Collaborative edge computing (CEC) is a recent popular paradigm where different edge devices collaborate by sharing data and computation resources. One of the fundamental issues in CEC is to make task offloading decision. However, it is a challenging problem to solve as tasks can be offloaded to a device at multi-hop distance leading to conflicting network flows due to limited bandwidth constraint. There are some works on multi-hop computation offloading problem in the literature. However, existing works have not jointly considered multi-hop partial computation offloading and network flow scheduling that can cause network congestion and inefficient performance in terms of completion time. This article formulates the joint multi-task partial computation offloading and network flow scheduling problem to minimize the average completion time of all tasks. The formulated problem optimizes several dependent decision variables including partial offloading ratio, remote offloading device, start time of tasks, routing path, and start time of network flows. The problem is formulated as an MINLP optimization problem and shown to be NP-hard. We propose a joint partial offloading and flow scheduling heuristic (JPOFH) that decides partial offloading ratio by considering both waiting times at the devices and start time of network flows. We also do the relaxation of formulated MINLP problem to an LP problem using McCormick envelope to give a lower bound solution. Performance comparison done using simulation shows that JPOFH leads to up to 32 percent improvement in average completion time compared to benchmark solutions which do not make a joint decision.

中文翻译：

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协作边缘计算中的多跳多任务部分计算卸载

协作边缘计算 (CEC) 是最近流行的一种范式，其中不同的边缘设备通过共享数据和计算资源进行协作。CEC 的基本问题之一是做出任务卸载决策。然而，这是一个需要解决的具有挑战性的问题，因为任务可以被卸载到多跳距离的设备上，从而由于有限的带宽限制导致网络流冲突。文献中有一些关于多跳计算卸载问题的工作。然而，现有的工作没有联合考虑多跳部分计算卸载和网络流量调度，这会导致网络拥塞和在完成时间方面的性能低下。本文制定了联合多任务部分计算卸载和网络流量调度问题，以最小化所有任务的平均完成时间。公式化的问题优化了几个相关的决策变量，包括部分卸载率、远程卸载设备、任务的开始时间、路由路径和网络流的开始时间。该问题被表述为一个 MINLP 优化问题，并显示为 NP-hard。我们提出了一种联合部分卸载和流调度启发式算法（JPOFH），它通过考虑设备的等待时间和网络流的开始时间来决定部分卸载率。我们还使用 McCormick 包络将公式化的 MINLP 问题放松到 LP 问题，以给出下界解决方案。