# Research on Localization Algorithms Based on Acoustic Communication for Underwater Sensor Networks
## 1 Introduction
Moreover, some localization schemes do not need the anchor nodes to help realize positioning. In [5; 6], the authors utilize the connectivity information to estimate the unknown node. Currently, researchers have proposed many localization algorithms for UWSNs. However, most of the survey papers do not focus on the positioning algorithms. In [7], the authors present the survey of routing protocols in UWSNs. A paper [8] collects the recent advances on UWSNs. Some researchers consider the security and privacy in the localization of UWSNs [5]. In [9], the application, advances, and challenges are presented. Of course, some papers focus on the positioning algorithms. The papers [4; 10; 11] classify the localization algorithms based on the distributed vs. centralized, and estimation vs. prediction. In fact, the papers [10; 11] just describe only the two types of algorithms and compare with a few type of aspects of the papers. The paper [4] is more detailed than [10; 11] and collects more than twenty types of algorithms. However, it is not enough. In [12], the authors collect the range-based algorithms and compare the features of the algorithms. However, the less than thirty algorithms collected and compared do not contain most of the localization algorithms. Then, in [13], the authors classify the localization algorithms according to the mobility of the sensor nodes. Compared with other survey papers, the paper collects more research results; however, the other UWSN related information is not informed. Only the papers published before 2012 are collected, and some new research results have been reported that are not included. Thus, it is necessary to do a new survey about the localization algorithms. Our paper collects the papers in this field from 2003 to 2016, which means that various localization algorithms will be presented in the next section. The advantage can help researchers quickly learn what types of methods have been used in UWSNs and which extent of the performance of various algorithms have been achieved. In addition, we classify the positioning algorithms based on different criterions. Here, we take five aspects into account, namely, computation algorithm, spatial coverage, range measurement, the state of the nodes and communication between nodes. In addition, much-related knowledge is contained in our paper such as acoustic communication, network architecture, routing techniques, challenges or open issues. The purpose of presenting our paper is that we hope a whole architecture of UWSNs will be built and provide a quick way to find the knowledge that the reader may need. In our paper, we concentrate on the localization algorithms and introduce numerous papers to show and compare with them. In addition, the comparison of survey papers for the localization algorithms in UWSNs is shown in Table 1.  
Our paper concentrates on a comprehensive survey of positioning technology for UWSNs and is organized as follows: we introduce the acoustic communication, the network architecture and routing techniques in Section 2. Sequentially, the localization algorithm taxonomy is presented in Section 3. For each taxonomy, we describe the difference of the localization algorithms and then use the references to show positioning performance of this technology. We discuss in Section 4 and provide a qualitative comparison of the positioning algorithms. In Section 5, numerous challenges and open issues are described. The conclusions are presented in Section 6.