I. Introduction
The ongoing evolution of wireless technologies has fostered the development of innovative network paradigms such as wireless body area networks (WBANs), where the pervasive deployment of wireless devices endowed with sensing capabilities interweaves the physical and digital worlds, thus enabling the development of enhanced services. WBANs, and, more specifically, body-to-body networks (BBNs), are emerging solutions for the monitoring of people's behavior and their interaction with the surrounding environment. In its most common configuration, a BBN consists of several WBANs, as shown in Fig. 1. Each WBAN is composed of wearable sensor nodes, connected through the 802.15.4 protocol (i.e., ZigBee) to their mobile terminal (MT). The set of wearable sensors may be used to consistently monitor people's vital signs, such as blood pressure, heart rate, skin temperature, or important environmental parameters such as temperature and humidity. Furthermore, wireless headsets can be used to enable communications among BBN users, whereas glasses such as those recently proposed by Google and Microsoft can be wirelessly connected with a smartphone to provide augmented reality [1].
Network scenario. Two BBNs corresponding to two different groups of people (i.e., black and gray) are using the same set of unlicensed channels.