## 2 Related Work  
In this section, well-known credit-based incentive systems are discussed later. The fairness principle for the credit-based incentive protocol is the major concern in Reference [23]. It presents a fair incentive protocol for four selfish conditions in MANETs. A trusted credit clearance service (TCCS) is used to perform trusted fair credit clearance when requested. As the destination has received the packet, TCCS charges credits values (n - 1) \(\alpha\_c\) + \(\beta\_c\) from the source node. Then it will deposit credit value \(\alpha\_c\) and \(\beta\_c\) to the first (n - 1) intermediate nodes and the last one, respectively, where \(\alpha\_c<\beta\_c\) because the last intermediate node must notify TCCS for clearing credits. In Reference [24], a mechanism is proposed to prevent selfish behavior according to the barter rules. It indicates that nodes may have different interests on different contents. There are two types of messages. The primary message is the one that a given node has interests in its content but the secondary one is a message that is not interesting to the given node. When two nodes enter communication range of each other, they exchange their message lists to check which messages they want to download from each other. This paper shows that selfishly downloading only those primary messages for a given node is not helpful for it later. It might be better for the node to download and carry the secondary messages such that the node can exchange them for the primary ones with other nodes. Obviously, these aforementioned methods will crash if the central control system fails. With the receipt counting method (RCM) [25], if an intermediate vehicle receives a new packet forwarded from a preceding vehicle, it returns a receipt for this packet to the preceding one. As soon as the destination has received this packet, every intermediate forwarding node would demand overall payments with the source node, based on the number of all receipts. Thus, the source node has to pay each intermediate node the total claimed rewards through the central control system Nonetheless, RCM undergoes the overspending problem, which means the source node is not able to limit its overall payments since it cannot estimate the number of total forwarding nodes ahead. It also suffers failure of the central control system. The authors in Reference [26] propose the Fair Reimbursement and Motivating swEepstake scheme (FRAME) with a sweepstake component and a weighted rewarding one. The weighted rewarding component computes the weight and corresponding rewards of every vehicle. Besides, the sweepstake component awards the winning vehicle in the forwarding process a constant amount of reward. Nonetheless, nodes may refuse to forward packets owing to the insignificant rewards paid in FRAME. MobiCent [27] proposes a credit-based incentive system for the Disruption Tolerant Network (DTN) and computes payment by a multiplicative decreasing reward (MDR) scheme. It helps clients to minimize cost or minimize delay. The edge insertion and hiding attacks among nodes are solved by integrating both credit and cryptographic techniques. However, both the source and destination have to access the network for sending control messages all the time. Moreover, it needs a convincing third party like TCCS to handle the confirmation and payment functions. The reciprocal incentive scheme (RIS) [28] analyzes how two types of selfish nodes choose appropriate data objects to maximize their profits under buffer constraints. It also studies the relationship between object selections of the nodes and the stored network information. Each node in the opportunistic network is assumed selfish. A-type nodes can freely download various data objects from Internet but the ISP charges B-type ones with high downloading fee. With RIS, B-type nodes can request data objects from A-type ones with lower cost, instead of downloading them directly from the Internet. However, these credit-based incentive approaches do not work for the SLNC-coded CCD process.