Showing papers on "Clock synchronization published in 2019"

Time, clocks, and the ordering of events in a distributed system

Abstract: The concept of one event happening before another in a distributed system is examined, and is shown to define a partial ordering of the events. A distributed algorithm is given for synchronizing a system of logical clocks which can be used to totally order the events. The use of the total ordering is illustrated with a method for solving synchronization problems. The algorithm is then specialized for synchronizing physical clocks, and a bound is derived on how far out of synchrony the clocks can become.

SnapLoc: an ultra-fast UWB-based indoor localization system for an unlimited number of tags

Abstract: A large body of work has shown that ultra-wideband (UWB) technology enables accurate indoor localization and tracking thanks to its high time-domain resolution. Existing systems, however, are typically designed to localize only a limited number of tags, and involve the exchange of several messages following a given schedule. As a result, the scalability of current solutions in terms of tag density is limited, as well as their efficiency and responsiveness. In this paper, we present SnapLoc, a UWB-based indoor localization system that allows an unlimited number of tags to self-localize at a theoretical upper bound of 2.3 kHz. In SnapLoc, a tag obtains the responses from multiple anchors simultaneously. Based on these signals, the tag derives the time difference of arrival between anchors and estimates its position. Therefore, SnapLoc does not require tags to actively transmit packets, but to receive only a single message. This allows tags to passively localize themselves and ensures that the performance of SnapLoc does not degrade with high node densities. Moreover, due to the (quasi-)simultaneous responses, a tight clock synchronization between anchors is not needed. We have implemented SnapLoc on a low-cost platform based on the De-cawave DW1000 radio and solved limitations in the transceiver's timestamp resolution to sustain a high localization accuracy. An experimental evaluation shows that SnapLoc exhibits a 90% error and median error of 33 cm and 18 cm, respectively, hence enabling decimeter-level accuracy at fast update rates for countless tags.

Symmetrical clock synchronization with time-correlated photon pairs

Abstract: We demonstrate a point-to-point clock synchronization protocol based on bidirectionally exchanging photons produced in spontaneous parametric down conversion. The technique exploits tight timing correlations between photon pairs to achieve a precision of 51 ps in 100 s with count rates of order 200 s−1. The protocol is distance independent, is secure against symmetric delay attacks, and provides a natural complement to techniques based on Global Navigation Satellite Systems. The protocol works with mobile parties and can be augmented to provide authentication of the timing signal via a Bell inequality check.

Numerical and Experimental Evaluation of Error Estimation for Two-Way Ranging Methods.

Abstract: The Two-Way Ranging (TWR) method is commonly used for measuring the distance between two wireless transceiver nodes, especially when clock synchronization between the two nodes is not available. For modeling the time-of-flight (TOF) error between two wireless transceiver nodes in TWR, the existing error model, described in the IEEE 802.15.4-2011 standard, is solely based on clock drift. However, it is inadequate for in-depth comparative analysis between different TWR methods. In this paper, we propose a novel TOF Error Estimation Model (TEEM) for TWR methods. Using the proposed model, we evaluate the comparative analysis between different TWR methods. The analytical results were validated with both numerical simulation and experimental results. Moreover, we demonstrate the pitfalls of the symmetric double-sided TWR (SDS-TWR) method, which is the most highlighted TWR method in the literature because of its highly accurate performance on clock-drift error reduction when reply times are symmetric. We argue that alternative double-sided TWR (AltDS-TWR) outperforms SDS-TWR. The argument was verified with both numerical simulation and experimental evaluation results.

Passive Localization of Standard WiFi Devices

Abstract: Ubiquitous wireless indoor localization can be achieved by leveraging the widespread deployment of WiFi systems. Most existing WiFi-based localization solutions are based on received signal strength (RSS) fingerprinting, which requires a database of the RSS values in the application environment to be built and maintained. The latest 802.11ac WiFi standard offers channels with wide bandwidths, which enables accurate timing-based positioning. This paper presents a passive localization system in which multiple sniffers monitor the WiFi traffic and locate the standard WiFi transmitters based on the time-of-arrival measurements. Multiple implementation issues are addressed, including sniffer clock synchronization and hardware delay calibration. The proposed system is evaluated experimentally using a prototype developed by us. It is shown that the positioning accuracy is significantly improved over existing systems.

PDMAC: A Priority-Based Enhanced TDMA Protocol for Warning Message Dissemination in VANETs.

Abstract: Vehicular ad hoc networks (VANETs) are the key enabling technology for intelligent transportation systems. Carrier-sense multiple access with collision avoidance (CSMA/CA) is the de facto media access standard for inter-vehicular communications, but its performance degrades in high-density networks. Time-division multiple access (TDMA)-based protocols fill this gap to a certain extent, but encounter inefficient clock synchronization and lack of prioritized message delivery. Therefore, we propose a priority-based direction-aware media access control (PDMAC) as a novel protocol for intra-cluster and inter-cluster clock synchronization. Furthermore, PDMAC pioneers a three-tier priority assignment technique to enhance warning messages delivery by taking into account the direction component, message type, and severity level on each tier. Analytical and simulation results validate the improved performance of PDMAC in terms of clock synchronization, channel utilization, message loss rate, end-to-end delays, and network throughput, as compared with eminent VANET MAC protocols.

Performance and Reliability Aspects of Clock Synchronization Techniques for Industrial Automation

Abstract: Modern distributed control systems comprise multiple intelligent devices capable of performing complex time and mission-critical tasks both independently of each other or partly jointly with each other. To do so, they strongly depend on an accurate common notion of time as well as a reliable shared communication medium for timely data exchange. Traditional legacy communication technologies (field bus systems) supported time transport to a certain extent or provided at least a common frequency. Due to its numerous undisputed advantages, Ethernet has become the only viable communication medium effectively replacing such systems. Being inherently asynchronous time and frequency transfer has to be accomplished using a packet-based approach when moving to Ethernet. After explaining the basic principles of packet-based time transfer, the most common standards are explained compared with each other with respect to their intended application domains. Special emphasis will be put on the Precision Time Protocol (PTP) as defined in the underlying IEEE 1588 standard and its variant IEEE 802.1AS used for time-sensitive networks. Maintaining a highly accurate common notion of time under all circumstances is a crucial prerequisite for most distributed systems. Although PTP has proven to provide sub-microsecond accuracies, it can cope only with a limited number of error conditions. This paper describes all major sources that can either deteriorate the accuracy or cause a total loss of synchronization altogether. Selected countermeasures and enhancements are presented, which can greatly improve the resilience of PTP against errors as well as malicious attacks. This paper concludes by presenting the selected measurements’ results of a novel proposed method.

Spectrum Allocation With Guaranteed Rendezvous in Asynchronous Cognitive Radio Networks for Internet of Things

Abstract: The massive usage of Internet-of-Things devices in various smart applications enables spectrum scarcity issues. In order to enhance the dynamic spectrum capability, cognitive radio network (CRN) is considered as a key technology to address the spectrum scarcity problem. However, the establishment of a common communication channel in CRN by considering the unlicensed heterogeneous devices in an asynchronous environment is a challenging problem. In this paper, a novel asymmetric asynchronous channel hopping mechanism is designed, where secondary users have different sets of available channels and can enter into the network without any global clock synchronization. The proposed algorithms can guarantee the rendezvous within a small interval of time with minimum inter rendezvous intervals. Simulation results show that the designed protocol outperforms over the existing channel hopping algorithms in terms of the degree of rendezvous, average time to rendezvous and throughput.

Self-Stabilizing Byzantine Clock Synchronization with Optimal Precision

Abstract: In the Byzantine-tolerant clock synchronization problem, the goal is to synchronize the clocks of n fully connected nodes. The clocks run at rates between 1 and 𝜗 > 1, and messages have a delay (including computation) between d − U and d. Moreover, up to f < n/3 of the nodes can fail by deviating arbitrarily from the protocol, i.e., are Byzantine. Despite this interference, correct nodes need to generate distinguished events (or pulses) almost simultaneously and periodically. The quality of the solution is measured by the skew, which is the maximum real time difference between corresponding pulses. In the self-stabilizing setting, in addition we allow for transient failures, possibly of all nodes. Once transient faults have ceased and at most f nodes remain faulty, the system should start generating synchronized pulses again. We design a self-stabilizing solution to this problem with asymptotically optimal skew. We achieve our goal by refining and extending the protocol of Lynch and Welch and make the following contributions in the process.

Diffusion-Based Reference Broadcast Synchronization for Molecular Communication in Nanonetworks

Abstract: Molecular communication is a novel inter-disciplinary communication methodology at the nanoscale, which uses chemical or biological molecules as the information carriers. For many prospective molecular communication applications, the clock synchronization is a major issue. However, the existing solutions use the molecule releasing time for the clock synchronization schemes but ignore the molecule synthesizing time, which is not practical. To overcome this issue, in this paper, we propose a reference broadcast synchronization scheme. One nanomachine sends a broadcast beacon and the other two nanomachines records their receiving times. The receiving times are exchanged by that two nanomachines, then, the clocks between these two nanomachines can be synchronized. Owing to the fact that the information molecules propagate slowly with a large propagation delay, which also depends on the transmitter–receiver distance, so a delay estimation method is adopted in the synchronization scheme. The simulation results evaluate proposed synchronization scheme and show that the proposed scheme outperforms other clock synchronization schemes for molecular communication.

Ouroboros Chronos: Permissionless Clock Synchronization via Proof-of-Stake.

Abstract: Clock synchronization allows parties to establish a common notion of global time by leveraging a weaker synchrony assumption, i.e., local clocks with approximately the same speed. The problem has long been a prominent goal for fault-tolerant distributed computing with a number of ingenious solutions in various settings. However, despite intensive investigation, the existing solutions do not apply to common blockchain protocols, which are designed to tolerate variable—and potentially adversarial—participation patterns, e.g., sleepiness and dynamic availability. Furthermore, because such blockchain protocols rely on freshly joining (or re-joining) parties to have a common notion of time, e.g., a global clock which allows knowledge of the current protocol round, it is not clear if or how they can operate without such a strong synchrony assumption. In this work, we show how to solve the global synchronization problem by leveraging proof of stake (PoS). Concretely, we design and analyze a PoS blockchain protocol in the above dynamic-participation setting, that does not require a global clock but merely assumes that parties have local clocks advancing at approximately the same speed. Central to our construction is a novel synchronization mechanism that can be thought as the blockchain-era analogue of classical synchronizers: It enables joining parties— even if upon joining their local time is off by an arbitrary amount—to quickly calibrate their local clocks so that they all show approximately the same time. As a direct implication of our blockchain construction—since the blockchain can be joined and observed by any interested party—we obtain a permissionless PoS implementation of a global clock that may be used by higher level protocols that need access to global time.

Globally Synchronized Time via Datacenter Networks

Abstract: Synchronized time is critical to distributed systems and network applications in a datacenter network. Unfortunately, many clock synchronization protocols in datacenter networks such as NTP and PTP are fundamentally limited by the characteristics of packet-switched networks. In particular, network jitter, packet buffering and scheduling in switches, and network stack overheads add non-deterministic variances to the round trip time, which must be accurately measured to synchronize clocks precisely. We present the Datacenter Time Protocol (DTP), a clock synchronization protocol that does not use packets at all, but is able to achieve nanosecond precision. In essence, the DTP uses the physical layer of network devices to implement a decentralized clock synchronization protocol. By doing so, the DTP eliminates most non-deterministic elements in clock synchronization protocols and has virtually zero protocol overhead since it does not add load at layer-2 or higher at all. It does require replacing network devices, which can be done incrementally and with very small amount of hardware resource consumption. We demonstrate that the precision provided by DTP in hardware is bounded by 4TD where D is the longest distance between any two nodes in a network in terms of number of hops and T is the period of the fastest clock. The precision can be further improved by combining DTP with frequency synchronization. By contrast, the precision of the state-of-the-art protocol (PTP) is not bounded: The precision is hundreds of nanoseconds in an idle network and can decrease to hundreds of microseconds in a heavily congested network.

Nanoseconds Timing System Based on IEEE 1588 FPGA Implementation

Abstract: Clock synchronization procedures are mandatory in most physical experiments where event fragments are readout by spatially dislocated sensors and must be glued together to reconstruct key parameters (e.g., energy and interaction vertex) of the process under investigation. These distributed data readout topologies rely on an accurate time information available at the front end, where the raw data are acquired and tagged with a precise timestamp prior to data buffering and central data collecting. This makes the network complexity and latency, between front-end and backend electronics, negligible within upper bounds imposed by the front-end data buffer capability where the raw data are stored waiting for the trigger validation. The proposed research work describes a field-programmable gate array (FPGA) implementation of IEEE 1588 Precision Time Protocol (PTP) that exploits the European Organization for Nuclear Research (CERN) timing, trigger, and control (TTC) system as a multicast messaging physical and data link layer. The hardware implementation extends the clock synchronization to the nanoseconds range, overcoming the typical accuracy limitations inferred by computers Ethernet-based local area network (LAN). Establishing a reliable communication between master and timing receiver nodes is essential in a message-based synchronization system. In the backend electronics, the serial data streams synchronization with the global clock domain is guaranteed by a hardware-based finite state machine that scans the bit period using a variable delay chain and finds the optimal sampling point. The validity of the proposed timing system has been proven in point-to-point data links as well as in star topology configurations over standard CAT-5e cables. The results achieved together with weaknesses and possible improvements are hereby detailed.

Signal processing with frequency and phase shift keying modulation in telecommunications

Abstract: In this paper represents research improving effectiveness of signal processing in telecommunication devices especially for its part, which relates to providing its noise resistance in conditions of noise and interference. This objective has been achieved through development of methods and means for optimization of filtering devices and semigraphical interpretation of clock synchronization systems in telecommunications with frequency shift keying on the base of stochastic models what determines relevance of the subject. Separately, in an article considered the urgent task is using of modified synchronization methods based on the interference influence of adjacent symbols on the phase criterion tract, in particular the use of the modified synchronization scheme, in order to get a formalized outlook representation of the synchronization schemas based on the polyphase structures with using a bank of filters, that allows to improve the characteristics of digital telecommunication channels. This work is devoted to the examination and modeling of these ways. The proposed ideas and results for the construction of synchronization systems can be used in modern means of telecommunication.

Enabling Air-to-Air Wideband Channel Measurements between Small Unmanned Aerial Vehicles with Optical Fibers

Abstract: In order to ensure safe and efficient operation and to prevent collisions, unmanned aerial vehicles (UAVs) need to communicate with each other with high reliability. To design respective communication systems, accurate air-to-air (A2A) channel models are needed, especially for urban environments, where the channel characteristics are hard to predict due to rich multipath propagation, diffractions and non line of sight (LOS) conditions. For these models, channel measurements in different scenarios are inevitable to model the real-world communication channel. However, small sized UAVs are very limited in carrying payload and in power supply, making it difficult or often impossible to use high performing channel-sounding hardware equipment. As a result, less resource demanding hardware with lower performance in the sense of clock synchronization, time resolution or dynamic range is usually applied leading to a limited propagation channel characterization. In this work, we describe a measurement setup that allows using arbitrary channel sounder hardware by exploiting analog optical links in order to enable A2A wideband channel measurements between small sized UAVs. We extend the operation of our MEDAV RUSKDLR channel sounder by guiding a 100 MHz bandwidth radio frequency (RF) signal at 5.2 GHz through two 600 m long optical fibers attached on two hexacopters after being converted with high bandwidth converters and show the feasibility of this setup with first flight trials in an urban scenario.

FAST: enabling fast software/hardware prototype for network experimentation

Abstract: The evolution of new technologies in network community is getting ever faster. Yet it remains the case that prototyping those novel mechanisms on a real-world system (i.e. CPU-FPGA platforms) is both time and labor consuming, which has a serious impact on the research timeliness. In order to bring researchers out of trivial process in prototype development, this paper proposed FAST, a software hardware co-design framework for fast network prototyping. With the programming abstraction of FAST, researchers are able to prototype (using C, verilog or both) a wide spectrum of network boxes rapidly based on all kinds of CPU-FPGA platforms. FAST framework takes care of managing DMA, PCIe and Linux Kernel while providing a unified API for researchers so they can focus only on the packet processing functions. We demonstrate FAST framework's easy to use features with a number of prototypes and show we can get over 10x gains in performance or 1000x better accuracy in clock synchronization compared with their software versions.

A Compensated Multi-Anchors TOF-Based Localization Algorithm for Asynchronous Wireless Sensor Networks

Abstract: Tag localization for asynchronous wireless sensor networks requires the development of a scheme for clock synchronization. This remains a difficult and open problem since the performance of tag localization can be adversely affected by complications such as reply time and relative clock skew. Joint clock synchronization and a tag localization algorithm that implements a multi-anchor compensated time-of-flight (TOF) to the asynchronous wireless sensor network is a possible and viable solution. Although previous methods that leverage TOF measurements are effective and easily conducted, their performance is not always superior due to the relative clock skew. In this paper, we propose to extend the joint clock/tag synchronization/localization algorithm by introducing a compensation factor that can cancel relative clock skews from multi-tag anchor pairs. We apply a least squares estimation (LSE) algorithm to both the time of emission (TOE) and time of arrival (TOA) for the clock synchronization step. Under the assumption of a Gaussian measurement noise model, the tag localization problem is approximately solved by maximum likelihood estimation (MLE). To assess the performance of our algorithm, we derive the mean square error (MSE) of both relative clock skew and tag location and numerically evaluate the Cramer–Rao lower bound (CRLB) as a benchmark. The simulation results show that the accuracy of the relative clock skew-based estimation and tag localization are significantly improved over traditional algorithms when the appropriate reply time is selected. This is what our proposed algorithm focuses on: it is robust to tag mobility to some extent. We test the performance of proposed algorithm using a well-designed experiment. Based on the experiment results, the localization algorithm can achieve high accuracy without an additional restriction on the reply time and the clock skew.

Dual-Hop TDA-MAC and Routing for Underwater Acoustic Sensor Networks

Abstract: This article investigates the application of underwater acoustic sensor networks (UASNs) for large scale monitoring of the ocean environment. The low propagation speed of acoustic waves presents a fundamental challenge for medium access control (MAC)—coordinating the access of multiple nodes to the shared acoustic communication medium. In this article, we propose sequential dual-hop transmit delay allocation MAC (SDH-TDA-MAC)—a centralized MAC and routing protocol that facilitates efficient dual-hop scheduling in UASNs without the need for clock synchronization among the sensor nodes. BELLHOP-based simulations of a 100 node network reveal that SDH-TDA-MAC can achieve full network connectivity with 16-dB lower transmit power, compared with the single-hop TDA-MAC protocol. This provides considerable energy savings, while still providing network goodput in excess of 50% of the channel capacity. We also present a method of incorporating routing redundancy into the SDH-TDA-MAC protocol that achieves a good tradeoff between the network throughput and reliability. For example, in a channel with 10% probability of link outage, incorporating double routing redundancy into SDH-TDA-MAC increases the packet delivery ratio from 81% to 95%, a significant improvement in network reliability, while still achieving the network goodput of 22% of the channel capacity, considerably higher than typical MAC protocols designed for UASNs. In summary, the high network goodput, low transmit power compared with the single-hop approach, no requirement for clock synchronization, and robust packet delivery via route diversity make SDH-TDA-MAC an efficient, reliable, and practical approach to data gathering in UASNs.

Linear TDA-MAC: Unsynchronized Scheduling in Linear Underwater Acoustic Sensor Networks

Abstract: Underwater acoustic sensor networks (UASNs) are a key enabling technology for live monitoring of subsea assets. This often involves networks with line topologies, e.g., sensor nodes attached to oil and gas pipelines. In this letter, we propose linear transmit delay allocation MAC (LTDA-MAC) for efficient packet scheduling in linear UASNs without clock synchronization at the sensor nodes. It is achieved via online heuristic optimization that produces schedules tailored to a given deployment scenario. Simulations of a subsea pipeline monitoring use case show that LTDA-MAC significantly outperforms spatial-TDMA in networks with long propagation delays.

Asymmetric delay attack on an entanglement-based bidirectional clock synchronization protocol

Abstract: We demonstrate an attack on a clock synchronization protocol that attempts to detect tampering of the synchronization channel using polarization-entangled photon pairs. The protocol relies on a symmetrical channel, where propagation delays do not depend on the propagation direction, for correctly deducing the offset between clocks—a condition that could be manipulated using optical circulators, which rely on static magnetic fields to break the reciprocity of propagating electromagnetic fields. Despite the polarization transformation induced within a set of circulators, our attack creates an error in time synchronization while evading detection.

Time Synchronization with Channel Hopping Scheme for LoRa Networks

Abstract: Low-Power Wide Area Networks (LPWAN) for resilient Internet of Things (IoT) ecosystems come with unprecedented cost for the minimal load of communication. Long Range (LoRa) Wide Area Network (LoRaWAN) is a LPWAN which has a long range, low bit rate and acts as a connectivity enabler. However, making an efficient collaborative service of clock synchronization is challenging. In this paper we tackle two problems of effective robustness in LoRa network. First, current research typically focuses on the benefits of LoRa but ignores the requirement of reliability, which may invalidate the expected benefits. To tackle this problem, we introduce a novel time synchronization scheme for radically reducing usage of existing Aloha type protocol that handles energy consumption and service quality. Second, we look into the security space of LoRa network, i.e. channel selection scheme for the given spectrum. Attacks like selective jamming are possible in LoRa network because the entire spectrum space is not used, and utilization of few channels are comparatively higher. To tackle this problem, we present a channel hopping scheme that integrates cryptographic channel selection with the time notion for the current communication. We evaluate time synchronization and the channel hopping scheme for a real-world deployed peer to peer (P2P) model using commodity hardware. This paper concludes by suggesting the strategic research possibilities on top of this platform.

A Novel Synchronization Scheme Based on a Dynamic Superframe for an Industrial Internet of Things in Underground Mining

Abstract: The Industrial Internet of Things (IIoT) has a wide range of applications, such as intelligent manufacturing, production process optimization, production equipment monitoring, etc. Due to the complex circumstance in underground mining, the performance of WSNs faces enormous challenges, such as data transmission delay, packet loss rate, and so on. The MAC (Media Access Control) protocol based on TDMA (Time Division Multiple Access) is an effective solution, but it needs to ensure the clock synchronization between the transmission nodes. As the key technology of IIoT, synchronization needs to consider the factors of tunnel structure, energy consumption, etc. Traditional synchronization methods, such as TPSN (Timing-sync Protocol for Sensor Networks), RBS (Reference Broadcast Synchronization), mainly focus on improving synchronization accuracy, ignoring the impact of the actual environment, cannot be directly applied to the IIoT in underground mining. In underground mining, there are two kinds of nodes: base-station node and sensor node, which have different topologies, so they constitute a hybrid topology. In this paper, according to hybrid topology of unground mining, a clock synchronization scheme based on a dynamic superframe is designed. In this scheme, the base-station and sensor have different synchronization methods, improving the TPSN and RBS algorithm, respectively, and adjusts the period of the superframe dynamically by estimating the clock offset. The synchronization scheme presented in this paper can reduce the network communication overhead and energy consumption, ensuring the synchronization accuracy. Based on theCC2530 (Asystem-on-chip solution for IEEE 802.15.4, Zigbee and RF4CE applications), the experiments are compared and analyzed, including synchronization accuracy, energy consumption, and robustness tests. Experimental results show that the synchronization accuracy of the proposed method is at least 11% higher than that of the existing methods, and the energy consumption can be reduced by approximately 13%. At the same time, the proposed method has better robustness.

Simulation Framework for Clock Synchronization in Time Sensitive Networking

Abstract: Hard real-time systems like industrial control applications have strict temporal requirements. Many hard real-time systems depend on a global time base for coordinating access to shared resources and for time-stamping events. Hence, the Time Sensitive Networking (TSN) task group introduces a fault-tolerant and robust clock synchronization mechanism (i.e. IEEE 802.1AsRev) that results in a synchronized network. This paper presents a simulation framework for IEEE 802.1AsRev to evaluate the reliability of the global time base in TSN-based systems. The simulation models are developed on top of our existing TSN models that support the time-based features of TSN (e.g. IEEE 802.1Qbv and IEEE 802.1Qci standards). Moreover, the evaluation of different TSN synchronization modules such as Best Master Clock Algorithm (BMCA), synchronization and peer delay measurement are carried out in our simulation framework. We also study the behavior of IEEE 802.1AsRev in the presence of either a node failure or a link failure using an example scenario of a train communication network. The experimental results validate the correctness and applicability of TSN clock synchronization for modern cyber physical systems with demanding timing requirements.

Exploiting Smartphone Peripherals for Precise Time Synchronization

Abstract: Achieving precise time synchronization across a collection of smartphones poses unique challenges due to their limited hardware support, exclusively wireless networking interface, and restricted timing stack control. Given the ubiquity and popularity of smartphones in modern distributed applications, clock discrepancies often lead to degraded application performance. In this paper, we present and evaluate alternative approaches to attain precise time synchronization by leveraging the various peripherals available on modern smartphone devices. Our evaluation across Android smartphones typically attains synchronization accuracy within (i) 200μs using audio, (ii) 3000μs using Bluetooth Low Energy, and (iii) 1000μs using Wi-Fi. Under certain conditions, we show that smartphones synchronized using one peripheral can accurately timestamp and generate synchronous events over other peripherals. The provided guide and accompanying open-source implementations offer developers a means to select the appropriate time synchronization technique when building distributed applications.

BLAS: Broadcast Relative Localization and Clock Synchronization for Dynamic Dense Multi-Agent Systems

Abstract: The spatiotemporal information plays crucial roles in a multi-agent system (MAS). However, for a highly dynamic and dense MAS in unknown environments, estimating its spatiotemporal states is a difficult problem. In this paper, we present BLAS: a wireless broadcast relative localization and clock synchronization system to address these challenges. Our BLAS system exploits a broadcast architecture, under which a MAS is categorized into parent agents that broadcast wireless packets and child agents that are passive receivers, to reduce the number of required packets among agents for relative localization and clock synchronization. We first propose an asynchronous broadcasting and passively receiving (ABPR) protocol. The protocol schedules the broadcast of parent agents using a distributed time division multiple access (D-TDMA) scheme and delivers inter-agent information used for joint relative localization and clock synchronization. We then present distributed state estimation approaches in parent and child agents that utilize the broadcast inter-agent information for joint estimation of spatiotemporal states. The simulations and real-world experiments based on ultra-wideband (UWB) illustrate that our proposed BLAS cannot only enable accurate, high-frequency and real-time estimation of relative position and clock parameters but also support theoretically an unlimited number of agents.

Quality Assessment of Synchronization Devices in Telecommunication

Abstract: This paper represents analysis of principles providing maximally reliable delay estimation of signal synchronization devices in telecommunication. Clock synchronization schemes on the base of stochastic models, graph-analytic interpretation, analytical functional description and their parameters selection in case of real complex hindrance are analyzed. Dependences between dispersion of maximally reliable estimation of synchronization devices and signal to noise ratio (SNR) are represented. Analytical expressions and dependences are obtained for deviation of synchronization error with respect to SNR at the output of discriminator. Diagrams of state are formed for assessment of digital synchronization device in case of error state. Average slip time of synchronization is calculated with respect to SNR.