals (MTs). The objective is to minimize the total over-the-air transmission latency under stringent UL-DL reliability constraints and power limit. The achievable rate formula of finite blocklength codes is used to explicitly model the relation between the transmission rate, latency and reliability. While the formulated problem is difficult to solve, we explore the problem structure by analyzing monotonicity and convexity of the objective function with respect to system variables. Then we develop an efficient alternating optimization (AO) algorithm to solve the considered problem. Simulation results demonstrate interesting trade off between various system parameters and show that the proposed AO algorithm yields near-optimal solutions.