The Research On Key Technologies Of Data Dissemination For Opportunistic Networks

Opportunistic network is self-organization Network that utilizes the mobile node contact opportunity to achieve data communications. It does not require one complete communication path exists between source and destination. As a new Network formation, it breaks through the data latency and transfer rate restrictions of traditional networks. Therefore, Opportunistic network has great potential applications in many areas. It is more suitable for practical self-organization network applications than traditional Mobile Ad Hoc Network in real environment. There are the following typical characteristics in data communication of opportunistic networks.1) The nodes move frequently with large range in opportunistic networks, the network is often divided into several sub-regions which are not mutually connected. Moreover, the low wireless channel capacity leads to the long data end to end latency.2) The data communication depends on contact chance arising from node movement. Thus the node mobile model that characterizes the probability of the node contact and time period data distribution becomes the key factor in network communication performance.3) Contradictions of node cache space are more prominent than the MANET, data lives long time in network because relay nodes adopt "store-carry-forward" pattern to transfer data. Therefore, relay node's cache space consume fast. It has a higher buffer capacity requirements comparing with traditional MANET.Difficulty of Opportunistic network data dissemination is to ensure its efficiency and reliability of data transmission in high latency and low data rate network environment. It needs to think about cooperative cache, cache replacement, routing and MAC layer protocol and so on because nodes adopt "cache-move-forward" mode to communication. Therefore, the main work and contributions are presented in the following aspects:(1) An Opportunistic network data cooperative caching policy based on mobile Patterns of Humans is proposed, which is characterized by the probability of the node contact and time period data distributionThe node movement pattern is not considered as an important factor in many of existing policies that has impact on cache performance. In fact, node movement trajectory affects collaborative relationships between nodes and the stability of the local network domain. Moreover, it has impact on the effectiveness and availability of data blocks. Therefore, a cooperative caching policy based on human mobility patterns is proposed, which is referred as HMP-Cache. HMP-Cache uses the standard of target address matching to choose cooperative caching nodes. Also, the sharing caching information is done by synchronization of caching table in local region. Therefore, the shortcoming of limited caching resources is compensated and the remote data latency is reduced. Moreover, the cache hit ratio is improved.(2) Taking the correlation between the nodes and the data item as replace standard, a cache replacement policy for opportunistic networks is further proposed, which is based on the foregoing cooperative caching policy.Most existing cache replace policies take the data access information as replace standard, such as access times, the data item size and the last access time. But the validity of data is not considered in existing research. Thus, a novel cache replacement policy is proposed, which referred as ON-CRP. ON-CRP chooses the data item to replace based on the correlation between the nodes and the item. It utilizes the probability of destination-matching to judge the correlation which is gotten from humans mobile patterns. Furthmore, the visit and update frequency ratio is used to design the standard of cache data replacement. In addition, the performance impact of Zipf distribution parameter is dicussed. The simulation results show that our policy can reduce the latency of remote data access while cache hit ratio of data is improved.(3) Using a general evaluating mechanism, an opportunistic networks routing policy based on node different movement staus is proposed, which uses hybird data forwarding behaviors.Most existing routing algorithms assume a single forward behavior during the entire data transfer process without considering human movement changes in mobility patterns. In the real world, however, a single forward behavior may not be applicable in different contexts. Therefore, we utilize different data forwarding behavior according to the node move staus. The key factor of data dissemination policy is discussed in depth. In normal move status, the network traffic and resource consumption caused by useless data dissemination of multiple hops are reduced efficiently through the design of selecting relaying nodes. In small move status, the limit flooding is used to reduce the data latency. Furthermore, a routing policy based on node different movement staus is proposed referred as HMP. Moreover the upper and lower bounds of HMP performance are analyzed.(4) A Bluetooth MAC layer protocol based on rateless coding theory is proposed, which is improved data transmission performance upon bluetorrent protocol.Bluetooth protocol is employed as the MAC layer protocol given its popularity and technical maturity in mobile devices. However, the Bluetooth is a low data rate and short distance communication protocol. The opportunistic networks mobile features make the packet loss rate, jitter and random link error increased in communication. Therefore, a novel Bluetooth protocol is proposed. It is improved upon Bluetorrent, referred as Bluetorrent-ED. Bluetorrent-ED optimizes Bluetooth communication parameters to improve the efficiency. Furthermore, to improve network reliability, On-Line coding algorithm is used for reduce the impact of data drop and optimization in data dissemination.