To relieve the shortage problem of licensed spectrum, the aggregation of licensed and unlicensed carriers has emerged as an attractive solution for opportunistically increasing the throughput of LTE systems while enhancing the utilization of unlicensed spectrum. As one of the representative aggregation technologies, LAA is in favor of the harmonious coexistence with WiFi systems by leveraging the LBT mechanism and different pre-defined access priorities. In this article, we present a general overview of the attractive benefits and technical challenges for aggregating licensed carriers with unlicensed carriers. We then introduce some fundamental features of the LBT based LAA, including transmission modes, ED threshold, random backoff within the contention window, and access priority classes. Under multiple unlicensed channels, we propose two novel multi-carrier LBT mechanisms to improve the transmission behavior and coexistence performance of LAA and WiFi. It is verified in terms of successful transmission probability and carrier utilization rate that two proposed multi-carrier LBT mechanisms can achieve much better performance than the conventional counterpart using random carrier selection.

中文翻译：

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无执照频谱中LAA和WiFi共存的多载波LBT设计

为了缓解许可频谱的短缺问题，已经出现了许可和非许可运营商的聚合作为有吸引力的解决方案，用于机会性地增加LTE系统的吞吐量，同时提高了非许可频谱的利用率。作为代表性的聚合技术之一，LAA通过利用LBT机制和不同的预定义访问优先级来支持与WiFi系统的和谐共存。在本文中，我们概述了将许可运营商与非许可运营商进行汇总所带来的诱人收益和技术挑战。然后，我们介绍基于LBT的LAA的一些基本功能，包括传输模式，ED阈值，竞争窗口内的随机退避以及访问优先级。在多个无牌渠道下，我们提出了两种新颖的多载波LBT机制，以改善LAA和WiFi的传输行为和共存性能。从成功的传输概率和载波利用率方面来看，两个提出的多载波LBT机制可以比使用随机载波选择的传统对等机制获得更好的性能。