Wireless Backhaul Technology in Wireless Sensor Networks: Basic Framework and Applications

Abstract

Setting up a wireless sensor network (WSN) requires installing multiple sensor nodes and gateways. Installation costs of existing WSNs tend to be high when the sensing areas become wide, because all of the sensor gateways are wired to a network for transmitting sensing data to networked servers. A wireless backhaul network is a wireless multi-hop network in which access points (APs) are linked wirelessly with the capability of relaying packets. This technology enables the achievement of a wide Wi-Fi coverage area without installing a huge number of access cables, and it is suitable for setting up WSNs. The number of access cables is reduced significantly by using wireless backhaul technology as a communication infrastructure for WSN; each sensor gateway is wired only to the most adjacent wireless AP. This article introduces a WSN that uses wireless backhaul technology. Four example applications are described: a ubiquitous camera network, a Wi-Fi tag tracking system, a criminal fishing system, and a networked vehicle. The ubiquitous camera network uses single-board computers with universal serial bus (USB) cameras and is capable of extracting spatial textual information. Bandwidth consumption can be reduced significantly by transmitting spatial textual information, instead of camera images, to a database. The pedestrian tracking system uses Wi-Fi beacons held by target persons and Wi-Fi APs placed widely and densely in a specified area. Target users’ positions are estimated on the basis of probe request signals broadcast by the Wi-Fi beacons. The criminal fishing system enumerates candidate media access control (MAC) addresses of a culprit’s device from probe request signals captured by APs during the period in which the culprit remains near the incident scene. The networked vehicle is a remote-controlled vehicle for which control commands are transmitted via a wireless backhaul network. This technology is capable of configuring frame relay routes among vehicles autonomously and dynamically. Images from the vehicle are also transmitted to a remote user via the network.