arXiv subjects

Zhe George Zhang

Publications and source records attributed to Zhe George Zhang.

3 recordsLinked to original sources

arXiv2022

A Closed Queueing Maintenance Network with Two Batch Policies

This paper discusses a maintenance network with failed items that can be removed, repaired, redistributed, and reused under two batch policies: one for removing the failed items from each base to a maintenance shop and the other for redistributing the repaired items from the maintenance shop to bases. This maintenance network can be considered a virtual closed queueing network, and the Markov system of each node is described as an elegant block-structured Markov process whose stationary probabilities can be computed by the RG-factorizations. The structure of this maintenance network is novel and interesting. To compute the closed queueing network, we set up a new nonlinear matrix equation to determine the relative arrival rates, in which the nonlinearity comes from two different groups of processes: the failure and removal processes and the repair and redistribution processes. This paper also extends a simple queueing system of a node to a more general block-structured Markov process which can be computed by the RG-factorizations. Based on this, the paper establishes a more general product-form solution for the closed queueing network and provides performance analysis of the maintenance network. Our method will open a new avenue for quantitative evaluation of more general maintenance networks.

cs.PF↗

arXiv2018

A $c/μ$-Rule for Service Resource Allocation in Group-Server Queues

In this paper, we study a dynamic on/off server scheduling problem in a queueing system with multi-class servers, where servers are heterogeneous and can be classified into $K$ groups. Servers in the same group are homogeneous. A scheduling policy determines the number of working servers (servers that are turned on) in each group at every state $n$ (number of customers in the system). Our goal is to find the optimal scheduling policy to minimize the long-run average cost, which consists of an increasing convex holding cost and a linear operating cost. We use the sensitivity-based optimization theory to characterize the optimal policy. A necessary and sufficient condition of the optimal policy is derived. We also prove that the optimal policy has monotone structures and a quasi bang-bang control is optimal. We find that the optimal policy is indexed by the value of $c - μG(n)$, where $c$ is the operating cost rate, $μ$ is the service rate for a server, and $G(n)$ is a computable quantity called perturbation realization factor. Specifically, the group with smaller negative $c - μG(n)$ is more preferred to be turned on, while the group with positive $c - μG(n)$ should be turned off. However, the preference ranking of each group is affected by $G(n)$ and the preference order may change with the state $n$, the arrival rate, and the cost function. Under a reasonable condition of scale economies, we further prove that the optimal policy obeys a so-called $c$/$μ$-rule. That is, the servers with smaller $c$/$μ$ should be turned on with higher priority and the preference order of groups remains unchanged. This rule can be viewed as a sister version of the famous $cμ$-rule for polling queues. With the monotone property of $G(n)$, we further prove that the optimal policy has a multi-threshold structure when the $c$/$μ$-rule is applied.

math.OC↗

arXiv2017

Groups of Repairmen and Repair-based Load Balancing in Supermarket Models with Repairable Servers

Supermarket models are a class of interesting parallel queueing networks with dynamic randomized load balancing and real-time resource management. When the parallel servers are subject to breakdowns and repairs, analysis of such a supermarket model becomes more difficult and challenging. In this paper, we apply the mean-field theory to studying four interrelated supermarket models with repairable servers, and numerically indicate impact of the different repairman groups on performance of the systems. First, we set up the systems of mean-field equations for the supermarket models with repairable servers. Then we prove the asymptotic independence of the supermarket models through the operator semi-group and the mean-field limit. Furthermore, we show that the fixed points of the supermarket models satisfy the systems of nonlinear equations. Finally, we use the fixed points to give numerical computation for performer analysis, and provide valuable observations on model improvement. Therefore, this paper provides a new and effective method in the study of complex supermarket models.

cs.PF↗