arXiv subjects

Michael Schubert

Publications and source records attributed to Michael Schubert.

11 recordsLinked to original sources

arXiv2026

Beyond UDP: RDMA as the Missing Link for Gigasample Software-Defined Radio

Software-defined radio (SDR) front ends have gained an order of magnitude in sample rate within a single product generation, while the transport that carries their output has not changed: samples are packed into Ethernet datagrams and reassembled by the host processor. At gigasample rates this fails on two counts at once, exhausting the time the host has per packet and the memory bandwidth it has for copying, and no amount of tuning or kernel bypass recovers both. The burden has instead been passed to the user, who must supply operating system expertise that has nothing to do with radio. We show that remote direct memory access removes the problem rather than relocating it. The SDR places received samples directly into memory the host has registered, and fetches samples for transmission from that memory when its converters require them. The processor leaves the data path in both directions, each sample byte crosses the memory bus once, and the transmit path loses the hard real-time pacing problem that has always accompanied it. What remains for the user application is the signal processing itself, which should be all an SDR requires, even at gigasample rates.

eess.SP↗

arXiv2025

Wideband Antenna Deconvolution for Bistatic Millimeter Wave Radar Reflectivity Measurements

Bistatic radar measurements offer unique spatial diversity and enhanced target characterization capabilities, rendering them increasingly vital for contemporary sensing application research. The reliability of such measurements is contingent upon precise system and antenna calibration. The prevailing technique is the substitution method, which involves the use of known reference objects. We propose an over-the-air calibration algorithm for spherical bistatic measurement systems. Our method is both significantly simpler and twice as fast as existing algorithms. The application of our technique to reflectivity measurements of a metal sphere from 76 to 81 GHz demonstrates a dynamic range enhancement of up to 40 dB when compared with uncalibrated data. A comparison with simulation data demonstrates a high degree of agreement between measurement and simulation.

eess.SP↗

arXiv2024

Accelerating Innovation in 6G Research: Real-Time Capable SDR System Architecture for Rapid Prototyping

The upcoming 3GPP global mobile communication standard 6G strives to push the technological limits of radio frequency (RF) communication even further than its predecessors: Sum data rates beyond 100 Gbit/s, RF bandwidths above 1 GHz per link, and sub-millisecond latency necessitate very high performance development tools. We propose a new SDR firmware and software architecture designed explicitly to meet these challenging requirements. It relies on Ethernet and commercial off-the-shelf network and server components to maximize flexibility and to reduce costs. We analyze state-of-the-art solutions (USRP X440 and other RFSoC-based systems), derive architectural design goals, explain resulting design decision in detail, and exemplify our architecture's implementation on the XCZU48DR RFSoC. Finally, we validate its performance via measurements and outline how the architecture surpasses the state-of-the-art with respect to sustained RF recording, while maintaining high Ethernet bandwidth efficiency. Building a 6G integrated sensing and communication (ISAC) example, we demonstrate its real-time and rapid application development capabilities.

eess.SP↗

arXiv2022

Receiver Bandwidth Extension Beyond Nyquist Using Channel Bonding

Current and upcoming communication and sensing technologies require ever larger bandwidths. Channel bonding can be utilized to extend a receiver's instantaneous bandwidth beyond a single converter's Nyquist limit. Two potential joint front-end and converter design approaches are theoretically introduced, realized and evaluated in this paper. The Xilinx RFSoC platform with its 5 GSa/s analog to digital converters (ADCs) is used to implement both a hybrid coupler based in-phase/quadrature (I/Q) sampling and a time-interleaved sampling approach along with channel bonding. Both realizations are demonstrated to be able to reconstruct instantaneous bandwidths of 5 GHz with up to 49 dB image rejection ratio (IRR) typically within 4 to 8 dB the front-ends' theoretical limits.

eess.SP↗

arXiv2022

Simulating the 1976 Teton Dam Failure using Geoclaw and HEC-RAS and comparing with Historical Observations

Dam failures occur worldwide, often from factors including aging structures, extreme hydrologic loading, and design oversights related to the changing climate. Understanding and mitigating risk to downstream inhabited areas require developing and improving low-cost high-fidelity tools, such as numerical models, which allow emergency managers to predict the consequences of dam failures better. Two-dimensional (2D) depth-averaged hydraulic models can provide valuable insights into the importance of breach parameters or downstream flow characteristics, but historical studies considering historic failures using real topographies are less common in literature. This study compares Geoclaw, a 2D hydraulic model with adaptive mesh refinement capabilities, to an industry-standard software HEC-RAS (Hydrologic Engineering Center - River Analysis System) using the 1976 Teton Dam failure as a case study. The suitability of Geoclaw for dam failure modeling is determined based on its capability to resolve inundation extent and flood wave arrival times. This study performs sensitivity analyses of the HEC-RAS model to compare an instantaneous dam breach assumption with a time-dependent breach formation for quantifying the model uncertainty. We find the 2D Geoclaw dam-break model results compare reasonably with historical gauge and field observational data and HEC-RAS results. The model demonstrates stability and relatively low computational costs. Our findings highlight opportunities for future work, with the Geoclaw software performance supporting continued studies to evaluate performance. Outcomes of this study will assist dam owners, floodplain managers, and emergency managers by providing an additional tool for estimating the impacts of dam failures to protect lives and infrastructure downstream.

physics.geo-ph↗

arXiv2019

Flows on signed graphs without long barbells

Many basic properties in Tutte's flow theory for unsigned graphs do not have their counterparts for signed graphs. However, signed graphs without long barbells in many ways behave like unsigned graphs from the point view of flows. In this paper, we study whether some basic properties in Tutte's flow theory remain valid for this family of signed graphs. Specifically let $(G,σ)$ be a flow-admissible signed graph without long barbells. We show that it admits a nowhere-zero $6$-flow and that it admits a nowhere-zero modulo $k$-flow if and only if it admits a nowhere-zero integer $k$-flow for each integer $k\geq 3$ and $k \not = 4$. We also show that each nowhere-zero positive integer $k$-flow of $(G,σ)$ can be expressed as the sum of some $2$-flows. For general graphs, we show that every nowhere-zero $\frac{p}{q}$-flow can be normalized in such a way, that each flow value is a multiple of $\frac{1}{2q}$. As a consequence we prove the equality of the integer flow number and the ceiling of the circular flow number for flow-admissible signed graphs without long barbells.

math.CO↗

arXiv2017

Plane graphs without 4- and 5-cycles and without ext-triangular 7-cycles are 3-colorable

Listed as No. 53 among the one hundred famous unsolved problems in [J. A. Bondy, U. S. R. Murty, Graph Theory, Springer, Berlin, 2008] is Steinberg's conjecture, which states that every planar graph without 4- and 5-cycles is 3-colorable. In this paper, we show that plane graphs without 4- and 5-cycles are 3-colorable if they have no ext-triangular 7-cycles. This implies that (1) planar graphs without 4-, 5-, 7-cycles are 3-colorable, and (2) planar graphs without 4-, 5-, 8-cycles are 3-colorable, which cover a number of known results in the literature motivated by Steinberg's conjecture.

math.CO↗

arXiv2016

Signed graphs with two negative edges

The presented paper studies the flow number $F(G,σ)$ of flow-admissible signed graphs $(G,σ)$ with two negative edges. We restrict our study to cubic graphs, because for each non-cubic signed graph $(G,σ)$ there is a set ${\cal G}(G,σ)$ of cubic graphs such that $F(G, σ) \leq \min \{F(H,σ_H) : (H,σ_H) \in {\cal G}(G)\}$. We prove that $F(G,σ) \leq 6$ if $(G,σ)$ contains a bridge and $F(G,σ) \leq 7$ in general. We prove better bounds, if there is an element $(H,σ_H)$ of ${\cal G}(G,σ)$ which satisfies some additional conditions. In particular, if $H$ is bipartite, then $F(G,σ) \leq 4$ and the bound is tight. If $H$ is 3-edge-colorable or critical or if it has a sufficient cyclic edge-connectivity, then $F(G,σ) \leq 6$. Furthermore, if Tutte's 5-Flow Conjecture is true, then $(G,σ)$ admits a nowhere-zero 6-flow endowed with some strong properties.

math.CO↗

arXiv2015

Approximation and Heuristic Algorithms for Computing Backbones in Asymmetric Ad-Hoc Networks

We consider the problem of dominating set-based virtual backbone used for routing in asymmetric wireless ad-hoc networks. These networks have non-uniform transmission ranges and are modeled using the well-established disk graphs. The corresponding graph theoretic problem seeks a strongly connected dominating-absorbent set of minimum cardinality in a digraph. A subset of nodes in a digraph is a strongly connected dominating-absorbent set if the subgraph induced by these nodes is strongly connected and each node in the graph is either in the set or has both an in-neighbor and an out-neighbor in it. Distributed algorithms for this problem are of practical significance due to the dynamic nature of ad-hoc networks. We present a first distributed approximation algorithm, with a constant approximation factor and O(Diam) running time, where Diam is the diameter of the graph. Moreover we present a simple heuristic algorithm and conduct an extensive simulation study showing that our heuristic outperforms previously known approaches for the problem.

cs.NI↗

arXiv2015

Nowhere-zero flows on signed regular graphs

We study the flow spectrum ${\cal S}(G)$ and the integer flow spectrum $\overline{\cal S}(G)$ of signed $(2t+1)$-regular graphs. We show that if $r \in {\cal S}(G)$, then $r = 2+\frac{1}{t}$ or $r \geq 2 + \frac{2}{2t-1}$. Furthermore, $2 + \frac{1}{t} \in {\cal S}(G)$ if and only if $G$ has a $t$-factor. If $G$ has a 1-factor, then $3 \in \overline{\cal S}(G)$, and for every $t \geq 2$, there is a signed $(2t+1)$-regular graph $(H,σ)$ with $ 3 \in \overline{\cal S}(H)$ and $H$ does not have a 1-factor. If $G$ $(\not = K_2^3)$ is a cubic graph which has a 1-factor, then $\{3,4\} \subseteq {\cal S}(G) \cap \overline{\cal S}(G)$. Furthermore, the following four statements are equivalent: (1) $G$ has a 1-factor. (2) $3 \in {\cal S}(G)$. (3) $3 \in \overline{\cal S}(G)$. (4) $4 \in \overline{\cal S}(G)$. There are cubic graphs whose integer flow spectrum does not contain 5 or 6, and we construct an infinite family of bridgeless cubic graphs with integer flow spectrum $\{3,4,6\}$. We show that there are signed graphs where the difference between the integer flow number and the flow number is greater than or equal to 1, disproving a conjecture of Raspaud and Zhu. The paper concludes with a proof of Bouchet's 6-flow conjecture for Kotzig-graphs.

math.CO↗

arXiv2013

Large-scale generation of computational models from biochemical pathway maps

Background: Systems biology projects and omics technologies have led to a growing number of biochemical pathway reconstructions. However, mathematical models are still most often created de novo, based on reading the literature and processing pathway data manually. Results: To increase the efficiency with which such models can be created, we automatically generated mathematical models from pathway representations using a suite of freely available software. We produced models that combine data from KEGG PATHWAY, BioCarta, MetaCyc and SABIO-RK; According to the source data, three types of models are provided: kinetic, logical and constraint-based. All models are encoded using SBML Core and Qual packages, and available through BioModels Database. Each model contains the list of participants, the interactions, and the relevant mathematical constructs, but, in most cases, no meaningful parameter values. Most models are also available as easy to understand graphical SBGN maps. Conclusions: to date, the project has resulted in more than 140000 models freely available. We believe this resource can tremendously accelerate the development of mathematical models by providing initial starting points ready for parametrization.

q-bio.MN↗