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Hoan, Tran Nhut Khai,Koo, Insoo IET 2016 IET COMMUNICATIONS Vol.10 No.6
<P>An optimal multi-slot channel sensing schedule is proposed in this study that considers an opportunistic spectrum access with the awareness of channel switching delay and imperfect sensing. A practical case is considered where channel availability statistics are usually correlated in time slots and in frequency channels. The switching delays between channels, hardware constraints, and collision with other cognitive users are considered to find an optimal sensing order of the channels that maximises throughput of cognitive user. The optimal sensing order is obtained using the partially observable Markov decision process framework. Throughput of cognitive user, with and without channel sensing errors, is analytically derived and for each case an algorithm is developed. The proposed scheme mitigates the effect of channel sensing errors on the throughput. Performance of the proposed scheme is evaluated through simulations by comparing it with the existing schemes in the literature.</P>
Nhut Khai Hoan, Tran,Koo, Insoo IEEE 2017 IEEE SENSORS JOURNAL Vol.17 No.7
<P>Herein, the authors consider harvested energy powered cognitive radio networks (CRNs) in which harvested energy is stored in a rechargeable battery which has finite capacity. In addition, a practical scenario in which the amount of harvested power is finite is taken into account. Cognitive users (CUs) opportunistically access a licensed channel (or primary channel); meanwhile, it should be ensured that their confidential communications are not leaked to an eavesdropper. We investigate an optimal spectrum sensing schedule and the optimal amount of transmission energy for the CUs in each processing time slot. In particular, at the beginning of each time slot, based on the remaining energy in the battery, CU transmitter decides either: 1) to be active to sense the channel and transmit its data if the channel is found vacant or 2) to stay inactive during the current time slot in order to save energy and wait for more incoming energy for use in the next time slots. The decision is based on expected secrecy transmission rate calculated for both cases over subsequent K time slots. The proposed scheme aims to improve long-term secrecy transmission rate of CRNs in comparison with a conventional scheme where the decision for the current time slot is made to maximize current secrecy transmission rate without considering any future reward.</P>
Energy-Efficient Data Encryption Scheme for Cognitive Radio Networks
Do-Vinh, Quang,Hoan, Tran-Nhut-Khai,Koo, Insoo IEEE 2018 IEEE SENSORS JOURNAL Vol.18 No.5
<P>In this paper, we investigate a security mode decision policy for a cognitive radio network (CRN) powered by a non-radio frequency energy harvester. In such a network, a cognitive user (CU), which has a finite battery capacity, senses the presence of the primary user and tries to access the time-slotted primary channel opportunistically to transmit data. However, communication can be vulnerable to sudden attacks that are carried out by hidden eavesdroppers. Therefore, we propose an energy-efficient data encryption scheme for CRNs to increase the effective security level under energy limitation constraints. The operation mode decision policy is formulated as a framework of a partially observable Markov decision process. In this approach, based on the sensing results and the remaining energy at the beginning of each time slot, CUs can decide to stay silent to save energy, or become active and encrypt data using opportune private-key encryption methods considering the effect of the current action on the future reward to maximize the effective security. Finally, we evaluate the performance of the proposed scheme by using numerical simulation results.</P>