Research On Position Optimization Of Untrusted Mobile Relay Based On Physical Layer Security

With the convenience provided by the wireless communication,the wireless network is widely adopted to transmit the sensitive and private messages in the daily life.The security of the conventional wireless network is guaranteed though the encryption techniques in upperlayer,which assume the computation capability of the attacker is limited.However,with the rapid development of distributed-computing technology,the computation capability of the attacker improves obviously,and thus such assumption becomes less reliable.The technology of physical layer security(PLS)has attracted more and more attention,because it avoids the aforementioned assumption.The technology of PLS is achieved by making some performance metric(e.g.,signal-to-noise ratio(SNR))of the legitimate receiver better than that of the attacker.Moreover,the technology of PLS represents an unexploited resource and does not only rely on the conventional upper-layer encryption techniques.Recently,to adopt some cooperative techniques into PLS attracted much attention due to their unique advantages,e.g.,relay selection technique and cooperative jamming technique.However,there is some obvious drawback in these cooperative techniques in the existing literatures,e.g.,the spatial distribution of relays limits the performance of relay selection technique.In order to overcome the above-mentioned drawback,this thesis proposes a new scheme of the untrusted mobile relay to improve the secrecy capacity.We assume that the untrusted mobile relay moves over the whole horizontal space and its movement according to the destination's feedback information or its own local information.The performance of the proposed scheme is not limited by the spatial distribution of mobile relay,but it requires not to sacrifice the wiretap capacity of attacker.Otherwise it will cause the suspicion of the untrusted mobile relay,and even make the untrusted mobile relay to betray the system.The most attractive feature of the proposed scheme is easy implementation,i.e.,only single antenna is required of all the communication nodes;only one bit feedback information is required for the destination to feedback;the feedback mechanism even can be cancelled,which makes the secure communication more covert.Meanwhile,the proposed scheme further improves the performance by introducing an adaptive adjustment mechanism of an artificial noise(AN)to confound the untrusted mobile relay.The proposed scheme is very suitable for the scenario that the source node with energy constrained requests an untrusted mobile relay to forward some confidential messages.We first apply the conventional position optimization algorithm with appropriate modification into the proposed scheme.Although it improves the secrecy capacity,it sacrifices the wiretap capacity under some situations,which causes the eavesdropper's conscious and violates the requirement of the proposed scheme as well.Based on the proposed scheme,this thesis further designs three implementation algorithms.The first proposed algorithm is the most straightforward one,which introduces the cooperative AN with fixed power and modifies the mechanism of decision feedback.Although the first one satisfies the requirement of the proposed scheme,its improvement gap is limited.The second one further improves the final performance by adjusting the power of the cooperative AN adaptively.The third one makes the secure communication more covert by cancelling the feedback mechanism from destination node.However,the improvement of the third one is small due to the harsh constraint condition.Through analysis and simulation results,the performance of the proposed three implementation algorithms are discussed.Moreover,we also investigate the impact of different parameters of the three proposed algorithms on their performance,and draw some useful conclusions.