# Eco-Efficient Mobility in Smart City Scenarios
## 2 Related Work  
As stated previously, although many works have explored the field of vehicular networks [9] and their related services [10], there is a lack of papers addressing the potential of the novel personal mobility ecosystem as a whole. However, some specific efforts have been devoted in the field of vehicular data gathering for enabling the cooperation among different-nature mobile devices.  
Data gathering in Vehicular Sensor Networks (VSNs) has partially addressed the issue of saving communication costs, such as the work in [11], which tried to reduce data rate by considering a trade-off with the required freshness of sensor reads for a concrete application. In [12], 4G communication was combined with WiFi offloading and a crowd-sensing approach, using regular smart phones as a communication relay. An equivalent approach with a mobile phone was adopted in [13] for monitoring vehicle emissions, and [14], which employed Bluetooth to interconnect on-board sensors. Recent proposals such as [15] took advantage of the mesh created by vehicular (ad-hoc) networks to spread mobile agents in charge of gathering data from a target area.  
Work in [16] proposed a holistic data gathering and processing platform for smart cities leveraging the potential of the IoT paradigm. The different connected objects included smart phones, infrastructure fixed stations as well as OBUs carried by public buses. Authors employed both 802.11 Outside the Context of a Basic Service Set (OCB), formerly known as 802.11p, and cellular communications, namely, 4G. A similar solution was presented in [17], where state-of-the-art visible light networks were also employed as a complementary data path.  
Regarding the development of OBUs considering the constraints of personal vehicles, few contributions can be found in the literature. Authors of [18] proposed the use of ZigBee-based connectivity in bicycle OBUs. The aim of this solution was to report sensed data and create convoys of bikes in order to improve their safety. In [19], Bluetooth was employed with a similar purpose, evidencing the limited communication range of this type of technologies. The authors of [20] developed a motorbike OBU using WiFi OCB, a technology that was also investigated in [21]. In addition, the latter also made use of an enhanced IEEE 802.15.4 link for V2V transmissions.  
Considering human-machine interaction, work in [22] presented an advanced navigation assistance system for bicycles by means of a vibrating belt and cellular communications. In turn, the authors of [23] also explored the direct interaction of the vehicle with the driver by connecting a helmet to an OBU implemented by means of a smart phone with cellular connectivity.  
Finally, it is worth mentioning some crowd-sensing solutions that have been specifically designed for bikes. An Arduino-based platform was adopted in [24] to retrieve and report pollution data employing cellular communications. The authors of [25] developed a similar sensing platform although they made use of a smart phone tethering to transmit the gathered data. A similar solution was presented in [26], in this case employing LoRa and WiFi as communication technologies.  
It is clear that the contributions to the field of sustainable personal mobility are limited. However, these vehicles are more and more common in our cities. For that reason, in this paper, we provide a detailed discussion addressing the potential opportunities and challenges brought by this specific vehicular segment. Future services, communication technologies, and current gaps within this novel ecosystem are explored. In addition, a novel OBU architecture and prototype considering the stringent requirements of these moving devices are proposed and a series of validation tests are presented, showing the performance of the solution using LPWAN communication technologies.