This paper presents a 6.8-GHz compact digital fractional-N PLL based on a pulse-shaped loop filter, enabling a loop bandwidth of$0.26f_{ref}$to suppress the ring oscillator’s phase noise. It leverages a constant-slope DTC with range extension technique to save 50% area of the capacitor array. The embedded nonlinearity cancellation and digital offset compensation further improve the spectrum purity. Fabricated in a 28-nm CMOS process, the pulse-shaper-based PLL occupies$\text {0.025mm}^{{2}}$core area, achieves an integrated jitter of 804 fs and −53.2 dBc fractional spur at near-integer channels with a power consumption of 5.68mW, obtaining a$\text {FoM}_{\text {Jitter-N-Area}}$of −269.9 dB.

Reconfigurable intelligent surface (RIS) is emerging as a promising technology to boost the energy efficiency (EE) of 5G beyond and 6G networks. Inspired by this potential, in this paper, we investigate the RIS-assisted energy-efficient radio access networks (RAN). In particular, we combine RIS with sleep control techniques, and develop a hierarchical reinforcement learning (HRL) algorithm for network management. In HRL, the meta-controller decides the on/off status of the small base stations (SBSs) in heterogeneous networks, while the sub-controller can change the transmission power levels of SBSs to save energy. The simulations show that the RIS-assisted sleep control can achieve significantly lower energy consumption, higher throughput, and more than doubled energy efficiency than no- RIS conditions.

Reconfigurable Intelligent Surfaces (RIS) are planar structures connected to electronic circuitry, which can be employed to steer the electromagnetic signals in a controlled manner. Through this, the signal quality and the effective data rate can be substantially improved. While the benefits of RIS-assisted wireless communications have been investigated for various scenarios, some aspects of the network design, such as coverage, optimal placement of RIS, etc., often require complex optimization and numerical simulations, since the achievable effective rate is difficult to predict. This problem becomes even more difficult in the presence of phase estimation errors or location uncertainty, which can lead to substantial performance degradation if neglected. Considering randomly distributed receivers within a ring-shaped RIS-assisted wireless network, this paper mainly investigates the effective rate by taking into account the above-mentioned impairments. Furthermore, exact closed-form expressions for the effective rate are derived in terms of Meijer’s G-function, which (i) reveals that the location and phase estimation uncertainty should be well considered in the deployment of RIS in wireless networks; and (ii) facilitates future network design and performance prediction.

This paper investigates the effective rate when the instantaneous received signal-to-noise ratio (SNR) could be modeled as the mixture Gamma (MG), mixture of Gaussian (MoG), and Fox’s H-function distributed random variable (RV), respectively. Three closed-form expressions are correspondingly derived in terms of the Fox’s H-function. The obtained analytical results are further examined by the Monte-Carlo simulation. One can observe that (i) the analytical solutions provide an excellent match with the Monte-Carlo simulation results; (ii) the MG and MoG approaches provide highly approximated solutions, and the MG is better due to a simpler form; and (iii) the Fox’s H-function solution is exact and offers a unified, general and flexible framework for the effective rate analysis.

Millimeter-wave (mmWave) multiple-input multiple-output (MIMO) system for the fifth generation (5G) cellular communications can also enable single-anchor positioning and object tracking due to its large bandwidth and inherently high angular resolution. In this paper, we introduce the newly invented concept, large intelligent surface (LIS), to mmWave positioning systems, study the theoretical performance bounds (i.e., Cramér-Rao lower bounds) for positioning, and evaluate the impact of the number of LIS elements and the value of phase shifters on the position estimation accuracy compared to the conventional scheme with one direct link and one non-line-of-sight path. It is verified that better performance can be achieved with a LIS from the theoretical analyses and numerical study.

We propose a decision triggered data transmission and collection (DTDTC) protocol for condition monitoring and anomaly detection in the industrial Internet of things (IIoT). In the IIoT, the collection, processing, encoding, and transmission of the sensor readings are usually not for the reconstruction of the original data but for decision making at the fusion center. By moving the decision making process to the local end devices, the amount of data transmission can be significantly reduced, especially when normal signals with positive decisions dominate in the whole life cycle and the fusion center is only interested in collecting the abnormal data. The proposed concept combines compressive sensing, machine learning, data transmission, and joint decision making. The sensor readings are encoded and transmitted to the fusion center only when abnormal signals with negative decisions are detected. All the abnormal signals from the end devices are gathered at the fusion center for a joint decision with feedback messages forwarded to the local actuators. The advantage of such an approach lies in that it can significantly reduce the volume of data to be transmitted through wireless links. Moreover, the introduction of compressive sensing can further reduce the dimension of data tremendously. An exemplary case, i.e., diesel engine condition monitoring, is provided to validate the effectiveness and efficiency of the proposed scheme compared to the conventional ones.

This paper investigates the upper and lower bounds on achievable secrecy rate of multiple-input multiple-output (MIMO) wiretap channels by employing zero-forcing (ZF) detectors at, both the legitimate and malicious receivers' sides. Particularly, both large (i.e., gamma distribution) and small scale (i.e., Rayleigh distribution) fadings are taken into considerationwith the purpose of better simulating some practical scenarios. Motivated by previous works, bounds of achievable secrecy rate for MIMO wiretap channels over uncorrelated and min semi-correlated Rayleigh fading are derived with closed-form expressions. Furthermore, an asymptotic scenario in which the number of antennas tends to infinity is evaluated. Finally, thecloseness of our analytical expressions is corroborated through simulation results.

Recently, a short reference differential chaos shift keying system (SR-DCSK) has been proposed to overcome the dominant drawbacks related to low data rate and energy efficiency fondness of conventional DCSK systems. The fact that terminals on a network have a limited battery capacity and are in desperate need to high energy efficiency transmission schemes compels us to tackle these crucial challenges. In this paper, we propose an SR-DCSK system that performs simultaneous wireless information and power transfer (SWIPT). This promising design exploits the saved time gained from the fact that reference signal duration of SR-DCSK scheme occupies less than half of the bit duration to transmit a signal. The aim of this system is to allow receivers to perform without being equipped with any external power supply. Furthermore, at the receiver side, an RF-to-dc conversion is first performed, followed by data recovery without the need to any channel estimator. Closed-form expressions of multiple-input single-output SR-DCSK SWIPT system, such as ergodic rate, harvesting time, energy shortage, and data outage as well as exact and approximate bit error rate probabilities are derived under Rayleigh fading channel and are validated via simulation. Our results show that the proposed solution saves energy without sacrificing the non-coherent fashion of the system or reducing the rate compared to conventional DCSK, while keeping the design simple.

In this paper, we deal with the problem of maximum likelihood (ML) estimation of the signal-to-noise ratio (SNR) parameter for frequency modulated differential chaos shift key (FM-DCSK) system over multipath Rayleigh fading channels. The ML estimators are derived for various scenarios including data-aided (DA), non-data aided (NDA) and joint DA-NDA estimation by using both the data and pilot symbols. For comparison purposes, the Cramér- Rao lower bounds (CRLBs) for the SNR estimators are derived. The performance of the estimators is evaluated by simulations and comparing with CRLBs in terms of the mean-square-error. Simulated results show that for a large spreading factor the proposed scheme performs well over a wide SNR range in comparisons with CRLBs

In this paper, we investigate the secrecy performance of the multiple-input multiple-output (MIMO) wiretap channels in the presence of an active full-duplex eavesdropper with consideration of channel estimation error at the legitimate destination and eavesdropper. For this purpose, the probability density functions (PDFs) and cumulative density functions (CDFs) of the receive signal-to-interference-plus-noise ratio (SINR) at the destination and eavesdropper are given by conducting the singular value decomposition (SVD) on the estimated channel coefficient matrices. Consequently, the closed- form expressions for the probability of positive secrecy capacity and secrecy outage probability over Rayleigh fading channels are derived. Finally, the Monte-Carlo simulation results are presented to validate the accuracy of our theoretical analysis.

Chaos-shift-keying (CSK) and differential CSK (DCSK) are the two popular coherent and non-coherent modulation schemes for ultra wide-band (UWB) communications. However, security of these schemes has never been studied formally from the information-theoretic perspective. In this paper, we investigate the physical layer security of CSK and DCSK modulation schemes over AWGN and Rayleigh fading channels from the information-theoretic manner. For this aim, the average secrecy capacity and outage probability are computed and analyzed by considering the variation of bit energy Eb coming from the use of chaotic signal to convey information. Our results show that CSK has better or close secrecy capacity and outage probability compared with DCSK and the conventional spread-spectrum modulation. Additionally, these metrics favor Rayleigh fading channels over AWGN channels. Finally, we conclude that the non-constant bit energy is useful to enhance the physical layer security.