An Image Transmission Protocol for Wireless Sensor Networks

Abstract

The integration of low-power wireless networking technologies with low-cost hardware such as complementary metal-oxide semiconductor cameras and small microphones has fostered the development of Wireless Multimedia Sensor Networks (WMSNs) that are able to ubiquitously retrieve multimedia data such as still images or voices and scalar data from the environment. WMSNs have many resource constraints in terms of energy consumption, bandwidth, and processing capability, and wireless links are unstable. Furthermore, the transmission of large amounts of data over WMSNs has stringent requirements such as high reliability in packet transmission to recover high quality multimedia data, low end-to-end delay in data transmission to make timely decisions, and high efficiency in energy management to extend the lifetime of network. However, it is not easy to achieve these requirements due to low bandwidth and link instability because of signal fading, high interference, and a lot of obstacles. Therefore, the design of a cross-layer protocol to meet the requirements for both data transmission within the constraints becomes a concern and should be carefully considered. We focus on the design and implementation of a pipelined cooperative transmission protocol for fast and reliable image delivery in wireless sensor networks (WSNs). 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, a distinct broadcast time slot is allocated to each tree level and 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. Furthermore, packets are transmitted in a pipelined manner using two channels thereby reducing the delay of image transmission greatly. After that, we propose a simple LoRa-WSN hybrid network protocol to transmit both scalar and multimedia data over WSNs efficiently. This approach utilizes the long-range (LoRa) transmission of a LoRa network to deliver scalar data and control messages directly and utilizes the high data rate and high reliability of a WSN for the transmission of an urgent image or voice. The selected multimedia node transmits an image packet in every transmission interval without using control messages such as RTS and CTS. Upon receiving an image packet, a node forwards it immediately and continues in receive mode to receive other image packets, leading to a decrease in image transmission time. Furthermore, the selected multimedia node uses the LoRa network to get information about lost packets for path-wide retransmission in order to meet the requirement for high reliability in data transmission. The approach also can avoid the overhead problem caused by flooding control messages, and it can simplify the operation of sensor nodes by removing the requirement for time synchronization.