## 1 Introduction  
Smart cities are complex environments where several areas of innovation meet in order to substantially improve socioeconomic development and quality of life [1]. Economic innovations, technological tools that encourage people to participate in governance processes and Internet-enabled city infrastructure services and utilities form a thriving research field. Although a widely-accepted definition of the concept of a smart city does not yet exist, there is a general agreement that one of the main goals of smart cities should be to improve the quality and efficiency of city services, while reducing operational costs and making better use of public resources [2]. In order to achieve these goals, vast networks of interconnected sensors are being deployed. Just a few examples are pollution detectors, water quality meters, noise indicators and power grid controllers. Actuators, such as water control valves or electrical switches, also need to be installed in order to both monitor and control public resources. The practical interconnection of such a large set of devices to fulfill specific optimization goals requires technological advances beyond the theoretical results for classic wireless sensor network (WSN) architectures. The increasing need for scalability and distributed control has led to the concept of the Internet of Things (IoT). The IoT paradigm, which transforms any object or appliance into part of a connected network, thus dissolving the barriers between the physical and virtual worlds, has become the cornerstone of many services in a smart city, including more efficient maintenance tasks. With the support of distributed sensor and actuator networks, it provides staff in the field with information as needed. This has been demonstrated in city-wide testbeds, such as Smart Santander [3], or the smart cities of Padova [2], Nice [4] and Oulu [5]. As stated in essential works on the topic [6], one of the main benefits of a world where everything is connected is that technology forms an invisible part of people's lives. This is where augmented reality (AR) interfaces can make a difference compared with more traditional approaches. Nowadays, city service maintenance agents often have difficulties identifying and fixing problems in city infrastructures, as there is little technology available to facilitate their work. The system described in this paper aims to facilitate this work through AR technology. We assume a scenario in which a sensor and actuator network is available throughout the city infrastructure. Traditional AR interfaces rely on static markers to determine the position and identifier (ID) of the object to which virtual information is linked. However, in this work, we propose a novel mechanism based on visible light communication (VLC) that not only provides the same identification and positioning information as AR markers, but also allows the transmission of small amounts of arbitrary data as a technological enabler to create more efficient services combining the IoT and AR paradigms. A VLC-based solution allows one to overcome some of the limitations of other near-range communication technologies. VLC has a higher range than RFID or NFC, limited to tens of centimeters at most. Therefore, the terminal camera may capture a wider scene while receiving data. This, combined with the high directionality of VLC, enables the implementation of smartphone AR interfaces. Besides, the proposed solution is also generalistic, since all smartphones include a camera, whereas RFID tags require too specific reader technologies (note that NFC technology, howbeit included in many commercial smartphone models, is not always available). Higher range radio beacons based on Bluetooth or WiFi are lowly directional, so they do not support AR rendering well. In addition, radio waves often propagate through walls, while VLC transmissions are always confined within the room where the beacon is installed.