According to the Smart City Council, an adequate telecommunications infrastructure is vital for the success of businesses, industries as well as residents of Smart cities. However, currently available standard and cellular technologies, such as 3/4G, GSM (Global System for Mobile Communications) and LTE (Long-Term Evolution), are rapidly reaching their limit mainly due to increased traffic demand. Such limitations are only going to worsen in the next years, due to the advent of Internet of Things technologies that are expected to interconnect billions of devices to the Internet. In this paper, we propose a novel network architecture that supports several delay-tolerant (non-real-time) Smart city applications and services (e.g., gathering air pollution information), and therefore, a promising approach to address the burdening of increased traffic demand to Smart city's legacy standard and cellular communication infrastructure. The proposed architecture is based on an innovative diverse band-aware Dynamic Spectrum Access (d-DSA) paradigm, that allows a certain wireless device to opportunistically access idle channels in multiple licensed/unlicensed spectrum bands. d-DSA radio devices are mounted on Smart city's urban vehicles (e.g., taxis) that act as mobile routers to gather, carry, and forward various types of data traffic. This results in a time-varying and unpredictable delay-tolerant network (DTN) where each node can access whitespace channels and transmit in multiple spectrum bands. Given lack of research in efficient routing schemes for such d-DSA DTN networks, we propose a distributed and lightweight d-DSA aware Geographical Routing (dDSA-GR) protocol, that utilizes a weighted linear metric for selecting a suitable spectrum band, and classic georouting principle for choosing next hop node in the path route between any node pair in d-DSA DTNs. Results on realistic traces based on the map of Lexington, KY, USA, show that our dDSA-GR routing protocol outperforms baseline approaches in terms of network delay, message delivery ratio, and energy efficiency, under all considered scenarios.

This paper presents a novel network architecture, termed neXt-generation CHAllenged NeTwork (X-CHANT), for improving connectivity in rural environments. The underlying idea is to deploy diverse Dynamic Spectrum Access (d-DSA) radio devices on the public transportation vehicles, such as buses. This results in a d-DSA enabled delay-tolerant network in which the devices can operate in various (un)licensed bands (e.g., TV, LTE, ISM, CBRS), if available. Given the lack of research in efficient routing for such time-varying d-DSA enabled networks, we propose a novel diverse DSA aware routing (dDSAaR) protocol that jointly exploits various (un)licensed bands besides the time-varying yet sufficiently predictable mobility of public transportation vehicles. We compare X-CHANT, utilizing dDSAaR, to the conventional non-DSA/DSA architectures, utilizing a standard (single band) routing protocol (e.g., Epidemic). We use real bus mobility traces collected at the University of Massachusetts, Amherst campus. Results show that X-CHANT achieves better message delivery, negligible message overhead, and better energy expenditure, at the expense of a slight increase in delay. Never-theless, the delay improves with higher predictable mobility.