Round-trip Propagation Delay Research Articles

Random Access Preamble Design and Timing Advance Estimation for OTFS Systems in High-Mobility Scenarios

The uplink timing synchronization is indispensable for establishing a reliable link between the base station and the user equipment (UE). To tackle this problem, a new random access preamble (RAP) waveform is designed for cellular communication systems operating in high-mobility scenarios for orthogonal time frequency space systems. Meanwhile, we also propose a scheme to detect access UEs and estimate the corresponding round-trip propagation delay (i.e., timing advance (TA)). Concretely, the RAP root sequence consists of chirp sequences in the delay-Doppler domain, and the set of available RAPs is generated by cyclic shifting the root sequence. Then, the cross-correlation in the fractional Fourier domain is carried out to achieve the RAP detection and TA estimation of the access UEs. Exhaustive numerical simulation results corroborate that the proposed scheme has a superior RAP detection and TA estimation performance and exhibits sufficient robustness regarding Doppler shifts and the number of UEs.

A Private SDR 5G SA Network: An Evaluation of the Quality of Service (QoS) and Computational Resource Allocation for eMBB Slice

This paper assesses the network performance in terms of Quality of Service (QoS) for the enhanced Mobile Broadband (eMBB) slicing of a private Stand-Alone (SA) network and a base station, identified as Next-Generation Node B (gNB), which is operating at 3.75GHz and using a Software Defined Radio (SDR) device. The contributions of this work are the evaluation of the computational resource allocation of a private 5G SA and the comparison of the QoS performance of the private SA network with a controlled laboratory testbed and a simulation tool, which is known as UERANSIM (User Equipment and Radio Access Network). Additionally, open-source monitoring systems were used in order to collect memory and CPU usage of the network during the experimentation. For the deployment of the SDR 5G SA gNB, the Universal Radio Software Peripheral (USRP) version B210 equipment was utilized. The results also consider the evaluation of QoS metrics i.e. throughput, jitter, round trip time and propagation delay to assess the performance of the private SDR 5G SA network.

OTFS Based Random Access Preamble Transmission for High Mobility Scenarios

We consider the problem of uplink timing synchronization for Orthogonal Time Frequency Space (OTFS) modulation based systems where information is embedded in the delay-Doppler (DD) domain. For this, we propose a novel Random Access (RA) preamble waveform based on OTFS modulation. We also propose a method to estimate the round-trip propagation delay between a user terminal (UT) and the base station (BS) based on the received RA preambles in the DD domain. This estimate (known as the timing advance estimate) is fed back to the respective UTs so that they can advance their uplink timing in order that the signal from all UTs in a cell is received at the BS in a time-synchronized manner. Through analysis and simulations we study the impact of OTFS modulation parameters of the RA preamble on the probability of timing error, which gives valuable insights on how to choose these parameters. Exhaustive numerical simulations of high mobility scenarios suggests that the timing error probability (TEP) performance of the proposed OTFS based RA is much more robust to channel induced multi-path Doppler shift when compared to the RA method in Fourth Generation (4G) systems.

Dither-Frequency Tuning Technique for RSOA-Based Coherent WDM PON

Increasing the transmission distance is an attractive technological option for lowering the cost of loopback-configured coherent wavelength-division-multiplexed passive optical networks implemented by using reflective semiconductor optical amplifiers (RSOAs). In this regard, it is necessary to increase the fiber launch power of the seed light provided from the central office. However, the stimulated Brillouin scattering (SBS) limits this power to less than 6 dBm. It is well-known that the frequency-dithering technique increases the SBS threshold effectively, allowing us to launch a higher-power continuous-wave light. However, the linewidth of the seed laser (caused by the frequency dither) makes the carrier phase estimation (CPE) very difficult at the coherent receiver. To solve this problem, we propose a dither-frequency tuning technique in this letter. We set the dither frequency to be the integer times the inverse of the round-trip propagation delay. Then, we can make the frequency dither of the upstream signal unseen at the receiver since it becomes in phase with the frequency dither of the local oscillator. Thus, the CPE performance would not be limited by the frequency dither, but by the natural linewidth of the seed laser. The efficacy of the proposed technique is experimentally demonstrated over a 60-km loopback link using a 28-Gb/s quadrature phase-shift keying signal generated from RSOA.

Protocols for Wireless Sensors Networks Connected by Radio-Over-Fiber Links

Radio-over-fiber (RoF) technology has been employed in network infrastructure due to its large capacity, low attenuation, and low operational costs, as well as due to the possibility of enlarging network coverage. This paper introduces a new approach for the interconnection of wireless sensor network (WSN) by employing RoF links, specifically wireless sensor network based on radio-over-fiber (WSN-RoF). The main contribution of this paper is the introduction of an architecture for the interconnection of WSN and two medium access control (MAC) protocols exclusively tailored to WSN-RoF architecture: scheduling of polling priority MAC and dynamic hybrid MAC for WSNs based on RoF access infrastructure. Both protocols deal with the main problems in WSN-RoF, i.e., the round-trip propagation delay in optical fiber links and the existence of two distinct collision domains: one wireless and the other optical. The performance of these two protocols shows their effectiveness in the interconnection of WSN through RoF links. Results of experiments demonstrate the benefits of using RoF links for the backhaul of WSN.

Localization of Hopping Rover Using Round-Trip Propagation Delay with Multiple Motion Models

Localization of Hopping Rover Using Round-Trip Propagation Delay with Multiple Motion Models

Sharing Bandwidth by Allocating Switch Buffer in Data Center Networks

In today's data centers, the round trip propagation delay is quite small. Therefore, switch buffer sizes are much larger than the Bandwidth Delay Product (BDP). Based on this observation, in this paper we introduce a new transport protocol which provides bandwidth Sharing by Allocating switch Buffer (SAB) for data centers. SAB sets the congestion windows for flows based on the buffer size of the switches along the path. On one hand, as long as the total buffer allocated to all the flows is larger than the BDP, the network bandwidth can be fully utilized. On the other hand, since SAB only allocates the buffer space to flows, the totally injected traffic will not exceed the network capacity. Thus, SAB rarely loses packets. SAB also reduces flow completion time by allowing flows to reach their fair share of bandwidth quickly. The results of a series of experiments and simulations demonstrate that SAB has the features of fast convergence and rare packet loss. It reduces the latency of short flows and solves theTCP Incast and TCP Outcast problems.

Experimental demonstration of coherent beam combining over a 7 km propagation path

We demonstrate coherent combining (phase locking) of seven laser beams emerging from an adaptive fiber-collimator array over a 7 km atmospheric propagation path using a target-in-the-loop (TIL) setting. Adaptive control of the piston and the tip and tilt wavefront phase at each fiber-collimator subaperture resulted in automatic focusing of the combined beam onto an unresolved retroreflector target (corner cube) with precompensation of quasi-static and atmospheric turbulence-induced phase aberrations. Both phase locking (piston) and tip-tilt control were performed by maximizing the target-return optical power using iterative stochastic parallel gradient descent (SPGD) techniques. The performance of TIL coherent beam combining and atmospheric mitigation was significantly increased by using an SPGD control variation that accounts for the round-trip propagation delay (delayed SPGD).

2.5 Gbit/s burst-mode receiver with power-level burst-detection for XG-PON1 systems

A 2.5 Gbit/s burst-mode receiver with power-level burst-detection and a time-critical control circuit is presented. With its unique topology, this receiver is successfully operated as a long-reach XG-PON1, where the quiet-window for ranging operation exceeds the time variation of the round-trip propagation delay for up to 40 km.

Three-Dimensional Humidity Retrieval Using a Network of Compact Microwave Radiometers to Correct for Variations in Wet Tropospheric Path Delay in Spaceborne Interferometric SAR Imagery

Spaceborne interferometric synthetic aperture radar (SAR) (InSAR) imaging has been used for over a decade to monitor tectonic movements and landslides, as well as to improve digital elevation models. However, InSAR is affected by variations in round-trip propagation delay due to changes in ionospheric total electron content and in tropospheric humidity and temperature along the signal path. One of the largest sources of uncertainty in estimates of tropospheric path delay is the spatial and temporal variability of water vapor density, which currently limits the quality of InSAR products. This problem can be partially addressed by using a number of SAR interferograms from subsequent satellite overpasses to reduce the degradation in the images or by analyzing a long time series of interferometric phases from permanent scatterers. However, if there is a sudden deformation of the Earth's surface, the detection of which is one of the principal objectives of InSAR measurements over land, the effect of water vapor variations cannot be removed, reducing the quality of the interferometric products. In those cases, high-resolution information on the atmospheric water vapor content and its variation with time can be crucial to mitigate the effect of wet-tropospheric path delay variations. This paper describes the use of a ground-based microwave radiometer network to retrieve 3-D water vapor density with fine spatial and temporal resolution, which can be used to reduce InSAR ambiguities due to changes in wet-tropospheric path delay. Retrieval results and comparisons between the integrated water vapor measured by the radiometer network and satellite data are presented.

Accurate Localization for Space Rovers and its Computational Reduction

AbstractTo localize a rover on small planetary body, a method using round-trip propagation delay of radio waves is most promising. In order to improve the estimation accuracy, it is necessary to estimate rotational motion of the small planetary body. A method of localization has been expanded to estimate also the rotational parameters of the small planetary body. The expanded problem includes complex nonlinear and dynamical issues that it cannot be solved analytically. So, the estimation problem has been formulated as an optimization problem to minimize the loss function defined based on the estimation errors derived in comparison with actual measurement data. A solution for the optimization problem has been proposed, which uses Powell's conjugate direction method for local searches. Although this solution does not require calculation of derivatives, it requires a large amount of computation since several forward calculations of the state are required for each minimum search. In this paper, a method to select measurement data is described, which provides as accurate estimation as the original results with reducing the computational amount. The main idea of selection is to conserve the sensitivity of the measurement data. The proposed method to select data is compared with the results using the decimated data of equal interval. Simulation results and experimental results are shown to evaluate computational reduction and estimation accuracy.

Measurement-Based Analysis, Modeling, and Synthesis of the Internet Delay Space

Understanding the characteristics of the Internet delay space (i.e., the all-pairs set of static round-trip propagation delays among edge networks in the Internet) is important for the design of global-scale distributed systems. For instance, algorithms used in overlay networks are often sensitive to violations of the triangle inequality and to the growth properties within the Internet delay space. Since designers of distributed systems often rely on simulation and emulation to study design alternatives, they need a realistic model of the Internet delay space. In this paper, we analyze measured delay spaces among thousands of Internet edge networks and quantify key properties that are important for distributed system design. Our analysis shows that existing delay space models do not adequately capture these important properties of the Internet delay space. Furthermore, we derive a simple model of the Internet delay space based on our analytical findings. This model preserves the relevant metrics far better than existing models, allows for a compact representation, and can be used to synthesize delay data for simulations and emulations at a scale where direct measurement and storage are impractical. We present the design of a publicly available delay space synthesizer tool called <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and demonstrate its effectiveness.

The persistent congestion problem of FAST‐TCP: analysis and solutions

AbstractFAST‐TCP achieves better performance than traditional TCP‐Reno schemes, but unfortunately it is inherently unfair to older connections due to wrong estimations of the round‐trip propagation delay.This paper presents a model for this anomalous behaviour of FAST flows, known as the persistent congestion problem. We first develop an elementary analysis for a scenario with just two flows, and then build up the general case with an arbitrary number of flows. The model correctly quantifies how much unfairness shows up among the different connections, confirming experimental observations made by several previous studies.We built on this model to develop an algorithm to obtain a good estimate of the propagation delay for FAST‐TCP that enables to achieve fairness between aged and new connections while preserving the high throughput and low buffer occupancy of the original protocol. Furthermore, our proposal only requires a modification of the sender host, avoiding the need to upgrade the intermediate routers in any way. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Optimizing Virtual Superimpositions: User–centered Design for a UAR Supported Smart Home System

To localize a rover on small planetary body, a method using round-trip propagation delay of radio waves is most promising. In order to improve the estimation accuracy, it is necessary to estimate rotational motion of the small planetary body. A method of localization has been expanded to estimate also the rotational parameters of the small planetary body. The expanded problem includes complex nonlinear and dynamical issues that it cannot be solved analytically. So, the estimation problem has been formulated as an optimization problem to minimize the loss function defined based on the estimation errors derived in comparison with actual measurement data. A solution for the optimization problem has been proposed, which uses Powell's conjugate direction method for local searches. Although this solution does not require calculation of derivatives, it requires a large amount of computation since several forward calculations of the state are required for each minimum search. In this paper, a method to select measurement data is described, which provides as accurate estimation as the original results with reducing the computational amount. The main idea of selection is to conserve the sensitivity of the measurement data. The proposed method to select data is compared with the results using the decimated data of equal interval. Simulation results and experimental results are shown to evaluate computational reduction and estimation accuracy.

Accurate Localization for Space Rovers and its Computational Reduction

To localize a rover on small planetary body, a method using round-trip propagation delay of radio waves is most promising. In order to improve the estimation accuracy, it is necessary to estimate rotational motion of the small planetary body. A method of localization has been expanded to estimate also the rotational parameters of the small planetary body. The expanded problem includes complex nonlinear and dynamical issues that it cannot be solved analytically. So, the estimation problem has been formulated as an optimization problem to minimize the loss function defined based on the estimation errors derived in comparison with actual measurement data. A solution for the optimization problem has been proposed, which uses Powell's conjugate direction method for local searches. Although this solution does not require calculation of derivatives, it requires a large amount of computation since several forward calculations of the state are required for each minimum search. In this paper, a method to select measurement data is described, which provides as accurate estimation as the original results with reducing the computational amount. The main idea of selection is to conserve the sensitivity of the measurement data. The proposed method to select data is compared with the results using the decimated data of equal interval. Simulation results and experimental results are shown to evaluate computational reduction and estimation accuracy.

Estimation Method of Rotation Parameters of a Small Planetary Body and Position of a Rover Based on Measurements of Round-trip Propagation Delay

Estimation Method of Rotation Parameters of a Small Planetary Body and Position of a Rover Based on Measurements of Round-trip Propagation Delay

1A2-B18 電波を用いた往復伝播時間測定による位置同定法の実験的研究

A method for accurate localization of a space rover on a surface of a small planetary body has been developed for guiding it to a destination point. The method uses round-trip propagation delay of radio waves, range, between a mother spacecraft and the rover. Numerical simulations proved that the developed method is able to estimate the position of the rover with reasonable accuracy assuming that the measurement noise is Gaussian. Laboratory experiments have been conducted via range measurement tool to validate the convergence of the proposed method of estimation, whose results are reported in this paper. These results proved that the estimation converges even the measurement data includes real noise existed in the range measurement tool, which supports the feasibility of the proposed method of estimation.

Online excess bandwidth distribution for Ethernet passive optical networks

Excess bandwidth distribution techniques have recently been proposed to improve the dynamic bandwidth allocation in Ethernet passive optical networks (EPONs). We compare existing offline excess bandwidth distribution with conventional limited interleaved polling with adaptive cycle time (IPACT-limited) in terms of packet delay performance. We identify the factors that result in packet delay reduction with excess bandwidth distribution compared to IPACT-limited and discover that existing offline excess distribution mechanisms become unstable at moderate to high loads in long-range EPONs with large round-trip propagation delays. We propose a novel online excess bandwidth distribution (OEBD) mechanism to provide stable excess bandwidth distribution even at high loads in long-range EPONs. We demonstrate how OEBD can be tuned via parameters to provide grant sizing between limited and gated service.

Simulation Perspectives on Link Buffer Sizing

The problem of determining the optimal buffer size for an Internet link has recently attracted the strong revived attention of networking scientists. While consonant in dissenting from the conventional wisdom to set the buffer size to the product of the link bitrate and round-trip propagation delay of served connections, the new studies often propose alternative guidelines that starkly contradict each other. In this paper, we review the problem of link buffer sizing from two simulation perspectives. First, we use the packet-level simulator ns-2, which is currently the predominant tool for evaluation of network designs, to explore the contradictions between the buffer sizing guidelines. We attribute the contradictions to differences in assumptions and goals of the earlier studies and present our own argument for using small constant buffer sizes. Second, we reflect on the suitability of ns-2 itself for studying the problem of link buffer sizing. We the identify ns-2 deficiencies that undermine the trustworthiness of results provided by this prevailing simulation tool. We also suggest directions and discuss challenges for designing a simulation methodology capable of providing undisputed answers on link buffer sizing.

FAST TCP: fairness and queuing issues

This letter considers problems of unfairness and excessive variations of the router queue associated with FAST TCP operations due to inaccurate estimation of the round-trip propagation delay. Using a simple example, we explain unfairness in FAST TCP caused by this inaccurate estimation. We also present analytical and simulation performance studies and show that improving this estimation by giving the first packet in every flow priority can improve fairness and reduce queuing variations.