  In this paper, we consider the power minimization problem of joint physical
resource block (PRB) assignment and transmit power allocation under specified
delay and reliability requirements for ultra-reliable and low-latency
communication (URLLC) in downlink cellular orthogonal frequency-division
multiple-access (OFDMA) system. To be more practical, only the imperfect
channel state information (CSI) is assumed to be available at the base station
(BS). The formulated problem is a combinatorial and mixed-integer nonconvex
problem and is difficult to tackle. Through techniques of slack variables
introduction, the first-order Taylor approximation and reweighted
$\ell_1$-norm, we approximate it by a convex problem and the successive convex
approximation (SCA) based iterative algorithm is proposed to yield sub-optimal
solutions. Numerical results provide some insights into the impact of channel
estimation error, user number, the allowable maximum delay and packet error
probability on the required system sum power.
