Experimental Investigation of User Identification and Delay Estimation for Asynchronous CDMA-Based UOWC

User asynchrony and near-far problem are two pivotal issues in the underwater optical wireless communication (UOWC) multiple access system. In this paper, asynchronous code division multiple access (CDMA) is introduced to the UOWC system. A subspace-based user identification and delay estimation algorithm is proposed to identify active users and estimate their delays, which requires only prior knowledge of spreading codes of all registered users. An underwater testbench facilitating three-user access is established to further demonstrate the feasibility of the proposed algorithm. Experimental results show that active users with large signal-to-noise ratio can be accurately identified given an appropriate threshold, and the signals of active users can be successfully acquired in the presence of multiple access interference (MAI).