Propagation Delay Differences Research Articles

Collaborative LEO Satellites for Secure and Green Internet of Remote Things

The Internet of Remote Things (IoRT) supported by Low Earth Orbit (LEO) satellites is becoming indispensable for remote sensing, and it will play an important role in the forthcoming sixth generation (6G) communication network. In exploring its applications in remote mining and smart grid, etc., it is found that the implementation of IoRT faces challenges, including limited energy supplies, high mobility, and security vulnerabilities. To address these challenges, we propose employing collaborative LEO satellites to enable the implementation of secure and green IoRT. By combining the uplink signals received at collaborative LEO satellites, the Signal-to-Noise Ratio (SNR) can be significantly improved, so that relieving the transmit power requirement of the energy-limited terminal. Aiming at constructing a collaborative LEO satellite-based IoRT network, this paper introduces the system design principles regarding to frequency planning, waveform selection, collaboration strategies, and terminal design. In order to obtain optimal collaboration performance, we propose a signal coherent combining scheme to compensate Doppler shift, propagation delay, and phase differences. Furthermore, we propose a modified SUMPLE algorithm to estimate and compensate phase differences among satellites, which is applicable to Direct Sequence Spread Spectrum (DSSS) signal scheme. Simulation results demonstrate that our proposed algorithm outperforms the traditional SUMPLE algorithm in combining gain.

Differential Propagation Delay Measurement of RSFQ Library Cells Using Ring Oscillators

Performing comprehensive timing characterization of library cells and establishing their model-to-hardware correlation are essential for building robust integrated circuits and scaling circuit complexity. To measure the propagation delay of fabricated library cells, we have designed a differential delay measurement scheme using SFQ ring oscillators. The reference and design-under-test (DUT) rings are designed using circuit elements that are either common to both rings or are of nominally similar design, except for the DUT. By inserting a single pulse in the ring, the oscillation period is measured using two methods: (1) direct voltage measurement, and (2) frequency measurement using a frequency divider followed by an SFQ-to-DC converter. Subtracting delay of the two rings gives us the propagation delay of the DUT. A 1 cm by 1 cm chip and another 5 mm by 5 mm chip, incorporating stand-alone ring oscillator test structures for different library cells, have been fabricated in the MIT-LL SFQ5ee process. The chips also contain test circuits to validate two variants of the input/output multiplexing scheme that facilitate reducing the pads requirement. Two copies of a chip with fifteen DUTs were tested. The measured and simulated results for the voltage and frequency of the ring are compared. The simulations account for critical current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> ) and sheet resistance (Rs) fabrication parameters. In addition, we have used the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> as a single free parameter to get a better matching with measurement results. For one of the chips, a 15% higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> in simulations results in better matching with measured frequency results for all the DUTs. For example, the discrepancy between simulated and measured DUT ring frequency for the NOT cell was reduced from 19% to 1% when the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> was changed from nominal to 15% higher in simulations. Detailed measurement and simulation results for several DUTs are presented.

EM-Based TDOA Estimation of a Speech Source via Gaussian Mixture Models in Noisy and Anechoic Environments

The propagation delay difference of a speech signal transmitted from the source to microphones, also known as time difference of arrival (TDOA), embodies the information of speech source position. The TDOA estimation plays a vital role in diverse systems such as teleconferencing and far-field speech recognition since the TDOA is a key parameter impacting quality of restored speech signals. This paper is devoted to estimating the TDOA of one speech source on a frame by frame basis in noisy and anechoic environments. First, we propose two variants of Gaussian mixture model to represent the speech signal received by a microphone pair, assuming Gaussianity of the signal and modeling speech sparsity by the speech presence probability (SPP). Second, after estimating the noise parameter in advance and formulating the speech parameters using the maximum likelihood principle, the proposed Gaussian mixture models are reduced to being dependent only on two unknowns, i.e. TDOA and SPP. Third, following these two models, we present two distinct estimators to estimate the TDOA and the SPP iteratively based on the expectation maximization algorithm. The proposed two estimators are free from the ad hoc parameter selection which is required in many classical approaches. Simulation results show that the TDOA estimated by them could be more accurate than that of the state-of-the-art GCC variants in a wide range of frames with specific SPP values. More importantly, the automatically estimated SPP which can be served as voice activity detection in a soft manner encodes the information of the TDOA estimation accuracy. In a speech frame, the estimated SPP with a large value indicates the estimated TDOA with small error. For example, when the SPP is larger than 0.76 and 0.87 in the two proposed estimators, respectively, the TDOA estimation error could be at most 19% of that in the worst case.

A Dielectric Panel Design for RCS Reduction and EM Shielding

A novel dielectric panel structure that contains no metal layer or conductive compound is proposed for electromagnetic shielding and radar cross section (RCS) reduction uses. It is configured as a planar slab with periodically positioned holes. By choosing appropriate slab thickness, material properties, aperture-to-dielectric area ratio, and hole spacing, the holey panel can suppress reflection and transmission at the same time for plane wave incidences. It conceals back scattering features of targets behind and the panel-to-target distance is not necessarily a fixed number. A thorough analysis is provided to explain how this metalless, nonabsorptive, periodic structure reduces the reflection level by deforming the plane wave with the propagation delay difference between air and dielectric regions. Simulated and measured results of a prototype designed in the E-band indicate that it can provide more than 15 dB RCS reduction at the designated transmission suppressing frequency and the 10 dB reduction bandwidth is more than 20%.

Study on the Solutions to Heterogeneous ONU Propagation Delays for Energy-Efficient and Low-Latency EPONs

The scattered Optical Network Units (ONUs) in an optical access network have different propagation delays. In an Ethernet passive optical network (EPON) adopting the traditional Interleaved Polling with Adaptive Cycle Time (IPACT) scheme, such ONU propagation delay difference will waste network resources and will degrade both network delay performance and network energy efficiency in delivering low-latency services. In this article, to deal with the heterogeneous ONU propagation delays problem, two solutions are proposed and investigated. The first solution, namely the Upstream Postponing with ONU Dozing (UP-OD) scheme, is to properly postpone the upstream transmissions of those ONUs having relatively short propagation delays to improve channel utilization efficiency, and ONU doze mode is incorporated to enhance network energy efficiency. The second solution, namely the Identical Fiber Length with ONU Sleeping (IFL-OS) scheme, is to adopt an identical distribution fiber length for ONUs to enhance channel utilization, and ONU sleep mode is incorporated for energy consumption reduction. Simulation results show that both the UP-OD scheme and the IFL-OS scheme reduce network delay and improve network energy efficiency in delivering low-latency (<; 1 ms) data, and the IFL-OS scheme shows lower energy consumption in transmitting per bit of low-latency (<; 1 ms) data compared with the UP-OD scheme. Further practical value discussion shows that for the case of serving services requiring 1 ms delay, the UP-OD scheme is suitable for applying in the 1G-EPONs, whereas the IFL-OS scheme is considerable for the 10G-EPONs.

Design and implementation of a ring oscillator-based physically unclonable function on field programmable gate array to enhance electronic security

Physically unclonable functions (PUFs) are functions that generate a set of random responses when stimulated by a set of pre-defined challenges. They are mostly used for hardware verification and/or device authentication mechanisms, access control, protection of sensitive intellectual property (IP) on devices and protection against insecure hardware connections and communications. In FPGA devices, PUFs are instantiated by exploiting the propagation delay differences of signals caused by manufacturing process variations. In this work, we describe a real implementation of ring oscillator-based PUF on Xilinx FPGAs and illustrate how such architecture is mapped into the FPGA fabric. Using this architecture, we obtained a unique 45-bit code which can be used to identify a chip between many similar devices of the same family in order to provide a reliable access control and authentication mechanism.

A 76-GHz to 81-GHz, 0.6° RMS Phase Error Multichannel Transmitter With a Novel Phase Detector and Compensation Technique

A multichannel transceiver operating in 76–81 GHz with precisely phase-controlled transmitter for the automotive radar application is presented. To achieve high phase accuracy of transmit signal, a novel phase detector using third-order distortion is proposed to compensate the phase control error. To avoid the insensitivity region on specific phase condition, the frequency-shifted method applying the propagation delay difference between transmit and reference signal path is also presented. The multichannel transmitter using proposed detector achieves less than 0.6° root-mean-square (RMS) phase error in 76-GHz to 81-GHz frequency range, over −40 °C–125 °C ambient temperature condition. Since the proposed phase detector does not use the other TX as reference, it is suitable for extending the number of channels. This transceiver, including the proposed phase detector is implemented in 65-nm CMOS technology. The phase detector consumes 1.8 mW per channel and occupies 0.15 mm2 per channel.

Conflux—An Asynchronous Two-to-One Multiplexor for Time-Division Multiplexing and Clockless, Tokenless Readout

This article describes an independent, self-arbitrating asynchronous two-to-one multiplexor called Conflux. Conflux can be used to implement clockless and tokenless time-division multiplexing between two sources. This capability can then be used to create a clockless and tokenless aggregate data bus that can be used as a complete asynchronous readout architecture for a chip, a part of a chip, or an entire multichip system. Conflux utilizes a classic, four-phased asynchronous handshake on both of its input ports as well as on its output port. Asynchronous Request is bundled with Data to ensure consistent propagation delay. The Request is also implemented as a differential signal to account for propagation delay differences between logical ones and zeros. Arbitration between the two Conflux input streams is accomplished by three Set–Reset Latches. Finally, Conflux cells were used successfully to implement the readout architecture of the FCP130 prototype chip. Tests indicate single Conflux stage delays of 1.8 ns and a bandwidth of approximately 11 Gb/s in 130-nm CMOS.

A Wi-Fi-Based Wireless Indoor Position Sensing System with Multipath Interference Mitigation.

Wi-Fi-based indoor position sensing solutions have the advantages of easy integration in mobile phones and low cost by using existing Wi-Fi access points. The mainstream methods are commonly based on the received signal strength indicator (RSSI), which suffers from multipath interference in complicated indoor environments. Through the in-depth analysis of the multipath interference, an RSSI-assisted time difference of arrival (TDoA) method is proposed for Wi-Fi-based indoor position sensing in this work. The key idea is to compensate for the multipath interference in the received signals based on the coarse estimation using RSSI and TDoA calculation. A prototype system has been implemented to validate the proposed method. Experimental results have demonstrated the effectiveness of the proposed method, especially for handling the multipath interference with small propagation delay difference. Experimental results show that the indoor position sensing system can achieve a 90th percentile error of 0.3 m. The proposed method can also achieve moderate computational complexity and moderate real-time performance compared to other methods.

A Sound Source Localization Device Based on Rectangular Pyramid Structure for Mobile Robot

A sound source localization device based on a multimicrophone array with the rectangular pyramid structure is proposed for mobile robot in some indoor applications. Firstly, a time delay estimation method based on the cross-power spectral phase algorithm and a fast search strategy of peak value based on the geometric distribution of microphones are developed to estimate the sound propagation delay differences between two microphones. Moreover, a rejection strategy is presented to evaluate the correctness of the delay difference values. And then, the device’s geometric equations based on the time-space mapping relationship are established to calculate the position of the sound source. For fast solving the equations, the multimicrophone array space is divided into several subspaces to narrow the solution range, and Newton iteration algorithm is introduced to solve the equations, while its solution is evaluated by an evaluation mechanism based on coordinate thresholds. Finally, some experiments are carried out to verify the performance of the device, of which the results show that the device can achieve sound source localization with a high accuracy.

Asynchronous Reception Effects on Distributed Massive MIMO-OFDM System

In a distributed massive multiple-input and multiple-output (DM-MIMO) orthogonal frequency division multiplexing (OFDM) system, each of the multiple receivers receives the OFDM signals simultaneously from all transmitters intended for itself and other receivers. Due to the distributed nature of the network and the differences in propagation delays, these OFDM signals received by any receiver are most likely not synchronized. We have analyzed analytically and numerically the asynchronous reception effects on a DM-MIMO OFDM system in this paper. It is shown that the desired signal power reduction due to phase shifts caused by timing offsets is the dominant performance degrading factor. Surprisingly, the increase of various interfering power (including multiuser, inter-carrier, and inter-symbol interference) due to timing offsets is negligible when compared with the desired signal power reduction. Two per-user rate lower bounds have been developed by averaging over small-scale fading. With the aids of these two lower bounds, averaged per-user rate over small- and large-scale fading have been simulated. It is found that around 50% reduction in per-user downlink rate could occur to the majority of users due to asynchronous reception in DM-MIMO OFDM systems. This important factor needs to be considered in implementing any future DM-MIMO system.

Thyristor voltage equalising network for crowbar application

Many high-voltage applications are realised with series connected thyristors. Voltage imbalance among series connected thyristors during steady state as well as in transients is one of the major concerns. This voltage imbalance is mitigated by using static and dynamic balancing network. Dynamic balancing networks are typically designed based on reverse recovery charge of the thyristor during turn-off, which suits many applications. But this is not the case for a crowbar application, where turn-off of the thyristor is not a major circuit constraint. This study proposes the design method for dynamic balancing network considering gate turn-on delay time and the balancing network component tolerances. The study derives two models for the dynamic balancing network based on its charge–discharge cycle. The importance of charge–discharge cycle in the design of dynamic balancing network during high d i / d t operation is emphasised. Influence of dynamic balancing resistance and crowbar current limiting inductance on voltage imbalance, charging current and discharging current is studied using the analytical model. The proposed design method also offers flexibility to incorporate differences in propagation delays among the thyristor drivers that are used to trigger individual thyristors. Such delays cannot be directly incorporated in the conventional balancing network design method based on reverse recovery. Further, it is also analytically shown that designing the dynamic balancing network based on reverse recovery charge makes the balancing network lossy and bulky for crowbar application. Simulation studies and experimental results on a 12 kV , 1 kA crowbar consisting of six series connected thyristors confirm the theoretical analysis and validate the proposed approach for crowbar applications.

PERFORMANCE ANALYSIS OF WSXC AND WIXC SSM OXC IN WDM OPTICAL NETWORKS

The impact of inband crosstalk on an optical signal passing through optical cross-connect nodes (OXC’s) in wavelength division multiplexing (WDM) optical network, is studied from the equation of electric field with crosstalk and the corresponding current. The analysis has been done for two SSM (space switching matrix) OXC architecture namely WSXC &amp; WIXC where later one has full wavelength conversion capability. Although WIXC attenuates more crosstalk though it is found that depending on the values of optical propagation delay differences, coherent time of lasers and time duration of one bit of the signal, the required power penalty in WIXC may be greater than that of WSXC in some cases. The analysis has been performed on the measures of Bit Error Rate (BER) and Power Penalty.

Development and Performance Evaluation of MMSE MacroDiversity Reception System With Delay Difference Correction

We have been developing a minimum-mean-square-error macrodiversity (MMSE-MD) reception system using distributed remote antennas and radio-on-fiber (RoF) links for use in live broadcasts of road races. The system selects remote antennas with good signal quality and combines their signals based on the MMSE algorithm to combat both small-scale and large-scale fading. For the system to be feasible, we have to consider propagation delay differences among diversity branches due to the RoF links and radio propagation. This paper describes a practical delay difference correction (DDC) technique that can keep signal continuity in any situation, the hardware implementation of an MMSE-MD receiver embodying the technique, and indoor and outdoor performance evaluations. Our prototype receiver perfectly corrected the propagation delay differences among diversity branches without losing signal continuity and maintained MD reception without signal outage across a wide area on an actual road-race course.

Propagation Delay Difference Estimation for Initial Random Access in LTE Compatible Mobile Satellite Communications System

In this paper, a two-step propagation delay difference estimation method is proposed for LTE compatible multi-beam satellite systems to ensure the initial random access (RA). For GEO satellite system, there exists a large propagation delay difference, we cannot directly apply the LTE delay estimation method. To deal with this issue, we first divide a satellite beam into some layered small sub-areas according to the different delay difference values. Then, two types of Physical Random Access Channel (PRACH) preamble burst format are given. The detailed PRACH parameters are provided. Finally, simulations are performed and the results verify the availability of our proposed design.

Physical unclonable function with multiplexing units and its evaluation

AbstractRecently, semiconductor counterfeiting has become an increasingly serious problem. Therefore, techniques to prevent counterfeiting by using random characteristic patterns that are difficult to control artificially have attracted attention. The physical unclonable function (PUF) is one of these techniques. It is a method of deriving ID information peculiar to a device by detecting random physical features that cannot be controlled during the device's manufacture. Because information such as the ID information is difficult to replicate, PUF is used as a technique to prevent counterfeiting. Several studies have been reported on PUF. The arbiter PUF, which utilizes the difference in signal propagation delay between selectors, is a typical method of composing PUF using delay characteristics. This paper proposes a new PUF which is based on the arbiter PUF. The proposed PUF introduces new multiplexing selector units. It attempts to generate an effective response using the orders of three signal arrivals. Experiments using FPGAs verify the validity of the proposed PUF. Although Uniqueness is degraded, Correctness, Steadiness, Randomness, and Resistance to machine learning attacks are improved in comparison with the conventional approach. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(6): 22–31, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11458

Coronal Density Structures and CMEs: Superior Solar Conjunctions of Mars Express, Venus Express, and Rosetta: 2004, 2006, and 2008

Coronal radio-sounding experiments were carried out using the S-band (2.3 GHz) and X-band (8.4 GHz) signals of the ESA Mars Express, Venus Express, and Rosetta spacecraft during five superior conjunctions occurring in 2004, 2006 (3×), and 2008/2009. Differential frequency and propagation delay (ranging) observations were recorded during these opportunities over the better part of a solar cycle, yielding information on the large-scale structure of the coronal electron-density distribution and its variations, including fluctuations on time scales from seconds to hours. These results concern primarily regions of slow solar wind because the radio propagation path is generally confined to the low heliolatitude regions by the conjunction. The mean frequency fluctuation and total electron content are determined as a function of heliocentric distance, and, with a few exceptions caused by streamers and CMEs, are found to be consistent with previous results from experiments on Ulysses. Dense coronal streamers and several coronal mass ejection (CME) events were identified in the radio-frequency data, some of which were observed in white light by the LASCO coronagraphs onboard SOHO. For those events with sufficient mutual coverage, good correlations are found between the electron-content fluctuations and structure imaged by the LASCO instrument.

Performance Assessment of Single Stage and Multi-Stage L-WIXCs Considering Coherent and Incoherent Crosstalk

The statistical impact of Coherent and Incoherent Crosstalk Contributions on the performance of a proposed single stage and a multi-stage Share-per- Node L − WIXC configuration and a multi-stage Share-per-Wavelength L − WIXC configuration in terms of different Optical Propagation Delay Differences, Bit Duration etc., is compared both theoretically and analytically. Besides, considering Coherent and Incoherent Crosstalk contributions for each of those cases, analytical expressions of Electric Field, Leakage Crosstalk, Bit-Error-Rate (BER) and Power Penalty (pp) are being developed. Finally, the results obtained numerically, are thoroughly compared on the basis of Optimum Number of Wavelength Converters, Number of Inputs and Number of Wavelengths per Input Channel.

Group Contention-Based OFDMA MAC Protocol for Multiple Access Interference-Free in WLAN Systems

In WLAN systems, the difference in propagation delay among stations (STAs) can exceed the predefined cyclic prefix length, leading to multiple access interference (MAI). To solve this MAI problem, it is necessary to use a longer cyclic prefix length for orthogonality between different subchannels; however, this sacrifices system efficiency due to the cyclic prefix overhead. In this paper, we propose a group contention-based OFDMA to solve the MAI problem with an adequate cyclic prefix length and support a larger number of STAs. The STAs within the cyclic prefix duration that are synchronized to an access point (AP), are included in the same contending group and compete with other STAs of the group in transmitting packets. The proposed scheme allows for the adoption of an adequate cyclic prefix length without MAI, and is able to reduce the cyclic prefix overhead. In addition, since no packet errors are induced by MAI in any of the STAs, the STAs can transmit simultaneously without redundant short interframe spaces (SIFSs) and other control packets. Through analysis and simulation, we show that for a large number of STAs, the proposed scheme achieves higher throughput than 802.11 protocols and a conventional CSMA combined with OFDMA.

Physical Unclonable Function with Multiplexing Units and its Evaluation

Recently, semiconductor counterfeiting has become an increasingly serious problem. Therefore, techniques to prevent the counterfeit by using random characteristic patterns that are difficult to control artificially have attracted attention. The physical unclonable function (PUF) is one of the techniques. It is a method to derive ID information peculiar to a device by detecting random physical features that cannot be controlled during the device's manufacture. Because information such as the ID information is difficult to replicate, PUF is used as a technique to prevent counterfeiting. Several studies have been reported on PUF. Arbiter PUF, which utilizes the difference in signal propagation delay between selectors, is the typical method of composing PUF using delay characteristics. This paper proposed a new PUF which is based on the arbiter PUF. The proposed PUF introduces new multiplexing selector units. It attempts to generate an effective response using the orders of three signal arrivals. Experiments using FPGAs verify the validity of the proposed PUF. Although Uniqueness is deteriorated, Correctness, Steadiness, Randomness and Resistance against the machine learning attacks are improved in comparison with conventional one.