IEEE Communications Surveys and Tutorials is an online journal published by the IEEE Communications Society that focuses on tutorials and surveys covering all aspects of the communications field. As telecommunications technology advances rapidly, the IEEE Communications Society is committed to providing researchers and professionals with the information and tools they need to stay informed. The journal aims to integrate and enhance understanding of existing literature on communications, placing results in context. Whether seeking in-depth information about a familiar area or an introduction to a new one, IEEE Communications Surveys and Tutorials strives to be the premier source of peer-reviewed, comprehensive tutorials and surveys, along with pointers to further resources. The journal publishes only articles specifically written for it, which undergo a rigorous review process before publication in quarterly issues. A tutorial article is designed to help readers become familiar with and learn something specific about a chosen topic. In contrast, a survey article provides a comprehensive review of developments in a selected area, covering its evolution from inception to the present and beyond, illustrated with extensive citations from the literature. Both tutorials and surveys should be instructional in nature and written in a style that is comprehensible to readers outside the specialty of the article.