Shujing Li

The advancement of wireless networks has spurred an increasing demand for high-quality maritime communication services. This study presents an innovative unicast-multicast access and backhaul maritime communication network (UMABMCN), in which a high-altitude platform (HAP) provides HAP-to-vessel (H2V) unicast services to vessels and backhaul support to unmanned aerial vehicles (UAVs) through HAP-to-UAV (H2U) links. Additionally, multiple UAVs are deployed to deliver UAV-to-vessel (U2V) multicast transmission services to vessels. Specifically, we formulate a HAP-UAV-assisted unicast-multicast cooperation multi-objective optimization problem (UMCMOP) aimed at maximizing the sum achievable rate of base stations (BS)-to-vessel (B2V), maximizing the sum backhaul rate of H2U, and minimizing the energy consumption of UAVs via jointly optimizing communication connection between BSs and vessels, power allocations of UAVs, along with the placement of UAVs. The formulated UMCMOP is a mixed integer non-linear programming (MINLP) problem. To address this, we propose an enhanced multi-objective multi-verse optimization (EMOMVO-CGD) algorithm, which integrates a chaos probability operator, gray wolf exploitation operator, and discrete update operator. To further validate the performance of EMOMVO-CGD, a joint communication connection, power allocation and placement optimization (JCCPAPO) method is proposed. Simulation results demonstrate that the two proposed algorithms outperform benchmark strategies in optimizing the aforementioned objectives.

Continuous and remote health monitoring medical applications with heterogeneous requirements can be realized through wireless body area networks (WBANs). Energy harvesting is adopted to enable low-power health applications and long-term monitoring without battery replacement, which have drawn significant interest recently. Because energy harvesting WBANs are obviously different from battery-powered ones, network protocols should be designed accordingly to improve network performance. In this article, an efficient cross-layer media access control protocol is proposed for radio frequency powered energy harvesting WBANs. We redesigned the superframe structure, which can be rescheduled by the coordinator dynamically. A time switching (TS) strategy is used when sensors harvest energy from radio frequency signals broadcast by the coordinator, and a transmission power adjustment scheme is proposed for sensors based on the energy harvesting efficiency and the network environment. Energy efficiency can be effectively improved that more packets can be uploaded using limited energy. The length of the energy harvesting period is determined by the coordinator to balance the channel resources and energy requirements of sensors and further improve the network performance. Numerical simulation results show that our protocol can provide superior system performance for long-term periodic health monitoring applications.

Vehicular ad hoc networks (VANETs) can improve the safety during the traffic by enabling cooperative communication among the vehicles. The media access control (MAC) protocol should be well designed so that cooperative messages can be exchanged efficiently and reliably. Because vehicles move fast on the road, the network topology changes rapidly, which makes it harder to design the MAC protocol. This article introduces SCMAC, a slotted-contention-based time-division multiple access MAC protocol. SCMAC combines the advantages of the contention-based protocols and the contention-free protocols, and hence, can accommodate different traffic densities and channel conditions. Each time slot is divided into two periods: 1) reservation period (RP) and 2) transmission period (TP) in the protocol. Nodes compete in the RP to confirm whether the channel can be used before the transmission can take place in the TP. Analysis and simulation results are also presented to evaluate the performance of SCMAC in various scenarios. The results show that SCMAC can adapt different traffic densities and channel conditions and can provide more real time and efficient services compared to the other protocols.

Recently, there has been increasing interest in intelligent transport systems and intelligent connected vehicles. Vehicular ad hoc networks play an important role in these areas. Many time‐division multiple access (TDMA)–based protocols have been proposed to obtain lower transmission delay and packet loss rate. However, transmission collisions occur when nodes that belong to the same two‐hop set use the same time slot in TDMA‐based protocols. Meanwhile, nodes reacquire slots because of the packet loss caused by poor channel conditions, which further lowers the protocol's performance. In this paper, we study TCGMAC, a combined TDMA and carrier‐sense multiple access (CSMA) medium access control (MAC)–layer protocol. Each time frame is divided into two parts: the TDMA period (TP) and the CSMA period (CP). TP is used for application data transmission, and CP is used for the slot requirement. If two or more nodes acquire the same time slot in the CP, game theory is used to improve the slot allocation efficiency. The simulation results demonstrate that TCGMAC performs well in different traffic densities and channel conditions.

Vehicles and roadside units can be connected by a vehicular ad hoc network (VANET), which is an important component of future intelligent transport systems that can support various safety and non-safety related services. The network topology changes rapidly in VANET due to the high mobility of vehicles, making it difficult to design a reliable and efficient medium access control (MAC) protocol. Many MAC protocols based on time-division multiple access (TDMA) have been proposed for VANET to optimize network performance, but few of them consider the different requirements of nodes. Nodes may have diverse requirements for spectrum access, and one node may have a diversified strategy for transmitting messages over time, as its motion and network topology change rapidly. The application layer should dynamically adjust the package generation frequency as needed to reduce unnecessary spectrum access. In this paper, we propose a novel application suitable time slot sharing MAC protocol (ASTSMAC) for the broadcasting of the basic safety messages (BSMs) that can adapt to different transmission cycle requirements in the application layer program. In our scheme, one slot can be shared by more than one node, even if they are in each other's communication range. Simulation results show that ASTSMAC can provide significantly higher packet delivery ratio and lower collision rate. Further, the network can accommodate more nodes when the traffic-density is high.