Accurate Long-Term Multiple People Tracking Using Video and Body-Worn IMUs

Most modern approaches for video-based multiple people tracking rely on human appearance to exploit similarities between person detections. Consequently, tracking accuracy degrades if this kind of information is not discriminative or if people change apparel. In contrast, we present a method to fuse video information with additional motion signals from body-worn inertial measurement units (IMUs). In particular, we propose a neural network to relate person detections with IMU orientations, and formulate a graph labeling problem to obtain a tracking solution that is globally consistent with the video and inertial recordings. The fusion of visual and inertial cues provides several advantages. The association of detection boxes in the video and IMU devices is based on motion, which is independent of a person's outward appearance. Furthermore, inertial sensors provide motion information irrespective of visual occlusions. Hence, once detections in the video are associated with an IMU device, intermediate positions can be reconstructed from corresponding inertial sensor data, which would be unstable using video only. Since no dataset exists for this new setting, we release a dataset of challenging tracking sequences, containing video and IMU recordings together with ground-truth annotations. We evaluate our approach on our new dataset, achieving an average IDF1 score of 91.2%. The proposed method is applicable to any situation that allows one to equip people with inertial sensors. © 1992-2012 IEEE

Robust and Interference-Resilient MAC/PHY Layer Strategies for WLANs

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2018. 2. 최성현.Thanks to the explosive growth of mobile devices such as smartphones and tablet PCs, IEEE 802.11 wireless local area network (WLAN), often referred to as WiFi, has become one of the most successful wireless access technologies, supporting ever increasing demand for high data rates at relatively low cost. Encouraged by this remarkable success, the state-of-the-art IEEE 802.11 WLAN provides a physical layer (PHY) data rate of Gb/s to a single user in the 5 GHz unlicensed band, by enabling multi-input and multi-output (MIMO) technology, which utilizes multiple antennas at both transmitter and receiver, and channel bonding which aggregates multiple 20 MHz channels up to 160 MHz bandwidth. Furthermore, as a key feature to enhance medium access control (MAC) efficiency, IEEE 802.11 standard defines frame aggregation called aggregate MAC protocol data unit (A-MPDU), which amortizes PHY protocol overhead over multiple frames by packing several MPDUs into a single frame. In this dissertation, we propose the following three strategies to enhance throughput performance in practice: (1) Mobility-aware PHY rate and A-MPDU length control, (2) Receiver-driven operating channel width adaptation, and (3) Receive architecture for eliminating time-domain interference not overlapping with the desired signal in frequency-domain. Firstly, a significant growth of mobile data traffic volume, primarily generated by portable devices, has led to a change of WLAN communication environmentsthe wireless channel condition in WLAN system is no longer quasi-stationary over the duration of a single frame reception. Especially, frame aggregation, i.e., A-MPDU, which lengthens frame duration significantly, causes the channel state information (CSI) obtained at the preamble can be no longer valid for successfully decoding the latter part of A-MPDUs, when the channel condition substantially changes during the A-MPDU reception. To cope with this problem, we analyze the wireless channel dynamics considering mobility through extensive measurements, and we then build a model which represents the impact of mobility with a noise vector in the I-Q plane, to investigate how the mobility affects the A-MPDU reception performance. Based on our analysis, we develop STRALE, a standard-compliant and mobility-aware PHY rate and A-MPDU length adaptation scheme with ease of implementation. Through extensive simulations with 802.11ac using ns-3 and prototype implementation with commercial 802.11n devices, we demonstrate that STRALE achieves up to 2.9 higher throughput, compared to a fixed duration setting according to IEEE 802.11 standard. STRALE simply requires to update device driver only at one end of the wireless link (i.e., transmitter), thus allowing it to be applicable to any kind of platforms. Second, IEEE 802.11ac supports bandwidth of 20, 40, and 80 MHz as a mandatory feature, and optionally supports 160 MHz bandwidth. To transmit and receive packets using such wide bandwidth, the 802.11ac devices need to increase the size of fast Fourier transform (FFT), equivalently, the baseband bandwidth, referred to as operating channel width (OCW). However, our experiment results reveal various situations where bandwidth adaptation without changing the receivers OCW, leads to poor reception performance due surprisingly to time-domain interference not overlapping with the incoming desired signal in frequency domain. To cope with this problem, we develop RECONN, a standard-compliant and receiver-driven OCW adaptation scheme with ease of implementation. Our prototype implementation in commercial 802.11ac devices shows that RECONN achieves up to 1.85x higher throughput by completely eliminating time-domain interference. To our best knowledge, this is the first work to discover the time-domain interference problem, and to develop OCW adaptation scheme in 802.11ac system. Finally, based on the observation that time-domain interference causes 1) packet detection and synchronization failure, 2) undesirable receive locking problem, and 3) automatic gain control (AGC) failure, we propose a receive architecture called REACTER to eliminate the impact of time-domain interference: REACTER digitally extracts the desired preamble signal not affected by time-domain interference, and provides interference-resilient A-MPDU reception performance by real-time AGC level adaptation during A-MPDU reception. The proposed receive architecture extensively evaluated via IT++ based link-level simulator, and the simulation results show that REACTER significantly improves the frame reception performance by completely eliminates the impact of time-domain interference. In summary, we identify the two existing problems through the extensive measurement and simulations, and we then propose compelling algorithms to improve the throughput performance. We demonstrate the feasibility of our approaches by implementing prototypes in off-the-shelf commercial 802.11n/ac devices, showing that our proposed algorithms fully comply with the 802.11 MAC and requires no PHY modification such that it can be applicable to the existing hardware platform by simply updating the device driver only at one end of the wireless link. Furthermore, we present a novel receive architecture which shows the ability to fundamentally enhance the performance of wide bandwidth operation with very low cost and complexity.1 Introduction 1 1.1 Motivation 1 1.2 Overview of Existing Approach 3 1.2.1 A-MPDU Length Adaptation 3 1.2.2 Wide Bandwidth Operation in IEEE 802.11ac WLANs 4 1.2.3 Receive Architecture for WLAN Devices 5 1.3 Main Contributions 6 1.3.1 Mobility-Aware PHY Rate and A-MPDU Length Adaptation 6 1.3.2 Receiver-Driven Operating Channel Width Adaptation 7 1.3.3 Rx Architecture for Eliminating Time-Domain Interference 7 1.4 Organization of the Dissertation 8 2 STRALE: Mobility-Aware PHY Rate and A-MPDU Length Adaptation in IEEE 802.11 WLANs 10 2.1 Introduction 10 2.2 Preliminaries . 12 2.2.1 Channel Estimation and Compensation 12 2.2.2 Frame Aggregation 14 2.2.3 Modulation and Coding Schemes 15 2.2.4 MIMO, SM, STBC and channel bonding 15 2.3 Case Study 16 2.3.1 Experimental Setting 16 2.3.2 Temporal Selectivity 17 2.3.3 Impact of Mobility 18 2.3.4 Impact of MCSs 21 2.3.5 IEEE 802.11n/ac Features 22 2.3.6 Rate Adaptation: Minstrel 23 2.4 Caudal Noise Model 25 2.4.1 Caudal Noise Modeling for n x n MIMO Channel 26 2.4.2 Impact of Caudal Noise 28 2.5 STRALE: Proposed Algorithm 30 2.5.1 Possible Solutions for Caudal Loss Problem 31 2.5.2 Operation of STRALE 32 2.6 Performance Evaluation 37 2.6.1 Methodology 37 2.6.2 Simulation Results 39 2.6.3 Prototype Implementation 44 2.7 Summary 46 3 RECONN: Receiver-Driven Operating Channel Width Adaptation in IEEE 802.11ac WLANs 48 3.1 Introduction 48 3.2 Preliminaries 51 3.2.1 Packet Detection and Initial Synchronization 51 3.2.2 Wide Bandwidth Operation 52 3.3 Cast Study 53 3.3.1 Motivation 55 3.3.2 Packet Detection and Synchronization Failure 57 3.3.3 Receive Locking to Interference Signal 59 3.3.4 AGC Failure 61 3.4 RECONN: Proposed Algorithm 64 3.4.1 Possible Solutions 64 3.4.2 RECONN 67 3.5 Performance Evaluation 70 3.5.1 One-to-One Scenario 72 3.5.2 Multi-station Scenario 74 3.6 Summary 75 4 REACTER: Receive Architecture for Eliminating Time-Domain Interference 76 4.1 Introduction 76 4.2 Preliminaries 78 4.2.1 Packet Detection and Synchronization 78 4.2.2 Automatic Gain Control in IEEE 802.11 WLAN 80 4.3 REACTER: Proposed Architecture 80 4.3.1 Simulation Methodology 80 4.3.2 Digital Low Pass Filter (DLPF) 82 4.3.3 Real-Time AGC 89 4.3.4 Structure of REACTER 96 4.4 Performance Evaluation 100 4.5 Summary 101Docto

A Statistical Approach to the Alignment of fMRI Data

Multi-subject functional Magnetic Resonance Image studies are critical. The anatomical and functional structure varies across subjects, so the image alignment is necessary. We define a probabilistic model to describe functional alignment. Imposing a prior distribution, as the matrix Fisher Von Mises distribution, of the orthogonal transformation parameter, the anatomical information is embedded in the estimation of the parameters, i.e., penalizing the combination of spatially distant voxels. Real applications show an improvement in the classification and interpretability of the results compared to various functional alignment methods

A comparison of the CAR and DAGAR spatial random effects models with an application to diabetics rate estimation in Belgium

When hierarchically modelling an epidemiological phenomenon on a finite collection of sites in space, one must always take a latent spatial effect into account in order to capture the correlation structure that links the phenomenon to the territory. In this work, we compare two autoregressive spatial models that can be used for this purpose: the classical CAR model and the more recent DAGAR model. Differently from the former, the latter has a desirable property: its ρ parameter can be naturally interpreted as the average neighbor pair correlation and, in addition, this parameter can be directly estimated when the effect is modelled using a DAGAR rather than a CAR structure. As an application, we model the diabetics rate in Belgium in 2014 and show the adequacy of these models in predicting the response variable when no covariates are available