# Blockchain Based Delay and Energy Harvest Aware Healthcare Monitoring System in WBAN Environment
## 1 Introduction  
A wireless body area network (WBAN) is a kind of sensor network that assists in resourceful patient healthcare monitoring. WBANs are also referred to as body sensor networks (BSNs). Many studies have recently been conducted in WBAN for continuous patient monitoring [1, 2, 3, 4, 5]. Unfortunately, the current WBAN does not meet the _QoS_ for a patient [6, 7]. _QoS_ provisioning is an important consideration in WBANs that is achieved by resolving three challenges: energy efficiency, mobility prediction (adaptiveness) and security [8, 9, 10]. In general, WBAN communications are classified into three layers ofcommunication: (1) intra-WBAN, (2) inter-WBAN and (3) beyond WBAN. Recent studies discussed any one of the WBAN communications [11].  
Integration between WBAN and IoT provides remote health monitoring services for patients [12]. Due to the limited resources of IoT sensors, they must be efficiently utilized, but solving this issue is a critical issue. In particular, when moving the patient's body, connectivity among sensor nodes and the sink node fails. This causes massive packet losses, and critical packets are dropped [13]. Clustering is one of the solutions to meet the energy consumption issue. In this approach, either a sink node or the best sensor node in the human body can act as a cluster head (CH). Through the CH, medical data packets are forwarded. This approach requires optimum and fast CH election to aggregate and transmit the packets [14]. Similar to energy efficiency, security is the biggest challenge in WBAN because nodes are communicated via a public channel, so it is vulnerable [15; 16; 17]. Blockchain is a promising solution to provide adequate security for WBAN [18; 19; 20]. It acts as a decentralized entity to avoid a single point of failure. However, the traditional blockchain architecture fails to provide data confidentiality for the resource-constrained environment.  
Blockchain technology is referred to as the transparent distributed technology in the networking domain in which all the participants can own a ledger. Blockchain technology is also referred to as a peer-to-peer method in which all the participants collaboratively manage the network. Blockchain technology has provided the following advantages such as interoperability, scalability, data integrity and traceability [21; 22]. There are four types of blockchain:  
* Public blockchain: All participants can have rights to read and write, no centralized entity, high credibility and also high throughput and energy consumption.
* Private blockchain: Only the particular organization that owns the blockchain could have rights to access or write. It is a centralized blockchain with less credibility. It consumes less energy with a high throughput.
* Consortium blockchain: It can be owned by a group of organizations to which all the group organization participants could have access to read and write. It is also referred to as a partially centralized blockchain and has less energy consumption with a high throughput.
* Hybrid blockchain: Similar to the public blockchain, a hybrid blockchain could give access to read and write to all the participants. It provides partial centrality with medium credibility.  
Due to the support of blockchain-based secure systems, medical records cannot be tampered with and protected from unauthorized access [23; 24; 25; 26]. The proposed work also adopts blockchain technology for secure data storing and managing purposes because the energy efficiency may be reduced by the security threats.