I. Introduction
A. Motivation
B. Related Surveys
C. Contributions
D. Organization
II. DSOC Advantages and Challenges
A. DS Communications Challenges
B. Link Engineering of DSOC
C. DSOC Promises and Challenges
III. DSOC Physical Layer Key Characteristics
IV. DSOC Physical Layer Performance Analysis
V. DSOC Networking Protocols
VI. Advances of DSOC
VII. Concluding Remarks