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By means of so-called Scatternets, Bluetooth provides the ability to construct robust wireless multi-hop networks. In this paper we propose a practical protocol for time synchronization of such Bluetooth multi-hop networks. Our protocol makes use of the internal clock maintained by Bluetooth, requires minimal communication overhead, and provides an...
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... the Bluetooth clocks of two connected nodes, the HCI Read Clock Offset command can be used. However, the clock offset returned by this command only contains bits 2-16 of the clock difference. We therefore need to reconstruct the complete clock difference. For this, a local Bluetooth time stamp is sent over an established connection as shown in Fig. 4. The method for reconstructing the missing bits of ∆ described below assumes that the transmission latency of the message is less than the clock offset range of 40.96 s, which is a reasonable ...
Citations
... Not only the methods applied in wireless sensor networks (WSN), as surveyed in Sundararaman et al. (2005) and Lasassmeh and Conrad (2010), but in particular those running on wearable devices, as discussed in Zheng et al. (2014), primarily focus on energy efficiency. As discussed in Barth et al. (2008), Mare and Kotz (2010), and Naganawa et al. (2015), radio transmission, applying e.g., the popular Bluetooth in Roberto Casas (2005), Ringwald and Romer (2007), and Pflugradt et al. (2014), suffers largely from a variable path loss, shadowing effects due to the devices' direct attachment to the water-rich human body. Offline Frontiers in Computer Science frontiersin.org . ...
With a smaller form factor and a larger set of applications, body-worn devices have evolved into a collection of simultaneously deployed hardware units, rather than into a single all-round wearable. The sensor data, logged by such devices across the user's body, contains a wealth of information but is often difficult to synchronize. Especially the application of machine learning techniques, e.g., for activity recognition, suffers from the inaccuracy of the devices' internal clocks. In recent years, intra-body communication emerged as a promising alternative to the traditional wired and wireless communication techniques. Distributed wearable systems will notably benefit from its advantages, such as a superior energy efficiency. However, due to the absence of commercially available platforms, applications using this innovative technique remain rare and underinvestigated. With IBSync, we present a novel concept in which artificial landmark signals are received by body-worn devices on touching, approaching, or passing certain areas, surfaces, or objects with embedded transmitter beacons. The landmark signals enable both the wearables' intentional or incidental synchronization as well as the implicit contextualization using supplementary information about the beacons' situational context. For the detection of the landmarks, we propose to repurpose the on-board ECG sensor front-end available in recent commercial wearable devices. Evaluated on a total of 215 min of recordings from two devices, we demonstrate the concept's feasibility and a promising synchronization error of 0.80±1.79 samples or 6.25±14.00 ms at a device's sampling rate of 128 Hz.
... Because of the limited resources on board, the methods for wireless sensor networks (WSN) [27,47] primarily focus on energy efficiency [55]. Nevertheless, also the mostly applied Bluetooth [41,43,44] suffers largely from shadowing effects due to the devices' direct attachment to the water-rich human body [6,31,37]. Offline synchronization methods, in contrast, use external incidents to align the signal channels afterwards, in a post-processing step. ...
The synchronization of wearable devices in distributed, multi-device systems is a persistent challenge. Particularly machine learning approaches suffer from the devices' inaccurate clock sources and unmatched time. While the online synchronization based on radio transmission is energy-intensive, offline approaches originated in activity recognition suffer from inaccurate motion patterns. In recent years, intra-body communication emerged as a promising technique that uses the human body as a limited and hence more efficient medium. Due to the absence of commercial platforms, applications are rare and underinvestigated. To boost their development and to enable the precise synchronization, we introduce IBSync and propose to repurpose the ECG sensor in commercial wearable devices to detect artificial signals induced into the skin. The short-time Fourier transform and Pearson's normalized cross-correlation are used to detect, precisely locate, and assign synchronization landmarks within the measurements. Based on a total of 105 min of recordings, we evaluated the concept and demonstrate its general feasibility with a promising accuracy of 0.203 ± 1.633 samples (1.587 ± 12.755 ms) in typical proximity to the transmitter.
... However, if Shimmer's built in synchronisation is enabled, the data streaming features are disabled. Other Bluetooth-based protocols like [12] require access to the Bluetooth module's clock, which is not granted by most device firmwares. To avoid these issues, it is common practice to use event-based synchronisation techniques [13]. ...
Synchronisation of wireless inertial measurement units in human movement analysis is often achieved using event-based synchronisation techniques. However, these techniques lack precise event generation and accuracy. An inaccurate synchronisation could lead to large errors in motion estimation and reconstruction and therefore wrong analysis outputs. We propose a novel event-based synchronisation technique based on a magnetic field, which allows sub-sample accuracy. A setup featuring Shimmer3 inertial measurement units is designed to test the approach. The proposed technique shows to be able to synchronise with a maximum offset of below 2.6~ms with sensors measuring at 100~Hz. Also, the results indicate a reliable event generation and detection. The investigated parameters suggest a required synchronisation time of eight seconds. Further research should investigate the temperature changes that the sensors are exposed to during human motion analysis and their influence on the internal time measurement of the sensors. In addition, the approach should be tested using inertial measurement units from different manufacturers to investigate an identified constant offset in the accuracy measurements.
... They can be divided into two fundamental categories. The first one, aiming for online synchronization, is usually network-based and relies on wireless technology such as Bluetooth [3]- [5]. The required protocols, however, result in an overhead in the already energy-intensive radio communication. ...
... The surveys [16] and [17] provide a brief overview of common online synchronization techniques for WSN. Based on the short-range wireless standard Bluetooth, approaches for synchronized measurements in body sensor networks (BSN) achieved accuracies ranging from 3.5 ms [3] over 100 µs using the sniff mode [4] to even 17.4 µs utilizing the spark state mechanism which, however, is not supported by all devices [5]. ...
Most off-the-shelf wearable devices do not provide reliable synchronization interfaces, causing multi-device sensing and machine learning approaches, e.g. for activity recognition, still to suffer from inaccurate clock sources and unmatched time. Instead of using active online synchronization techniques, such as those based on bidirectional wireless communication, we propose in this work to use the human heartbeat as a reference signal that is continuously and ubiquitously available throughout the entire body surface. We introduce PulSync, a novel approach that enables the alignment of sensor data across multiple devices utilizing the unique fingerprint-like character of the heart rate variability interval function. In an evaluation on a dataset from 25 subjects, we demonstrate the reliable alignment of independent ECG recordings with a mean accuracy of -0.71 ± 3.44 samples, respectively -2.86 ± 11.43 ms at 250 Hz sampling rate.
... The sleeping time period in ONs are established based on the global clock synchronization in application layer. If the short range communication technology use the Bluetooth, one approach is adopt Bluetooth clock to synchronized the slaves by master or layer-2 techniques [17,18]. Each node is awaked during the time point _ and _ . ...
One of the purposes of Internet of Things (IoT) is to reach more deeper perception. For this purpose, the efficient energy consumption is necessary among intelligent devices that make up the part of Opportunistic Networks (ONs). It is irrational for an ONs without any sleep scheduling because of awful user experience. We explore a sleeping schedule which is based on duty cycling for mobile devices to reduce energy consumption of ONs. To see how schedule affects the performance of ONs, we took a series of simulations and the results indicated that the sleeping schedule is an efficient method for prolonging the network life time in ONs. The successful delivery ratio can increase two to three times when factor Tr equal 0.2. We also observed that the network matrices are acceptable, and the network survival time can be extended effectively in ONs.
... For example, the sniffer nodes of SNIF [3] use a synchronization mechanism developed by its authors in [23]. This mechanism exploits some characteristics and available functions of Bluetooth connection, by interchanging the offsets of Bluetooth clocks interfaces, and comparing them. ...
Monitoring is one of the best ways to evaluate the behavior of computer systems. When the monitored system is a distributed system-such as a wireless sensor network (WSN)-the monitoring operation must also be distributed, providing a distributed trace for further analysis. The temporal sequence of occurrence of the events registered by the distributed monitoring platform (DMP) must be correctly established to provide cause-effect relationships between them, so the logs obtained in different monitor nodes must be synchronized. Many of synchronization mechanisms applied to DMPs consist in adjusting the internal clocks of the nodes to the same value as a reference time. However, these mechanisms can create an incoherent event sequence. This article presents a new method to achieve global synchronization of the traces obtained in a DMP. It is based on periodic synchronization signals that are received by the monitor nodes and logged along with the recorded events. This mechanism processes all traces and generates a global post-synchronized trace by scaling all times registered proportionally according with the synchronization signals. It is intended to be a simple but efficient offline mechanism. Its application in a WSN-DMP demonstrates that it guarantees a correct ordering of the events, avoiding the aforementioned issues.
... The related work can be divided into three categories: single-technology, hybrid-technology, and cross-technology communications. has been widely deployed in smartphones, laptops and sensor nodes [31,23,49,37] to support some IoT applications such as localization [14], health assisting [47], and social sensing [11]. BLE is inteneded to reduce power consumption while maintaining a similar communication range as the classical Bluetooth, which makes BLE particularly suitable for energy-sensitive IoT applications, such as human behavior sampling [47], wearable devices [4,38], localization [24], and low-energy devices [9]. ...
The exponentially increasing number of internet of things (IoT) devices and the data generated by these devices introduces the spectrum crisis at the already crowded ISM 2.4 GHz band. To address this issue and enable more flexible and concurrent communications among IoT devices, we propose B2W2, a novel communication framework that enables N-way concurrent communication among WiFi and Bluetooth Low Energy (BLE) devices. Specifically, we demonstrate that it is possible to enable the BLE to WiFi cross-technology communication while supporting the concurrent BLE to BLE and WiFi to WiFi communications. We conducted extensive experiments under different real-world settings and results show that its throughput is more than 85X times higher than the most recently reported cross-technology communication system [22], which only supports one-way communication (i.e., broadcasting) at any specific time.
... However, multi-modal signal acquisition procedures as PAT determination require a very accurate synchronization among the engaged sensors. The field of wireless synchronization mechanisms has been thoroughly researched including different radio protocols and architectures [7,8,14,58,60]. ...
... Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 2/17/16 3:02 PM In wireless personal area networks (WPAN), Zigbee [14,67], ANT [60] and bluetooth [8,58] belong to the most common choices of wireless technologies. Whereas ANT and Zigbee offer relatively low maximum data rates (20 kbps and 250 kbps, respectively), the BT specification allows up to 2.1 Mbps. ...
Wearable home-monitoring devices acquiring various biosignals such as the electrocardiogram, photoplethysmogram, electromyogram, respirational activity and movements have become popular in many fields of research, medical diagnostics and commercial applications. Especially ambulatory settings introduce still unsolved challenges to the development of sensor hardware and smart signal processing approaches. This work gives a detailed insight into a novel wireless body sensor network and addresses critical aspects such as signal quality, synchronicity among multiple devices as well as the system's overall capabilities and limitations in cardiovascular monitoring. An early sign of typical cardiovascular diseases is often shown by disturbed autonomic regulations such as orthostatic intolerance. In that context, blood pressure measurements play an important role to observe abnormalities like hypo- or hypertensions. Non-invasive and unobtrusive blood pressure monitoring still poses a significant challenge, promoting alternative approaches including pulse wave velocity considerations. In the scope of this work, the presented hardware is applied to demonstrate the continuous extraction of multi modal parameters like pulse arrival time within a preliminary clinical study. A Schellong test to diagnose orthostatic hypotension which is typically based on blood pressure cuff measurements has been conducted, serving as an application that might significantly benefit from novel multi-modal measurement principles. It is further shown that the system's synchronicity is as precise as 30 μs and that the integrated analog preprocessing circuits and additional accelerometer data provide significant advantages in ambulatory measurement environments.
... Timer synchronization plays an important role in the development of wireles sensor networks and is a crucial parameter [19], ANT [20] and Bluetooth [21] [22] belong to the most common wireless technologies. Whereas ANT and Zigbee offer relatively low maximum datarates (20 kBps and 250 kBps respectively), the Bluetooth specification allows up to 2.1 MBps. ...
... There are some published works already reporting on the achievements of timer synchronization based on Bluetooth. In [21] a Bluetooth synchronization mechanism based on periodic inqueries of neighboured slaves is described. In that application, the slave devices try to correct the timer offset of the corresponding master device achieving an accuracy of 3.5 ms. ...
Wearable Monitoring Systems recording vital signs as the Electrocardiogram (ECG) or the Photoplethysmogram (PPG) have become very popular and are widely spread since the last decade. Numerous heart rate monitors, pulseoximeters, step counters or activity recorders are commercially available and already play an important role in common everyday lives. However, synchronicity among multiple devices, sensor fusion approaches, automatic signal quality estimation and further multi-modal signal processing steps still pose significant challenges to current developments and future projects. This work touches upon these problems and gives an insight of the recent achievements by presenting a novel pulseoximeter suited for transmissive and reflexive measurements. The systems' accuracy regarding timer-synchronization and overall hardware performance are presented in the scope of a combined heart rate pulse rate detection application.
... The master after issuing and establishing a connection using Serial Port Profile (SPP) to slave nodes, was able to send commands to manage sensor's operations and eventually to receive data from them. In addition if Bluetooth implements 1 3 Last data from sensor is collected Fig. 5. Description of how the "read clock" command is processed by a Bluetooth module [22] a Health Device Profile (HDP), SPP has been chosen since for data streaming the two profiles are comparable in terms of packet loss [21]. ...
... Our hypothesis is that the command is received and processed in a constant time, but the response time can vary according to how busy the host controller is. Figure 5 represents what happens when a command is issued to Bluetooth node. It is possible that when the command is issued (t 1 ), the host controller is busy for other operations [22], and the response does not occur soon after processing (t 2 ), but instead may be delayed and sent after completing other operations (t 3 ). It has to be noted that the Bluetooth module does not transmit any data while in command mode, but it can accept incoming connections and is visible to other devices. ...
Wireless Body Area Networks (WBANs) can take advantage of many wireless protocols. Among them, Bluetooth is a good candidate since its widespread adoption guarantees compatibility with a number of devices and significantly reduces development time. In most cases data collected from different sensors on different nodes need to be synchronized. We present a synchronization protocol that makes use of Bluetooth piconet internal clock to achieve near-millisecond accuracy with minimal radio communication overhead. Experimental results show that Bluetooth low power modes does not affect negatively accuracy, but improves it, obtaining less power consumption and higher synchronization accuracy.
