Search

As the demand for vehicle-to-everything communication (V2X) band in the 5.9 GHz increases, the millimeter-wave spectrum offers alternative options in unlicensed or radar-dedicated bands with wider bandwidth. Joint radar-communication (JRC) systems emerge as a comprehensive solution to effectively utilize these bands by integrating both functions within the same waveform and hardware. In this work, we present a multiple-input and multiple-output (MIMO) JRC testbed, operating in the 24 GHz mmWave band, utilizing orthogonal frequency division multiplexing (OFDM) waveform that simultaneously carries data across all subcarriers. In particular, we develop a real-time operating, full-duplex JRC prototype with a fully-digital front-end and software-defined radios, providing enhanced flexibility and capability. Additionally, for systems with high computational power, we introduce a high-resolution range-angle processing method based on the MUSIC algorithm. Through mobile experiments with multiple targets, we showcase simultaneous data transmission and high-resolution radar processing capabilities enabled by the fully-digital MIMO architecture. By leveraging radar’s tracking capability, we propose a radar-assisted precoding approach, offering a low-complexity beamforming solution with reduced feedback overhead. Our experimental results demonstrate that the proposed precoding method achieves comparable performance compared to the conventional precoding method.

We introduce an RF nanoreceiver, based on a forest of carbon nanotube (CNT) antennas packaged together. Based on the physical model of a charged carbon nanotube under RF exposure, which is significantly different from a typical RF antenna, we analyze the performance of our nanoreceiver. We show that, for low signalbandwidth applications, our nanoreceiver is highly robust, allowing for continual operation over extended periods of time at low probabilities of error at reasonably low SNR values. For high signal-bandwidth applications, we show that at a given SNR, the achieved rate grows as n1/4 with the number, n, of the CNTs, at reasonably low probabilities of error. Due to the extremely small scale of the CNTs, many millions of CNTs can be packed into very small areas (e.g., hundreds of millions in 1 mm2) to achieve rates comparable to the commercially available wireless receivers. Hence, significant spatial miniaturization is achieved by our nanoreceiver compared to a classical RF receiver without a loss in the achievable rates.

AbstractThere is an accelerating trend to upgrade and replace nuclear power plant analog instrumentation and control systems with digital systems. While various methodologies are available for the reliability modeling of these systems for plant probabilistic risk assessments, there is no benchmark system that can be used as the basis for methodology comparison. A system representative of the steam generator feedwater control systems in pressurized water reactors is proposed for such a comparison. Dynamic reliability modeling of the benchmark system for an example initiating event is illustrated using the Markov/cell-to-cell mapping technique and dynamic flowgraph methodologies.

Increased access to broadband networks has led to a fast-growing demand for voice and video over IP (VVoIP) applications such as Internet telephony (VoIP), videoconferencing, and IP television (IPTV). For pro-active troubleshooting of VVoIP performance bottlenecks that manifest to end-users as performance impairments such as video frame freezing and voice dropouts, network operators cannot rely on actual end-users to report their subjective quality of experience (QoE). Hence, automated and objective techniques that provide real-time or online VVoIP QoE estimates are vital. Objective techniques developed to-date estimate VVoIP QoE by performing frame-to-frame peak-signal-to-noise ratio (PSNR) comparisons of the original video sequence and the reconstructed video sequence obtained from the sender-side and receiver-side, respectively. Since processing such video sequences is time consuming and computationally intensive, existing objective techniques cannot provide online VVoIP QoE. In this paper, we present a novel framework that can provide online estimates of VVoIP QoE on network paths without end-user involvement and without requiring any video sequences. The framework features the "G AP-model", which is an offline model of QoE expressed as a function of measurable network factors such as bandwidth, delay, jitter, and loss. Using the GAP-model, our online framework can produce VVoIP QoE estimates in terms of "Good", "Acceptable", or "Poor" (GAP) grades of perceptual quality solely from the on-line measured network conditions.

Abstract The rapid growth of Internet-based applications pushes broadband satellite networks to carry on IP traffic. In previously proposed connectionless routing schemes in satellite networks, the metrics used to calculate the paths do not reflect the total delay a packet may experience. In this paper, a new Satellite Grouping and Routing Protocol (SGRP) is developed. In each snapshot period, SGRP divides Low Earth Orbit (LEO) satellites into groups according to the footprint area of the Medium Earth Orbit (MEO) satellites. Based on the delay reports sent by LEO satellites, MEO satellite managers compute the minimum-delay paths for their LEO members. Since the signaling traffic is physically separated from the data traffic, link congestion does not affect the responsiveness of delay reporting and routing table calculation. The snapshot and group formation methods as well as fast reacting mechanisms to address link congestion and satellite failures are described in detail. The performance of SGRP is evaluated through simulations and analysis.

To accomplish network layer integration of terrestrial and satellite IP networks, special exterior gateway protocols are needed. In this work, a new exterior gateway protocol called Border Gateway Protocol – Satellite version(BGP-S) is introduced that enables automated discovery of paths that go through the satellite network. This protocol is designed to work in only one terrestrial gateway in every Autonomous System and enables the forwarding of discovered paths in the Internet using the BGP-4 protocol. The performance of BGP-S is investigated through simulations.

In this paper, a distributed multicast routing scheme is introduced for multi-layered satellite IP networks, which include GEO, MEO, and LEO layers. This scheme aims to minimize the total cost of multicast trees in the satellite network. Multicast trees are constructed and maintained in the dynamic satellite network topology in a distributed manner. Simulation results are provided to evaluate the performance of the new scheme in terms of end-to-end delay and multicast tree cost.

Wireless communications systems enable the end users to be mobile. The majority of the wireless communications networks are cellular networks. Several methods are developed to increase the performance of the cellular networks, which depends on the correct determination of the design parameters as well as the architecture of the system and the traffic requirements. In this study, we introduce a Simulated Annealing (SA) based method to determine the design parameters of a multi-tier cellular network, for which the implementation cost is minimized. The cellular system employs guard channels and allows calls to overflow to upper tiers. We conducted experiments with the SA-based technique on different example problems in two-tier cellular networks and obtained promising results.