Research On Reliable And Secure Data Transmissions In Wireless Sensor Networks

Wireless sensor network is usually deployed in harsh and dynamic environment for many applications,and its data transmissions are inevitably confronted with some problems including the inner reliability and the outer security.The inner reliability addresses random packet losses coming from practical topology changes,dynamic links,human disturbances,channel interferences and collisions,which may reduce transmission reliability and efficiency.The outer security rises from intrusion attacks and security threats in hostile military battlefields and commercial applications,which may destroy data integrity,confidence,verification and availability.Those problems above can be referred to the issue of network reliability in a general sense.In this dissertation,from the perspective of both inner reliability and outer security,some studies have been made about the reliability of data transmissions in wireless sensor networks.The main contributions are as follows:(1)First,the inner reliability for data transmissions is studied.Based on the broadcast feature of wireless channel,a general cooperative converge-casting topology model(GCCT)is proposed,where there are a certain number of relay nodes on each hop to forward packets collaboratively.GCCT absorbs diverse cooperative relationships to guarantee the reliability hop by hop,and transfers temporal redundancy(retransmissions)into spatial redundancy(link diversity)to guarantee transmission reliability and reduce time delay as well.Meanwhile,a novel analysis model is built,based which the performances for GCCT in terms of transmission reliability and transmission overhead can be analyzed theoretically.(2)On the basis of GCCT,a distributed width-controllable braided multipath routing WC-BMR and its improved version MCWC-BMR are proposed.Data transmissions from the source to the sink are binded near the main route(namely,the shortest-hop path from the source to the sink)as a braided crossing way,which expands the traditional converge-casting tree,and prevents path diffusions in GCCT.Heterogeneous transmission widths,namely,different widths on different hops from the source to the sink,can also be supported to adapt to the dynamic and heterogeneous wireless links.In order to avoid packet collisions among two hop's transmissions,a novel time schedule strategy is given.In addition,a kind of less cooperative topology(LC-Topology)in WC-BMR is found,where the local reliability depends overly on nodes or links on the main route,which brings less or no reliability gain.At last,modified cooperative WC-BMR(MCWC-BMR)with the detection algorithm of LC-Topology is proposed to maintain the high reliability and efficiency,which allows parents nodes to choose the best main route locally and dynamically.(3)A distributed compressive redundancy control based multi-path network coding DCRC-NC for multi-hop end-to-end communications is proposed to control the coding behavior of forwarder nodes in a distributed way,and achieve higher network performances,i.e.,decoding reliability,delay,and efficiency.Coding index(CI)is first introduced to track coded packets generated on previous hop which are mixed into a new coded packets generated on following hop,and helps reduce useless redundancy.Two kinds of algorithms are designed to compress the total transmissions by each hop and guarantee the decoding efficiency as well,of which one is centralized f-or ideal channels without losses among the same hop's transmissions,and the other one is distributed completely for practical losses.(4)Considering many-to-one communications in wireless sensor networks,an opportunistic converge-casting network coding protocol ConvergeCode is designed to enhance the reliability and efficiency of data collections.Firstly,Instead of ACK feedbacks link by link,the normal packet can be regarded as implicit feedback to inform downstream nodes of the information already owned by the upstream nodes to refresh their buffers and which packets need to be rescued as well,thereby helping compress the useless redundancy network coding brings.Besides,benefiting from the tree structure,an efficient local feedback scheme is given to avoid the feedback flooding from the sink over the network for decoding reliability.In addition,coding redundancy can be adjusted in a distributed way with the help of implicit and explicit feedbacks in order to adapt to the varying wireless links.Furthermore,even as the number of data flows gets smaller,ConvergeCode can be degraded as the traditional end-to-end opportunistic routing by overhearing.(5)With regard to the outer security for data transmissions,the reseach related to self-healing key management for wireless sensor networks under the lossy environment is made to overcome some existing shortcomings,such as the inefficiency of broadcasts,lack of broadcast authentication,limited sessions for key issues,the disastrous risk of access polynomials and the vulnerability of collusion attacks.First,a modified security model is given,where collusion resistance capability is redefined from the perspective of session interval from node revocation to node addition,and does not depend on the number of collusive nodes.Then,a kind of disastrous attack PF-Attack is introduced to break the security of access polynomials thoroughly.Next,two modified access polynomial based self-healing key management schemes with broadcast authentication and enhanced collusion resistance are proposed to strengthen the security and tolerate packet losses,which allow pairwise keys between member nodes and group manager to be updated dynamically.(6)The size of sliding window for self-healing key management schemes is studied,which may effect the self-healing capability and the transmission overhead.Here,some security indices for self-healing key managent are given,such as key synchronization,security association and security service performance.By using the probability knowledge,the mathematical model is built,which reflects the influence of both the size of sliding window and packet loss rate of wireless links on the performance of key synchronization,security association and security service.Then,the adjustment mechanism for sliding window is proposed to adapt to dynamic changes of broadcast links,where the lookup table is utilized to improve the computation and storage overhead.