We evaluated the transmission performance, including received power and transmission throughput characteristics, in 4×4 single-user multiple-input multiple-output (SU-MIMO) transmission for synchronous time division duplex (TDD) and downlink data channels in comparison with single-input single-output (SISO) transmission in an environment where a local 5G wireless base station was installed on the roof of a research building at our university. Accordingly, for the received power characteristics, the difference between the simulation value, which was based on the ray tracing method, and the experimental value at 32 points in the area was within a maximum difference of approximately 10 dB, and sufficient compliance was obtained. Regarding the transmission throughput versus received power characteristics, after showing a simulation method for evaluating throughput characteristics in MIMO, we compared the results with experimental results. The cumulative distribution function (CDF) of the transmission throughput shows that, at a CDF of 50%, in SISO transmission, the simulated value is approximately 115Mbps, and the experimental value is 105Mbps, within a difference of approximately 10Mbps. By contrast, in MIMO transmission, the simulation value is 380Mbps, and the experimental value is approximately 420Mbps, which is a difference of approximately 40Mbps. It was shown that the received power and transmission throughput characteristics can be predicted with sufficient accuracy by obtaining the delay profile and the system model at each reception point using the both ray tracing and MIMO simulation methods in actual environments.

This paper presents a power amplifier (PA) designed as a part of a transceiver front-end fabricated in 130-nm SiGe BiCMOS. The PA shares its output antenna port with a low noise amplifier using a low-loss transmission/reception switch. The output matching network of the PA is designed to provide high output power, low AM-AM distortion, and uniform performance over frequencies in the range of 24.25-29.5GHz. Measurements of the front-end in TX mode demonstrate peak S21 of 30.3dB at 26.7GHz, S21 3-dB bandwidth of 9.8GHz from 22.2to 32.0GHz, and saturated output power (Psat) above 20dBm with power-added efficiency (PAE) above 22% from 24 to 30GHz. For a 64-QAM 400MHz bandwidth orthogonal frequency division multiplexing (OFDM) signal, -25dBc error vector magnitude (EVM) is measured at an average output power of 12.3dBm and average PAE of 8.8%. The PA achieves a competitive ITRS FoM of 92.9.

High-accuracy wideband signal transmission is essential for 5G and Beyond wireless communication systems. Memory nonlinearity in transmitters is a serious issue for the goal, because it deteriorates the quality of signal and lowers the system performance. This paper studies a post-reception nonlinear compensation (PRC) schemes consisting of frequency domain equalizers (FDEs) and a blind nonlinear compensator (BNLC). A frequency-domain memory nonlinearity modeling approach is employed, and several PRC configurations with FDEs and BNLC are evaluated through computer simulations. It is concluded that the proposed PRC schemes can effectively compensate memory nonlinearity in wideband transmitters via frequency-selective propagation channel. By implementing the PRC in a base station, uplink performance will be enhanced without any additional cost and power consumption in user terminals.

The non-orthogonal multiple access (NOMA) approach has been developed in the fifth-generation mobile communication systems (5G) and beyond, to improve the spectrum efficiency and accommodate a large number of IoT devices. Although power domain NOMA is a promising candidate, it is vulnerable to the nonlinearity of RF circuits and cannot achieve high-throughput transmission using high-level modulations in nonlinear environments. This study proposes a novel post-reception nonlinear compensation scheme consisting of two blind nonlinear compensators (BNLCs) and a frequency-domain equalizer (FDE) to reduce the effect of nonlinear distortion. The improvement possible with the proposed scheme is evaluated by using the error vector magnitude (EVM) of the received signal, which is obtained through computer simulations. The simulation results confirm that the proposed scheme can effectively improve the quality of the received downlink power-domain NOMA signal and enable high-throughput transmission under the transmitter (Tx) and receiver (Rx) nonlinearities via a frequency-selective fading channel.

Regarding the enlarged array size for the 5G new radio (NR) millimeter-wave phased-array transceivers, an improved phase tuning resolution will be required to support the accurate beam control. This paper introduces a CMOS implementation of an active vector-summing phase shifter. The proposed phase shifter realizes a 6-bit phase shifting with an active area of 0.32mm2. To minimize the gain variation during the phase tuning, a gain error compensation technique is proposed. After the compensation, the measured gain variation within the 5G NR band n257 is less than 0.9dB. The corresponding RMS gain error is less than 0.2dB. The measured RMS phase error from 26.5GHz to 29.5GHz is less than 1.2°. Gain-invariant, high-resolution phase tuning is realized by this work. Considering the error vector magnitude (EVM) performance, the proposed phase shifter supports a maximum data rate of 11.2Gb/s in 256QAM with a power consumption of 25.2mW.

This paper presents a 1024-QAM OFDM signal capable WLAN receiver in 65nm CMOS technology. Thermal noise-based IQ frequency-independent mismatch correction and IQ frequency-dependent mismatch correction with baseband loopback are proposed for the self-calibration in the receiver. The measured image rejection ratio of the self-calibration is -56.3dB. The receiver achieves the extremely low EVM of -37.1dB even with wide channel bandwidth of 80MHz and has the ability to receive the 1024-QAM signal. The result indicates that the receiver is extendable for the 802.11ax compliant receiver that supports a higher density modulation scheme of MIMO.

This paper introduces a reversible watermarking algorithm that exploits an adaptable predictor and sorting parameter customized for each image and each payload. Our proposed method relies on a well-known prediction-error expansion (PEE) technique. Using small PE values and a harmonious PE sorting parameter greatly decreases image distortion. In order to exploit adaptable tools, Gaussian weight predictor and expanded variance mean (EVM) are used as parameters in this work. A genetic algorithm is also introduced to optimize all parameters and produce the best results possible. Our results show an improvement in image quality when compared with previous conventional works.

This paper presents a novel CMOS bias topology serving as not only a bias circuit but also an adaptive linearizer for SiGe HBT power amplifier (PA) IC. The novel bias circuit can well keep the base-to-emitter voltage (Vbe) of RF amplifying HBT constant and adaptively increase the base current (Ib) with the increase of the input power. Therefore, the gain compression and phase distortion performance of the PA is improved. A three-stage 5-GHz band PA IC with the novel bias circuit for WLAN applications is designed and fabricated in IBM 0.35µm SiGe BiCMOS technology. Under 54Mbps OFDM signal at 5.4GHz, the PA IC exhibits a measured small-signal gain of 29dB, an EVM of 0.9% at 17dBm output power and a DC current consumption of 284mA.

In the optimization of decision diagrams, variable reordering approaches are often used to minimize the number of nodes. However, such approaches are less effective for analysis of multi-state systems given by monotone structure functions. Thus, in this paper, we propose algorithms to minimize the number of edges in an edge-valued multi-valued decision diagram (EVMDD) for fast analysis of multi-state systems. The proposed algorithms minimize the number of edges by grouping multi-valued variables into larger-valued variables. By grouping multi-valued variables, we can reduce the number of nodes as well. To show the effectiveness of the proposed algorithms, we compare the proposed algorithms with conventional optimization algorithms based on a variable reordering approach. Experimental results show that the proposed algorithms reduce the number of edges by up to 15% and the number of nodes by up to 47%, compared to the conventional ones. This results in a speed-up of the analysis of multi-state systems by about three times.

In the recently developed Flexible Wireless System (FWS), the same platform needs to deal with different wireless systems. This increases nonlinear distortion in its wideband power amplifier (PA) because the PA needs to concurrently amplify multi-band signals. By taking higher harmonics as well as inter- and cross-modulation distortion into consideration, we have developed a method to analytically evaluate the adjacent channel leakage power ratio (ACPR) and error vector magnitude (EVM) on the basis of the PA's nonlinear characteristics. We devise a novel method for modeling the PA amplifying dual-band signals. The method makes it possible to model it merely by performing a one-tone test, making use of the Volterra series expansion and the general Wiener model. We then use the Mehler formula to derive the closed-form expressions of the PA's output power spectral density (PSD), ACPR, and EVM. The derivations are based on the assumption that the transmitted signals are complex Gaussian distributed in orthogonal frequency division multiplexing (OFDM) transmission systems. We validate the method by comparing measurement and simulation results and confirm it can appropriately predict the ACPR and EVM performance of the nonlinear PA output with OFDM inputs. In short, the method enables correct modeling of a wideband PA that amplifies dual-band signals merely by conducting a one-tone test.

The author developed a wideband precise I/Q modulator using GaAs pHEMT technology. In this technology, pHEMT has 0.22 µm metallurgical gate length and ft=51 GHz at Vds=5V. With the careful design of the wideband phase shifter, this IQ modulator achieved a large wideband frequency range of 250 MHz to 8 GHz and good EVM performance after calibration. For overall frequency range, low distortion performance is obtained, where third order intermodulation is less than -42 dBc. Also the ACPR at 2.2 GHz for W-CDMA application is less than -74 dBc.

This paper proposes a high-speed architecture to realize two-variable numeric functions. It represents the given function as an edge-valued multiple-valued decision diagram (EVMDD), and shows a systematic design method based on the EVMDD. To achieve a design, we characterize a numeric function f by the values of l and p for which f is an l-restricted Mp-monotone increasing function. Here, l is a measure of subfunctions of f and p is a measure of the rate at which f increases with an increase in the dependent variable. For the special case of an EVMDD, the EVBDD, we show an upper bound on the number of nodes needed to realize an l-restricted Mp-monotone increasing function. Experimental results show that all of the two-variable numeric functions considered in this paper can be converted into an l-restricted Mp-monotone increasing function with p=1 or 3. Thus, they can be compactly realized by EVBDDs. Since EVMDDs have shorter paths and smaller memory size than EVBDDs, EVMDDs can produce fast and compact NFGs.

Nonlinear distortions in power amplifiers (PAs) generate spectral regrowth at the output, which causes interference to adjacent channels and errors in digitally modulated signals. This paper presents a novel method to evaluate adjacent channel leakage power ratio (ACPR) and error vector magnitude (EVM) from the amplitude-to-amplitude (AM/AM) and amplitude-to-phase (AM/PM) characteristics. The transmitted signal is considered to be complex Gaussian distributed in orthogonal frequency-division multiplexing (OFDM) systems. We use the Mehler formula to derive closed-form expressions of the PAs output power spectral density (PSD), ACPR and EVM for memoryless PA and memory PA respectively. We inspect the derived relationships using an OFDM signal in the IEEE 802.11a WLAN standard. Simulation results show that the proposed method is appropriate to predict the ACPR and EVM values of the nonlinear PA output in OFDM systems, when the AM/AM and AM/PM characteristics are known.

This letter evaluates a transmitter architecture using harmonic images in D/A conversion for generating RF signals. In generating harmonic images, the problems such as intermodulation distortion of DAC were investigated. We developed an evaluation system with two bandpass filter and a buffer amplifier. It was experimentally found that the RF signal up to around 400 MHz can be generated by a commonly used 14-bit DAC at the sampling rates of around 40 MHz with EVM less than 6.6%. This letter also presents a more feasible transmitter example having an IF stage with harmonic image extraction scheme and a typical RF upconversion stage.

The author developed a GaAs wideband IQ modulator IC, which is utilized in RF signal source instruments with direct-conversion architecture. The layout is fully symmetric to obtain a temperature-stable operation. However, the actual temperature drift of EVM (Error Vector Magnitude) is greater in some frequency and temperature ranges than the first generation IC of the same architecture. For applications requiring the precision of electric instrumentation, temperature drift is highly critical. This paper clarifies that linear phase error is the dominant factor causing the temperature drift. It also identifies that such temperature drift of linear phase error is due to equivalent series impedance, especially parasitic capacitance of the phase shifter. This effect is verified by comparing the SSB measurements to a mathematical simulation using an empirical temperature-dependent small-signal FET model.

We derived explicit formulas for evaluating the error vector magnitude (EVM) from the amplitude distortion (AM-AM) and phase distortion (AM-PM) of power amplifiers (PAs) in orthogonal frequency-division multiplexing (OFDM) systems, such as the IEEE 802.11a/g wireless local area networks (WLANs) standards. We demonstrated that the developed formulas allowed EVM simulation of a memoryless PA using only a single-tone response (i.e. without OFDM modulation and demodulation), thus enabling us to easily simulate the EVM using a harmonic-balance (HB) simulator. This HB simulation technique reduced the processing time required to simulate the EVM of a PA for the IEEE 802.11a standard by a factor of ten compared to a system-level (SL) simulation. We also demonstrated that the measured EVM of a PA module for the IEEE 802.11g could accurately be predicted by applying the measured static AM-AM and AM-PM characteristics to the derived formulas.

Undersampling (or bandpass sampling) phase modulated signals directly at high frequency band, the harmful effects of the aperture jitter characteristics of ADCs (Analog-to-Digital converters) and sampling clock instability of the system can not be ignored. In communication systems the sampling jitter brings additional phase noise to the constellation pattern besides thermal noise, thus the BER (bit error rate) performance will be degraded. This paper examines the relationship between the input frequency to ADC and the sampling jitter in digital IF (Intermediate Frequency) downconversion receivers with undersampling scheme. This paper presents the measurement results with a real hardware prototype system as well as the computer simulation results with a theoretically modeled IF sampling receiver. We evaluated EVM (Error Vector Magnitude) in various clock jitter configurations with commonly used and reasonable cost ADCs of which sampling rates was 40 MHz. According to the results, the IF input frequencies of QPSK (16 QAM) signals were limited below around 290 (210) MHz for wireless LAN standard, and 730 (450) MHz for W-CDMA standard, respectively, in our best configuration.