The deployment of multiple small-Unmanned Aerial Vehicles (UAVs) in various applications has gained considerable attention from researchers and business organizations. Recent studies on UAV networks show paramount magnification in the calibre of interest to deploy UAVs in both military and civilian sectors. Despite salutary in deployment, UAVs face a crucial challenge in radio allocation, timing control, and channel access. Majority of these issues are due to inefficient Medium Access Control (MAC) protocols as most of the applications with UAVs use subsisting MAC protocols, which are only congruous for traditional networks. The MAC protocols for existing networks face an issue of applicability to UAV-based communication network due to the requirements of highly dynamic and mobile scenarios. This paper tries to highlight such issues and challenges and presents a detailed review of the MAC protocols applicable for UAV-based communication ecosystems. Moreover, mechanisms to fit the existing protocols into UAV scenarios are additionally discussed along with key technologies and standards. Finally, the article provides future challenges about UAV communications.

在各种应用中部署多种小型无人机（UAV）已引起研究人员和商业组织的极大关注。对无人机网络的最新研究表明，将无人机部署到军事和民用领域的最大兴趣在于其放大倍数。尽管部署上很有益，但无人机在无线电分配，定时控制和信道访问方面面临着严峻的挑战。这些问题多数是由于无效的媒体访问控制（MAC）协议造成的，因为大多数带有无人机的应用程序都使用现有的MAC协议，而后者仅适用于传统网络。由于高度动态和移动场景的需求，用于现有网络的MAC协议面临适用于基于UAV的通信网络的问题。本文试图强调此类问题和挑战，并对适用于基于无人机的通信生态系统的MAC协议进行了详细回顾。此外，还与关键技术和标准一起讨论了将现有协议适合UAV场景的机制。最后，本文提供了有关无人机通信的未来挑战。