• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6A
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• pp.547-554
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• 2010

Recently, the multi-band orthogonal frequency division multiplexing(MB-OFDM) system, one of UWB system, can satisfy the requirement and can be applied to various wireless communication services because ultra-wideband(UWB) is a wireless communication technique that supports high data rate with low power. In this paper, the method applying Alamouti's space time block code(STBC) and cyclic delay diversity(CDD) is proposed. The proposed method can be easily applied with arbitrary number of relays and only needs two time slots of quasi stationary assumption. And it is applied to the MB-OFDM system. Second, an optimal relaying scheme based on decode-and-forward(DF) method is proposed which is provides good error performance compared to conventional schemes.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.901-906
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• 2019

UAV (Unmanned Aerial Vehicle) is widely used in various areas such as civil and military applications including entertainment industries. Among them, UAV based communication system is also one of the important application areas. Relays have been received much attention in communication system due to its benefits of performance enhancement and coverage extension. In this paper, we investigate UAVs as relays especially focusing on physical layer. First, we introduce the research on UAV application for the relays, then the basic performance of relay networks in dual-hop communication system is analyzed by adopting decode-and-forward (DF) relaying protocol. The performance is represented using symbol error rate (SER) and UAV channels are applied by assuming asymmetric environments. Based on the performance analysis, we discuss performance enhancement issues by considering physical layer.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.8
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• pp.1770-1785
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• 2013

In this paper, a multi-hop transmission protocol based on parallel communication of secondary users (SUs) is proposed. The primary multi-hop network coexists with a set of SUs by cooperative spectrum sharing. The main optimization target of our protocol is the overall performance of the secondary system with the guarantee of the primary outage performance. The energy consumption of the primary system is reduced by the cooperation of SUs. The aim of the primary source is to communicate with the primary destination via a number of primary relays. SUs may serve as extra decode-and-forward relays for the primary network. When an SU acts as a relay for a primary user (PU), some other SUs that satisfy the condition for parallel communication are selected to simultaneously access the primary spectrum for secondary transmissions. For the proposed protocol, two opportunistic routing strategies are proposed, and a search algorithm to select the SUs for parallel communication is described. The throughput of the SUs and the PU is illustrated. Numerical results demonstrate that the average throughput of the SUs is greatly improved, and the end-to-end throughput of the PU is slightly increased in the proposed protocol when there are more than seven SUs.