Mission-critical applications are of significant importance to sixth generation (6G)’s massive and ubiquitous Internet of things (IoT) communications. The mission-critical applications mostly fall within the scope of finite blocklength (FBL), and in order to assess the information freshness, age of information (AoI) has been introduced. However, packet error is inevitable in the FBL regime, which exerts impacts on the time for successful packet transmission, and thus increases the AoI. To optimize the performance of AoI, the management of queue packets is an effective way. Motivated by optimizing the AoI performance in the FBL regime, we consider a system equipped with a single buffer, and propose two schemes of packet management in this article. We subsequently derive the closed-form expressions for the average AoI and the average peak AoI and we discuss the relationship between AoI and the factors, i.e. the blocklength, data generation rate and signal-to-noise ratio. Afterwards, we give the optimal blocklength expression associated with the optimal AoI. In order to examine the information timeliness in the network under the proposed schemes, the closed-form expressions of the average delay are deduced. The simulation results validate the theoretical analysis and demonstrate the advantage of the proposed scheme in terms of the performance of AoI, delay, and their trade-off.

The aircraft is the sharpest sword of the carrier, and the lifetime of the replaceable units determines its availability. At present, few studies refer to the hybrid impact of maintenance and degradation on the lifetime. This article proposes a model for predicting the remaining useful life of the replaceable units, which considers the combination of imperfect maintenance and nonlinear degradation. The problem of remaining useful life estimation of carrier-based aircraft replaceable units considering the degradation process with the time-varying nonlinear coefficient and condition-based maintenance has been studied. The composition and original data of the replaceable unit system have been analyzed. A condition-based maintenance with time-varying nonlinear model and decision model has been established considering assumptions and characteristics. The condition-based maintenance decision model is established by taking the total cost rate of the whole life process of the carrier-based aircraft replaceable unit as the decision target. Besides, the multidimensional search method is used to obtain the optimal condition-based maintenance threshold and maximum number of condition-based maintenance, to achieve the ultimate goal of reducing the maintenance cost of the carrier-based aircraft replaceable unit system. Finally, the simulation confirms that predictions of remaining useful life with the proposed model are more accurate than those with a linear model and a hybrid remaining useful life prediction method.