Bike-sharing systems (BSS) have raised in popularity in the last years due to their potential share in sustainable cities. Although the first attempts to implement a bike-sharing public service date back to 1965 (Amsterdam), their widespread use arrived with the millennium becoming a vibrant research area whose activity has increased steadily in the last decade. Several authors have attempted to summarize the current state of the art, but the literature on BSS is still scattered in different fields. Thus, there is a lack of literature that summarizes and categorizes the available research on BSS. In this paper, we perform a thorough review of the challenges behind rebalancing in bike-sharing systems. The objectives of this paper are to collect papers on the repositioning problem in dock-based bike-sharing services, classify them and point to novel research venues. We render a keyword analysis in the literature and a timeline that shows the evolution of those keywords throughout the last decade. We also include an exhaustive table that will assist researchers from different disciplines to address the open challenges in the field and to transition towards more sustainable cities.

Bluetooth has become an ubiquitous technology present in almost every electronic device. A question often asked by manufacturers and final users is whether it can be used for other uses different from the ones for which it was designed. In particular, for improved multimedia traffic support, with the fewest modifications in the implementation of the protocol (both hardware and software). In this paper we analyze the impact on performance of the lowest levels of the Bluetooth architecture through a relevant parameter known as the polling time, t_poll. We propose a novel algorithm (EMAAA Tpoll) that allows to adapt dynamically the value of the t_poll parameter during the transmission. Our results provide definite criteria about how to optimize the transmission of multimedia traffic over piconets at the lowest layers of the Bluetooth architecture. Specifically, we show that our algorithm can result in a significant energy saving (of 10%-20%) with respect to the Bluetooth specification.

Bluetooth has become a ubiquitous technology present in almost every electronic device. A question often asked by manufacturers and final users is whether it can be used for uses other than the ones for which it was designed; in particular, for improved multimedia traffic support, with the fewest modifications in the implementation of the protocol (both hardware and software). In this article we analyze the impact on performance of the lowest levels of the Bluetooth architecture through a relevant parameter known as the polling time, T_poll. Here, we report on simulations of specific algorithms that allow to dynamically adapt the network to an optimal value of T_poll during transmission. We place special emphasis on the role of the kind of traffic on the network (e.g., constant bit rate, burst, multimedia-like). In addition, we analyze the results of simulations by comparing these algorithms with the static allocation value defined in the Bluetooth specification. Our results provide insight on how to optimize the transmission of multimedia traffic over piconets at the lowest layers of the Bluetooth architecture.