In this paper, we propose an ultra wide band (UWB)-based full-body motion capture system for gait analysis. The system is designed to reduce the implementation complexity and cost of current gait analysis setups, which require expensive locomotion laboratories and equipment. The solution exploits recent developments in wearable computing (i.e., electronic textiles) and relies on estimating the relative distance between body-worn sensors through time-of-flight measurements. While such a system may find application in several areas, substantial research is still required to prove its feasibility and accuracy. From this perspective, the present contribution addresses two key aspects to enable its development: i) the interaction between UWB electromagnetic pulses and the human body is analyzed and, by contrast to most results in the literature, the body- induced pulse distortion is characterized in terms of an equivalent channel impulse response, and ii) by explicitly taking into account that body-induced distortion, the accuracy of various time-of- flight-based ranging algorithms is investigated.

Pulse Shape Distortion and Ranging Accuracy in UWB-Based Body Area Networks for Full-Body Motion Capture and Gait Analysis

We present herein an error model that characterizes on-body range measurements based on time of arrival (TOA) estimation in Impulse radio-ultra wideband, wireless body area networks. Considering real channel measurements over two representative on-body links for repeated walk cycles, the model is drawn as a conditional mixture, accounting for signal to noise ratio (SNR) variations and non line of sight (NLOS) channel obstructions caused by the body. Key model parameters are then investigated as a function of the previous obstruction and SNR configurations, illustrating missed/false path detection effects at low SNR. On this occasion, two TOA estimators are compared, namely a strongest path detection scheme through matched filtering and a first path detection scheme relying on high-resolution channel estimation. Finally, we discuss the possibility to generalize the previous model to any kind of on-body link, based on empirical observations regarding the dynamic range of the channel power transfer function under mobility. Accordingly, the resulting final model could integrate basic elements of classification, such as the instantaneous LOS/NLOS and static/dynamic link status.

On-body TOA-based ranging error model for motion capture applications within wearable UWB networks

Ultra-wide band (UWB) communication is expected to play a key role in next generation broadband intra vehicle wireless applications. The car compartment differs significantly from other well studied indoor or outdoor environments. Hence, channel sounding experiments are crucial for gaining a thorough knowledge of the UWB signal propagation characteristics in such a medium. Time domain channel sounding campaigns often employ some sort of deconvolution during measurement post processing as the measured signal in these experiments is the convolution of the channel response and the probing pulse which violates the Nyquist criterion. In this study, a comparison of two variants of time-domain serial subtractive deconvolution algorithm, popularly known as CLEAN, is presented. Appropriate statistical metrics for assessing the relative merit of a deconvolution technique are identified in the context of intra vehicle UWB transmission, and the better algorithm is selected based on its performance over a standard IEEE channel simulation testbed. The chosen method is then applied to extract power delay profile and delay parameters from an empirical time domain sounding experiment performed inside a passenger car. The effects of passenger occupancy, transmitter receiver separation and absence of direct transmission path are studied.

/pdf/serial-subtractive-deconvolution-algorithms-for-time-domain-52x8h4u7wz.pdf

Serial subtractive deconvolution algorithms for time-domain ultra wide band in-vehicle channel sounding

The PhD investigations aim at exploring new WBAN cooperative localization mechanisms, which could benefit jointly from on-body links, body-to-body links between distinct mobile users or off-body links with respect to the infrastructure. Following a multidisciplinary approach, we have thus addressed theoretical questions related to physical modeling or to algorithmic and cross-layer design. A few more practical aspects have also been dealt with. More specifically, based on WBAN channel measurements, single-link ranging error models are first discussed for more realistic performance assessment. Then a Constrained Distributed Weighted Multi-Dimensional Scaling (CDWMDS) positioning algorithm is put forward for relative MoCap purposes, coping with on-body nodes' asynchronism to reduce system latency and exploiting the presence of constant-length radio links for better accuracy. Subsequently we consider extending this algorithm for larger-scale asbolute MoCap applications within a 2-step localization approach that incorporates additional off-body links in a heterogeneous WBAN framework. Then, both individual and collective kinds of navigation are addressed. In both MoCap and navigation scenarios, low-complexity solutions exploiting on-body deployment diversity enable to combat error propagation and strong range biases due to body shadowing, relying on on-body nodes' dispersion or graph neighborhood to approximate the corrupted distances. Finally, experiments based on real IR-UWB radio platforms validate in part the previous proposals, while showing their practical limitations.

https://tel.archives-ouvertes.fr/tel-00920213/document

Contributions to cooperative localization techniques within mobile wireless bady area networks

Ultra-Wideband Communication is increasingly being considered as an attractive solution for high data rate short range wireless and position location applications. Knowledge of the statistical nature of the channel is necessary to design wireless systems that provide optimum performance. This thesis investigates the spatial characteristics of the channel based on measurements conducted using UWB pulses in an indoor office environment. The statistics of the received signal energy illustrate the low spatial fading of UWB signals. The distribution of the Angle of arrival (AOA) of the multipath components is obtained using a two-dimensional deconvolution algorithm called the Sensor-CLEAN algorithm. A spatial channel model that incorporates the spatial and temporal features of the channel is developed based on the AOA statistics. The performance of the Sensor-CLEAN algorithm is evaluated briefly by application to known artificial channels. UWB systems co-exist with narrowband and other wideband systems. Even though they enjoy the advantage of processing gain (the ratio of bandwidth to data rate) the low energy per pulse may cause these narrow band interferers (NBI) to severely degrade the UWB system's performance. A technique to suppress NBI using multiple antennas is presented in this thesis which exploits the spatial fading characteristics. This method exploits the vast difference in fading characteristics between UWB signals and NBI by implementing a simple selection diversity scheme. It is shown that this simple scheme can provide strong benefits in performance.

Ultra-Wideband for Communications: Spatial Characteristics and Interference Suppression

The Applicability of the Tap-Delay Line Channel Model to Ultra Wideband

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The Applicability of the Tap-Delay Line Channel Model to Ultra Wideband