An Integrated Credit-Based Incentive Protocol for Symbol-Level Network-Coded Cooperative Content Distribution among Vehicular Nodes  
[PERSON] 1,*  
1 Department of Computer Science and Information Engineering, National Changhua University of Education, Changhua 50007, Taiwan; f91 [EMAIL_ADDRESS]  
2 Department of Early Childhood Development and Education, Chaoyang University of Technology, Taichung 41349, Taiwan; [EMAIL_ADDRESS]  
Correspondence: [EMAIL_ADDRESS]; Tel. : +886-4-723-2105  
2018 October 2018 October 201815 September 20  
like electronic advertisements or coupons, through VANET to on board units (OBU) of vehicles in a given geographical area of interest (AoI). Because the contact duration between the RSU and the fast-moving vehicular node is short, the vehicular node may only receive parts of content data. Hence, the vehicular node uses several kinds of approaches to forward its content pieces to all nearby nodes when it disconnects from the RSU. First, the P2P approach is proposed to exchange received content pieces [8; 9; 10]. However, it incurs huge overhead due to high mobility and poor propagation condition in the vehicular environment. For overcoming this problem, the network coding (NC) technology is then used for CCD [11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. It encodes original packets at every source node, which then floods these NC-coded packets to nearby nodes. Whenever the nearby node has received one NC-coded packet, it must verify linear independence of all received packets. After receiving a certain number of linearly independent packets, the receiver can solve them to reconstruct original packets. With the merit of NC, vehicular nodes in AoI can effectively collect all content data to increase throughput, reliability and security in communication and further reduce duplicate transmissions. In Reference [13], nodes compare each other to find out which node has received most file blocks and let this node broadcasts its blocks. If this node holds the transmission opportunity too long, this approach suffers from degraded network performance when VANET topology changes rapidly. The pull-based approach is used in References [14; 15]. Each node first exchanges its block availability to others and then a node can pull blocks from others. Because the node only issues its blocks after receiving the content request from its neighbor, network bandwidth is wasted due to this passive pulling. In Reference [16], after the node receiving a coded packet, it defers transmission of the re-coded packet until a fixed timer expires. There is no transmission scheduling for nodes, which may introduce serious packet collisions. Recently, the symbol-level network coding (SLNC) technique has been proposed to support robust transmission and stimulates more active simultaneous transmissions [17]. For alleviating the aforementioned problems, the SLNC-based CCD approach, for example, CodeOn [18], CodePlay [19] and so forth, has been proposed [17; 18; 19; 20; 21]. In every control time slot, each vehicle broadcasts the reception status of content data in a safety message to its neighbors. For coordinating the broadcast among vehicles, these SLNC-based CCD approaches adopt the prioritized relay selection scheme to calculate the value of utility, which is defined as the number of valuable SLNC-coded content pieces that a node contributes to its neighbors through its broadcast. However, these approaches do not differentiate content pieces of a node from those of its neighbors. If each node owns the same number of content pieces, these SLNC-based CCD approaches will terminate their operations because the utility value between any two nodes is zero, in spite of some content pieces are distinct indeed. Furthermore, these SLNC-based CCD approaches ignore nodes in VANET having distinct levels of interests and selfishness for different kinds of content data, which then prevents these vehicular nodes from forwarding their content information to other nodes.