Existing terrestrial synchronization protocols including RBS, FTSP, TPSN, LTS and TSHL have already achieved high precision in radio networks, but none of them perform well in high latency networks like acoustic sensor networks. In this paper, we present Tri-Message: a lightweight time synchronization protocol for high latency and resource-constrained networks. As its name suggests, only three message exchanges are required in one synchronization process. Meanwhile, Tri-Message utilizes very simple mathematical operations to calculate the clock skew and offset. Specially, Tri-Message is feasible for many extremely long latency applications such as space exploration because it has an increasing synchronization precision with the increasement of distance.

History-independent modelling systems are more flexible than history-based ones. They let designers manipulate the model in a more associative, rather than prescribed, way. In this paper, an approach based on 2D geometric constraint solving and a topological entity naming mechanism (TENM) is presented to solve the geometric constraints between features in 3D space. Firstly, in order to break the unidirectional dependency between features in a history-based modelling system, a data structure named feature constraint graph(FCG) is adopted to represent the geometric constraints between features in 3D space. Then a solving sequence is obtained using degree-of-freedom (DOF) based graph analysis. And finally, during the evaluation of the solving sequence, the dimensions in 3D space are mapped to 2D space, the dimensions in 3D space are satisfied indirectly by solving the corresponding 2D geometric constraint system. An example is given to illustrate the process of our approach.

Reduced latency versions of i terative decoding of turbo codes are analyzed in this paper. The proposed schemes converge faster than the standard and plain shuffled approaches. EXIT chart is used to analyze the performance of the proposed algorithms. Both theoretica1 analysis and simdation resuits show that the new schedules offer better performance / com-pIexity trade-offs.