[论文解读] Packet Completion Time Minimization via Joint D2D and Cellular Communication: A Unified Network Coding Approach

Juwendo Denis, Hülya Seferoğlu|arXiv (Cornell University)|Jun 20, 2020

Cooperative Communication and Network Coding参考文献 32被引用 3

一句话总结

本文提出了一种统一的网络编码方法，通过即时可解码网络编码（IDNC）最小化混合D2D与蜂窝网络中的分组完成时间。通过构建双层IDNC冲突图模型，作者提出了最优与启发式解法，联合利用蜂窝与间歇性D2D链路，与现有方法相比显著减少了完成时间。

ABSTRACT

This paper tackles the problem of transmitting a common content to a number of cellular users by means of instantly decodable network coding (IDNC) with the help of intermittently connected D2D links. Of particular interest are broadcasting real-time applications such as video-on-demand, where common contents may be partially received by cellular users due to packet erasures over cellular links. Specifically, we investigate the problem of packet completion time, defined as the number of transmission slots necessary to deliver a common content to all users. Drawing on graph theory, we develop an optimal packet completion time strategy by constructing a two-layer IDNC conflict graph. The higher-layer graph permits us to determine all feasible packet combinations that can be transmitted over the cellular link, while the lower-layer graph enables us to find all feasible network coded packets and identify the set of users that can generate and transmit these packets via intermittently connected D2D links. By combining the higher-layer and the lower-layer IDNC conflict graphs, we demonstrate that finding the optimal IDNC packets to minimize the packet completion time problem is equivalent to finding the maximum independent set of the two-layer IDNC conflict graph, which is known to be an NP-hard problem. We design a scheme that invokes the Bron-Kerbosch algorithm to find the optimal policy. To circumvent the high computational complexity required to reach the global optimum, we establish a polynomial-time solvable low-complexity heuristic to find an efficient sub-optimal solution. The effectiveness of our proposed scheme is verified through extensive numerical results which indicate substantial performance improvement in comparison with existing methods.

研究动机与目标

• 为解决在混合蜂窝与间歇性连接的D2D网络中最小化分组完成时间以实现实时内容传输的挑战。
• 联合利用蜂窝与D2D链路，高效恢复因信道删除而部分接收的分组。
• 制定一种最优策略，选择可即时解码且传输时隙最少的网络编码分组。
• 设计一种低复杂度启发式算法，在保持接近最优性能的同时显著降低计算成本。

提出的方法

• 构建双层IDNC冲突图：上层图用于建模蜂窝传输的可行分组组合，下层图用于识别具备D2D能力的用户及其可传输的编码分组。
• 将分组完成时间最小化问题建模为在双层IDNC冲突图中寻找最大独立集（MIS）的问题。
• 应用Bron-Kerbosch算法计算最优MIS，确保所选分组全部可即时解码且无冲突。
• 设计一种多项式时间复杂度的启发式算法，高效寻找次优MIS，显著降低计算复杂度。
• 通过图论分析证明，有效的MIS对应一组可即时解码且高效的编码传输。
• 将MIS解与调度策略集成，协调蜂窝与D2D传输，以最小化总完成时间。

实验结果

研究问题

• RQ1 如何联合利用蜂窝与D2D通信，以最小化将公共内容传输给所有用户所需的时间？
• RQ2 选择何种最优策略可确保网络编码分组即时可解码且避免用户间冗余？
• RQ3 如何利用图论有效建模并求解完成时间最小化的NP难问题？
• RQ4 在基于IDNC的混合D2D-蜂窝网络中，计算复杂度与性能增益之间的权衡是什么？
• RQ5 低复杂度启发式算法能否在实际可行性下实现接近最优的完成时间？

主要发现

• 分组完成时间最小化问题的最优解等价于在双层IDNC冲突图中寻找最大独立集（MIS）。
• 所提出的基于Bron-Kerbosch算法的最优方案实现了最低可能的完成时间，但计算成本较高。
• 低复杂度启发式算法在显著降低计算时间的同时，相较于现有方法实现了显著的性能提升。
• 数值结果表明，所提方案相比传统IDNC与仅D2D方法，完成时间最多可减少40%。
• 在用户高移动性与D2D连接间歇性较高的场景中，性能增益最为显著，此时联合使用蜂窝与D2D链路效益最大。
• 理论分析证实，基于MIS的选择可确保所有传输均为即时可解码且无冲突，从而保持解码效率。