The 3GPP vehicle-to-everything (C-V2X) technology is a key solution to provide communication services for intelligent transportation systems (ITS) applications. According to the C-V2X specification, vehicles can communicate with each other without the help of cellular networks and can select subchannels (i.e. radio resources) by themselves. However, this design will induce subchannel collisions because of the mobility of vehicles. This work aims to relieve the aforementioned problem. We observe that subchannel collisions can be reduced by considering traffic conditions. Therefore, we design an adaptive transmit power control (APC) mechanism that infers traffic conditions by fuzzy logic and then adjusts the transmit power levels of vehicles. The simulation results indicate that the proposed schemes can effectively reduce subchannel collision ratio for the network.

In recent years, the 3GPP Cellular Vehicle to Everything (C-V2X) communication protocol has been widely discussed as a standard for vehicle communications. The 3GPP C-V2X defines a mode 4 operation mode, which allows vehicles to directly communicate with each other without relying on base stations or road-side units (RSUs). According to the mode 4 specification, vehicles adopt a semi-persistent scheduling method to select subchannels (i.e., radio resources) by themselves. However, the SPS method will induce a subchannel collision problem due to location changes of vehicles. When subchannel collisions occur, vehicles may not correctly receive broadcast data from their neighbor, and thus transmission reliability cannot be preserved. In this paper, we propose a localized subchannel selection method. The basic idea is that each vehicle infers its moving status by the received information from other vehicles, and then refers to its moving status to select subchannels. According to our simulation results, the proposed scheme can effectively reduce subchannel collision ratio and increase packet reception ratio.

Recently, researchers have paid attention to designing indoor navigation services for smartphone users. Conventional indoor navigation systems highly rely on well-known indoor information and prior training phase for localization, and thus it is time- and labor-consuming to bootstrap indoor navigation services. Without too much prior configurations, the proposed indoor navigation system, called ezNavi, utilizes trajectory information (reported by users) to generate indoor pathway and point of interests (POIs). The proposed system consists of a front-end mobile application (APP) and a back-end server. The mobile APP infers users' walking trajectories according to sensory values from smartphones. The back-end server processes crowdsourced trajectories with the help of deployed Bluetooth low energy beacon devices, and then produces pathways of the indoor environment. After obtaining more trajectories, the ezNavi can further refine the derived pathways to provide more efficient guidance services for users. Our experiment and prototyping results reveal that the ezNavi can effectively derive users' walking trajectories, produces indoor pathways, and indicates directions for users.

Recently, many Internet of Things (IoT) or wireless sensor network (WSN) applications adopt ZigBee as their communication protocol. In these applications, messages may need to be disseminated to some specific objects or nodes using multicast transmissions. However, we observe that the original ZigBee multicast protocol causes extremely high packet overhead and energy consumption. In this work, we propose a ZigBee-compatible energy efficient multicast protocol, which allows nodes to execute the designed procedures in a distributed manner. By our scheme, each node uses the designed maintenance module to manage its neighbors. When multicasting, a node utilizes the designed multicasting module to compete for being a relay node by the proposed backoff mechanism. In addition, each node overhears its neighbors' broadcasts to avoid unnecessary transmissions and to ensure that the transmitted multicast packets are successfully received. Our results indicate that the proposed protocol can indeed lengthen network lifetime, reduce redundant packets, and preserve network reliability.

The Sensor Relocation (SR) problem is an important issue in Wireless Sensor Networks (WSNs). For WSNs with an ongoing surveillance task, it is necessary to follow a strict response time requirement when relocating redundant sensors to the requesting places. In this study, we revisit the SR problem in mobile WSNs. The proposed algorithm can find the redundant sensor nearest to the requesting place with low message overhead. The performance evaluation done in this research has confirmed its superior performances.

Convergecast is a fundamental operation in wireless sensor networks. This paper uses ZigBee tree-based, beacon-enabled networks to support convergecast. In the network, ZigBee routers form a tree backbone and ZigBee end devices connect to routers. Some previous works have discussed to use ZigBee tree networks to support regular data reporting. In this work, we further consider the event data reporting scenario, where the network may randomly have urgent events. We assign each router a regular mode slot and several event mode slots. To support regular data reporting, routers and their child devices periodically wake up in their regular mode slots to sense and to report. When an event happens, devices nearby the event can wake up more times in their event mode slots, and routers can collect more event data from child devices and report more frequently. In this paper, we design tree formation algorithms, slot assignment rules, and event mode operations to support event data reporting. Simulation results show that our designs can indeed support both regular and event data reporting.

ZigBee is a communication standard which is considered to be suitable for wireless sensor networks. In ZigBee, a device (with a permanent 64-bit MAC address) is said to join a network if it can successfully obtain a 16-bit network address from a parent device. Parent devices calculate addresses for their child devices by a distributed address assignment scheme. This assignment is easy to implement, but it restricts the number of children of a device and the depth of the network. We observe that the ZigBee address assignment policy is too conservative, thus usually making the utilization of the address pool poor. Those devices that cannot receive network addresses will be isolated from the network and become orphan nodes. In this paper, we show that the orphan problem can be divided into two subproblems: the bounded-degree-and-depth tree formation (BDDTF) problem and the end-device maximum matching (EDMM) problem. We then propose algorithms to relieve the orphan problem. Our simulation results show that the proposed schemes can effectively reduce the number of orphan devices compared to the ZigBee strategy.

Wireless sensor networks (WSNs) have been extensively researched recently. This paper makes two contributions to this field. First, we promote a new concept of long-thin (LT) topology for WSNs, where a network may have a number of linear paths of nodes as backbones connecting to each other. These backbones are to extend the network to the intended coverage areas. At the first glance, a LT WSN only seems to be a special case of numerous WSN topologies. However, we observe, from real deployment experiments, that such a topology is quite general in many applications and deployments. The second contribution is that we show that the address assignment and thus the tree routing scheme defined in the original ZigBee specification may work poorly, if not fail, in a LT topology. We thus propose simple, yet efficient, address assignment and routing schemes for a LT WSN. Simulation results and prototyping experiences are also reported.

ZigBee is a standard which is considered to be suitable for wireless sensor networks. In ZigBee, a device is said to join a network if it can obtain a network address from a parent device. Devices calculate addresses for their child devices by a distributed address assignment scheme. This assignment is easy to implement, but it restricts the number of children of a device and the depth of the network. We observe that if one uses the random formation policy specified in ZigBee, the utilization of the address pool will be very low. Those devices that can not receive network addresses will be isolated from the network and become orphan nodes. In this paper, we model the orphan problem by two subproblems: the bounded-degree-and-depth tree formation (BDDTF) problem and the end-device maximum matching (EDMM) problem. We then present solutions to these problems. The results can be applied to network formation in ZigBee networks.