boxes,and a set of Impinj E41-B tags.The reader works at the frequency band 920.625~924.375MHz.The antenna is fixed on the motion controller which enables the linear movement along the horizontal direction and the vertical direction. Software:We have implemented 3DLoc in Java and we run the software in a terminal PC which is connected to the Reader with the Low-level Reader Protocol.The motion controller is programmed to move at the speed of 15cm/s for the 3D ader localization of the tagged objects. Fig.11.Experiment scene B.Deployment We conduct our experiments in the indoor environment. obviously as we increase the distance between the tags:the Fig.11 shows the experiment scene and specifies the coordinate error drops from 15.2cm to 7.3cm as the tag distance changes system.The antenna is fixed on the motion controller,which from 3cm to 15cm.In free space,the localization error changes supports the antenna's movement along the X axis and the slightly when the distance changes from 3cm to 9cm and the Z axis.For the tagged object,we deploy three sets of tag localization errors are all around 7cm.If we further increase arrays along mutually orthogonal directions on three mutually the distance to 12cm,the error becomes 4.3cm.In conclusion. orthogonal surfaces.For each tag array,since the tag coupling it is more useful to increase the distance between the two effect will distort the phase value [14,15],we ensure that two adjacent tags for the tag array in the multipath environment adjacent tags are deployed with opposite orientations as shown since the localization error in free space is small. in Fig.11. Tag number of the tag array vs.Localization error: Generally,more tags in the tag array contributes to a lower C.Micro-Benchmark localization error.We set the distance between the two adjacent Experimental setup:The experiments are performed in tags to be 9cm and change the the number of tags in the tag two cases:free space and multipath environment.We have array.As shown in Fig.15,in the multipath environment,the designed four experiments to evaluate the performance of localization errors decrease when we increase the total number the multipath suppression algorithm and analyze how the tag of the tags from 2 to 5:the localization error changes from numbers and tag distances influence the localization accuracy. 17cm to 9cm.For the free space scenario,the error for the 2- Since the 3D localization is expanded from the 2D plane,we tag array is 7.1cm,thus obvious improvement cannot been seen first focus on the 2D localization of the tags.The antenna and for the localization accuracy when we increase the number of the tags are all put at a height of 80cm from the ground. the tags in the tag array. Metrics:We use error(cm)to indicate the localization accuracy for a single tag and the tag array.Specifically for D.Macro-Benchmark the tag array,the center of the tag array are considered as our Experimental setup:We put the antenna on the motion localization target. controller to move along the X and Z axes to localize three Determine a proper window size for multipath suppres- tagged objects.The size of the object is 45 x 40 x 30cm and it sion:The slide window separates the point set for removing is attached with three four-tag arrays in which the distance of the outliers in the AoA-based localization.As illustrated in the two adjacent tags is 9cm.In the experiment,we place three Fig.12,the localization error is 15cm when we set the window tagged objects in different locations with different orientations. size to 5.The error decreases as we increase the window size Metrics:In the evaluation of 3DLoc,the localization errors from 5 to 15.However,the error increases again if we go on are calculated both for the target tag array and the object.We increasing the window size w.Therefore,we set w to 15cm consider the center of the tag array and the centroid of the as a trade-off. object as the localization target for the target tag array and With or without multipath suppression:To evaluate the object,respectively. the performance of the multipath suppression algorithm,we In the first experiment,we evaluate 3DLoc in comparison localize four tags in different locations.The coordinates of with the Hologram-based method.Since the orientation of the the four tags are Ti(0,120),T2(-20,140),T3(20,140),and object cannot be estimated by the Hologram-based method T4(-20,160).As shown in Fig.13,the localization error compared with 3DLoc,we cannot estimate location of the decreases sharply when we adopt the proposed multipath centroid of object.Thus We only compare the localization suppression algorithm,i.e.,the error for T2 decreases from results of the given target tag array.As shown in Fig.16, 45cm to 15cm. two methods both perform well in the free space.However, Tag distance of the tag array vs.Localization error:in the multipath environment,the errors for 3DLoc and the Intuitively,a larger distance between the tags results in a Hologram-based method are 8cm and 16.7cm respectively.So higher localization accuracy.We localize a four-tag array in 3DLoc outperforms the Hologram-based method significantly both free space and the multipath environment while changing in the multipath environment. the distance between two adjacent tags.As shown in Fig.14, In the second experiment,we place three objects in different in the multipath scenario,the localization error decreases locations and orientations,and localize them by 3DLoc in theboxes, and a set of Impinj E41-B tags. The reader works at the frequency band 920.625∼924.375MHz. The antenna is fixed on the motion controller which enables the linear movement along the horizontal direction and the vertical direction. Software: We have implemented 3DLoc in Java and we run the software in a terminal PC which is connected to the Reader with the Low-level Reader Protocol. The motion controller is programmed to move at the speed of 15cm/s for the 3D localization of the tagged objects. B. Deployment We conduct our experiments in the indoor environment. Fig.11 shows the experiment scene and specifies the coordinate system. The antenna is fixed on the motion controller, which supports the antenna’s movement along the X axis and the Z axis. For the tagged object, we deploy three sets of tag arrays along mutually orthogonal directions on three mutually orthogonal surfaces. For each tag array, since the tag coupling effect will distort the phase value [14, 15], we ensure that two adjacent tags are deployed with opposite orientations as shown in Fig.11. C. Micro-Benchmark Experimental setup: The experiments are performed in two cases: free space and multipath environment. We have designed four experiments to evaluate the performance of the multipath suppression algorithm and analyze how the tag numbers and tag distances influence the localization accuracy. Since the 3D localization is expanded from the 2D plane, we first focus on the 2D localization of the tags. The antenna and the tags are all put at a height of 80cm from the ground. Metrics: We use error(cm) to indicate the localization accuracy for a single tag and the tag array. Specifically for the tag array, the center of the tag array are considered as our localization target. Determine a proper window size for multipath suppres￾sion: The slide window separates the point set for removing the outliers in the AoA-based localization. As illustrated in Fig.12, the localization error is 15cm when we set the window size to 5. The error decreases as we increase the window size from 5 to 15. However, the error increases again if we go on increasing the window size w. Therefore, we set w to 15cm as a trade-off. With or without multipath suppression: To evaluate the performance of the multipath suppression algorithm, we localize four tags in different locations. The coordinates of the four tags are T1 (0, 120), T2 (−20, 140), T3 (20, 140), and T4 (−20, 160). As shown in Fig.13, the localization error decreases sharply when we adopt the proposed multipath suppression algorithm, i.e., the error for T2 decreases from 45cm to 15cm. Tag distance of the tag array vs. Localization error: Intuitively, a larger distance between the tags results in a higher localization accuracy. We localize a four-tag array in both free space and the multipath environment while changing the distance between two adjacent tags. As shown in Fig.14, in the multipath scenario, the localization error decreases Z Y X Motion controller Reader Antenna Tag array Different orientation O Fig. 11. Experiment scene obviously as we increase the distance between the tags: the error drops from 15.2cm to 7.3cm as the tag distance changes from 3cm to 15cm. In free space, the localization error changes slightly when the distance changes from 3cm to 9cm and the localization errors are all around 7cm. If we further increase the distance to 12cm, the error becomes 4.3cm. In conclusion, it is more useful to increase the distance between the two adjacent tags for the tag array in the multipath environment since the localization error in free space is small. Tag number of the tag array vs. Localization error: Generally, more tags in the tag array contributes to a lower localization error. We set the distance between the two adjacent tags to be 9cm and change the the number of tags in the tag array. As shown in Fig.15, in the multipath environment, the localization errors decrease when we increase the total number of the tags from 2 to 5: the localization error changes from 17cm to 9cm. For the free space scenario, the error for the 2- tag array is 7.1cm, thus obvious improvement cannot been seen for the localization accuracy when we increase the number of the tags in the tag array. D. Macro-Benchmark Experimental setup: We put the antenna on the motion controller to move along the X and Z axes to localize three tagged objects. The size of the object is 45 × 40 × 30cm and it is attached with three four-tag arrays in which the distance of the two adjacent tags is 9cm. In the experiment, we place three tagged objects in different locations with different orientations. Metrics: In the evaluation of 3DLoc, the localization errors are calculated both for the target tag array and the object. We consider the center of the tag array and the centroid of the object as the localization target for the target tag array and the object, respectively. In the first experiment, we evaluate 3DLoc in comparison with the Hologram-based method. Since the orientation of the object cannot be estimated by the Hologram-based method compared with 3DLoc, we cannot estimate location of the centroid of object. Thus We only compare the localization results of the given target tag array. As shown in Fig.16, two methods both perform well in the free space. However, in the multipath environment, the errors for 3DLoc and the Hologram-based method are 8cm and 16.7cm respectively. So 3DLoc outperforms the Hologram-based method significantly in the multipath environment. In the second experiment, we place three objects in different locations and orientations, and localize them by 3DLoc in the