This paper proposes a hybrid visible light communication/radio frequency (VLC/RF) system with simultaneous lightwave information and power transfer (SLIPT) utilizing relay selection to take the advantages of both VLC and RF systems in terms of spectrum efficiency and coverage. The relay is selected from multiple devices in the VLC coverage and equipped with both solar cell and RF antenna for energy harvesting, receiving signal and transmitting message to the end user. Especially, the devices in optical communication range are randomly located with the uniform distribution, and the light intensity from the light emitting diode (LED) contains alternating current (AC) and direct current (DC) elements for the signal detection and energy harvesting. The relay decodes the signal to retransmit to the end user by harvested power via RF channels in the second hop. Then, we derive the closed-form of the outage probability (OP) of the proposed system. The analytical expression of the OP performance is validated by simulation results, and the impacts of parameters of the system are examined. The results show that the increase in the number of the relay can reduce the OP and transmitted power. The high value of threshold of transmission rate at the relay can increase the error in the performance. In addition, decreasing AC value and boosting DC value can enhance OP performance of the system, and vice versa. Moreover, the optimization problem is formulated to minimize the OP performance subject to AC peak value and DC bias to satisfy linear characteristics of the LED operation. To solve the optimization problem, the particle swarm optimization (PSO) algorithm is deployed and modified to attain the optimal solution. The PSO algorithm greatly improves the OP performance in comparison to the numerical method.

The proposed protocol features reliable and fast image transmission while periodically transmitting scalar data without interruption by allowing two networks, a LoRa network and a wireless sensor network, with different transmission characteristics to cooperate. It adopts the RT-LoRa protocol for periodic scalar data transmission and uses a WSN-based pipelined transmission method that leverages single-hop message transmission of a LoRa network for image transmission. Thus, it can not only eliminate the control message overhead for time synchronization, slot scheduling, and path establishment for pipelined image transmission in WSNs but also eliminate interferences within WSNs, such as data collisions and data and message collisions, during pipelined image transmission, thereby enabling high reliability and fast transmission. According to experimental results obtained inside a university building, the proposed protocol achieved an image transfer rate of approximately 96% without packet loss, transmitted one 24 KB image in approximately 0.3 s, and achieved an image transfer rate of 100% under the tolerance of one image packet loss. These results indicate a speedup of about 25% compared to a recent pipelined protocol while ensuring near-perfect image transmission quality.

In industrial monitoring and control applications, a server often has to send a command to a node or group of nodes in wireless sensor networks. Flooding achieves high reliability of message delivery by allowing nodes to take the redundancy of receiving the identical message multiple times. However, nodes consume much energy due to this redundancy and the long duty cycle. A reliable slotted broadcast protocol (RSBP) tackles this problem by allocating a distinct broadcast slot (BS) to every node using a tree topology. Not only does it remove collision, but it also minimizes energy consumption such that every node remains active only during its parent’s broadcast slot and its own broadcast slot to receive and rebroadcast a message, respectively. However, it suffers from low reliability in harsh environments due to the compete removal of redundancy and low responsiveness to the changes in network topology due to the global scheduling of slots. Our approach allocates one distinct broadcast sharable slot (BSS) to each tree level, thus making a BSS schedule topology-independent. Then, nodes at the same level compete to rebroadcast a message to nodes at one level higher within the BSS, thus allowing the redundancy. In addition, it uses a slot-scheduled transmission within BSS that can further improve reliability by reducing message collisions and also enables the precise management of energy. According to simulations and experiments, the proposed approach can achieve high reliability comparable to flooding and low-energy consumption comparable to RSBP.

Multimedia applications using wireless sensor networks often require bounds for end-to-end delay and packet loss rate in addition to energy efficiency in delivering a series of packets sliced from an image. This paper proposes a pipelined cooperative transmission (PCT) protocol for fast and reliable image delivery based on a tree topology originating from a sink, and allocation of a distinct time slot to each tree level. In this approach, if a sink needs an image from a specific multimedia node, it establishes a cooperative path such that a path node, a node on the tree path from the multimedia node to the sink, selects a cooperating node from its neighboring nodes at the same tree level. Then, the cooperating node assists its counterpart using the information obtained by means of overhearing message or data in order to forward a packet reliably to the nodes one level lower. This transmission mechanism improves the reliability of hop-by-hop transmission greatly without relying on retransmissions while making the packet move fast. Packets are transmitted in a pipelined manner using two channels such that different nodes at every other level send packets simultaneously. The proposed protocol is verified by analysis, simulation, and experiment, showing that it far outperforms the recent best approach in terms of end-to-end delay and energy consumption while achieving a high packet delivery rate.

Wireless image sensor networks equipped with tiny cameras face significant challenges in achieving reliable, timely, and energy-efficient image transmission due to the bursty nature of image data and the limitations of sensor nodes. This research introduces a cooperative-schedule priority transmission protocol (CSPTP), designed to overcome these challenges. CSPTP leverages a multi-resolution discrete wavelet transform to compress captured images, decomposing them into sub-bands with varying levels of importance. The protocol establishes a data path consisting of path nodes and cooperative nodes to efficiently manage the bursty nature of image packets. Priority levels are assigned to nodes based on their roles in image transmission and to packets based on their importance in image reconstruction. Nodes collaborate through overhearing, which enhances transmission reliability and accelerates packet delivery. The proposed protocol was rigorously evaluated through comparative analyses and experimental validation. Analytical results demonstrated that CSPTP significantly reduces image transmission time and balances energy consumption, outperforming existing protocols. Experimental validation further confirmed substantial improvements in packet delivery reliability, achieving success rates of 99.5% for important packets and 98.3% for other packets when the source multimedia node is at level five, and 99% and 96%, respectively, at level eight.