Yongchul Kim

Asynchronous Channel-Hopping Scheme under Jamming Attacks

Cognitive radio networks (CRNs) are considered an attractive technology to mitigate inefficiency in the usage of licensed spectrum. CRNs allow the secondary users (SUs) to access the unused licensed spectrum and use a blind rendezvous process to establish communication links between SUs. In particular, quorum-based channel-hopping (CH) schemes have been studied recently to provide guaranteed blind rendezvous in decentralized CRNs without using global time synchronization. However, these schemes remain vulnerable to jamming attacks. In this paper, we first analyze the limitations of quorum-based rendezvous schemes called asynchronous channel hopping (ACH). Then, we introduce a novel sequence sensing jamming attack (SSJA) model in which a sophisticated jammer can dramatically reduce the rendezvous success rates of ACH schemes. In addition, we propose a fast and robust asynchronous rendezvous scheme (FRARS) that can significantly enhance robustness under jamming attacks. Our numerical results demonstrate that the performance of the proposed scheme vastly outperforms the ACH scheme when there are security concerns about a sequence sensing jammer.

Friend-safe evasion attack: An adversarial example that is correctly recognized by a friendly classifier

Abstract Deep neural networks (DNNs) have been applied in several useful services, such as image recognition, intrusion detection, and pattern analysis of machine learning tasks. Recently proposed adversarial examples-slightly modified data that lead to incorrect classification-are a severe threat to the security of DNNs. In some situations, however, an adversarial example might be useful, such as when deceiving an enemy classifier on the battlefield. In such a scenario, it is necessary that a friendly classifier not be deceived. In this paper, we propose a friend-safe adversarial example, meaning that the friendly machine can classify the adversarial example correctly. To produce such examples, a transformation is carried out to minimize the probability of incorrect classification by the friend and that of correct classification by the adversary. We suggest two configurations for the scheme: targeted and untargeted class attacks. We performed experiments with this scheme using the MNIST and CIFAR10 datasets. Our proposed method shows a 100% attack success rate and 100% friend accuracy with only a small distortion: 2.18 and 1.54 for the two respective MNIST configurations, and 49.02 and 27.61 for the two respective CIFAR10 configurations. Additionally, we propose a new covert channel scheme and a mixed battlefield application for consideration in further applications.

MAC prioritization scheme resolving unfairness problem

IEEE 802.11e is an extension of IEEE 802.11 for the Quality of Service (QoS) enhancement for wireless LAN application using MAC layer priority scheme. The IEEE 802.11e standard divides the network traffic into four different categories by the traffic type. Delay-sensitive applications need a high media access priority, which can be achieved by using different MAC parameters. The priority scheme is also used for resolving the unfairness and bottleneck problems of multihop wireless networks, where nodes operate as host or relay nodes. It is well-known that these problems occur since there may exist overloaded nodes that the packets from various source nodes converge on. Fine control of access opportunity at MAC layer can deal with this unfairness situation. In this paper, we provide an analysis of the priority scheme based on CWmin which can induce a required throughput ratio, and verify it with simulation results. Also, the simulation results are given to verify that the unfairness and bottleneck problems in multihop networks are solved by using the proposed priority scheme.

Generalized Hybrid Scheduling Scheme for Multihop Relaying WiMAX Networks

In this paper, we propose a heuristic scheduling scheme, named hybrid resource allocation scheme that can reduce the time complexity of scheduling scheme and im- prove the efficiency of resource utilization while minimizing interference. We first focus on the two-hop relaying scenario, since this scenario has the largest throughput gain, and then explore an extension of the proposed hybrid scheme to a general multihop relaying scenario. We evaluate the performance of our proposed hybrid scheme by comparing it with the optimal scheduling scheme as well as the well- known two schemes, namely, orthogonal and overlapped in terms of cell throughput, outage rate, and computation time. The numerical results show that the proposed hybrid scheme achieves a higher throughput than the orthogonal scheme while maintaining as low an outage rate as orthogonal scheme. In addition, the computational time is significantly less than the optimal scheme at the expense of minimal throughput degradation.