| 1. |
- Aabel, Lise, et al.
(författare)
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A TDD Distributed MIMO Testbed Using a 1-bit Radio-Over-Fiber Fronthaul Architecture
- 2024
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- We present the uplink and downlink of a time-division duplex distributed multiple-input multiple-output (D-MIMO) testbed, based on a 1-bit radio-over-fiber architecture, which is low cost and scalable. The proposed architecture involves a central unit (CU) that is equipped with 1-bit digital-to-analog and analog-to-digital converters, operating at 10 GS/s. The CU is connected to multiple single-antenna remote radio heads (RRHs) via optical fibers, over which a binary radio frequency (RF) waveform is transmitted. In the uplink, a binary RF waveform is generated at the RRHs by a comparator, whose inputs are the received RF signal and a suitably designed dither signal. In the downlink, a binary RF waveform is generated at the CU via bandpass sigma-delta modulation. Our measurement results show that low error-vector magnitude (EVM) can be achieved in both the uplink and the downlink, despite 1-bit sampling at the CU. Specifically, for point-to-point over-cable transmission between a single user equipment (UE) and a CU equipped with a single RRH, we report, for a 10-MBd signal using single-carrier (SC) 16 quadratic-amplitude modulation (QAM) modulation, an EVM of 3.3% in the downlink, and of 4.5% in the uplink. We then consider a CU connected to three RRHs serving over the air two UEs, and show that, after over-the-air reciprocity calibration, a downlink zero-forcing precoder designed on the basis of uplink channel estimates at the CU achieves an EVM of 6.4% and 10.9% at UE 1 and UE 2, respectively. Finally, we investigate the ability of the proposed architecture to support orthogonal frequency-division multiplexing (OFDM) waveforms, and its robustness against both in-band and out-of-band interference.
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| 2. |
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| 3. |
- Alex-Amor, Antonio, et al.
(författare)
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Glide-Symmetric Metallic Structures With Elliptical Holes for Lens Compression
- 2020
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Ingår i: IEEE transactions on microwave theory and techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 68:10, s. 4236-4248
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we study the wave propagation in a metallic parallel-plate structure with glide-symmetric elliptical holes. To perform this study, we derived a mode-matching technique based on the generalized Floquet theorem for glide-symmetric structures. This mode-matching technique benefits from a lower computational cost since it takes advantage of the glide symmetry in the structure. It also provides physical insight into the specific properties of Floquet modes propagating in these specific structures. With our analysis, we demonstrate that glide-symmetric structures with periodic elliptical holes exhibit an anisotropic refractive index over a wide range of frequencies. The equivalent refractive index can be controlled by tuning the dimensions of the holes. Finally, by combining the anisotropy related to the elliptical holes and transformation optics, a Maxwell fish-eye (MFL) lens with a 33.33% size compression is designed. This lens operates in a wideband frequency range from 2.5 to 10 GHz.
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| 4. |
- An, Sining, 1991, et al.
(författare)
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Coded Pilot Assisted Baseband Receiver for High Data Rate Millimeter-Wave Communications
- 2020
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 68:11, s. 4719-4727
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Tidskriftsartikel (refereegranskat)abstract
- A coded pilot assisted high data rate millimeter-wave receiver topology is presented in this article. A low data rate and low power pseudorandom noise (pn) coded pilot signal is superimposed at the transmitter, and the receiver can use such pilot for carrier recovery (CR) and/or channel estimation regardless of modulation scheme or communication data rate. The proposed baseband receiver has an analog-digital hybrid structure where a low-cost digital signal processor is used. This structure requires only a low-cost analog-to-digital converter (ADC) with a sampling rate of 40 MSPS. A proof-of-concept communication link at E-band is demonstrated with 18 Gbps 64-quadrature amplitude modulation (QAM) and 24 Gbps 16-QAM.
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| 5. |
- Brihuega, Alberto, et al.
(författare)
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Piecewise Digital Predistortion for mmWave Active Antenna Arrays: Algorithms and Measurements
- 2020
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 68:9, s. 4000-4017
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we describe a novel framework for digital predistortion (DPD)-based linearization of strongly nonlinear millimeter-wave active antenna arrays. Specifically, we formulate a piecewise (PW) closed-loop (CL) DPD solution and low-complexity gradient-adaptive parameter learning algorithms, together with a region partitioning method, which can efficiently handle deep compression of the PA units. The impact of beamsteering on the DPD performance is studied, showing strong beam-dependence, thus necessitating frequent updating of the DPD. In order to facilitate fast adaptation, an inexpensive, noniterative, pruning algorithm is introduced, which allows us to significantly reduce the number of model coefficients. The proposed methods are validated with extensive over-the-air RF measurements on a 64-element active antenna array transmitter operating at 28-GHz carrier frequency and transmitting a 400-MHz 5G new radio (NR) standard-compliant orthogonal frequency-division multiplexing waveform. The obtained results demonstrate the excellent linearization capabilities of the proposed solution, conforming to the new 5G NR requirements for frequency range 2 (FR2) in terms of both in-band waveform quality and out-of-band emissions. The proposed PW-CL DPD is shown to outperform the state-of-the-art PW DPD based on the indirect learning architecture, as well as the classical single-polynomial-based DPD solutions in terms of linearization performance and computational complexity by a clear margin.
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| 6. |
- Campion, James, 1989-, et al.
(författare)
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Silicon Micromachined Waveguide Calibration Standards for Terahertz Metrology
- 2021
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Ingår i: IEEE transactions on microwave theory and techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 69:8, s. 3927-3942
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Tidskriftsartikel (refereegranskat)abstract
- This article presents precision silicon micromachined waveguide calibration standards for use with terahertz vector network analyzers. This enables the creation of precise, highly repeatable, and traceable terahertz waveguide standards, surpassing the limits of current metrology techniques. A single silicon-on-insulator wafer with the appropriate device and handle layer thicknesses is used to implement a wide range of calibration and verification standards. The design of the standards is discussed from mechanical, electrical, and end-user perspectives. Silicon is shown to be the most promising material for the realization of precision metrology standards. We outline the potential to scale the presented design to at least 2.6 THz. Eight types of WM-570 standard, totaling 15 prototypes, are fabricated and characterized between 325 and 500 GHz. Despite some fabrication anomalies, all devices offer excellent performance. The best micromachined standards offer a return loss in excess of 40 dB, an insertion loss of below 0.1 dB, and a phase error of less than 1 degrees. The standards are utilized in both one- and two-port calibrations, including the multiline through-reflect-line algorithm. These are benchmarked against calibrations performed using conventional metallic standards, with a high degree of agreement observed between error-corrected measurements of a range of test devices.
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| 7. |
- Cao, Wenhui, 1990, et al.
(författare)
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Complexity Optimized Digital Predistortion Model of RF Power Amplifiers
- 2022
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 70:3, s. 1490-1499
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Tidskriftsartikel (refereegranskat)abstract
- A novel behavioral modeling technique for digital predistortion of radio frequency power amplifiers (PAs) is proposed. The proposed basis-propagating selection (BAPS) model has an advantage on complexity since its basis functions are constructed as delay or a combination of existing basis functions. The BAPS model effectively optimizes the running time complexity while maintaining the generality of a full Volterra series. A greedy search procedure is applied to select the optimal basis functions. Compared with truncated Volterra models and pruned models obtained by popular pruning techniques, the superior performance of the BAPS model, in terms of accuracy and identification stability, has been fairly justified. The linearization measurements on different types of PAs illustrate that the BAPS model can robustly outperform other models from literature while achieving a low running complexity.
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| 8. |
- Cao, Wenhui, 1990, et al.
(författare)
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Low-Complexity Digital Predistortion of Concurrent Multiband RF Power Amplifiers
- 2022
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; In Press, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The complexity of digital predistortion (DPD) for the concurrent multiband (MB) power amplifier (PA) has been a bottleneck for 5G wireless communication. A low-complexity MB DPD model has been proposed to reduce the running time complexity of DPD models for concurrent MB scenarios. The proposed MB model can generate the Volterra format basis functions with odd orders, including in-band, cross-band, and intermodulation (IMD) basis terms for arbitrary carrier configurations with an arbitrary number of bands. The optimal basis functions within the band of interests will be selected using a basis-function search algorithm. The lower cost complexity and high model accuracy of the proposed MB model have been validated by the PA linearization experiments in comparison with the memory polynomial MB model.
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| 9. |
- Chen, Qiao, et al.
(författare)
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Accurate Characterization and Design Guidelines of Glide-Symmetric Holey EBG
- 2020
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Ingår i: IEEE transactions on microwave theory and techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 68:12, s. 4984-4994
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Tidskriftsartikel (refereegranskat)abstract
- The dispersion characteristics of a glide-symmetric holey periodic surface are investigated, with special emphasis on a detailed study of its stopbands. The unit cell is modeled as a multiport network associated with multiple modes at each of the lattice boundaries. Enforcing the periodic conditions, the real and imaginary parts of the wavenumbers of the Floquet modes are calculated through an eigenproblem posed in terms of the generalized multimodal transfer matrix, which is computed from the scattering parameters obtained with a full-wave simulator. This procedure allows us to take into account the higher order modal couplings between adjacent unit cells that are crucial for accurate dispersion analysis. The resulting simulation-assisted approach provides both a convenient computational tool and a very fruitful physical insight that reveals the existence of complex modes, the convergence of opposite-parity modes, and the anisotropy in both passband and stopband. This approach enables a precise calculation of the attenuation constant, which is not possible with conventional techniques as the eigenmode solvers of commercial software. Based on this approach, an extensive parametric study is carried out, rigorously establishing a set of critical criteria for the use of such a periodic surface as an electromagnetic bandgap structure in gap waveguide technology. Moreover, the analysis of the directional properties of the structure is applied to further suppress the leakage.
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| 10. |
- Gonzalez-Gallardo, David, et al.
(författare)
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Hybrid Glide-Symmetric Unit Cell for Leakage Reduction in Millimeter-Wave PCB Interconnections to Waveguide Components
- 2022
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Ingår i: IEEE transactions on microwave theory and techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 70:5, s. 2631-2641
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we propose a hybrid glide-symmetric metasurface which presents an electromagnetic bandgap (ERG) behavior at the Ka-band. The innovative part of this work is the hybrid nature of the periodic structure, which is implemented with holes on two different technologies: printed circuit board (PCB) and metallic waveguide. These holes avoid propagation in an undesired parallel plate created between a PCB and a metallic waveguide. To demonstrate the potential of this concept, a hybrid glide-symmetric configuration was placed surrounding a PCB-waveguide transition at the Ka-band to reduce the leakage created by undesired air gaps. A prototype was manufactured and measured to corroborate the effectiveness of this technique to reduce losses and crosstalk.
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