We developed a mantle-cloak antenna by controlling the surface reactance of a dielectric-loaded dipole antenna. First, a mantle-cloak antenna with an assumed ideal metasurface sheet was designed, and band rejection characteristics were obtained by controlling the surface reactance of the mantle cloak. The variable range of the frequency spacing between the operating and stopband frequencies of the antenna was clarified by changing the value of the surface reactance. Next, a mantle-cloak antenna that uses vertical strip conductors was designed to clarify the characteristics and operating principle of the antenna. It was confirmed that the stopband frequency was 1130MHz, and the proposed antenna had a 36.3% bandwidth (|S11| ≤ -10dB) from 700 to 1010MHz. By comparing the |S11| characteristics and the input impedance characteristics of the proposed antenna with those of the dielectric-loaded antenna, the effect of the mantle cloak was confirmed. Finally, a prototype of the mantle-cloak antenna that uses vertical strip conductors was developed and measured to validate the simulation results. The measurement results were consistent with the simulation results.

In this paper, a planar balun having simple and compact features with slit ground was proposed. The operating frequency can be designed by the length and position of the defected ground slits. The 20 dB bandwidth of the common mode rejection ratio of the measuring balun was over 90%.

Backscatter wireless communications offer advantages such as batteryless operations, small form factor, and radio regulatory exemption sensors. The major challenge ahead of backscatter wireless communications is synchronized multicarrier data collection, which can be realized by rejecting mutual harmonics among backscatters. This paper analyzes the mutual interferences of digitally modulated multicarrier backscatter to find interferences from higher frequency subcarriers to lower frequency subcarriers, which do not take place in analog modulated multicarrier backscatters, is harmful for densely populated subcarriers. This reverse interference distorts the harmonics replica, deteriorating the performance of the existing method, which rejects mutual interference among subcarriers by 5dB processing gain. To solve this problem, this paper analyzes the relationship between subcarrier spacing and reverse interference, and reveals that an alternate channel spacing, with channel separation twice the bandwidth of a subcarrier, can provide reasonably dense subcarrier allocation and can alleviate reverse interference. The idea is examined with prototype sensors in a wired experiment and in an indoor propagation experiment. The results reveal that with alternate channel spacing, the reverse interference practically becomes negligible, and the existing interference rejection method achieves the original processing gain of 5dB with one hundredth packet error rate reduction.

This paper presents a 6th-order quadrature bandpass delta sigma AD modulator (QBPDSM) with 2nd-order image rejection using dynamic amplifier and noise coupling (NC) SAR quantizer embedded by passive adder for the application of wireless communication system. A novel complex integrator using dynamic amplifier is proposed to improve the energy efficiency of the QBPDSM. The NC SAR quantizer can realize an additional 2nd-order noise shaping and 2nd-order image rejection by the digital domain noise coupling technique. As a result, the 6th-order QBPDSM with 2nd-order image rejection is realized by two complex integrators using dynamic amplifier and the NC SAR quantizer. The SPICE simulation results demonstrate the feasibility of the proposed QBPDSM in 90nm CMOS technology. Simulated SNDR of 76.30dB is realized while a sinusoid -3.25dBFS input is sampled at 33.3MS/s and the bandwidth of 2.083MHz (OSR=8) is achieved. The total power consumption in the modulator is 6.74mW while the supply voltage is 1.2V.

A design method of the differential N-path filter with sampling computation is proposed. It enables the scale of the whole filter to be reduced by approximately half for easier realization. On top of that, the proposed method offers the ability to eliminate the harmonic passbands of the clock frequency and an increase of harmonic rejection. By using the proposed method, previous work involving an 8-path filter can be reduced to 5-path. The proposed differential 5-path filter reduces the scale of the circuit and at the same time has the performance of a 10-path filter from previous work. An example of differential 7-path filter using the same proposed design method is also stated in comparison of the differential 5-path filter. The differential 7-path filter offers the ability to eliminate all the passbands below 10 times the clock frequency with a tradeoff of an increase in circuit scale.

This paper applies minimum mean square error (MMSE) interference rejection followed by joint maximum likelihood detection (MLD) to a receiver in a distributed antenna network (DAN). DAN receivers capture not only the desired signals, but also the interference signals from nearby uncoordinated antennas. For the overloaded signal situation, non-linear detection schemes such as joint MLD can be applied to the received signals. However, the amount of metric calculations in joint MLD increases exponentially with the number of signal streams. Therefore, MMSE interference rejection followed by MLD detection is proposed. The proposed scheme reduces the complexity by a factor of 1/2M(NT-1) where NT is the number of interference signals with 2MQAM modulation. The effect of residual interference after the MMSE interference rejection is evaluated. Numerical results obtained through computer simulation and experiment show that the performance of the proposed scheme is about 4.0dB worse at a bit error rate (BER) of 10-3 than that of the joint MLD while its complexity is four times lower for QPSK signal streams. The BER performance degradation can be suppressed to about 2.5dB by adjusting the value of the coefficient in the MMSE matrix.

Discrete Gaussian is a cornerstone of many lattice-based cryptographic constructions. Aiming at the orthogonal lattice of a vector, we propose a discrete Gaussian rejection sampling algorithm, by modifying the dynamic programming process for subset sum problems. Within O(nq2) time, our algorithm generates a distribution statistically indistinguishable from discrete Gaussian at width s>ω(log n). Moreover, we apply our sampling algorithm to general high-dimensional dense lattices, and orthogonal lattices of matrices $matAinZ_q^{O(1) imes n}$. Compared with previous polynomial-time discrete Gaussian samplers, our algorithm does not rely on the short basis.

An improved radiometric calibration algorithm by extending the Mitsunaga and Nayar least-square minimization based algorithm with two major ideas is presented. First, a noise & outlier removal procedure based on the analysis of brightness transfer function is included for improving the algorithm's capability on handling noise and outlier in least-square estimation. Second, an alternative minimization formulation based on weighted least square is proposed to improve the weakness of least square minimization when dealing with biased distribution observations. The performance of the proposed algorithm with regards to two baseline algorithms is demonstrated, i.e. the classical least square based algorithm proposed by Mitsunaga and Nayar and the state-of-the-art rank minimization based algorithm proposed by Lee et al. From the results, the proposed algorithm outperforms both baseline algorithms on both the synthetic dataset and the dataset of real-world images.

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.

To support the rapid increase of mobile traffic, the LTE-based air interface is expected to be employed in the unlicensed spectrum known as “Licensed-Assisted Access (LAA).” The LAA terminal, which employs an LTE-based air interface, suffers from interference from WiFi access points as well as the LAA base station. The interference rejection combining (IRC) receiver, which employs a linear minimum mean square error (MMSE) filter, can suppress this interference from WiFi access points in addition to that of the LAA base station. The IRC receiver is effective, since it requires no knowledge of the interference, which is generally difficult to obtain for different systems. In this paper, we use a link-level simulation to evaluate the performance of the IRC receiver in suppressing the interference from WiFi access points, and show that the IRC receiver can effectively cancel the interference from WiFi systems as well as LTE systems, although we observed a slight performance degradation due to the covariance matrix estimation error caused by the WiFi interference fluctuation in the frequency-domain.

This paper proposes a novel multiple access method that enables concurrent sensor data streaming from multiple batteryless, wireless sensor tags. The access method is a pseudo-FDMA scheme based on the subcarrier backscatter communication principle, which is widely employed in passive RFID and radar systems. Concurrency is realized by assigning a dedicated subcarrier to each sensor tag and letting all sensor tags backscatter simultaneously. Because of the nature of the subcarrier, which is produced by constant rate switching of antenna impedance without any channel filter in the sensor tag, the tag-to-reader link always exhibits harmonics. Thus, it is important to reject harmonics when concurrent data streaming is required. This paper proposes a harmonics rejecting receiver to allow simultaneous multiple subcarrier usage. This paper particularly focuses on analog sensor data streaming which minimizes the functional requirements on the sensor tag and frequency bandwidth. The harmonics rejection receiver is realized by carefully handling group delay and phase delay of the subcarrier envelope and the carrier signal to accurately produce replica of the harmonics by introducing Hilbert and inverse Hilbert transformations. A numerical simulator with Simulink and a hardware implementation with USRP and LabVIEW have been developed. Simulations and experiments reveal that even if the CIR before harmonics rejection is 0dB, the proposed receiver recovers the original sensor data with over 0.98 cross-correlation.

This paper presents accurate DC and high frequency power-supply rejection (PSR) models for low drop-out (LDO) regulators using different types of active loads and pass transistors. Based on the proposed PSR model, we suggest design guidelines to achieve a high DC PSR or flat bandwidth (BW) by choosing appropriate active loads and pass transistors. Our PSR model captures the intricate interaction between the error amplifiers (EAs) and the pass devices by redefining the transfer function of the LDO topologies. The accuracy of our model has been verified through SPICE simulation and measurements. Moreover, the measurement results of the LDOs fabricated using the 0.18 µm CMOS process are consistent with the design guidelines suggested in this work.

A high-image-rejection wireless receiver with an N-phase active RC complex filter is proposed and analyzed. Signal analysis shows that the double-conversion receiver with (N+N2) mixers corrects the gain and phase mismatches of the adjacent image. Monte Carlo simulations evaluate the relation between image-rejection performances and the dispersions of device parameters for the double-conversion wireless receiver. The Monte Carlo simulations show that the image rejection ratio of the adjacent image depends almost only on R and C mismatches in the complex filter.

This paper presents a 60 GHz analog/digital beamforming receiver that effectively suppresses interference signals, targeting the IEEE 802.11ad/WiGig standard. Combining two-stream analog frontends with interference rejection digital signal processing, the analog beamforming steers the antenna beam to the desired direction while the digital beamforming provides gain suppression in the interference direction. A prototype has been built with 40 nm CMOS analog frontends as well as offline baseband digital signal processing. Measurements show a 3.1 dB EVM advantage over conventional two-stream diversity during a packet collision situation.

This paper proposes a high clutter-rejection technique for wall-penetrating frequency-modulated continuous-wave (FMCW) radar. FMCW radars are widely used, as they moderate the receiver saturation problem in wall-penetrating applications by attenuating short-range clutter such as wall-clutter. However, conventional FMCW radars require a very high-order high-pass filter (HPF) to attenuate short-range clutter. A delay-line (DL) is exploited to overcome this problem. Time-delay shifts beat frequencies formed by reflection waves. This means that a proper time-delay increases the ratio of target-beat frequency to clutter-beat frequency. Consequently, low-order HPF fully attenuates short-range clutter. A third-order HPF rejects more than 20 dB and 30 dB for clutter located at 6 m and 3 m, respectively, with a target located at 9 m detection with a 10,000 GHz/s chirp rate and a 28 ns delay-line.

In this paper, an interference rejection combining (IRC) technique is proposed for SFBC-OFDM cellular systems that exhibit multiple carrier frequency offsets (CFOs). The IRC weight and the corresponding value for CFO compensation in the proposed technique are obtained by maximizing the post-SINR, i.e., minimizing both the interference signal and inter-channel interference (ICI) terms caused by multiple CFOs. The performance of the conventional IRC and proposed IRC techniques is evaluated by computer simulation for an SFBC-OFDM cellular system with multiple CFOs.

Microwave systems have a number of promising applications in surveillance and monitoring systems. The main advantage of microwave systems is their ability to detect targets at distance under adverse conditions such as dim, smoky, and humid environments. Specifically, the wide bandwidth of ultra-wideband radar enables high range resolution. In a previous study, we proposed an accurate shape estimation algorithm for multiple targets using multiple ultra-wideband Doppler interferometers. However, this algorithm produces false image artifacts under conditions with severe interference. The present paper proposes a technique to suppress such false images by detecting inconsistent combinations of the radial velocity and time derivative of image positions. We study the performance of the proposed method through numerical simulations of a two-dimensional section of a moving human body, and demonstrate the remarkable performance of the proposed method in suppressing false image artifacts in many scenarios.

In this paper, we present a modified image rejection method that uses imbalance compensation techniques for phase and gain in low-intermediate frequency (IF) software-defined radio (SDR) receivers. In low-IF receivers, the image frequency signal interferes with the desired signal owing to the phase and gain imbalances caused by analog devices. Thus, it is difficult to achieve the required image rejection ratio (IRR) of over 60dB without compensation. To solve this problem, we present modified blind compensation techniques based on digital signal processing using a feedback control loop with a practical computation process. The modified method can reduce the complexity when a hardware logic circuit is used, like an FPGA. The simulation and experimental results verify that the modified method achieves an IRR greater than 50-60dB for both the carrier and the modulated waves.

A novel method was developed to expand and adjust the bandwidth of long-period fiber gratings (LPFGs) as band-rejection filters. The band-rejection filters were constructed by concatenating two LPFGs with an appropriate space, that causes a $pi$-phase shift. The component LPFGs with the same period and the different numbers of periods are designed to have $-$3-dB transmission at wavelengths on both sides of a resonance wavelength symmetrically, and the transmission loss of the concatenated LPFGs peaks at the -3-dB transmission wavelengths. The rejection bandwidth was widened by changing the interval between the -3-dB transmission wavelengths. The concatenated LPFGs were simulated by using a transfer-matrix method based on a discrete coupling model, and were fabricated by a point-by-point arc discharge technique on the basis of the simulation results. It was demonstrated that the rejection bandwidth at 20-dB attenuation reached 26.6,nm and was 2.7 times broader than that of a single uniform LPFG.

In this study, a new method for Decode-Distributed Beamforming (D-DB) relaying is proposed. Each relay node decodes the source symbol by maximum likelihood detection. The detected symbol is entered into the stored Quantized Equal-gain (QE) codebook, where the label of the phase region is provided by a feedback link from the destination node. Therefore, the proposed relay network forms a Decode-Distributed QE (D-DQE) relay network. The performances of the D-DQE codebooks are examined by Monte-Carlo simulations, in which the feedback links and channel estimations are assumed to be error-free. The simulation results reveal that the symbol error rates of the D-DQE relay system improve the error performance of the QE codebooks when relay nodes are close to the source node. When error-free feedback bits are provided, the performance of the proposed D-DQE is better than that of Alamouti's Decode-Distributed Space-Time Coding (D-DSTC) relay network. The weakest relays are rejected to improve the performance of the D-DQE codebooks and reduce the number of feedback bits. This relay network is called Decode-Relay Rejection for Distributed Beamforming (D-RRDB) relay networks.