• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.53-58
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• 2011

In this paper, we firstly propose a novel cooperative transmission protocol, which utilizes the advantages of mid-notes in the route from the source to the destination. Taking benefits from balancing between the received packet from the source and acknowledge message from the destination, the mid-node between the source and the destination is firstly considered to be the broadcaster. If its signal is successfully received from the source, it leads to consider the next nodes, which has closer distance to the destination than it. If one of these nodes correctly receives the signal, it performs broadcasting the signal to the destination instead of mid-node. Otherwise, the mid-node directs attention to these nodes being near to the destination. As the result, some nodes are unnecessary to be considered and passed over time. After that, we analyze some published selection relaying schemes based on geographic information to choose the best nodes instead of the instantaneous SNR as before. Finally, simulation results are given to demonstrate the correctness of the performance analyses and show the significant improvement of the selection relaying schemes based geographic information compared to the other ones.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.3
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• pp.354-361
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• 2011

In this paper, we propose a spectrum sharing system that enable secondary user's spectrum access in cooperative communication scheme. At phase 1, a transmitter in primary system broadcasts signals to the rest nodes. And then, at phase 2, a transmitter in secondary system combines the decoded signals after received from a transmitter in primary system and its own signal. And then transmitter of secondary system broadcasts the combined signals to receivers of primary and secondary systems. At this time, due to the process of combining signals, receivers of primary and secondary systems experiences a performance degradation. Therefore, we propose a novel adaptive incremental decode-andforward(AIDF) protocol to overcome this problem. By using AIDF protocol, we show performance improvement of total system through various simulations.

• ETRI Journal
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• v.37 no.3
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• pp.460-470
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• 2015

Orthogonal frequency-division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM-based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify-and-Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF-relay, and incremental relaying modes. The outage performance of the proposed AF relay-based CR network is proven to be better than that of direct mode.