Wireless sensor network (WSN) consists of a number of nodes that are mostly distributed in a random way to monitor or control different phenomena, such as military operations, earthquake monitoring, environmental monitoring, factory automation and security. A sensor network is formed from a large number of tiny, low energy, limited processing capability and low-cost devices called sensor nodes (SNs) that communicate with each other in an ad-hoc fashion. SNs gather and forward data in order to achieve targeted missions. However, the manual configuration for any sensor network is difficult especially when they are distributed in such a harsh environment. The task of determining the exact position of SNs in WSNs is known as localization, which is an important factor in all WSNs applications that deal with monitoring or controlling phenomena. The localization accuracy varies from one application to another; localization techniques are deployed in different applications based on given requirements. Localization techniques are categorized into two groups: range free and range based. In range-free techniques, localization depends on the relationship between nodes and topological information of sensor nodes; however, in the range-based group, it is required to calculate the distance between sensor nodes. The scope of this paper is on the range-free localization techniques only. First, we survey different range-free localization techniques and discuss some of the localization-based applications where the location of the SNs is vital and sensitive. Then, we describe five localization algorithms: Centroid, Amorphous, approximate point in triangle, DV-Hop and DV-HopMax. After that, we simulate these algorithms using MATLAB based on different setups and topologies. Finally, we make a comparative study between aforementioned localization algorithms based on different performance metrics showing their pros and cons such as localization accuracy and energy consumption.

无线传感器网络（WSN）由许多节点组成，这些节点大多数以随机方式分布，以监视或控制不同的现象，例如军事行动，地震监视，环境监视，工厂自动化和安全性。传感器网络由大量微型，低能耗，有限的处理能力和称为传感器节点（SN）的低成本设备组成，它们以自组织方式相互通信。SN收集并转发数据以实现目标任务。但是，任何传感器网络的手动配置都是困难的，尤其是当它们分布在如此恶劣的环境中时。确定SN在WSN中的确切位置的任务称为定位，这是所有处理监视或控制现象的WSN应用中的重要因素。定位精度因一个应用程序而异。本地化技术根据给定的要求部署在不同的应用程序中。本地化技术分为两类：无范围和基于范围。在无范围技术中，定位取决于节点与传感器节点的拓扑信息之间的关系。但是，在基于范围的组中，需要计算传感器节点之间的距离。本文的范围仅涉及无范围定位技术。首先，我们调查了不同的无范围定位技术，并讨论了基于SN的位置至关重要且敏感的基于定位的应用程序。然后，我们描述了五种定位算法：质心，无定形，三角形近似点，DV-Hop和DV-HopMax。之后，我们使用基于不同设置和拓扑的MATLAB仿真这些算法。最后，我们基于不同的性能指标对上述定位算法进行了比较研究，显示了它们的优缺点，例如定位精度和能耗。