Collision Response, Multi-Level Interest Management And Synchronization Control For Distributed Virtual Environment

DVE (Distributed Virtual Environment) is a kind of virtual reality system that simultaneously runs on computers connected by network. It allows distributed users to interact real-time with each other sharing a virtual world. DVE has effulgent application future in numerous domains such as military affairs, cooperative work, network games, etc. In this dissertation, our research is focused on three typical problems, i.e. collision detection and response algorithm, multi-level interest management mechanism and synchronization control method.A Petri net model of distributed implementation for collision detection is built and a time-stamp-based method to ensure uniqueness of collision response is amended which is presented by Wang Zhao-qi. In this paper, we analyze existing algorithm in detail, and then find that it can not ensure uniqueness, and it is incompatible with DR technique too. So we modify the meaning of item named TimeStamp of collision list in the existing algorithm, introduce a variable named A T , and discuss how to get value of variable named A T and A t. The amended method can ensure uniqueness and is used with DR technique together.Contrasting with NPSNET mechanism for single level interest management, Singhal mechanism for multi-level interest management can increase the number of transmitted package while decreasing the number of receiving package. A new network communication implementing mechanism ETLIM (Enhanced Two Level Interest Management) is presented for multi-level interest management. In ETLIM, the whole interest entity set and high interest entity listen to the different multicast address. The transmitter only transmits a package from the multicast address to which the whole interest entity set listens when it needs to send synchronously package to the higher and the lower interest entity set. When modes sending data to the higher and the lower interest entity set are both periodic which is prevalent sending mode in the existing DVE and this two sending frequencies is integer multiple, the performance of ETLIM is satisfied. Now the number of package transmitted equals to that of NPSNET mechanism,and the number of package received equals to that of Singhal mechanism.A new prediction mechanism based on synchronization control is proposed. Contrasting with existing mechanisms, the new mechanism has characteristics as following. At first each entity is in charge of prediction task itself instead of a certain avatar that is the head of the entity multicast group. Because the mechanism utilizes entity's moving information besides avatar's information, it can predict interaction between avatars and the moving entity. Thirdly, avatars don't ask a token in advance. So the new mechanism can predict interaction between avatars and the moving entity and decrease the network loads while not decreasing the probability of correct prediction.The synchronization control algorithm for entity set in CIAO (Collaborative Immersive Architectural layOut) is amended. Within the amended algorithm, semi-optimistic locking mechanism in CIAO is replaced by token mechanism, and Receiver-reliable multicast based on the father node number is proposed to enhance robustness of system. Entities and avatars in scene are organized the structure of tree. Its father node number is augmented in each entity's ESPDU (Entity State Protocol Data Units). The receiver adjusts the structure of local scene tree according to the node number of package received. When package is sent periodically, the algorithm can ensure real-time of interaction, and improve robustness of system.The effectiveness of the work stated above is proved by simulation experiments and theoretical analysis.