Multiscale Spatial-Temporal Representation Learning for mmWave Radar 3-D Human Pose Estimation

Millimeter-wave (mmWave) radar has emerged as a promising sensing modality for 3-D human pose estimation in ubiquitous Internet of Things (IoT) applications, owing to its privacy-preserving nature and robustness under challenging illumination conditions. However, accurate skeletal reconstruction remains difficult due to the inherent sparsity, nonuniform distribution, and instability of radar point clouds. To address these challenges, this article proposes MS-STPoseNet, a unified multiscale spatio-temporal learning framework for robust mmWave-based human pose estimation. For spatial representation, MS-STPoseNet employs a hierarchical multiscale spatial encoder built upon PointNet++, which leverages multiscale grouping (MSG) to effectively capture body structures across different spatial resolutions, from fine-grained joint regions to limb- and torso-level configurations, under irregular radar observations. For temporal modeling, a multibranch temporal convolutional network (TCN) with different dilation rates is introduced to model multirate motion dynamics, enabling effective representation of both rapid limb movements and smoother torso motions. An attention mechanism is further incorporated to enhance informative temporal features while suppressing noise. The entire framework is trained end-to-end to estimate per-frame 3-D poses by exploiting short-term temporal context, thereby improving robustness under noisy sensing conditions. Extensive experiments conducted on a self-collected dataset and two public benchmarks demonstrate that MS-STPoseNet consistently outperforms state-of-the-art methods in terms of pose estimation accuracy and cross-subject generalization, achieving an MPJPE of 3.08 cm on the self-collected dataset. In addition, the proposed framework exhibits favorable computational efficiency and a compact model size, highlighting its potential applicability to practical IoT sensing systems.