This article investigates the covert communication in a D2D underlaying cellular network consisting of a cellular transmitter, a base station, a cellular receiver, multiple colluding wardens, and an underlaid D2D pair with a transmitter and a receiver. For multiple colluding wardens, they fuse their observations to a fusion center (FC) with the maximum ratio combining (MRC) scheme and the equal gain combining (EGC) scheme. To protect the covert communication between the cellular transmitter and the base station from being detected by multiple colluding wardens, the underlaid D2D transmitter reuses the spectrum of the cellular user to transmit its signal to the D2D receiver with a random power to deliberately confuse multiple colluding wardens. We first provide the basic theoretical results for the detection performance of FC under MRC and EGC, respectively, i.e., the optimal detection threshold, the minimum detection error probability and its average value. We then explore the modeling of the average covert rate as well as the optimal power control for average covert rate maximization to enhance the covert performance under MRC and EGC. Finally, extensive numerical and simulation results are presented to validate theoretical analysis and also to illustrate the effects of some important system parameters on the average minimum detection error probability, the average covert rate, and the maximum average covert rate under MRC and EGC, respectively. We can find that the detection performance of multiple colluding wardens under the MRC scheme is better than that under the EGC scheme.

Emergencies often lead to multi-modal and unbalanced distribution of urban rail transit passenger flows. Aiming at this problem, a emergency control method of multi-modal passenger flow is proposed under the premise of comprehensively considering the operation cost and passenger travel efficiency of urban rail transit(URTS).The main work includes: 1) From the perspective of train scheduling, designing and developing a contingency strategy for multi-modal passenger flow by combining the train operation plan based on full-length and short-turn routing, station passenger flow restrictions, and dynamic train departure intervals; 2) From the perspective of train operation and passenger travel synergy, the emergency control model of passenger flow is established with the objective of minimizing the total train operation time and average passenger waiting time; 3) A multi-agent deep reinforcement learning(MDRL) method with a new action selection, reward and double loop mechanism-ARDQMIX is proposed to realize emergency autonomous perception and control of passenger flow in urban rail transit. The simulation results show that the emergency control method of multi-modal proposed in this study has a good utility for improving passenger travel efficiency and reducing operation cost.Note to Practitioners—Urban rail transit system(URTS) is punctual, fast, safe and large capacity, and has gradually become the preferred means of transportation for passengers. However, due to the rapid growth of travel demand, the URTS in the morning and evening peak hours traffic problems are particularly serious, will produce a multi-modal passenger travel demand, such as can not be quickly alleviated, the traffic problem will be caught in a vicious circle, leading to the urban rail transit system service capacity decline, and even lead to the potential safety problems. Aiming at this problem, a emergency control method of multi-modal passenger flow is proposed under the premise of comprehensively considering the operation cost and passenger travel efficiency of URTS.

This paper explores the joint covert and secure communications in a device-to-device (D2D)-enabled cellular system (DCS) consisting of a base station BS, an eavesdropper Eve, and two user equipments UE and UR. To conduct secure communications with UE against Eve, BS works either under the cellular mode using direct transmission or under the D2D mode replying through UR, while UR is greedy since it opportunistically transmits its own covert message to UE against the detection from BS. To understand the fundamental performance of secrecy rate and covert rate in DCS, we first develop theoretical models to depict the detection probability/secrecy rate of BS and covert rate of UR under different modes (i.e., underlay, overlay, or cellular). Based on these models, we further explore the secrecy rate maximization (SRM) for BS subject to the constraints of detection probability at BS and transmit power at both BS and UR, as well as the covert rate maximization (CRM) for UR subject to the constraints of covertness requirement and covert transmit power. Finally, we employ the Newton-based searching method to solve the SRM/CRM problems and illustrate via numerical results the achievable secrecy rate and covert rate of BS and UR under various DCS scenarios.

The similarity measurement method is the key part of the normal cloud model as well as its applications. Too much attention has been paid on geometric and numerical features, leading to the weak interpretability and unreasonable results in the similarity measurement method of the normal cloud models. A bidirectional and weighted similarity measurement (BWSM) method is proposed by the number distribution and membership of cloud droplets on a normal cloud model. First, the cloud droplets are analyzed, and their characteristics of number distribution and membership that belong to different cloud models are obtained. Second, the similarity measurement strategy of the normal cloud models is analyzed and used to propose a BWSM method, which is compared with two commonly used similarity measurement methods of normal cloud models. The influence of expectation, entropy, and hyper entropy on the similarity measurement method of the normal cloud models is analyzed. Finally, the method is applied on the operational status perception and computing of urban rail transit. Results show the method has high rationality, validity, and applicability for perceiving and computing the operational status of urban rail transit. The method improves the interpretability of the similarity measurement of the normal cloud models and the credibility of the research based on the similarity measurement of the normal cloud models.

Emergency events such as fire, flood and COVID-19 occurred in urban rail transit (URT) usually triggered chain effect and evolved into huge disaster. This kind of chain with complexity and uncertainty evolution brought great challenges to the safety management of the system. Thus, the coupling effects of emergencies and then its relationship with the chain evolution is necessary to analyze emphatically. A Graph Evaluation and Review Technique Simulation (GERTS) evolution network is firstly constructed to describe the coupling effect and chain evolution of emergencies. Then, considering the internal and external influencing factors of the emergency chain, a dynamic evolution model of the emergency chain based on Coupled Map Lattice (CML) is proposed. This paper takes fire chain of URT as an example to simulate the evolution process of emergency chain, and analyze the impact of different coupling effects and various influencing factors on the evolution of emergency chain. The results of numerical simulation show that the AND-coupling can significantly inhibit the evolution of emergency events, while the OR-coupling and CO-coupling can expand the impact scope of emergency events. In addition, the evolution speed of emergency events can be controlled by increasing the coupling action time and improving the URT repair ability. When an emergency event occurs, the analysis of coupling effect and the accompanied chain evolution will help managers to make scientific judgment on the development trend of the emergency events and make targeted emergency defense measures.

This paper investigates the fundamental covert rate performance in a D2D-enabled cellular network consisting of a cellular user Alice, a base station BS, an active warden Willie, and a D2D pair with a transmitter$D_{t}$and a full-duplex receiver$D_{r}$. To conduct covert communication between Alice and BS, the full-duplex$D_{r}$transmits jamming signal to confuse the active Willie and also receives signal from$D_{t}$simultaneously. With spectrum sharing,$D_{t}$can operate over either an underlay mode reusing cellular spectrum or an overlay mode using dedicated spectrum. With power control,$D_{r}$can send jamming signal to confuse Willie's detection of the transmission from Alice. We first provide theoretical results for the outage probabilities of the cellular and D2D transmissions, the average minimum detection error probability at Willie, and the achievable covert rate from Alice to BS. We then explore the power control for covert rate maximization (CRM) under the underlay mode as well as the joint designs of power control and spectrum partition for CRM under the overlay mode. We further consider a mode selection that flexibly switches between these two modes with a probability, and also investigate the covert rate modeling and joint designs of power control, spectrum partition and mode selection probability for CRM. Finally, numerical results are presented to illustrate the covert rate performances of the network under the underlay mode, overlay mode and mode selection.

This paper investigates the joint secrecy and covert communication in a two-hop relaying system consisting of a transmitter Alice, a receiver Bob, an eavesdropper Eve and a Relay. Eve always overhears the secret message from Alice. Meanwhile, Alice transmits covert message on top of secret message without being detected by Relay. First, we propose a covert transmission scheme that Alice will transmit covert message only when the signal-to-interference-plus-noise-ratio (SINR) of the secret message is greater than a threshold. Then, we provide the closed-form expressions of covert performance, i.e., the optimal detection threshold of Relay and the corresponding minimal detection error probability as well as the average minimum detection error probability. Finally, extensive numerical results are presented to illustrate the impacts of the system parameters on covert performances. Remarkably, the corresponding theoretical results well match with the simulation ones indicating that our theoretical analysis can accurately model the covert performance of the considered system.

This article investigates the covertness and secrecy of wireless communications in an untrusted relay-assisted device-to-device (D2D) network consisting of a full-duplex base station (BS), a user equipment (UE), and an untrusted relay${R}$. For the covertness, we attempt to prevent Willie from detecting the very existence of communications via a D2D link from UE to R and cellular link from R to BS, while for the secrecy, we aim to prevent the untrusted relay from eavesdropping the UE message. To explore the fundamental covertness and secrecy in such a network, we first provide theoretical modelings for the average minimum detection error rate of Willie, and the average covert/secrecy rate from UE to BS under the underlay and overlay modes, respectively. Based on these models, th we further explore the optimal power control at UE, R, and BS to achieve the average covert rate maximization (MCR) for UE with the constraints of covertness and security requirements under the underlay mode. We also identify the optimal transmit powers and the optimal spectrum partition factor for MCR under the overlay mode. Finally, the exhaust searching method is adopted to solve the MCR problems, and extensive numerical and simulation results are presented to validate our theoretical analysis and to illustrate the average covert rate and secrecy rate of UE under various scenarios.

This paper investigates the fundamental covert rate performance in a wireless relaying system consisting of a source-destination pair, a full-duplex (FD) relay and a warden, where the relay can work at either the FD mode or the half-duplex (HD) mode. We first provide theoretical modeling for the instantaneous/average covert rate when the system works solely under the FD mode or HD mode, and then explore the corresponding optimal transmit power control of relay for the covert rate maximization. For an improvement of covert rate, we further propose a joint FD/HD mode that flexibly switches between the FD and HD modes depending on channel state of the relay self-interference channel. Under the joint FD/HD mode, we also examine the related problems of theoretical modeling for covert rate and optimal transmit power control of relay for covert rate maximization. Finally, extensive numerical results are provided to illustrate the covert rate performances of the relaying system under the FD, HD and joint FD/HD modes.

The past decade has witnessed the emergence and progress of multimedia social networks (MSNs), which have explosively and tremendously increased to penetrate every corner of our lives, leisure and work. Moreover, mobile Internet and mobile terminals enable users to access to MSNs at anytime, anywhere, on behalf of any identity, including role and group. Therefore, the interaction behaviors between users and MSNs are becoming more comprehensive and complicated. This paper primarily extended and enriched the situation analytics framework for the specific social domain, named as SocialSitu , and further proposed a novel algorithm for users’ intention serialization analysis based on classic Generalized Sequential Pattern (GSP). We leveraged the huge volume of user behaviors records to explore the frequent sequence mode that is necessary to predict user intention. Our experiment selected two general kinds of intentions: playing and sharing of multimedia, which are the most common in MSNs, based on the intention serialization algorithm under different minimum support threshold ( Min_Support ). By using the users’ microscopic behaviors analysis on intentions, we found that the optimal behavior patterns of each user under the Min_Support , and a user's behavior patterns are different due to his/her identity variations in a large volume of sessions data.