Open research questions in Indoor and Outdoor Localization Technologies

What the literature leaves open

• Another challenge is the unknown, time-varying noise under NLOS/multipath conditions in UWB ranging. The approach also needs to address the issue of reliable communication between platforms and potential communication delays or data loss.

  UAV–UGV Collaborative Localization in GNSS-Denied Large-Scale Environments: An Anchor-Free VIO–UWB Fusion with Adaptive Weighting and Outlier Suppression · 2026 · DOI

• Traditional fingerprint-based methods are limited by their reliance on coordinate weighting based on signal similarity. The topological mismatch between signal space and physical space in indoor non-line-of-sight environments is not adequately addressed. Existing methods do not effectively mitigate neighborhood distortion and false matching risks.

  Total Variational Indoor Localization Algorithm for Signal Manifolds in the Energy Domain · 2026 · DOI

• There is a lack of discussion on methods that utilize multiple sensors for fused localization. Prior work has focused on individual positioning techniques, but there is a need for a comprehensive review of multi-source sensor fusion methods. The paper identifies a gap in the analysis of the complementary advantages of various sensors for indoor localization.

  Indoor Localization Methods for Smartphones with Multi-Source Sensors Fusion: Tasks, Challenges, Strategies, and Perspectives · 2025 · DOI

• The paper identifies the need for accurate localization of drones to improve the performance of anti-drone systems. Existing techniques have limitations in terms of localization accuracy.

  Performance Enhancement of Drone Acoustic Source Localization Through Distributed Microphone Arrays · 2025 · DOI

• The need for substantial annotated training data for Human Activity Recognition using Wi-Fi Channel State Information. Class imbalance and poor generalisability in complex, multi-user environments. Limited existing research on device-free HAR systems using Wi-Fi Channel State Information.

  Enhancing Multi-User Activity Recognition in an Indoor Environment with Augmented Wi-Fi Channel State Information and Transformer Architectures · 2025 · DOI

• Most existing studies are based on datasets collected in specific scenarios with limited trajectory diversity and sensing modalities. The features derived from a single wireless modality are often fragile to variations in environmental layouts and walking trajectories.

  XGait: A Multi-Modality Wireless Sensing Dataset for Indoor Human Tracking and Identification · 2026 · DOI

• Addressing the privacy concerns and limited field of view of vision-based approaches.

  Human Activity Recognition Through Augmented WiFi CSI Signals by Lightweight Attention-GRU · 2025 · DOI

• Integrating distributed optimization into the current framework - Integrating learned NLOS classifiers into the current framework - Benchmarking on public…

  UAV–UGV Collaborative Localization in GNSS-Denied Large-Scale Environments: An Anchor-Free VIO–UWB Fusion with Adaptive Weighting and Outlier Suppression · 2026 · DOI

• The study is based on simulation experiments, - the window length T affects the computational accuracy and real-time performance of the algorithm, - further increasing the window length results in a minimal improvement…

  Time-Division-Based Cooperative Positioning Method for Multi-UAV Systems · 2026 · DOI

• Investigating the impact of different window lengths on the algorithm's performance, - exploring the application of the proposed method in various fields such as military operations, agriculture, logistics, disaster…

  Time-Division-Based Cooperative Positioning Method for Multi-UAV Systems · 2026 · DOI

• Validation on multiple public datasets - Dynamic loss weighting strategy - Simple yet effective pure CNN…

  Deep Learning-Based Indoor Localization by Using WiFi Fingerprinting and a CNN Algorithm · 2026 · DOI

• Investigating the impact of core parameters on localization accuracy, - Exploring the application of the EFM-GTV algorithm in other…

  Total Variational Indoor Localization Algorithm for Signal Manifolds in the Energy Domain · 2026 · DOI

• The study does not consider the need for synchronization at the network level across the gNBs - The analysis is based on a simulated environment - The number of training plates and their heights can impact the model's accuracy…

  Indoor UAV 3D Localization Using 5G CSI Fingerprinting · 2026 · DOI

• Investigating the impact of different numbers and heights of training plates on the model's accuracy and reliability - Exploring the use of dictionary learning techniques in image classification for indoor positioning - Developing alternative localization methods for UAV…

  Indoor UAV 3D Localization Using 5G CSI Fingerprinting · 2026 · DOI

• Linking spatial visitor behavior with neurophysiological responses, - Improving visitor engagement and supporting interactive cultural heritage experiences, - Evaluating positioning accuracy in a real, non-controlled…

  Ultra-Wideband System for Museum Visitors Tracking: Towards the Integration of the Positioning System with the Vision Sensors · 2026 · DOI

• High dependence on physical anchor nodes in UWB indoor positioning. Severe gross error interference in ranging observations. Difficulty in eliminating systematic errors such as electronic delay.

  Construction of Ultra-Wideband Virtual Reference Station and Research on High-Precision Indoor Trustworthy Positioning Method · 2026 · DOI

• Small sample size (N = 9 for the initial study, n = 18 for the user study), - Limited to a specific outdoor setting (a busy campus quad), - No comparison to other obstacle detection systems, - Limited generalizability to other populations…

  Exploration of radar-based obstacle visualizations to support safety and presence in camera-free outdoor VR · 2026 · DOI

• Investigating the effectiveness of WaveWalker in different outdoor environments, - Comparing WaveWalker to other obstacle detection systems, - Exploring the impact of WaveWalker on user experience in various VR…

  Exploration of radar-based obstacle visualizations to support safety and presence in camera-free outdoor VR · 2026 · DOI

• Exploring the application of the proposed method to other modalities - Investigating the use of other data augmentation and pruning techniques - Applying the proposed method to larger and more diverse…

  Human Activity Recognition Through Augmented WiFi CSI Signals by Lightweight Attention-GRU · 2025 · DOI

• The model was limited to single-actor scenarios in previous studies, - The system assumed consistent motion during data collection, - The model recognized only predefined…

  Enhanced Human Activity Recognition Using Wi-Fi Sensing: Leveraging Phase and Amplitude with Attention Mechanisms · 2025 · DOI

• Applying the PA-CSI model to more complex environments, - Exploring the use of the PA-CSI model in multi-actor…

  Enhanced Human Activity Recognition Using Wi-Fi Sensing: Leveraging Phase and Amplitude with Attention Mechanisms · 2025 · DOI

• Evaluating the system's performance in larger or more complex environments, - Comparing the proposed method with other state-of-the-art indoor positioning methods, - Investigating the use of other deep learning architectures for indoor…

  A Bluetooth Indoor Positioning System Based on Deep Learning with RSSI and AoA · 2025 · DOI

• Device heterogeneity poses a significant challenge to the accuracy and reliability of IPSs - Calibration drift and hardware heterogeneity challenge consistent performance - Lack of standardization and interoperability across IPS…

  Indoor Positioning Systems as Critical Infrastructure: An Assessment for Enhanced Location-Based Services · 2025 · DOI

• Addressing trade-offs between accuracy, energy efficiency, scalability, and deployment cost - Exploring collaborative and infrastructure-free positioning systems - Developing universally compatible…

  Indoor Positioning Systems as Critical Infrastructure: An Assessment for Enhanced Location-Based Services · 2025 · DOI

• Investigating the application of the proposed framework in other environments. Exploring the use of other data augmentation techniques. Developing more advanced deep learning architectures for CSI-based HAR.

  Enhancing Multi-User Activity Recognition in an Indoor Environment with Augmented Wi-Fi Channel State Information and Transformer Architectures · 2025 · DOI

Most-cited papers in Indoor and Outdoor Localization Technologies

• Integrated Sensing and Communications: Toward Dual-Functional Wireless Networks for 6G and Beyond · IEEE Journal on Selected Areas in Communications · 2022 · 3,778 citations
• Location systems for ubiquitous computing · Computer · 2001 · 1,958 citations
• Integrating Sensing and Communications for Ubiquitous IoT: Applications, Trends, and Challenges · IEEE Network · 2021 · 1,127 citations
• A Survey on Fundamental Limits of Integrated Sensing and Communication · IEEE Communications Surveys & Tutorials · 2022 · 1,119 citations
• A Survey on Indoor Positioning Systems for IoT-Based Applications · IEEE Internet of Things Journal · 2022 · 526 citations
• Joint Design of Communication and Sensing for Beyond 5G and 6G Systems · IEEE Access · 2021 · 494 citations
• WiFi CSI Based Passive Human Activity Recognition Using Attention Based BLSTM · IEEE Transactions on Mobile Computing · 2018 · 452 citations
• Varieties of Positioning · Journal for the Theory of Social Behaviour · 1991 · 440 citations
• A Review of Indoor Localization Techniques and Wireless Technologies · Wireless Personal Communications · 2021 · 406 citations
• Wayfinding with a GPS-based mobile navigation system: A comparison with maps and direct experience · Journal of Environmental Psychology · 2007 · 363 citations

Most recent work

• Robust Optimization for Movable Antenna-Aided Cell-Free ISAC With Time Synchronization Errors · IEEE Transactions on Wireless Communications · 2026
• A Survey on Wi-Fi Sensing Generalizability: Taxonomy, Techniques, Datasets, and Future Research Prospects · IEEE Communications Surveys & Tutorials · 2026
• Low-Complexity Angle-of-Arrival Estimation Using 1-bit Conversion · IEEE Transactions on Instrumentation and Measurement · 2026
• Consistency-Aware Anchor Pyramid Network for Crowd Localization · IEEE Transactions on Pattern Analysis and Machine Intelligence · 2026
• RadioDiff-Inverse: Diffusion Enhanced Bayesian Inverse Estimation for ISAC Radio Map Construction · IEEE Transactions on Wireless Communications · 2026
• Statistical Channel-Based Low-Complexity Rotation and Position Optimization for 6D Movable Antennas Enabled Wireless Communication · IEEE Transactions on Wireless Communications · 2026
• An optimized GRU-RNN framework for real-time human interaction recognition using WiFi channel state information with integrated GUI for smart environments · Multimedia Tools and Applications · 2026
• Reliability-governed scaling of mobile crowdsensing-based 3D radio mapping for ubiquitous indoor positioning: An uncertainty-aware lifecycle review and deployment-oriented pipeline · Information Fusion · 2026
• UAV–UGV Collaborative Localization in GNSS-Denied Large-Scale Environments: An Anchor-Free VIO–UWB Fusion with Adaptive Weighting and Outlier Suppression · Drones · 2026
• A UWB Positioning Method Based on Clustering for NLOS Identification and Mitigation · IEEE Transactions on Industrial Electronics · 2026

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