Energy efficiency is one of the critical issues for Wireless Sensor Networks (WSN). IEEE 802.15.4 beacon-enabled MAC protocol achieves low energy consumption by having periodical inactive portions, where nodes run in low power. However, IEEE 802.15.4 beacon-enabled protocol cannot respond to dynamic changes in the number of sensor nodes and data rates in WSN because its duty cycle is fixed and immutable. In this paper, we propose a dynamic superframe duration adaptation scheme based on the Markov chain-based analysis methods for IEEE 802.15.4 beacon-enabled protocol. The proposed methods are flexible enough to accommodate changes in the number of sensor nodes and differences in data rates in WSNs while maintaining low latency and low energy consumption despite slight degradation in packet delivery ratio.

Frequency-hopping sequence (FHS) sets with low-hit-zone (LZH) can be well applied in quasi-synchronous (QS) frequency-hopping multiple-access (FHMA) systems to reduce the mutual interference among different users. On the other hand, LHZ-FHS sets with wide-gap (WG) property can effectively resist the broadband blocking interference, the single frequency narrowband interference, the multipath fading and the tracking interference. In this letter, a new family of WG-LHZ-FHS sets is constructed. Besides, these new WG-LHZ-FHS sets possess optimal average periodic Hamming correlation (APHC) properties.

A hard-type oscillator is defined as an oscillator having stable fixed points within a stable limit cycle. For resonant tunneling diode (RTD) oscillators, using hard-type configuration has a significant advantage that it can suppress spurious oscillations in a bias line. We have fabricated hard-type oscillators using an InGaAs-based RTD, and demonstrated a proper operation. Furthermore, the oscillating properties have been compared with a soft-type oscillator having a same parameters. It has been demonstrated that the same level of the phase noise can be obtained with a much smaller power consumption of approximately 1/20.

We propose an efficient network upgrade and expansion method that can make the most of the next generation channel resources to accommodate further increases in traffic. Semi-flexible grid configuration and two cost metrics are introduced to establish a regularity in frequency assignment and minimize disturbance in the upgrade process; both reduce the fragmentation in frequency assignment and the number of fibers necessary. Various investigations of different configurations elucidate that the number of fibers necessary is reduced about 10-15% for any combination of upgrade scenario, channel frequency bandwidth, and topology adopted.

A method for detecting the timing of photodiode (PD) saturation without using an in-pixel time-to-digital converter (TDC) is proposed. Detecting PD saturation time is an approach to extend the dynamic range of a CMOS image sensor (CIS) without multiple exposures. In addition to accumulated charges in a PD, PD saturation time can be used as a signal related to light intensity. However, in previously reported CISs with detecting PD saturation time, an in-pixel TDC is used to detect and store PD saturation time. That makes the resolution of a CIS lower because an in-pixel TDC requires a large area. As for the proposed pixel circuit, PD saturation time is detected and stored as a voltage in a capacitor. The voltage is read and converted to a digital code by a column ADC after an exposure. As a result, an in-pixel TDC is not required. A signal-processing and calibration method for combining two signals, which are saturation time and accumulated charges, linearly are also proposed. Circuit simulations confirmed that the proposed method extends the dynamic range by 36 dB and its total dynamic range to 95 dB. Effectiveness of the calibration was also confirmed through circuit simulations.

In this letter, we give a recursive construction of q-ary almost periodic complementary pairs (APCPs) based on an interleaving technique of sequences and Kronercker product. Based on this construction, we obtain new quaternary APCPs with new lengths.

This paper theoretically presents that a terahertz (THz) oscillator using a resonant tunneling diode (RTD) and a rectangular cavity, which has previously been proposed, can radiate high output power by the impedance matching between RTD and load through metal-insulator-metal (MIM) capacitors. Based on an established equivalent-circuit model, an equation for output power has been deduced. By changing MIM capacitors, a matching point can be derived for various sizes of rectangular-cavity resonator. Simulation results show that high output power is possible by long cavity. For example, a high output power of 5 mW is expected at 1 THz.

A scheme is proposed for generation of large-amplitude short pulses using a transmission line with regularly spaced series-connected tunnel diodes (TDs). In the case where the loaded TD is unique, it is established that the leading edge of the inputted pulse moves slower than the trailing edge, when the pulse amplitude exceeds the peak voltage of the loaded TD; therefore, the pulse width is autonomously reduced through propagation in the line. In this study, we find that this property is true even when the several series-connected TDs are loaded periodically. By these mechanisms, the TD line succeeds in generating large and short pulses. Herein, we clarify the design criteria of the TD line, together with both numerical and experimental validation.

Inspired by an idea due to Levenshtein, we apply the low correlation zone constraint in the analysis of the weighted mean square aperiodic correlation. Then we derive a lower bound on the measure for quasi-complementary sequence sets with low correlation zone (LCZ-QCSS). We discuss the conditions of tightness for the proposed bound. It turns out that the proposed bound is tighter than Liu-Guan-Ng-Chen bound for LCZ-QCSS. We also derive a lower bound for QCSS, which improves the Liu-Guan-Mow bound in general.

The partial-period autocorrelation of sequences is an important performance measure of communication systems employing them, but it is notoriously difficult to be analyzed. In this paper, we propose an algorithm to design unimodular sequences with low partial-period autocorrelations via directly minimizing the partial-period integrated sidelobe level (PISL). The proposed algorithm is inspired by the monotonic minimizer for integrated sidelobe level (MISL) algorithm. Then an acceleration scheme is considered to further accelerate the algorithms. Numerical experiments show that the proposed algorithm can effectively generate sequences with lower partial-period peak sidelobe level (PPSL) compared with the well-known Zadoff-Chu sequences.

This paper is focused on constructing even-length binary Z-complementary pairs (EB-ZCPs) with new length. Inspired by a recent work of Adhikary et al., we give a construction of EB-ZCPs with length 8N+4 (where N=2α 10β 26γ and α, β, γ are nonnegative integers) and zero correlation zone (ZCZ) width 5N+2. The maximum aperiodic autocorrelation sums (AACS) magnitude of the proposed sequences outside the ZCZ region is 8. It turns out that the generated sequences have low PAPR.

In this paper, a compact microwave push-push oscillator based on a resonant tunneling diode (RTD) has been fabricated and demonstrated. A symmetrical spiral inductor structure has been used in order to reduce a chip area. The designed symmetric inductor is integrated into the InP-based RTD monolithic microwave integrated circuit (MMIC) technology. The circuit occupies a compact active area of 0.088 mm2 by employing symmetric inductor. The fabricated RTD oscillator shows an extremely low DC power consumption of 87 µW at an applied voltage of 0.47 V with good figure-of-merit (FOM) of -191 dBc/Hz at an oscillation frequency of 27 GHz. This is the first implementation as the RTD push-push oscillator with the symmetrical spiral inductor.

The transition dynamics of a multistable tunnel-diode oscillator is characterized for modulating amplitude of outputted oscillatory signal. The base oscillator possesses fixed-point and limit-cycle stable points for a unique bias voltage. Switching these two stable points by external signal can render an efficient method for modulation of output amplitude. The time required for state transition is expected to be dominated by the aftereffect of the limiting point. However, it is found that its influence decreases exponentially with respect to the amplitude of external signal. Herein, we first describe numerically the pulse generation scheme with the transition dynamics of the oscillator and then validate it with several time-domain measurements using a test circuit.

This paper presents a conformal retrodirective metagrating with multi-azimuthal-angle operating ability. First, a flat metagrating composed of a periodic array of single rectangular patch elements, two-layer stacked substrates, and a ground plane is implemented to achieve one-directional retroreflection at a specific angle. The elevation angle of the retroreflection is manipulated by precisely tuning the value of the period. To control the energy coupling to the retrodirective mode, the dimensions of the length and width of the rectangular patch are investigated under the effect of changing the substrate thickness. Three values of the length, width, and thickness are then chosen to obtain a high retroreflection power efficiency. Next, to create a conformal design operating simultaneously at multiple azimuthal angles, the rectangular patch array using a flexible ultra-thin guiding layer is conformed to a dielectric cylindrical substrate backed by a perfect electric conductor ground plane. Furthermore, to further optimize the retroreflection efficiency, two circular metallic plates are added at the two ends of the cylindrical substrate to eliminate the specular reflection inside the space of the cylinder. The measured radar cross-section shows a power efficiency of the retrodirective metagrating of approximately 91% and 93% for 30° retrodirected elevation angle at the azimuthal angles of 0° and 90°, respectively, at 5.8GHz.

We evaluated the noise properties of a periodically poled lithium niobite phase-sensitive amplifier (PSA) using a phase-locked local oscillator as a pump generated by an optical phase-locked loop (OPLL-LO). To examine whether or not the LO pump generated by an OPLL degrades the noise figure (NF) of the PSA, we compared the noise levels of a PSA using an OPLL-LO with that of one using a master local oscillator (M-LO) that utilizes the master light itself as a pump in the electrical domain. With the OPLL, the phase-locked local light had almost the same frequency noise components as the master light. We observed almost the same output noise spectra for the OPLL-LO PSA and M-LO PSA and confirmed the absence of excess noise components in the OPLL-LO PSA in the 0.1 to 20-GHz range. The OPLL-LO PSA exhibited low-noise amplification with an average NF of 1.7-dB at a 23.2-dB gain within an input power range of -31 to -21dBm, which is a feasible input power for repeater amplifiers used in the optical signal transmission systems. We also investigated the influence of the noisy master light, which emulates the accumulation of optical noise from the amplifiers in the transmission system. The OPLL-LO PSA was highly tolerant to the optical noise because the difference in the NF was negligibly small within a master light OSNR range of 5 to 55dB. These results indicate that the OPLL-LO PSA will be useful as a low-noise repeater amplifier for the spectrally efficient large-capacity photonic networks of the future.

In this paper, we analyzed the pulse responses of dispersion medium with periodically conducting strips by using a fast inversion Laplace transform (FILT) method combined with point matching method (PMM) for both the TM and TE cases. Specifically, we investigated the influence of the width and number of the conducting strips on the pulse response and distribution of the electric field.

We developed a polarization-independent and reserved-band-less complementary spectral inverted optical phase conjugation (CSI-OPC) device using dual-band difference frequency generation based on highly efficient periodically poled LiNbO3 waveguide technologies. To examine the nonlinearity mitigation in a long-haul transmission using a large number of OPCs, we installed a CSI-OPC device in the middle of a pure silica core fiber-based recirculating loop transmission line with a length of 320km. First, we examined the fiber-input power tolerance after 5,120-km and 6,400-km transmission using 22.5-Gbaud PDM-16QAM 10-channel DWDM signals and found a Q-factor improvement of over 1.3dB along with enhanced power tolerance thanks to mitigating the fiber nonlinearity. We then demonstrated transmission distance extension using the CSI-OPC device. The use of multiple CSI-OPCs enables an obvious performance improvements attained by extending the transmission distance from 6,400km to 8,960km, which corresponds to applying the CSI-OPC device 28 times. Moreover, there was no Q-factor degradation for the link in a linear regime after applying the CSI-OPC device more than 16 times. These results demonstrate that the CSI-OPC device can improve the nonlinear tolerance of PDM-16QAM signals without an excess penalty.

In this paper, the influence of high-temperature sputtering on the nitrogen-doped (N-doped) LaB6 thin film formation utilizing RF sputtering was investigated. The N-doped LaB6/SiO2/p-Si(100) MOS diode and N-doped LaB6/p-Si(100) of Schottky diode were fabricated. A 30 nm thick N-doped LaB6 thin film was deposited from room temperature (RT) to 150°C. It was found that the resistivity was decreased from 1.5 mΩcm to 0.8 mΩcm by increasing deposition temperature from RT to 150°C. The variation of work function was significantly decreased in case that N-doped LaB6 thin film deposited at 150°C. Furthermore, Schottky characteristic was observed by increasing deposition temperature to 150°C. In addition, the crystallinity of N-doped LaB6 thin film was improved by increasing deposition temperature.

This work reports a new technique to suppress the undesirable multiple-triggering effect in the typical diode triggered silicon controlled rectifier (DTSCR), which is frequently used as an ESD protection element in the advanced CMOS technologies. The technique is featured by inserting additional N-Well areas under the N+ region of intrinsic SCR, which helps to improve the substrate resistance. As a consequence, the delay of intrinsic SCR is reduced as the required triggering current is largely decreased and multiple-triggering related higher trigger voltage is removed. The novel DTSCR structures can alter the stacked diodes to achieve the precise trigger voltage to meet different ESD protection requirements. All explored DTSCR structures are fabricated in a 65-nm CMOS process. Transmission-line-pulsing (TLP) and Very-Fast-Transmission-line-pulsing (VF-TLP) test systems are adopted to confirm the validity of this technique and the test results accord well with our analysis.

Periodic sequences, used as keys in cryptosystems, plays an important role in cryptography. Such periodic sequences should possess high linear complexity to resist B-M algorithm. Sequences constructed by cyclotomic cosets have been widely studied in the past few years. In this paper, the linear complexity of n-periodic cyclotomic sequences of order 2 and 4 over 𝔽p has been calculated, where n and p are two distinct odd primes. The conclusions reveal that the presented sequences have high linear complexity in many cases, which indicates that the sequences can resist the linear attack.