# Moving Towards Body-to-Body Sensor Networks for Ubiquitous Applications: A Survey
## 1 Introduction
Others have been interested in the on-body antenna design [10; 11] yielding channel models or scenario-based approaches, so that to enhance the average channel gain measured for each on-body link (head-to-belt, head-to-wrist, belt-to-wrist, etc.). Few works have been carried out to characterize the off-body [12; 13; 14] and body-to-body [15; 16] channel models involving indoor and outdoor environments, body shadowing and human mobility, in the unlicensed industrial, scientific, and medical (ISM) band (2.45 GHz). Others classified the WBAN technologies, with respect to the WBAN communication architecture, into three components: intra-WBAN, inter-WBAN and beyond-WBAN communications, and addressed the different issues related to each [6; 17]. In most of the literature studies, WBAN applications were highlighted and classified into medical and non-medical [6; 18; 19], or in-body and on-body applications [5; 9; 19]. Furthermore, the growing trend of using humans as network relays gave rise to new concepts, such as the internet of everything and everybody [20], or the internet of people (IoP) [21], along with their related design requirements, especially the data handling and management in next generation internet (NGI). Indeed, such human-centric technology should involve additional data processing criteria to the NGI devices and protocols. Recent works turned towards the integration issue of WBANs into the existing information technology infrastructures [22; 23; 24; 25; 26]. Indeed, according to the nature of WBAN services, which range from entertainment and gaming to high priority emergency traffic, the network resources should provide the ability to aggregate hierarchical information and priority-based data dissemination. Thus, a crucial collaboration between technology engineers and medicine experts to help defining the specifications and priorities of WBAN services, severely constrains the BBN opportunities. Indeed, such a network presents several challenges like the problem of heterogeneous devices and traffic, interference and coexistence, wireless environment properties, etc. Among the more challenging issues in BBNs, we focus on four principal axes: the energy-efficiency, the quality-of-service (QoS), the human mobility prediction, and the data security. Energy-efficiency: is one of the foremost challenges of BBNs. The energy efficiency consists of reducing the amount of energy required to provide the different services, so that frequent replacement of the batteries should be avoided, especially for implanted sensors [27]. In this paper, we study a number of works that propose solutions, protocols and mechanisms to reduce energy consumption. The main objective of these solutions is to increase the lifetime of the network and balance the energy consumption among WBANs/sensor nodes. Quality-of-service (QoS): is the set of characteristics involved in a telecommunication service that ensure its ability to meet the user needs and requirements [28]. In this paper, we present a number of QoS-aware protocols that are in use today, and that compete in optimizing the whole network throughput, delay and traffic priority management, in order to ensure a better QoS in the WBAN communications. Mobility prediction: in mobile scenarios, WBANs connectivity could be altered, and the whole network performance would degrade consequently [29]. If the WBAN mobility could be predicted prior to service breakdown, most of the link failures would be avoided, which could promote the quality of BBN applications. The mobility prediction mechanisms are crucial for the network layer to ensure reliable routing and for network resource allocation. Security: security and privacy preoccupations are a hot topic for BBNs, due to the implication of human information. Indeed, biomedical sensors implanted in the human body for healthcare monitoring, will communicate with neighboring WBANs as well as with external networks; this increases the BBN security risk [30].