Trajectory clustering is a cornerstone task in the field of trajectory mining. With the proliferation of deep learning, deep trajectory clustering has been widely researched to mine mobility patterns from massive unlabeled trajectories. Nevertheless, existing methods mostly ignore trajectories' temporal regularities, which are essential for mining fine-grained mobility patterns for applications including traveling group identification, transportation mode discovering, social security emergency, etc. To fill this gap, we propose ConDTC, a contrastive deep trajectory clustering method targeting for fine-grained mobility pattern mining. Specifically, we first design a spatial-temporal trajectory representation learning method which can capture both spatial and temporal regularities of trajectories synchronously. The proposed trajectory representation model can be used as a pre-trained model to serve various downstream trajectory mining tasks. Then, we construct a contrastive trajectory clustering module which optimizes trajectory representations and clustering performance simultaneously. Experimental results on three datasets validate that ConDTC can identify fine-grained mobility patterns by clustering trajectories with similar spatial-temporal mobility patterns together while separating those with different mobility patterns apart. Actually, ConDTC outperforms all state-of-the-art competitors substantially in terms of effectiveness, efficiency and robustness.

Trajectory data often suffer from sparsity and a lack of ground truth data, presenting challenges for map-matching.Traditional map-matching approaches struggle with sparse data, and deep learning methods are hindered by data scarcity.To address these issues, we propose a two-stage map-matching method.In the first stage, we use synthetic trajectory data to pre-train a deep learning model, overcoming data scarcity.We introduce a token mixing scheme during pre-training to clarify the interrelations between GPS-based and segment-based trajectory data.In the second stage, we fine-tune the model with limited ground truth data using a Transformer architecture.Empirical evaluations show that our model achieves 3.69%, 2.21% average precision and recall improvements over the best baseline model with various sparseness.

In the realm of human mobility data analysis, a multitude of constraints result in the publication of sparse, non-uniform implicit trajectories without explicit location information, such as coordinates. Researchers have dedicated substantial efforts towards trajectory recovery, aiming to densify trajectories and gain a more comprehensive understanding of human mobility. However, existing trajectory recovery methods focus on explicit trajectories, and require extensive historical data to capture users' mobility patterns. Nevertheless, implicit trajectories are usually more sparse than explicit trajectories. Addressing these challenges, we propose TrajBERT, an innovative BERT-based trajectory recovery method with spatial-temporal refinement. TrajBERT employs the Transformer encoder to learn mobility patterns bi-directionally and enhances the predictions by cross-stage temporal refinement. Subsequently, we design an output layer with global spatial refinement with a novel spatial-temporal aware loss function. To evaluate the performance of TrajBERT, we conduct a series of experiments on real-world datasets. Remarkably,TrajBERT yields at least 8.2% performance improvement compared to the state-of-the-art trajectory recovery approachs. Furthermore, TrajBERT successfully mitigates the cold start problem commonly experienced with new users lacking historical trajectories. It also shows superior robustness when faced with extremely sparse trajectories, thus demonstrating its potential as a practical tool in the field of human mobility analysis.

Trajectory clustering is a cornerstone task in trajectory mining. Sparse and noisy trajectories like Call Detail Records (CDR) have become popular with the rapid development of mobile applications. However, existing trajectory clustering methods' performance is limited on these trajectories. Therefore, we propose a dual Self-supervised Deep Trajectory Clustering (SDTC) method, to optimize trajectory representation and clustering jointly. First, we leverage the BERT model to learn spatial-temporal mobility patterns and incorporate them into the embeddings of location IDs. Second, we fine-tune the BERT model to learn cluster-friendly representations of trajectories by designing a dual self-supervised cluster layer, which improves the intra-cluster similarities and inter-cluster dissimilarities. Third, we conduct extensive experiments with two real-world datasets. Results show that SDTC improves the clustering accuracy by 12.1% (on a noisy and sparse dataset) and 3.8% (on a very sparse dataset) compared with SOTA deep clustering methods.

Mobile positioning plays an essential role in smart city services. This paper proposes a fingerprint positioning framework based on massive Minimization of Drive Test (MDT) data to provide accurate and efficient city-scale positioning without additional equipment and measures. First, a multi-level fingerprint construction method is proposed using the Timing Advance (TA), Reference Signal Receiving Power (RSRP), and Reference Signal Receiving Quality (RSRQ) of the serving cell and neighboring cell. Then, an adaptive online fingerprint matching method is employed to extract and match online data fingerprints. Experiments show that the median positioning error is 29.97 meters with city-scale MDT data. It outperforms the reported accuracy of the state-of-the-art fingerprint positioning method.

Summary In order to improve the quality of multi‐disk laser output beam quality, a theoretical method of astigmatism self‐compensation in multi‐disks resonator is developed based on which the maximization pre‐compensation of static aberration in the multi‐disk laser resonator is realized with the geometrical superposition of the astigmatism coefficient using the exhaustive method. In order to verify the theoretical method, a self‐compensating experiment has designed based on the theoretical method, which shows a clear improvement of the beam quality β.