# Moving Towards Body-to-Body Sensor Networks for Ubiquitous Applications: A Survey
## 1 Introduction  
Due to the growing need of current internet of things (IoT) infrastructures, in terms of connectivity and network capacity, connected people have an aspiring potential to form an imminent access network that extends the IoT coverage, through achieving ubiquitous and real-time applications (healthcare, social interactions, sports and entertainment, etc. ), thus ensuring anywhere and anytime people connectivity. In this context, using network subscribers themselves as relays could complement and extend existing infrastructure networks, while improving network capacity and promoting radio spectrum usage. Indeed, each user will be equipped by a wireless body area network (WBAN), which is a wireless network of small computing devices. These sensor devices can be embedded inside the human body or under the skin, mounted on the body (wearable), or carried by humans as portable devices. Around 1995, the idea of using wireless personal area networks (WPAN) as transmission technology among humans started, to enable communications on, around, and next to the human body [1; 2]. Nowadays, WBANs have evolved into an interdisciplinary area that provides real-time healthcare services with reduced costs and ubiquitous medical records in the network servers. This area relies on the feasibility of fixing (implanting) very small biosensors on (inside) the human body that are comfortable and that do not impair normal activities. The biosensors are fixed or implanted on/insidethe human body comfortably and without altering the normal activity of the individual. Then, sensors collect the human sensing information which allows us to monitor the health status of the patient whatever his location. The sensing data is transmitted over wireless links to a remote processing unit. In case of emergency threat, an alert is generated to prevent the patient and the medical staff. WBAN solutions have gradually developed over the last years through the implementation of novel WBAN-based applications, giving rise to body-to-body networks (BBNs) that we can characterize as a group of WBANs, interacting between them, so as to guarantee a range of services that satisfy genuine social advantages. Indeed, network operators, that are already planning for the IoT and cloud computing technologies integration, should also think about this new possibility of creating a new type of mobile ad hoc network, so that a radio device situated on one person gathers the sensor data from the sensor nodes worn by that person, and transmit them to a transceiver situated on another person in the nearby area, in order to be processed or relayed to other BBN users. Furthermore, the other motivation behind BBNs is to overcome the problems of coexistence and performance degradation of closely located WBANs, by involving them in mutual interactions and cooperation [3]. In this survey, we review and synthesize the relevant features of WBANs in order to exploit the opportunities of cooperation between them, forming a BBN. This survey is an exhaustive extension of our previous work done in [4]. WBAN issues have been tackled by a number of surveys that investigate the fundamental mechanisms of WBAN including architecture and topology, types of WBAN sensors, low-power medium access control (MAC), implant communication and routing protocols. Authors in [5; 6] discussed some solutions for WBANs at physical (PHY), MAC, and network layers. Power consumption of WBAN wireless transceivers and microprocessors was thoroughly discussed and investments in increasing sensor battery capacities were also explored [7], such as energy harvesting from ambient sources, sunlight or vibration. WBAN antenna design is also a prominent issue that has been considered by several researchers. Some focused on the electrical properties of the body tissue and the in-body antenna design to meet the requirements of the MICS band (402-405 MHz) designated for in-body communications [8; 9].