## 2 Related Work
### Hybrid PSOGWO Principle
#### 2.2.2 Gwo
### Performance Evaluation

To verify the effectiveness and feasibility of ILP-PSOGWO, four aspects, including the LOS and NLOS environment, area of localization region, the number of reference points and number of iterations, are selected to evaluate the precision of the proposed method. Precision is the main index to evaluate the performance of a localization method, and it is also an important standard to evaluate the quality of a set of localization models. Localization precision is usually measured using the Euclidean distance between the estimated location and the true location, known as the localization error. The smaller the localization error, the higher the localization precision. The localization error is denoted by \(error_{i}\), and it can be calculated as follows:

\[error_{i}=\sqrt{(x_{true}-x_{est})^{2}+(y_{true}-y_{est})^{2}} \tag{22}\]

where \((x_{true},y_{true})\), \((x_{est},y_{est})\) represent the actual and estimated location of the target node \(i\), respectively. #### 4.2.1 Impact of Area of Localization Region on Localization Precision

When the number of reference points is 5, we tested the impact of different areas of the localization region on the localization precision of the four methods in indoor LOS and NLOS, respectively. Figure 12(a) describes the influence of the area of localization region on the localization precision in LOS. With the increase in area, the localization error of ILP-PSOGWO and EWCL methods increases. The localization error obtained by PSO and GWO methods shows an unstable trend. This is because they search for feasible solutions in the whole localization region, and the search direction and speed are not fixed, leading to unstable localization results. ILP-PSOGWO narrows the search space of feasible solutions before using the PSOGWO, so it can obtain stable and more accurate localization results. Figure 12(b) indicates the influence of the area of localization region on the localization precision in NLOS. The localization errors of the four methods increase accordingly. Compared with EWCL and ILP-PSOGWO, the PSO and GWO are more sensitive to the environment and have larger localization errors. #### 4.2.2 Impact of Location of Test Point on Localization Precision

During the experiment, when the area of localization region is 17 \(\times\) 10 and the number of reference points is 5, we assume that there are 6 target nodes needed to be located, and their locations are different. The experimental results are shown in Table 2. Compared with NLOS, the localization errors obtained by the four methods in the LOS are lower. This is because in the NLOS, the RSS is easily affected by the environment. Table 2 also describes that the localization errors measured by PSO and GWO in the two environments are quite different. However, the difference in localization errors measured by EWCL

Figure 13: Impact of area of localization region on localization error. (**a**) LOS. (**b**) NLOS. and ILP-PSOGWO is little in the LOS and NLOS, indicating that the two methods have good stability. #### 4.2.3 Impact of the Number of Reference Point on Localization Precision

The number of reference points is one of the factors that affect the localization precision of the target node. To observe the influence of the number of reference points on the localization precision, when the area of localization region is 17 \(\times\) 10, we select the number of reference points as 3, 5, 7, 9, 11 and 13 for the experiment. Figure 14 depicts the influence of the number of reference points on the localization precision of the three methods in LOS and NLOS. Figure 14a shows that when the number of reference points increases, the localization errors of the three methods decrease accordingly, and the localization errors of the three methods are all kept within 1.5 m. Figure 14b reveals that compared with GWO and ILP-PSOGWO, the change in the number of reference points has a greater impact on the localization results of PSO.