The Research On Fault-tolerant Mechanism In Opportunistic Networks

Opportunistic networks is one kind of wireless ad hoc networks,in many realistic application environment,nodes form a disconnected network for most of the time. However, opportunistic networks doesn't require at least one path existing from source to destination nodes,it can utilize the communication opportunistic arising from node movement to forward messages,and this communication model is totally different from the traditional route way, captures great interests from researchers in lots of aspects,and this thesis have researched fault-tolerant algorithm emphatically.This thesis elaborates on a fault-tolerant algorithm based on interleaved coding to solve data packets-loss problem which caused abruptly in opportunistic networks.The algorithm can solve date-loss problem in two aspects-sending and receiving data. While sending data, algorithm can disperse data packets through the thought of interweaving transport,while receiving data,because data in opportunistic networks have a trait of autocorrelation,by using interpolation the lost data can be recovered. The experiment results showed that fault-tolerant algorithm based on interweaved coding can efficiently recover the lost data. Moreover, algorithm can maintain good function even data packets lose more.But interleaving coding takes the time as price,that is to say that transmission delay will increase with the increasing of interleaving depth. To deal with this problem,the thesis proposed a fault-tolerant algorithm based on principal component analysis (PCA).First, carries on the feature extraction to the data,because the PCA has a function of reducing data dimensionality. And then,selects the appropriate principal components to use the ACK mechanism,under the premise of retaining the main message of original data,reduce the transmission delay and save the network overhead.The simulation results show that the algorithm has a good function of recovering the lost data.However,the PCA is not suitable for all data sets,its application has some limitations. So, a fault-tolerant algorithm based on multi-resolution Haar wavelets was proposed to deal with the problem of concentrated data packets lost in opportunistic networks.The basic idea of algorithm can be described as follows. First,the signals are decomposed by wavelet transformation to get the low-frequency coefficients and high-frequency coefficients before it is sent. The ARQ mechanism is used to transfer the low-frequency coefficients. The high-frequency is transferred directly. Then,the signals are restored based on conversation of energy in the receiver. Theoretic analysis and simulation results show that the proposed algorithm can efficiently recover the original signal and maintain good fault-tolerant performance even continuous packets lost because of the bad disturbance.