This paper proposes a novel location-based resource selection (LoRS) scheme for periodic message delivery in an NR-V2X network. The proposed LoRS scheme utilizes vehicles’ geographic location information to generate indexes for vehicles and makes resource selection for the vehicles based on the indexes. In particular, it introduces two novel feedback mechanisms to alleviate resource conflicts caused by the hidden-node problem and half-duplex transmission constraint. A packet reception status feedback mechanism is designed to avoid packet collisions and an index update conflict feedback mechanism is designed to avoid vehicle indexing errors and unnecessary index updates. Simulation results show that compared to the SB-SPS scheme, the LoRS scheme can significantly improve the packet delivery performance of the network in terms of the average packet reception rate (PRR) in the network.

This paper proposes an enhanced resource selection (eInP-RS) scheme for efficient intra-platoon message delivery of cooperative awareness messages (CAMs) and decentralized environmental notification messages (DENMs). To achieve this goal, the eInP-RS scheme allows each vehicle to transmit CAM and DENM packets on a C-V2X channel (CH1) and an 802.11p channel (CH2), separately, and introduces four mechanisms to enhance the standardized sensing-based SPS scheme. A contention window (CW) size adjustment mechanism is introduced to enable a vehicle to adjust its CW size according to the information it collects on CH1 in order to avoid potential packet collisions on CH2; a resource partition mechanism is introduced to divide frequency-time resources in a selection window into two sets in order for vehicles moving in opposite directions to select different resources and thus avoid potential merging collisions on CH1; an intra-platoon cooperation mechanism is introduced to enable the PL of a platoon to know the resource and channel occupation information of the platoon's hidden nodes on CH1 and CH2; and a packet collision detection mechanism is used to enable a non-platoon vehicle to detect packet collisions occurring on both channels after a lane-changing maneuver to avoid potential merging collisions. Simulation results show that the proposed eInP-RS scheme outperforms the standardized sensing-based SPS scheme in terms of the intra-platoon CAM/DENM delivery ratio and the average intra-platoon DENM delivery delay.

This article proposes a cellular vehicle-to-everything (C-V2X) mode 4 and 802.11p-based resource selection (eInP-RS) scheme for efficient intraplatoon message delivery. The proposed eInP-RS scheme is intended to improve the delivery performance of cooperative awareness messages (CAMs) and decentralized environmental notification messages (DENMs) within a platoon. To achieve this goal, it allows each vehicle to transmit CAM and DENM packets on a C-V2X channel (CH1) and an 802.11p channel (CH2), separately, and introduces four mechanisms to enhance the standardized sensing-based semi-persistent scheduling (SPS) scheme. A contention window (CW) size adjustment mechanism is introduced to enable a vehicle to adjust its CW size according to the information it collects on CH1 in order to avoid potential packet collisions on CH2; a resource partition mechanism is introduced to divide frequency-time resources in a selection window into two sets in order for vehicles moving in opposite directions to select different resources and thus avoid potential merging collisions on CH1; an intraplatoon cooperation mechanism is introduced to enable a platoon leader to know the resource and channel occupation information of the platoon’s hidden nodes on CH1 and CH2; and a packet collision detection mechanism is used to enable a nonplatoon vehicle to detect packet collisions occurring on both channels after a lane-changing maneuver to avoid potential merging collisions. Simulation results show that the proposed eInP-RS scheme outperforms the standardized sensing-based SPS scheme in terms of the CAM/DENM delivery ratio and average DENM delivery delay of a platoon vehicle.

Broadcasting is an important routing strategy for message delivery in a VANET. However, the broadcast storm caused by loads of duplicate data packets can be severe, which leads to intense contention among vehicle nodes and a large number of dropped packets. In this case, the efficiency of message delivery is limited. This paper considers a broadcast routing protocol specially designed for urban areas with dense traffic and a huge amount of data traffic, and proposes a Preferred-Zone based broadcast (PreZcast) protocol. To alleviate the broadcast storm and improve the efficiency of message delivery, PreZcast only allows neighbors located within a Preferred Zone (PreZ) of a source node to rebroadcast a received packet. The PreZ is chosen based on the initial location and the distribution of two-hop neighbors of the source node. To further validate PreZcast in a more realistic and irregular topology, we evaluate PreZcast with real datasets issued from Bologna road traffic. Moreover, MultiPoint Relay (MPR) is introduced to further reduce duplicate packets in the network. Simulation results show that as compared with the Flooding protocol, PreZcast approximately improves 15% of broadcast efficiency and reduces 65% of packets transmitted with 5% more energy consumption, while PreZcast with MPR improves 10% of broadcast efficiency and reduces 70% of packets transmitted with only 0.5% more energy consumption.

New radio-based access to unlicensed bands (NR-U) multichannel access procedures are 3GPP standards for supporting 5G NR-U and WiFi coexistence in unlicensed frequency bands. NR-U provides a new solution to alleviating the severe spectrum scarcity problem of 5G cellular networks in licensed frequency bands for supporting diverse Internet of Things (IoT) services. This article studies the performance modeling of an NR-U and WiFi coexistence system using the NR-U Type B multichannel access procedure and the WiFi DCF procedure and focuses on a system model with two unlicensed channels: 1) a primary channel and 2) a secondary channel. 2-D Markov models are first built to describe the NR-U category-4 LBT procedure and the WiFi DCF procedure on the primary channel, respectively. A 3-D Markov model is then built to describe the WiFi DCF procedure on the secondary channel, taking into account the effect of the NR-U Type B multichannel access procedure. Based on the built Markov models, performance models are further derived for analyzing the system performances in terms of system throughput and packet delay on the primary channel and/or secondary channel. The derived performance models are validated through simulation results. The impacts of the number of NR-U gNBs/WiFi APs and major system parameters on the system performances are investigated based on the derived performance models.

This article studies the performance modeling of an NR-U and WiFi coexistence system using the NR-U category-4 listen-before-talk (LBT) procedure and 802.11e enhanced distributed channel access (EDCA) mechanism in the presence of hidden nodes. 3-D Markov models are first developed to describe the NR-U category-4 LBT procedure for a priority-${p}$queue of an NR-U gNB and the 802.11e EDCA mechanism for an AC-${q}$queue of a WiFi AP, taking into account the effects of hidden nodes and the transmission of different-priority data. Based on the Markov models, theoretical models are derived for analyzing the mean throughput of a priority-${p}$queue in an NR-U gNB and that of an AC-${q}$queue in a WiFi AP as well as the mean transmission delay of an NR-U priority-${p}$data packet and that of a WiFi AC-${q}$data packet. The derived theoretical performance models are validated through simulation results. Based on the performance models, the impacts of major system parameters on the system performance are investigated, including the density of NR-U gNBs, the sensing distance and channel transmission rate of an NR-U gNB, and the data packet arrival rate at an NR-U gNB.

In this paper, a theoretical model is derived to analyze the intra-platoon message delivery delay (InP-delay) for an autonomous platoon to enable each platoon member to receive a message transmitted from the platoon leader via multi-hop unicast. Both platoon vehicles and non-platoon vehicles employ a carrier sense multiple access (CSMA/CA) mechanism to contend for channel access. Since the delay of delivering a message within a platoon may affect the platoon stability, the effects of major system parameters on the InP-delay are investigated, including the platoon size, the intra-platoon spacing, the density of non-platoon vehicles, the transmission range and carrier sensing range of vehicles. This work is of help to the stability maintenance of an autonomous platoon by providing reference values for system parameter configuration under different use case requirements.

Summary Secure mechanisms have been adapted to satisfy the needs of mobile subscribers; however, the mobile environment is quite different from a desktop PC or laptop‐based environment. The existing attack patterns in mobile environments are also quite different, and the countermeasures applied should be enhanced. In regards to usability, the mobile environment is based on mobility, and thus, mobile devices are designed and developed to enhance the owner's efficiency. To avoid forgetting passwords, people are willing to adopt simple alphanumeric‐character combinations, which are easy to remember and convenient to enter. As a result, the passwords have a high probability of being cracked or exposed. In this paper, we study the potential security problems caused by simple and weak passwords, discuss drawbacks of some conventional works, and propose 3 creative schemes to increase the complexity and strength of passwords by applying the envisioned features. Note that our proposals are based on the assumption that the textual passwords are not difficult for users to remember or enter and do not cause inconvenience to users. In other words, the proposed methods can increase the complexity of simple passwords without the awareness of users.

Smart devices have already become a dally necessity of our life since they play a pivot role to record massive amount of Information of our personal life. Current Internet of TWngs era has been seeing more and more people relying on their devices. However, most people are losing patience to set complex passwords to ensure the security for their devices. To avoid forgetting the passwords, people are more willing to choose simple alphanumeric character combinations that are easy for them to remember and convenient to enter. Therefore, their passwords are of high probability to be cracked or exposed. In tWs paper, we study the potential security problems caused by simple and weak passwords, discuss the drawbacks of some conventional works, and propose three schemes to Increase the complexity of simple passwords. Note that our proposals are based on the prediction that the textual passwords are not difficult for users to remember or enter and the proposed schemes can effldently prevent passwords from being cracked or exposed.