The research community has already identified that, by 2030, 5G networks will reach the capacity limits, and hence, will be inadequate to support next generation bandwidth-hungry, ubiquitous, intelligent services, and applications. Therefore, in view of sustaining the competitive edge of wireless technology and stratifying the next decade's communication requirements both, industry and research community have already begun conceptualizing the 6G technology. This article presents a detailed survey on the recent technological trends which address the capacity issues and enhance the spectrum-efficiency in 6G Communications. We present these trends in detail and then identify the challenges that need solutions before the practical deployment to realize 6G communications. Our survey article attempts to significantly contribute to initiating future research directions in the area of spectrum-efficiency in 6G communications.

翻译：研究界已经确认,到2030年,5G网络将达到能力极限,因此不足以支持下一代带宽饥饿、无处不在、智能服务和应用,因此,为了保持无线技术的竞争优势和限制下一个十年的通信需求,工业和研究界已经开始构思6G技术,这篇文章详细介绍了解决能力问题和提高6G通信频谱效率的最新技术趋势。我们详细介绍了这些趋势,然后确定了在实现6G通信实际部署之前需要解决的挑战。我们的调查文章试图大力推动6G通信频谱效率领域的未来研究方向。