Tham khảo tài liệu 'mobile robots book 2011 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Indoor Localization Techniques based on Wireless Sensor Networks 291 To compare the performance quantitatively we calculate the total errors of Figure 7- e which is shown in Figure 7- f . The total errors are calculated as en 7 xn - x 2 Yn - y 2 14 where x y are true position values of the tag. From Figure 7- f we can see that the proposed-method has a better performance than cc2431. Figure 8- a to Figure 8- f show the test result when the tag is placed nearby the wall. As shown in Figure 8- f the proposed-method has a better performance than cc2431. For the experimental test of the algorithm described by Equations 7-12 let us call this method as the second method we carried out experimental tests by repetition. For this test we simply turned-off all mobile reference tags shown in Figures 3-4 and placed a reference mobile reference tag inside the office. This reference tag placed inside the office acts as a mobile reference. Fig. 7- a . Experimental test results inside the sensor network. 292 Mobile Robots - State of the Art in Land Sea Air and Collaborative Missions Fig. 7- b . Experimental test results inside the sensor network. x-axis meters Fig. 7- c . Experimental test results inside the sensor network. Indoor Localization Techniques based on Wireless Sensor Networks 293 Ũ 50 10Ũ I U-- í I I I I I I I I From the proposed method From Chipcon CC2431 True x-value I T T 1 . 1 - V - - 4 I I 1 1 1 1 1 1 Ij 1 1 1 t 1 J T t t t - From the proposed method From Chipcon CC2431 True y-value 150 200 250 300 350 400 Sampling time Fig. 7- d . Experimental test results inside the sensor network. 2 From the proposed method From Chipcon CC2431 Sampling time Fig. 7- e . Experimental test results inside the sensor .