Information Transmission Mechanism
To introduce the information transmission mechanism clearly, nodes in the network can have three states: ignorant, spreading and recovered. A node is ignorant if it is interested in the information but has not yet received it. Nodes that have possessed a copy of information and are willing to disseminate the information to others can be seen as spreading nodes. If a node is not interested in the information and not willing to disseminate it either, this node can be looked upon as a recovered node.
Combined with three states of mobile nodes mentioned above, the detailed information dissemination process is introduced. Usually, users may be willing to help their friends rather than anyone upon contact, which is a practical concern in the real world but ignored in most of previous studies. In MSNs, we consider that there is only one node having the information initially, which is the spreading node. All of other nodes are interested in the information at first, and willing to receive the information. However, most of the nodes cannot always maintain the same interest. Some ignorant nodes may lose the interest later, and refuse to receive it. In other words, an ignorant node can directly become a recovered node, which is called pre-immunity. An information delivery occurs from one node to another node only when they are friends and encounter with each other. In the real world, a spreading node cannot successfully deliver the information to its friends all the time due to the constraints of QoS during data transmission. A spreading node successfully forwards the informa?tion to one of its ignorant friends with a certain probability. In addition, a spreading node may stop dissemination when it encounters a recovered friend-node, which is called immunity. Moreover, spreading nodes may stop dissemination without any contacts due to their disinclination to deliver the information.
According to the information dissemination process, we summarize the following four rules.
- 1. When a spreading node meets an ignorant friend-node, the ignorant node receives the information from the spreading node and becomes a spreading node with probability в, which is called spreading parameter.
- 2. An ignorant node may lose interests and directly become a recovered node. We assume that this change is based on an exponential distribution with parameter X, where this assumption is also used in .
- 3. When a spreading node meets a recovered friend-node, the spreader becomes a recovered node with probability 5, which is called immune parameter.
- 4. Due to the decrease of interest in information, the spreading node may cease delivering information and become a recovered node spontaneously without meeting other nodes. The spreading node becomes recovered node based on an exponential distribution with the parameter v.
Parameters x and v are the self-immune parameter of ignorant nodes and spreading nodes, respectively. According to these four dissemination rules, the state transition diagram of a node can be shown by Fig. 2.2.
Fig. 2.2 State transition diagram of a node. Symbols I, S, and R represent the ignorant, spreading and recovered state, respectively