# A Novel Wireless-Netted UWB Life-Detection Radar System for Quasi-Static Person Sensing
## 6 Experiments and Results  
In this section, three types of experimental scenes are designed to simulate complex through-wall conditions. The corresponding experiments were carried out to verify the performance of the proposed multiple observation point detection system. Two layers of brick walls or reinforced concrete floors were penetrated to detect human respiration in type-I (see Figure 6a) and type-II (see Figure 6b) experimental scenes, respectively. For the type-III scene, the propagation distance effect in the through-wall condition is considered. Because of the high radar prototype cost, two Golay complementary coded UWB life-detection radars were used in three experiments. For simplicity, the two radars are labeled as radars No.1 and No.2, respectively. The tested human subject is indicated by the dotted frame in the figure. As shown in Figure 6a, the type-I experiment was carried out in an apartment unit with various sundry items such as a refrigerator, TV and desktop computer, and the two Golay complementary coded UWB life-detection radars are placed on the same side of the 27 cm brick wall 1.5 m apart. The tested human subject with weak respiration stood at a distance of 4.7 m from radar No.1 and 4.8 m from radar No.2. The type-II experiment was carried out in a building under construction, as shown in Figure 6b. There was electromagnetic interference caused by signal transmission lines and cars. Two radars were placed on the fourth floor 1 m apart. The width of the reinforced concrete floor was 12 cm. The tested human subject lay on the second floor. The distances between him and radars No.1 and No.2 were 6.7 m and 6.8 m, respectively. The type-III experiment was carried out in a stadium, as shown in Figure 6c. An air conditioner and high-power lighting facilities were the main sources of electromagnetic interference. The two radars were placed on the same side of a 37 cm brick wall 2.2 m apart. The tested human subject stood behind the wall, at a distance of 21.6 m from radar No.1 and 21.3 m from radar No.2. Normally, the echoes from a single radar can be processed by any fast Fourier transform (FFT)-based respiration detection method--for example, the one in [33]--to extract the human breathing frequency. However, due to the low signal to noise ratio (SNR) in these three types of experimental scenes, as shown in Figure 7, all the output range-frequency images are too noisy to distinguish the vital sign features (VSFs). Under the architecture of the proposed multiple observation point detection system, the echoes from the two Golay complementary coded UWB life-detection radars were suitable for association processing to generate the new form of the VSF. Figure 6: Experimental scenes: (**a**) type-I scene, (**b**) type-II scene, (**c**) type-III scene. According to our proposed multi-observation point detection method, when weak respiration movement is present, a new type of VSFs of the tested human subject may appear in the output cross-correlated range-frequency 3D image. The three dimensions of the output cross-correlated range-frequency 3D image represent the range from radar No.1, the range from radar No.2 and the respiration frequency, respectively. As shown in Figure 8a-c, by finding a suitable threshold, the VSFs for the three types of experiments are remarkable. The respiration frequencies indicated by the VSFs are 0.32 Hz, 0.3 Hz and 0.28 Hz, respectively, which are consistent with the actual situation. To further understand the VSFs in the output cross-correlated range-frequency 3D images, 2D slice (range \(\times\) range) images corresponding to the specific respiration frequencies of 0.32 Hz, 0.3 Hz and 0.28 Hz are presented in Figure 9a-c, respectively. Figure 7: The output range-frequency images using the normal fast Fourier transform (FFT)-based respiration detection methods using the echoes from a single radar. (**a**,**b**) Type-I experimental results. (**c**,**d**) Type-II experimental results. (**e**,**f**) Type-III experimental results.