MmWave extra-large-scale MIMO based active user detection and channel estimation for high-speed railway communications

The current High-Speed Railway(HSR)communications increasingly fail to satisfy the massive access services of numerous user equipment brought by the increasing number of people traveling by HSRs.To this end,this paper investigates millimeter-Wave(mmWave)extra-large scale(XL)-MIMO-based massive Internet-of-Things(loT)access in near-field HSR communications,and proposes a block simultaneous orthogonal matching pursuit(B-SOMP)-based Active User Detection(AUD)and Channel Estimation(CE)scheme by exploiting the spatial block sparsity of the XLMIMO-based massive access channels.Specifically,we first model the uplink mmWave XL-MIMO channels,which exhibit the near-field propagation characteristics of electromagnetic signals and the spatial non-stationarity of mmWave XL-MIMO arrays.By exploiting the spatial block sparsity and common frequency-domain sparsity pattern of massive access channels,the joint AUD and CE problem can be then formulated as a Multiple Measurement Vectors Compressive Sensing(MIMV-CS)problem.Based on the designed sensing matrix,a B-SOMP algorithm is proposed to achieve joint AUD and CE.Finally,simulation results show that the proposed solution can obtain a better AUD and CE performance than the conventional CS-based scheme for massive IoT access in near-field HSR communications.

Development of an onsite calibration device for robot manipulators

A novel in-contact three-dimensional(3D)measuring device,called MultiCal,is proposed as a convenient,low-cost(less than US$5000),and robust facility for onsite kinematic calibration and online measurement of robot manipulator accuracy.The device hasμm-level accuracy and can be easily embedded in robot cells.During the calibration procedure,the robot manipulator first moves automatically to multiple end-effector orientations with its tool center point(TCP)constrained on a fixed point by a 3D displacement measuring device(single point constraint),and the corresponding joint angles are recorded.Then,the measuring device is precisely mounted at different positions using a well-designed fixture,and the above measurement process is repeated to implement a multi-point constraint.The relative mounting positions are accurately measured and used as prior information to improve calibration accuracy and robustness.The results of theoretical analysis indicate that MultiCal reduces calibration accuracy by 10%to 20%in contrast to traditional non-contact 3D or six-dimensional(6D)measuring devices(such as laser trackers)when subject to the same level of artificial measurement noise.The results of a calibration experiment conducted on a Staubli TX90 robot show that MultiCal has only 7%to 14%lower calibration accuracy compared to a measuring arm with a laser scanner,and 21%to 30%lower time efficiency compared to a 6D binocular vision measuring system,yielding maximum and mean absolute position errors of 0.831 mm and 0.339 mm,respectively.

A Multi-module Controller for Walking Quadruped Robots

Motion control based on biologically inspired methods,such as Central Pattern Generator(CPG)models,offers a promising technique for robot control.However,for a quadruped robot which needs to maintain balance while performing flexible movements,this technique often requires a complicated nonlinear oscillator to build a controller,and it is difficult to achieve agility by merely modifying the predefined limit cycle in real time.In this study,we tried to solve this problem by constructing a multi-module controller based on CPG.The different parallel modules will ensure the dynamic stability and agility of walking.In the proposed controller,a specific control task is accomplished by adding basic and superposed motions.The basic motions decide the basic foot end trajectories,which are generated by the predefined limit cycle of the CPG model.According to conventional kinematics-based design,the superposed motions are generated through different modules alter the basic foot end trajectories to maintain balance and increase agility.As a considerable stability margin can be achieved,different modules are designed separately.The proposed CPG-based controller is capable of stabilizing a walking quadruped robot and performing start and stop movements,turning,lateral movement and reversal in real time.Experiments and simulations demonstrate the effectiveness of the method.