The explosive increase of the availability of personal mobile devices has brought about a significant amount of peer-to-peer communication opportunities upon their encountering, which can be exploited to realize distributed message transmission among mobile devices. However, the opportunistic encountering among mobile devices, which is determined by the mobility of their holders, has introduced great difficulties on efficiently transmitting a message to its designated destination. Actually, people usually present a certain pattern on daily mobility. Further, device holders often belong to a certain social network community. Therefore, in this paper, we propose a social- based cyber-physical system for distributed message transmission, namely SocMessaging, by integrating both the mobility pattern and the social network of device holders. When selecting an encountered node for message relay, in addition to the node's historical encountering records with the destination node, SocMessaging also considers its social closeness with the destination node. Then, the message is always transmitted to the node that is most likely to meet its destination. As a result, SocMessaging closely connects the cyber world (i.e., network), physical world (i.e., people) and social network (i.e., social connection). Finally, our experimental results demonstrate the efficiency of the proposed system in message transmission between device holders.
Question and Answering (Q/A) systems aggregate the collected intelligence of all users to provide satisfying answers for questions. A well-developed Q/A system should provide high question response rate, low response delay and good answer quality. Previous works use reputation systems to achieve the goals. However, these reputation systems evaluate a user with an overall rating for all questions the user has answered regardless of the question categories, thus the reputation score cannot accurately reflect the user's ability to answer a question in a specific category. In this paper, we propose TtustQ, a category reputation based Q/A System. TtustQ evaluates users' willingness and capability to answer questions in different categories. Considering a user has different willingness to answer questions from different users, TtustQ lets each node evaluate the reputation of other nodes answering its own questions. User a calculates user <i>b</i>'s final reputation by considering both user <i>a</i>'s direct rating and the indirect ratings on user <i>b</i> from other nodes. The reputation values facilitate forwarding a question to potential answerers, which improves the question response rate, response delay and answer quality. Our trace-driven simulation on PeerSim demonstrates the effectiveness of TtustQ in providing good user experience in terms of response rate and latency, and the answer quality.