# Blockchain-Empowered Fair Computational Resource Sharing System in the D2D Network +
## 2 Related Work  
### Abundance of Spare Resources in D2D Networks  
To relieve the burden of wireless cellular networks and the cloud, mobile data and computational traffic can be delivered through other means to the users (e.g., WiFi, D2D communications). This is known as mobile data and computation offloading. Several works have identified the benefits of WiFi data offloading [13; 14; 15]. The work in [13] showed that deferring the uploading tasks until WiFi access points are available can save the energy of smartphones. By jointly considering the power consumption and link capacity of wireless network interfaces, [PERSON] et al. in [14] studied the criterion of downloading data from WiFi, as well as the WiFi access point selection problem. However, mobile data traffic cannot always be offloaded to WiFi networks since the number of open-accessible WiFi access points is limited [14], just as the availability of affordable cloud computing services may be quite limited [5]. To fully exploit the benefits of data and computation offloading, mobile traffic and computational works can also cooperate in D2D networks. Specifically, mobile devices in close proximity can be connected via WiFi Direct [16], Bluetooth, etc., in a D2D manner for data and task cooperation between users. This is referred to as D2D data and computation offloading. The works in [7; 8] explore task cooperation of mobile devices in the D2D network and showed that significant execution time and device energy can be saved. The authors of [17] presented a framework for opportunistic storage and processing in the mobile cloud. The work in [18] considers D2D technologies as candidates to deal with most local communications and time-sensitive computations in the near future. A D2D network should make use of Bluetooth, WiFi-Direct and other protocols to more efficiently provision services to applications such as video gaming and image processing. It has been shown in [6] that the computational power of our smart mobile devices is idle and wasted for most of the time before these devices become outdated and replaced with newer models. The work in [19] presents that contemporary smart devices (mostly quad-core devices) use less than two cores on average in their non-idle states with the consideration of simultaneously running applications in the background, not to mention the computing power that these devices can provide in their idle states. It is generally true that building more data centres can provision more computational power for end users. However, a data centre needs to be built and maintained at a very high cost, which encourages us to exploit the task cooperation possibilities in D2D networks bearing users' mobility. Considering the mobile nature of smart device users in ad hoc networks, [PERSON] et al. in [20] proposed a metric, expected available duration (EAD), based on the mobility and similarities of users' interests in the D2D network. EAD indicates the statistically determined expected duration of each user's files of interest in the D2D network. With this metric, this work presents an optimization and performance promotion of a file sharing system in the D2D network to reduce the expensive data charge from cellular carriers and download more data from neighbours. The work in [11] presented a reputation system incorporated with an ad hoc cloud gaming system that can reduce system players' overall bandwidth consumption while keeping fairness among them, without which players with higher network quality will be sacrificing significantly higher bandwidth. Similarly, if a user in our D2D computation offloading system can choose not to share spare computational resources while only receiving help from peers, it is unfair for those helpers contributing their computational resources. Consequently, we need to add a reliable credit system for our computational resource sharing system to enforce fairness among users, but not affecting system effectiveness too much.