Require Clock Synchronization Research Articles

ALOHA-NUI: A collision-free version of ALOHA using a Neighborhood-Understood Index

ALOHA with priority acknowledgments (ACK) is transformed into a collision-free channel access method by means of a neighborhood-understood index (NUI). Each node maintains the NUI, which allows nodes to remember all nodes that requested to share the channel and the order in which they should be allowed to transmit. The resulting protocol, ALOHA-NUI, adds signaling packets and NUI information in data packets to maintain the NUI, rather than just remembering that a data packet was sent successfully as in ALOHA. This results in ALOHA-NUI, which is compared with TDMA assuming a fixed transmission schedule, ALOHA with priority ACK’s, and CSMA with priority ACK’s analytically and by simulation. ALOHA-NUI is shown to attain the high throughput of collision-free transmission scheduling methods that usually require clock synchronization while maintaining most of the simplicity of ALOHA with priority ACK’s. ALOHA-NUI is also shown to be fair and to reach stable transmission schedules very quickly.

PEASE: A PUF-Based Efficient Authentication and Session Establishment Protocol for Machine-to-Machine Communication in Industrial IoT

Machine-to-machine (M2M) communication is one of the critical technologies of the industrial Internet of Things (IoT), which consists of sensors, actuators at the edge, and servers. In order to solve the security and availability problems regarding communication between edge devices with constrained resources and servers in M2M communication, in this study we proposed an authentication and session establishment protocol based on physical unclonable functions (PUFs). The scheme does not require clock synchronization among the devices, and it circumvents the situation where the authentication phase has to use a high computational overhead fuzzy extractor due to PUF noise. The protocol contains two message interactions, which provide strong security and availability while being lightweight. The security modelling is based on CPN Tools, which verifies security attributes and attack resistance in the authentication phase. After considering the design of the fuzzy extractor and scalability, the proposed scheme significantly reduces the computational overhead by more than 93.83% in the authentication phase compared with other schemes using PUFs. Meanwhile, under the guarantee of availability, the communication overhead is maintained at a balanced and reasonable level, at least 19.67% lower than the solution using XOR, hashing, or an elliptic curve.

Accurate indoor positioning using IEEE 802.11mc round trip time

WiFi time of flight (ToF) measurement has been supported recently by the wireless LAN protocols to improve WiFi localization. Specifically, the IEEE 802.11-2016 standard has a fine-time measurement (FTM) protocol that can be used to measure the WiFi signal round trip time (RTT). In this paper, we present the design and implementation of WiNar, a WiFi RTT-based indoor location determination system that combines the advantages of both fingerprint and ranging-based techniques to overcome the different challenges of indoor environments. Using commercial-off-the-shelf access points and mobile phones, WiNar leverages both the propagation time and received signal strength of the wireless signal with a fingerprinting model to address the multipath, non-line-of-sight, signal attenuation, and interference challenges of the indoor environments. Moreover, when leveraging the round trip time measurements, WiNar does not require clock synchronization between the transmitter and the receiver. We discuss the different components of the system and its implementation on the Android operating system. Our results show that WiNar has a sub-meter localization accuracy with an average localization error of less than 0.77 meters for two different testbeds. This accuracy outperforms the performance of the traditional signal strength (RSS) fingerprinting technique by at least 50% and ranging-based multi-lateration technique by at least 193%. Finally, our system is also robust to heterogeneous devices.

An Efficient Algorithm for Partial Discharge Localization in High-Voltage Systems Using Received Signal Strength.

The term partial discharge (PD) refers to a partial bridging of insulating material between electrodes that sustain an electric field in high-voltage (HV) systems. Long-term PD activity can lead to catastrophic failures of HV systems resulting in economic, energy and even human life losses. Such failures and losses can be avoided by continuously monitoring PD activity. Existing techniques used for PD localization including time of arrival (TOA) and time difference of arrival (TDOA), are complicated and expensive because they require time synchronization. In this paper, a novel received signal strength (RSS) based localization algorithm is proposed. The reason that RSS is favoured in this research is that it does not require clock synchronization and it only requires the energy of the received signal rather than the PD pulse itself. A comparison was made between RSS based algorithms including a proposed algorithm, the ratio and search and the least squares algorithm to locate a PD source for nine different positions. The performance of the algorithms was evaluated by using two field scenarios based on seven and eight receiving nodes, respectively. The mean localization error calculated for two-field-trial scenarios show, respectively, 1.80 m and 1.76 m for the proposed algorithm for all nine positions, which is the lowest of the three algorithms.

On Channel Hopping Sequences With Full Rendezvous Diversity for Cognitive Radio Networks

In cognitive radio networks, establishing a communication link between a pair of secondary users (SUs) requires them to rendezvous on a commonly available channel. Asynchronous channel hopping sequences with full rendezvous diversity (AFCHS) enable a pair of SUs to meet on every channel without requiring clock synchronization, and hence minimize rendezvous failures due to the appearance of primary user signals. Maximum conditional time-to-rendezvous (MCTTR) and maximum time-to-rendezvous (MTTR) are two primary metrics for evaluating the worst-case time-to-rendezvous of AFCHS under two extreme scenarios. In this letter, we derive lower bounds on the MCTTR and MTTR of AFCHS, and then propose a scheme with the minimum MCTTR and small MTTR. When the number of channels is odd, the proposed scheme has the minimum MTTR.

Acoustical positioning method using transponders with adaptive signal level normalizer

Acoustical indoor positioning — a technology to locate objects or people inside a building using acoustical signals — is a key technology for contextual awareness and ubiquitous computing. To achieve simple localization, in this paper, we propose a transponder-based indoor positioning method. The proposed method does not require clock synchronization for accurate positioning. Furthermore, by using an adaptive signal level normalizer, the terminal can receive acoustic signals with appropriate levels resulting in accurate positioning. We designed a transponder-based indoor positioning method using audible sound and evaluated its performance in experiments. In experiments, three anchors (transponders) of known position are installed on a ceiling of an anechoic chamber, and positioning is performed by setting a terminal in various points. Positioning experiment results showed that the proposed method can achieve on the order of 0.08 ± 0.02 m positioning.

Convergence of Desynchronization Primitives in Wireless Sensor Networks: A Stochastic Modeling Approach

Desynchronization approaches in wireless sensor networks converge to time-division multiple access (TDMA) of the shared medium without requiring clock synchronization amongst the wireless sensors, or indeed the presence of a central (coordinator) node. All such methods are based on the principle of reactive listening of periodic “fire” or “pulse” broadcasts: each node updates the time of its fire message broadcasts based on received fire messages from some of the remaining nodes sharing the given spectrum. In this paper, we present a novel framework to estimate the required iterations for convergence to fair TDMA scheduling. Our estimates are fundamentally different from previous conjectures or bounds found in the literature as, for the first time, convergence to TDMA is defined in a stochastic sense. Our analytic results apply to the Desync algorithm and to pulse-coupled oscillator algorithms with inhibitory coupling. The experimental evaluation via iMote2 TinyOS nodes (based on the IEEE 802.15.4 standard) as well as via computer simulations demonstrates that, for the vast majority of settings, our stochastic model is within one standard deviation from the experimentally-observed convergence iterations. The proposed estimates are thus shown to characterize the desynchronization convergence iterations significantly better than existing conjectures or bounds. Therefore, they contribute towards the analytic understanding of how a desynchronization-based system is expected to evolve from random initial conditions to the desynchronized steady state.

Asynchronous Session Reservation Multi-Channel MAC for Ad Hoc Networks

The use of multi-channel MAC protocols for mobile ad hoc networks has been seen as a very potent method of improving the throughput capacity of such networks. In recent past, a number of multi-channel MAC protocols have been proposed for mobile ad hoc networks that have increased the overall network throughput by quite some margin compared to their single channel counterparts. However, there are still many issues with these protocols that need to be resolved. Clock synchronization is one of the major overhead in a majority of the proposed multi-channel MAC protocols. In this paper we propose a new asynchronous multi-channel MAC protocol that does not require clock synchronization between mobile nodes. Our proposed protocol is an asynchronous solution that uses multiple channels for data transmission. In our proposed protocol, nodes use a single base channel when the network load is considerably lower and migrates to other channels when the network load increases beyond a threshold value. Also, nodes share multi-channel cooperation messages with their neighbors to further improve throughput. We have conducted extensive simulations to compare the performance of our protocol against the traditional IEEE 802.11b single channel and MMAC protocol. Simulation results show that our proposed protocol outperforms both IEEE 802.11b and MMAC protocol.

A tree-based mobility management using message aggregation based on a skewed wait time assignment in infrastructure based MANETs

For the effective mobility management of mobile nodes in Infrastructure-based Mobile Ad Hoc Networks, every mobile node is obliged to send a registration message to the Internet Gateway (IG) periodically. Not only do the registration messages and the additional control messages to establish paths from mobile nodes to the IG to send the registration messages incur a considerable amount of control overhead, but also they impose high traffic congestion on the mobile nodes in the vicinity of the IG which is referred to as the "funneling effect." The control overhead and the funneling effect make it hard to handle mobility management with little impact on the performance of a routing protocol. Therefore, in this paper we propose a tree-based mobility management approach using a message aggregation technique that employs a novel timing model suitable for tree topology, referred to as a skewed wait time assignment technique, in order to maximize message aggregation. Despite its superior performance, this wait time assignment technique differs from the other techniques in that it does not require clock synchronization over nodes. By resorting to simulations, we show that the proposed approach can significantly alleviate the funneling effect as well as improve the performance of mobility management compared with the Tree-based and Quasi-tree based mobility management schemes.

Maximizing Rendezvous Diversity in Rendezvous Protocols for Decentralized Cognitive Radio Networks

In decentralized cognitive radio (CR) networks, establishing a link between a pair of communicating nodes requires that the radios rendezvous” in a common channel-such a channel is called a rendezvous channel-to exchange control information. When unlicensed (secondary) users opportunistically share spectrum with licensed (primary or incumbent) users, a given rendezvous channel may become unavailable due to the appearance of licensed user signals. Ideally, every node pair should be able to rendezvous in every available channel (i.e., maximize the rendezvous diversity) so that the possibility of rendezvous failures is minimized. Channel hopping (CH) protocols have been proposed previously for establishing pairwise rendezvous. Some of them enable pairwise rendezvous over all channels but require global clock synchronization, which may be very difficult to achieve in decentralized networks. Maximizing the pairwise rendezvous diversity in decentralized CR networks is a very challenging problem. In this paper, we present a systematic approach for designing CH protocols that maximize the rendezvous diversity of any node pair in decentralized CR networks. The resulting protocols are resistant to rendezvous failures caused by the appearance of primary user (PU) signals and do not require clock synchronization. The proposed approach, called asynchronous channel hopping (ACH), has two noteworthy features: 1) any pair of CH nodes are able to rendezvous on every channel so that the rendezvous process is robust to disruptions caused by the appearance of PU signals; and 2) an upper bounded time-to-rendezvous (TTR) is guaranteed between the two nodes even if their clocks are asynchronous. We propose two optimal ACH designs that maximize the rendezvous diversity between any pair of nodes and show their rendezvous performance via analytical and simulation results.

Synchronization Design for Multi-Channel Data Acquisition System

In land seismic data acquisition systems, as seismic exploration goes towards to cover large area, a multi-channel structure is needed. In such systems, synchronization is very important, which has great influence on data acquisition and transmission. In this paper, a clock synchronization scheme for seismic exploration is proposed. In the scheme, LVDS serial transmission is used so that the whole system clocks can be made to have the same frequency through clock data recovery technique. Moreover, to compensate the effect caused by transmission delay, an effective algorithm based on PLL phase locked and FPGA logic is proposed in this scheme. The test results show that this scheme meets the system clock synchronization requirements well with the error precision less than 1ns, which fully demonstrates the feasibility and reliability of the scheme. The scheme proposed here can be used in related systems which require clock synchronization.

Comparison of Proactive vs. Reactive Localization Protocols for Wireless Sensor Networks

Comparison of Proactive vs. Reactive Localization Protocols for Wireless Sensor Networks Randomly deployed nodes in a wireless sensor network (WSN) gain benefit of being aware of their location for routing or delivering meaningful information to the base station. Many WSN localization methods have been investigated in terms of their convergence, position refinement or need of a reference coordinate system. In this paper, we present a study on two possible ways of using twoway ranging technique for range based sensor node localization. Two-way ranging technique has gained popularity in WSNs since it does not require clock synchronization in inexpensive and energy constrained sensor nodes. We present two distributed techniques for localization using two-way ranging. These techniques use two different approaches for localization, one is the proactive approach and the other is the reactive approach. In the proactive approach, localization process is initiated by the localized nodes, whereas, the later the process is initiated by the non-localized nodes. We compare the two techniques in terms of their convergence condition, convergence delay and communication cost.

A 5.4-Gbit/s Adaptive Continuous-Time Linear Equalizer Using Asynchronous Undersampling Histograms

We demonstrate a new type of adaptive continuous-time linear equalizer (CTLE) based on asynchronous undersampling histograms. Our CTLE automatically selects the optimal equalizing filter coefficient among several predetermined values by searching for the coefficient that produces the largest peak value in histograms obtained with asynchronous undersampling. This scheme is simple and robust and does not require clock synchronization for its operation. A prototype chip realized in 0.13-μm CMOS technology successfully achieves equalization for 5.4-Gbit/s 231 - 1 pseudorandom bit sequence data through 40-, 80-, and 120-cm PCB traces and 3-m DisplayPort cable. In addition, we present the results of statistical analysis with which we verify the reliability of our scheme for various sample sizes. The results of this analysis are confirmed with experimental data.

Distributed power control over multiple channels for ad hoc wireless networks

In this paper, we investigate the deficiency of uncontrolled asymmetrical transmission power over multiple channels in ad hoc environments. We further propose a novel distributed transmission power control protocol called the distributed power level DPL protocol for multi-channel ad hoc networks without requiring clock synchronization. Specifically, different transmission power levels are assigned to different channels, and nodes search for an idle channel on the basis of the received power so that the maximum allowable power of the preferred data channel is larger than or equal to the received power. If the most preferred channel of the least maximum power is busy, the nodes are able to select the next channel and so forth. As a result, interference is reduced over channels because the nodes that require higher transmission power are separated from interfering with the nodes that require lower transmission power. Two transmission power control modes are introduced for DPL: symmetrical and asymmetrical. For the symmetrical DPL protocol mode, nodes transmit at the same power level assigned to the selected channel. On the other hand, for the asymmetrical DPL protocol, nodes are allowed to transmit at a lower or equal power level that is assigned to the selected channel. Extensive ns-2-based simulation results are presented to demonstrate that the proposed protocols can enhance the network throughput compared with the existing uncontrolled asymmetrical transmission power protocol. Copyright © 2012 John Wiley & Sons, Ltd.

Interval-based flow watermarking for tracing interactive traffic

Tracing interactive attack traffic that traverses stepping stones (i.e., intermediate hosts) is challenging, as the packet headers, lengths, and contents can all be changed by the stepping stones. The traffic timing (delays between packets) has therefore been studied as a means of tracing traffic. One such technique uses traffic timing as a side channel into which a watermark, or identifying tag, can be embedded to aid with tracing. The effectiveness of such techniques is greatly reduced when the packet count of the traffic is changed at the stepping stone. Such transformations may occur as a result of either active countermeasures (e.g. chaff packets, flow splitting) by an adversary attempting to defeat tracing, or by incidental repacketization of the traffic by network interfaces.This paper presents a new method of embedding a watermark in traffic timing, for purposes of tracing the traffic in the presence of flow splitting, chaff packets, timing perturbation, and repacketization. This method uses an invariant characteristic of two connection flows which are part of the same stepping stone chain, namely, the elapsed time of the flows. The duration of each flow is sliced into short fixed-length intervals. Packet timing is adjusted to manipulate the packet count in specific intervals (without adding or deleting any packets), for purposes of embedding the watermark. The method is self-synchronizing and does not require clock synchronization between the watermark encoder and decoder.A statistical analysis of the method, with no assumptions or limitations concerning the distribution of packet times, proves the effectiveness of the method given a sufficient number of packets, despite natural and/or deliberate repacketization and countermeasures by an adversary. The method has been implemented and tested on a large number of SSH traffic flows. The results demonstrate that 100% detection rates and very low false positive rates are achieved under conditions of multiple countermeasures, and using only a few hundred packets.

Searchlight

The rapid deployment of millions of handheld communication devices has resulted in a demand for physical proximitybased opportunistic networking. However, the success of these emerging ad hoc networks requires that a device should be able to search and find other devices in its vicinity without infrastructure support, without consuming too much battery power, and preferably without requiring clock synchronization. While approaches exist to solve this problem of energy-efficient asynchronous neighbor discovery, they present an unpleasant trade-off between good average-case performance (probabilistic approaches) and strict bound on worstcase discovery latency (deterministic approaches). In response to these limitations, we present Searchlight, an asynchronous neighbor discovery protocol that has both deterministic and probabilistic components, a novel combination that enables it to have both good average-case performance and the best worst-case bound for any given energy budget.

Relativistic quantum cryptography for open space without clock synchronization on the receiver and transmitter sides

The security of keys in quantum cryptography is based on fundamental quantum mechanical exclusions (the exclusion of cloning and copying of nonorthogonal quantum states. The physical type of a quantum object that carries information (photon, electron, atom, etc.) is insignificant; only its state vector is important. In relativistic quantum cryptography for open space, both the time of the information carrier (photon that propagates with the extremely allowable velocity in a vacuum) and its quantum state are of fundamental importance. Joint fundamental constraints that are dictated by both special relativity and quantum mechanics on the discrimination of nonorthogonal quantum states allow one to formulate fundamentally new key distribution protocols that are stable against any attacks on a key and guarantee the security of keys for a nonstrictly single-photon source and any losses in the communication channel. Although this protocol is a real-time protocol in the Minkowski space-time, where the attack to the communication channel is detected by the delay of eavesdropper measurement results, the protocol does not require clock synchronization on the transmitter and receiver sides.

Multichannel medium access control for ad hoc wireless networks

ABSTRACTIn this paper, we study the multichannel exposed terminal problem in multihop wireless networks. We propose a multichannel medium access control (MAC) protocol, called multichannel MAC protocol with hopping reservation (MMAC‐HR), to resolve the multichannel exposed terminal problem. MMAC‐HR uses two radio interfaces; one interface is fixed over the control channel, and the other interface switches dynamically between data channels. The fixed interface supports broadcast information and reserves a data channel for any data transmission. The switchable interface, on other hand, is for data exchanges and follows independent slow hopping without requiring clock synchronization. In addition, the proposed protocol is a distributed one. By using the ns‐2 simulator, extensive simulations are performed to demonstrate that MMAC‐HR can enhance the network throughput and delay compared with existing multichannel MAC protocol. Copyright © 2011 John Wiley & Sons, Ltd.

Achieving a Realistic Notion of Time in Discrete Event Simulation

Distributed sensor systems require clock synchronization between all sensor nodes to provide consistent view of the overall system. Owing the growing size of networks, the evaluation of the synchronization performance becomes difficult, if done by means of experiments. Simulation is another method to tackle this issue. Realistic simulation of synchronization schemes requires accurate modelling of oscillators which are the driving timers generating various events. One way to characterise oscillators is to utilize the Allan variance, which can be used to generate a phenomenological model based on power spectral density. Since discrete event simulation (DES) tools are widely used to model network protocols, models which combine accuracy and performance are needed. This paper presents a model that was optimised for use in DES. To verify that the simulation results sufficiently match measurements, an implementation in OMNeT++ was done. The results show that the behaviour of distributed sensor systems, resulting from imperfect timebases, can be accurately simulated.

Measurement Scheme for One-Way Delay Variation with Detection and Removal of Clock Skew

One-way delay variation (OWDV) has become increasingly of interest to researchers as a way to evaluate network state and service quality, especially for real-time and streaming services such as voice-over-Internet-protocol (VoIP) and video. Many schemes for OWDV measurement require clock synchronization through the global-positioning system (GPS) or network time protocol. In clock-synchronized approaches, the accuracy of OWDV measurement depends on the accuracy of the clock synchronization. GPS provides highly accurate clock synchronization. However, the deployment of GPS on legacy network equipment might be slow and costly. This paper proposes a method for measuring OWDV that dispenses with clock synchronization. The clock synchronization problem is mainly caused by clock skew. The proposed approach is based on the measurement of inter-packet delay and accumulated OWDV. This paper shows the performance of the proposed scheme via simulations and through experiments in a VoIP network. The presented simulation and measurement results indicate that clock skew can be efficiently measured and removed and that OWDV can be measured without requiring clock synchronization.