Orthogonal Counterpart Research Articles

Interference-Aware Accurate Signal Recovery in Sub-1 GHz UHF Band Reuse-1 Cellular OFDMA Downlinks

Reuse-1 systems operating in the sub-1 GHz UHF band are limited by substantial co-channel interference (CCI). In such orthogonal frequency division multiple access (OFDMA) cellular systems, the inter-sector or inter-tower interference (ITI) makes accurate signal recovery quite challenging as sub-1 GHz bands only support single-input single-output (SISO) links. Interference-aware receiver algorithms are essential to mitigate the ITI in such low-frequency bands. Such algorithms enable ubiquitous mobile broadband access over the entire homeland, say with >95% geographical coverage with quality of service guarantees. One element of the interference-aware signal recovery is the least-squares-based joint channel estimation scheme that uses non-orthogonal pilot subcarriers. This estimator is then compared with a variant that uses orthogonal pilot subcarriers to bring out the advantage of this joint estimator. It is shown that the proposed joint estimator requires fewer pilots to be well-determined when compared to its under-determined orthogonal counterpart. Moreover, it is easy to implement and does not require any knowledge of channel statistics. This work also derives a compensation factor needed for the interference-aware detector in the presence of inter-carrier interference (ICI) originating from multiple transmitters. Simulation results show that the proposed joint channel estimator outperforms traditional estimators at moderate to high frequency selectivity. The proposed compensation factor to the joint detector is found to be essential for recovering the transmitted signal in the absence of phase-tracking pilots.

A Robust Platform for Unnatural Amino Acid Mutagenesis in E. coli Using the Bacterial Tryptophanyl-tRNA synthetase/tRNA pair

We report the development of a robust user-friendly Escherichia coli (E. coli) expression system, derived from the BL21(DE3) strain, for site-specifically incorporating unnatural amino acids (UAAs) into proteins using engineered E. coli tryptophanyl-tRNA synthetase (EcTrpRS)-tRNATrp pairs. This was made possible by functionally replacing the endogenous EcTrpRS-tRNATrp pair in BL21(DE3) E. coli with an orthogonal counterpart from Saccharomyces cerevisiae, and reintroducing it into the resulting altered translational machinery tryptophanyl (ATMW-BL21) E. coli strain as an orthogonal nonsense suppressor. The resulting expression system benefits from the favorable characteristics of BL21(DE3) as an expression host, and is compatible with the broadly used T7-driven recombinant expression system. Furthermore, the vector expressing the nonsense-suppressing engineered EcTrpRS-tRNATrp pair was systematically optimized to significantly enhance the incorporation efficiency of various tryptophan analogs. Together, the improved strain and the optimized suppressor plasmids enable efficient UAA incorporation (up to 65% of wild-type levels) into several different proteins. This robust and user-friendly platform will significantly expand the scope of the genetically encoded tryptophan-derived UAAs.

Multiband and multifunctional polarization converter using an asymmetric metasurface

A compact and asymmetric multi-band reflective polarization converter metasurface has been offered in this paper. The proposed simple converter can effectively convert an incident linearly polarized EM wave to its orthogonal counterpart and circular polarized waves (RHCP and LHCP) at two frequency bands. The design consists of a square with two curves on the top right and lower left corners and a square Split Ring Resonator (SRR) responsible for linear-to-linear and linear-to-circular polarization conversions, respectively. The simulated results show that the converter successfully transforms a y-polarized incident wave to its orthogonal counterpart in a frequency range of 15.5–16.5 GHz with unity conversion at 16 GHz and circularly-polarized (RHCP) wave at 13 GHz and (LHCP) at 18 GHz, verified through the fabricated and measured sample. Wide angular stability up to 60° oblique incidence along with high efficiency reveals the good applicability of the structure. Moreover, the root cause of the cross-polarization conversion has been analyzed and confirmed through Bi-Mode Foster equivalent circuit and surface current distribution as well. Finally, a fabricated prototype is tested to validate the simulated results through measurement.

Flexible NOMA-based NOHO-OFDM scheme for visible light communication with iterative interference cancellation.

In this paper, a flexible non-orthogonal multiple access (NOMA) based optical orthogonal frequency division multiplexing (OFDM) modulation scheme, called non-orthogonal hybrid optical OFDM (NOHO-OFDM), is proposed to increase the achievable data rate of the visible light communication system with high efficiency. In addition, a receiver with iteratively successive interference cancellation (ISIC) is investigated, which can reduce the estimation error. Then, the achievable data rate of the proposed NOHO-OFDM with the ISIC scheme is analyzed. Experiment results show that the bit error rate of the NOHO-OFDM can be significantly reduced by the proposed ISIC scheme, and the NOHO-OFDM is superior than the orthogonal scheme in terms of data rates. Meanwhile, simulation results show that the achievable data rate region of the proposed NOHO-OFDM scheme is larger than that of the orthogonal counterpart.

Index modulation for OFDM RadCom systems

This paper studies a novel Radar and wireless communication fusion system namely, RadCom, using orthogonal frequency division multiplexing index modulation waveforms. From the communication perspective, information is conveyed not only through modulated orthogonal frequency division multiplexing subcarriers but also by the active subcarrier indices that are dynamically updated at the transmitted symbol rates. When compared with conventional orthogonal frequency division multiplexing communication systems, only a subset of subcarriers is activated in the proposed orthogonal frequency division multiplexing index modulation system, which reduces signal peak-to-average ratios, leading to enhanced power amplifier efficiency. From the Radar sensing perspective, the Radar range-velocity profile obtained using compressed sensing approach is simulated and presented. It is shown that orthogonal frequency division multiplexing index modulation RadCom system can enhance the transmission data rates when low-order modulation schemes are adopted e.g. binary phase shift keying, and maintain similar Radar performance compared with the orthogonal frequency division multiplexing counterpart when the system is carefully designed.

Hybrid Multicast/Unicast Design in NOMA-Based Vehicular Caching System

In this paper, we investigate a hybrid multicast/unicast scheme for a multiple-input single-output cache-aided non-orthogonal multiple access (NOMA) vehicular scenario in the face of rapidly fluctuating vehicular wireless channels. Considering a more practical situation, imperfect channel state information is taking into account. In this paper, we formulate an optimization problem to maximize the unicast sum rate under the constraints of the peak power, the peak backhaul, the minimum unicast rate, and the maximum multicast outage probability. To solve the formulated non-convex problem, a lower bound relaxation method is proposed, which enables a division of the original problem into two convex sub-problems. Computer simulations show that the proposed caching-aided NOMA is superior to the orthogonal multiple access counterpart.

Reconfigurable Intelligent Surface Aided NOMA Networks

Reconfigurable intelligent surfaces (RISs) constitute a promising performance enhancement for next-generation (NG) wireless networks in terms of enhancing both their spectrum efficiency (SE) and energy efficiency (EE). We conceive a system for serving paired power-domain non-orthogonal multiple access (NOMA) users by designing the passive beamforming weights at the RISs. In an effort to evaluate the network performance, we first derive the best-case and worst-case of new channel statistics for characterizing the effective channel gains. Then, we derive the best-case and worst-case of our closed-form expressions derived both for the outage probability and for the ergodic rate of the prioritized user. For gleaning further insights, we investigate both the diversity orders of the outage probability and the high-signal-to-noise (SNR) slopes of the ergodic rate. We also derive both the SE and EE of the proposed network. Our analytical results demonstrate that the base station (BS)-user links have almost no impact on the diversity orders attained when the number of RISs is high enough. Numerical results are provided for confirming that: i) the high-SNR slope of the RIS-aided network is one; ii) the proposed RIS-aided NOMA network has superior network performance compared to its orthogonal counterpart.

Energy-Efficient Massive MIMO Multi-Relay NOMA Systems With CSI Errors

We consider a massive multi-input multi-output (mMIMO) system where in a base station (BS) serves its users via multiple relays by employing non-orthogonal multiple access (NOMA). We practically model this system by considering channel estimation errors both at the BS and at the users, which consequently perform imperfect successive interference cancellation. We consider these two artifacts, and derive a lower bound on the spectral efficiency (SE) of this multi-relay NOMA system, which is valid for arbitrary number of BS antennas. We then jointly allocate the BS and relay powers to optimize non-convex global energy efficiency (GEE) and the weighted sum energy efficiency (WSEE) metrics, which are fractional functions of sum-of-products/ratios of optimization variables. These two optimizations require extension of an existing fractional programming framework, which we do by proposing two novel transformations. We analytically prove the monotonic convergence of the transformed problems to a stationary point of their respective original counterparts. We numerically show that i) a multi-relay mMIMO NOMA system outperforms its orthogonal counterpart only with accurate channel information; and ii) the proposed GEE and WSEE algorithms significantly improve the energy efficiency by avoiding additional power use, after attaining optimal value.

Metasurfaces for Wideband and Efficient Polarization Rotation

An efficient wideband polarization-rotation thin metasurface based on oval pattern is presented. The aim of this structure is to manipulate the polarization of incident electromagnetic waves in reflect band. The oval pattern is split by strip lines to outperform the results. It is shown that the proposed polarization converter converts the incident linearly or circularly polarized waves into orthogonal counterpart over a frequency band of 10.2–20.5 GHz. A prototype of the proposed structure is fabricated to validate the numerical simulation. The experimental and simulation results confirm that polarization conversion ratio (PCR) is greater than 90% at the same frequency band with high stability to oblique incidence angle. Numerical simulation reveals that the strong electric and magnetic resonances between top and bottom layers lead to wideband polarization conversion. Equivalent impedance surface method is discussed to further analysis the polarization conversion mechanism.

Ultra-wideband tri-layer transmissive linear polarization converter for terahertz waves

Polarization control is shown to enhance functionalities of terahertz waves in various applications. As a step toward introducing efficient practical devices operating in the terahertz band, we propose and experimentally validate a free-standing three-layer polarization converter operating in transmission. The device can efficiently convert a linearly polarized terahertz wave to its orthogonal counterpart. Our device comprises split-ring and H-shaped resonators inserted between two layers of orthogonal wire gratings. The sole dielectric material is a cyclic olefin copolymer (COC) that has exceptionally low-loss to terahertz waves. The measurement demonstrates a conversion efficiency of >80%, over 0.2–1.0 THz, giving an ultra-wide bandwidth of 133%. The wide bandwidth is attributed to multiple resonances of the two resonators in a unit cell. Importantly, an unconventional fabrication process yields a multi-layer low-loss COC that leads to high efficiency. The proposed design can also be tailored for practical applications across the electromagnetic spectrum.

Sharply Increased Current in Asymmetrically Aligned Polycrystalline Polymer Transistors With Sub-Domain-Size Channels

Shortening channels to the feature length of polymer domains is important to understand the charge transport in semiconducting polymers from macroscopic to microscopic scales. In this work, we fabricated polymer transistors with sub-domain-size channels by electron-beam lithography and asymmetrically aligned domains by off-center spin coating, in which a dry self-patterning method with hexagonal boron nitride was developed to eliminate parasitic leakage. The current sharply increased by 60 times when the channel length was shortened from 200 to 80 nm. The device with an 80 nm-long channel in the direction parallel to the aligned polymer domains delivered a saturation current 160 times higher than that of the orthogonal counterpart. These results and a velocity calculation suggested that the bottleneck of charge transport in electronic devices is domain boundaries. These results highlight the importance of high-efficiency intra-domain charge transport and also the inter-domain limitation. Our findings will contribute to further polymer optimization to improve the performance of polymer devices.

Analysis of Non-Orthogonal Sequences for Grant-Free RA With Massive MIMO

Massive MIMO based grant-free random access (mGFRA) is a promising RA technique for massive access with low signaling overhead. However, due to a limited orthogonal preamble size, preamble collision is a key factor that constrains the success probability of mGFRA. In this paper, we examine the potential of applying non-orthogonal preambles to mitigate the issue, where two typical non-orthogonal sequences, i.e., Gaussian distribution sequences and Zadoff-Chu (ZC) sequences, are taken into account. Asymptotic behaviors of the success probabilities with the non-orthogonal preamble sequences are analyzed and compared using derived closed-forms. Through the analysis we reveal that ZC sequences outperform Gaussian ones. However, though non-orthogonal sequences are able to reduce or even alleviate the preamble collision, they do not necessarily provide better performance than the orthogonal counterpart. In addition, regarding orthogonal sequences as a single-root case of ZC sequences, we show that there exists an optimal number of ZC roots that maximizes the success probability for mGFRA, which is low-bounded by orthogonal baseline. Simulation results evaluate the performance of non-orthogonal sequences in mGFRA under various practical system parameters, and validate our analysis.

Energy minimization for delay constrained mobile edge computing with orthogonal and non-orthogonal multiple access

Mobile edge computing (MEC) is envisioned as a promising technology for enhancing the computation capacities and prolonging the lifespan of mobile devices, by enabling mobile devices to offload computation-intensive tasks to servers in close proximity. For wireless communication, MEC introduces a new scenario, where computations are performed directly at the receiving side of the wireless links. Our objective is therefore to evaluate the importance of joint radio-and-computational resource allocation and spectral efficiency enhancing techniques in this new scenario. We formulate the resource allocation problem to minimize the energy consumption of computation offloading of delay sensitive tasks and propose near-optimal solutions for both orthogonal and non-orthogonal multiple access schemes, with the optimal joint allocation of computing resources and transmission power. Our numerical results demonstrate the superiority of non-orthogonal multiple access over its orthogonal counterpart and the importance of joint resource allocation, especially in scenarios with strict delay limits, where both the transmission and the computational resources are scarce.

MBER Criterion Assisted Power NOMA Design and Performance Analysis With Estimated Channel

In this treatise, we consider a power non-orthogonal multiple access (NOMA) design based on the minimum bit error ratio (MBER) criterion. Existing literatures have shown that the MBER based works show a considerable performance improvement in terms of bit error ratio (BER) for a communication system. We have proposed to design the power coefficients for multiple users with the aid of optimized BER, which is adopted as the cost function. In this work, we have considered a transceiver system having a single-input single-output (SISO) antenna configuration with the $M$ -quadrature amplitude modulation ( $M$ -QAM) signal constellation. The optimization ensures that each user maintains a minimum rate requirement. In this work, we have extensively analyzed the BER performance due to estimated channel for any link. The numerical results demonstrate an overall BER improvement compared to the existing schemes, albeit, the scheme attracts large computational complexity. We have also proposed a variation of the MBER based optimization algorithm, which improves the BER performance. This variation is based on the splitting of the search space for the algorithm and it results in a better performance benefit. Traditionally, NOMA increases the spectral efficiency compared to its orthogonal counterpart. Nevertheless, our proposed solution will still hold this feature along with a better BER performance, though its spectral efficiency will be slightly less compared to the traditional sum-rate based power NOMA.

A reconfigurable ultra-wideband polarization converter based on metasurface incorporated with PIN diodes

A reconfigurable ultra-wideband reflective polarization conversion metasurface (RUR-PCM) is proposed. The unit cell of the RUR-PCM consists of an anisotropic metal patch incorporated with a voltage controlled PIN diode, a dielectric layer, and a metal ground. When the PIN diode is switched on, the RUR-PCM can convert an incident linearly polarized electromagnetic (EM) wave to its orthogonal counterpart; when the PIN diode is switched off, the RUR-PCM can convert a linearly polarized EM wave to a circularly polarized one. The performance of the RUR-PCM is further improved by adding the superstrate and the “double L” metal patch to the unit cell of the RUR-PCM. Simulated and experimental results show that the RUR-PCM is able to achieve linear-to-linear (LTL) polarization conversion in the frequency range of 6.5–19.9 GHz with the polarization conversion ratio higher than 90%, and linear-to-circular (LTC) polarization conversion in the frequency range of 7.6–23.6 GHz, with the axial ratio better than 3 dB. Therefore, the LTL and the LTC polarization conversion methods are integrated into one metasurface in an ultra-wideband range, and each unit uses only one PIN diode, which makes the RUR-PCM have a broad application prospect in secure communication and polarization compatibility.

Robust Beamforming Design in a NOMA Cognitive Radio Network Relying on SWIPT

This paper studies a multiple-input single-output non-orthogonal multiple access cognitive radio network relying on simultaneous wireless information and power transfer. A realistic non-linear energy harvesting model is applied and a power splitting architecture is adopted at each secondary user (SU). Since it is difficult to obtain perfect channel state information (CSI) in practice, instead either a bounded or Gaussian CSI error model is considered. Our robust beamforming and power splitting ratio are jointly designed for two problems with different objectives, namely, that of minimizing the transmission power of the cognitive base station and that of maximizing the total harvested energy of the SUs, respectively. The optimization problems are challenging to solve, mainly because of the non-linear structure of the energy harvesting and CSI errors models. We converted them into convex forms by using semi-definite relaxation. For the minimum transmission power problem, we obtain the rank-2 solution under the bounded CSI error model, while for the maximum energy harvesting problem, a two-loop procedure using a 1-D search is proposed. Our simulation results show that the proposed scheme significantly outperforms its traditional orthogonal multiple access counterpart. Furthermore, the performance using the Gaussian CSI error model is generally better than that using the bounded CSI error model.

An ultra-wideband linear polarization conversion metasurface

An ultra-wideband reflective polarization conversion metasurface (PCM) is designed, which has a periodic multi-V-shaped subwavelength structure printed on a metallic plate backed with a dielectric substrate. Four resonances are generated under the normal incidence of plane waves, which leads to bandwidth expansion of the cross-polarization reflection. The proposed PCM can efficiently convert linear polarized waves to their orthogonal polarization counterpart in an ultra-wideband ranging from 14.3 to 43.2 GHz efficiently with an average polarization conversion ratio (PCR) of 96.7%.

An Ultrathin Cross-Polarization Converter With Near Unity Efficiency for Transmitted Waves

We present the design, analysis, fabrication, and measurement of an ultrathin cross-polarization converter in the transmission mode with near unity conversion efficiency. The converter is constructed of a periodic array of the dielectric substrate sandwiched with simply artificial structures, in which the top layer and bottom layer are connected by metallic vias. The proposed polarizer can convert the linearly polarized incident electromagnetic wave to its orthogonal counterpart in the transmission mode. The conversion mechanism is explained by both equivalent circuit model and full-wave simulations. The simulation and measured results have a good agreement in the entire frequency range. Such a scheme of the ultrathin cross-polarization converter has simple geometry and can be used in microwave communications, remote sensing, and imaging.

Arithmetic intersection on GSpin Rapoport–Zink spaces

We prove an explicit formula for the arithmetic intersection number of diagonal cycles on GSpin Rapoport–Zink spaces in the minuscule case. This is a local problem arising from the arithmetic Gan–Gross–Prasad conjecture for orthogonal Shimura varieties. Our formula can be viewed as an orthogonal counterpart of the arithmetic–geometric side of the arithmetic fundamental lemma proved by Rapoport–Terstiege–Zhang in the minuscule case.

Dual-broadband and near-perfect polarization converter based on anisotropic metasurface

A novel dual-broadband and near-perfect reflective polarization converter based on anisotropic metasurface is presented and analyzed in this paper. The unit cell of the proposed converter is composed of a double-cut slotted metallic split-ring and a metallic ground sheet separated by an F4B-2 substrate. Both numerical analysis and measured results demonstrate that the proposed converter has five plasmon resonance frequencies, and can near-completely convert the x- or y-polarized incident wave to its orthogonal counterpart in two frequency bands (9.5–12.9 GHz, 16.1–20.2 GHz). The corresponding polarization conversion ratio is more than 98.3% in the first frequency band and 99.7% in the second one. In addition, the bandwidths and central frequencies of the two frequency bands can be effectively tuned over a wide range by adjusting the geometrical dimensions of the metasurface, while the high conversion efficiency is preserved. The proposed polarization converter may have great potentials in electromagnetic polarization control applications.