# Difference DV_Distance Localization Algorithm Using Correction Coefficients of Unknown Nodes
## 1 Introduction
Usually, because of unavoidable error in the phase of distance estimation, the localization accuracy of range-free based algorithms is still relatively poor. Compared with range-free localization algorithms, range-based localization can provide higher localization accuracy, and the ranging methods obtain information, including distance or angle between sensor nodes, by ranging techniques such as Received Signal Strength Indicator (RSSI) [17], Time-Difference-of-Arrival (TDOA) [18], Time-of-Arrival (TOA) [19], and Angle-of-Arrival (AOA) [20]. TDOA, TOA, and AOA have higher requirements for node hardware, while RSSI is a low power and inexpensive ranging method only relying on the acceptance strength of wireless signals. At present, DV_Distance, proposed by [PERSON] and [PERSON] [21], is a typical range based node localization  
Figure 1: An example of wireless sensor networks (WSNs). algorithm, and RSSI is used to measure the distance between adjacent nodes, and then the actual Euclidean distance can be replaced by the accumulated hop distance. Because the DV_Distance algorithm is sensitive to the ranging error, and meanwhile the accumulated hop distance is generally larger than the actual Euclidean distance, thus localization error comes up inevitably. In order to further reduce localization error, some correction model or coefficients are designed to modify the accumulated hop distance between nodes, so that the corrected distance is more similar to the actual Euclidean distance. In this paper, a difference DV_Distance localization algorithm using correction coefficients of unknown nodes is proposed. To the best of knowledge, our contributions are as follows:  
1. The correction model based on unknown nodes is used, so that the unknown nodes can have their own correction coefficients, instead of using the correction coefficients from their nearest anchor nodes, and thus the difference of correction coefficients for unknown nodes can be reflected. 2. The difference of accumulated hop distance and actual Euclidean distance between anchor nodes is used to design correction coefficients. Because of no position information of unknown nodes, the distance difference from unknown nodes to anchor nodes cannot be directly computed. Therefore, we use the information of anchor nodes distributed in different direction to indirectly compute the distance difference. 3. According to the actual contribution of anchor nodes in different direction, the weighting process is put forward to get the final correction coefficient of unknown nodes, which can further improve the localization accuracy of the proposed algorithm. The remainder of this paper is organized as follows. In Section 2, we briefly review other researchers' study on DV_Distance improvement which we have realized. In Section 3, the basic DV_Distance localization algorithm is briefly introduced. We introduce how we refine the DV_Distance algorithm in Section 4. Section 5 illustrates the simulation results, and also we compare and analyze the difference between our proposed algorithm and other improved DV_Distance localization algorithms. Finally, we present our conclusions in Section 6.