The concept of Digital Twin has recently emerged, which requires the transmission of a massive amount of sensor data with low latency and high reliability. Analog error correction is an attractive method for low-latency communications; hence, in this paper, we propose the use of complex-valued neural networks and Quaternionic Neural Networks (QNNs) to decode analog codes. Furthermore, we propose mapping our codes to the baseband of the frequency domain to enable easy time and frequency synchronization as well as to mitigate frequency-selective fading using robust estimation theory. This is accomplished by applying inverse Discrete Fourier Transform (DFT) modulation, which achieves a significant reduction in hardware complexity, power, and cost as compared to our previously proposed analog coding scheme. Additionally, we introduce a scaled version of our previous analog codes that enables statistical signal processing, something we have not been able to achieve until now. This achieves significant noise immunity with drastic performance improvements at low Signal-to-Noise Ratios (SNR) and a small loss at high SNR.

Recent research in ultra-reliable and low latency communications (URLLC) for future wireless systems has spurred interest in short block-length codes. In this context, we analyze arbitrary harmonic bandwidth (BW) expansions for a class of high-dimension constant curvature curve codes for analog error correction of independent continuous-alphabet uniform sources. In particular, we employ the circumradius function from knot theory to prescribe insulating tubes about the centerline of constant curvature curves. We then use tube packing density within a hypersphere to optimize the curve parameters. The resulting constant curvature curve tube (C3T) codes possess the smallest possible latency, i.e., block-length is unity under BW expansion mapping. Further, the codes perform within 5 dB signal-to-distortion ratio of the optimal performance theoretically achievable at a signal-to-noise ratio (SNR)$ < -5$dB for BW expansion factor$n \leq 10$. Furthermore, we propose a neural-network-based method to decode C3T codes. We show that, at low SNR, the neural-network-based C3T decoder outperforms the maximum likelihood and minimum mean-squared error decoders for all$n$. The best possible digital codes require two to three orders of magnitude higher latency compared to C3T codes, thereby demonstrating the latter’s utility for URLLC.

Higher spectral and energy efficiencies are the envisioned defining characteristics of next-generation high data-rate sixth-generation (6G) wireless networks. One of the enabling technologies to meet these requirements is index modulation (IM), which transmits information through permutations of indices of spatial, frequency, or temporal media. In this paper, we propose novel electromagnetics-compliant designs of reconfigurable intelligent surface (RIS) apertures for realizing IM in 6G transceivers. We consider RIS modeling and implementation of spatial and subcarrier IMs, including beam steering, spatial multiplexing, and phase modulation capabilities. Numerical experiments for our proposed implementations show that the bit-error-rates obtained via RIS-aided IM outperform traditional implementations. We further establish the programmable ability of these transceivers to vary the reflection phase and generate frequency harmonics for IM through full-wave electromagnetic analyses of a specific reflect-array metasurface implementation.

We introduce a new geometric construction of cyclic group codes in odd-dimensional spaces formed by intersecting even-dimensional constant curvature curves with hyperplanes of one less dimension. This allows us to recast the cyclic group code as a uniform sampling of a constant curvature curve whereby the design of the constant curvature curve controls code performance. Using a tool from knot theory known as the circumradius function, we derive properties of cyclic group codes from properties of the constant curvature curve passing through every point of the spherical code. By relating the distribution of the squared circumradius function of the connecting curve to the distribution of the pairwise distances of the cyclic group code, we show that the distance spectrum of cyclic group codes achieves optimality in the sense of matching the random spherical code distance distribution bound as the block length grows large.

In this study we introduce a new class of bandwidth-expansion source-channel codes for analog error correction that can work in any even dimensional space and show superior performance in the low SNR region. Our codes are constructed as geodesics on flat tori as previous studies have done, but we use a tube radius construct derived from the global circumradius function. We prove that geodesics on flat tori lead to constant generalized curvature curves and exploit that property to give a single-argument form for the circumradius function. We optimize encoder parameters by minimizing the global radius of curvature subject to harmonic frequency structure which leads to closed twisted tubes with maximal tube radius on the tori. We exploit the isometry of the flat torus with the hyperrectangle to derive simple closed-form decoders based on torus projections that come with 2 dB of the maximum likelihood decoder.

Ground penetrating radar (GPR) is widely studied for detection of landmines and mine-like targets; GPR is particularly useful for detecting minimum metal mines which are harder to detect using traditional metal detection devices alone. In order to expand the phenomenology for GPR, careful measurements of homogeneous and heterogeneous soils with and without targets (landmine simulants and metal objects) are performed in a controlled environment. These measurements will aid in the development of models for soil response beyond the initial air-ground interface. Such explicit models for soil will increase the effectiveness of algorithms designed to discriminate between returns from targets and from naturally occurring geologic materials and interfaces. Furthermore, careful measurement of soil characteristics will enable comparison and refinement of models of soil with embedded targets developed in electromagnetic simulations (using finite-difference time-domain codes (FDTD), e.g.).

This paper studies the in-band interference of timehopping spread spectrum (TH-SS) UWB signals to narrow band receivers. Based on the analysis of general power spectral density (PSD) of TH-SS UWB signal, the interference of UWB signal can be partitioned into two parts: (1) additive white Gaussian noise interference (2) jamming tone interference. Following this framework, a novel analytical symbol error rate (SER) evaluation method of BPSK signal due to UWB interferences is proposed. It has been found out that as the number of inband jamming tones increases, the UWB interference effect tends to be closer to the effect of equivalent Gaussian noise.

The evolution of satellite antennas over the past quarter of a century is presented. Five major areas of advances in communications satellite antenna technology are reviewed: single offset reflectors with feed arrays, shaped reflector systems, active phased arrays, phased-array-fed dual reflector systems, and lightweight feed elements. Examples are given of existing systems and of the ongoing development of new technologies.>

A lightweight, broad-band, 8 × 8 crossbar microwave switch matrix (MSM) has been developed for satellite-switched timedivision multiple-access (SS/TDMA) operation anywhere in the 6 GHz up-link and/or 4 GHz down-link bands. The nearly transparent performance characteristics in the 3.5-6.5 GHz band, for any of the highly flexible interconnect possibilities, have been facilitated by the design of a low-power-consuming resistively matched PIN diode switch. Broad-band push-pull connectors are used to simplify assembly and disassembly of this modular three-dimensional matrix. The switch control electronics (SCE) circuits have been implemented as custom-designed LSI chips for integration within the MSM input distribution networks. Design considerations and performance characteristics of the satellite switch matrix are presented.