# Opportunistically Exploiting Internet of Things for Wireless Sensor Network Routing in Smart Cities
## 1 Introduction  
In this era, there are billions of sensor-enabled intelligent devices on the Internet that collectively form a huge entity known as Internet of Things (IoTs) [1]. According to Cisco [2], by 2020 fifty billion devices will be connected to the Internet, thus depicting the potential and complexity of using such an inter-connectivity. An underlying simple concept of \"Anything connected at anytime\" [3] in an IoT opens new ways of interdisciplinary research. From bare hardware sensing platforms to upper most application layer, IoTs has created new horizons for researchers. IoT devices are spread city wide, perform their functions and share information for the betterment of quality of citizens' lives. It is important to notice similarities in the aims and objectives of both Smart City and IoTs [1]. IoTs encapsulate Wireless Sensor Networks (WSN) as an important component. WSN emerged as a dominant technology, much before the emergence of IoT, addressing a wide spectrum of application domains [4, 5]. With successful deployment of IoT infrastructure and Smart City test-beds in real cities, i.e., Padova [6] and Santander [7], more and more government municipalities and corporations are interested to leverage the strengths of Smart City. The aim is to make better use of public resources, increasing the quality of life of the citizens, while minimizing the operational costs. For monitoring and surveillance of a Smart City application, sensors are deployed in a large area, city wide. Typical examples include traffic management systems [8], structural health management systems [9], traffic signal monitoring [8], electronic toll collection systems [10], highway data collection [8], and automatic number plate recognition systems [11]. Routing is essentially a service required in a WSN wherein sensors sense data using individual inexpensive sensor nodes and routes the data towards the sink for drawing meaningful conclusions. Since the advent of WSN in 1960's [12], there is a plethora of techniques and protocols proposed for routing and data aggregation in WSN [13; 14; 15]. Though sensors are becoming smarter, cheaper, and smaller in size, they are always energy constrained [4]. Therefore, there is an unparalleled need for developing innovative energy efficient routing approaches. In the applications mentioned above, often data has to traverse through a long series of intermediate sensors before it reaches the sink. Thus, much of the WSN energy is consumed in multi-hop routing. Practically, Smart City and IoTs in our cities are currently in infancy. There are very few fully functional IoTs serving the objective of a Smart City. The majority of research works are related to IoT frameworks, ideas, prototypes, and use cases, which is quite common for an emerging technology. The ultimate aim of a deployed IoT in the context of Smart City is that every IoT device can be connected and can share data with other devices for the public betterment. Recent developments in Low Power Long Range (LPLR) network protocols [16] e.g., LoRa, SigFox, offer low power alternative for sensors. Yet, they also have shortcomings and cannot be used in each and every application where sensors are required [16; 17]. Moreover, with trends towards Heterogeneous ad hoc networks [18], a wide community still uses and will keep using traditional mutltihop WSN as a part of their solution [19], and may use LPLR as well. Thus, our approach can be easily integrated in such scenarios. In practice, there is a transitional phase where existing deployed WSNs are working, functioning, serving, and administered separately, while other smart devices are around them, achieving basic goals of a Smart City and being administered by public sector or a private organization. In our work, we aim to exploit the IoT devices opportunistically in routing data of separately administered WSN. Sensors essentially use their energy resources in (i) sensing, (ii) local computation, (iii) communication of its own data, and (iv) communication of other sensors data.