Keonkook Lee

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Spectrum leasing via cooperation refers to the possibility for primary users to lease part of the spectral resources to secondary users in exchange for cooperation. This paper proposes a novel implementation of this concept in which secondary cooperation aims at improving the secrecy of the primary link. In particular, a secondary transmission with multiple(More)
It was shown that the required transmit power to support a target achievable rate is inversely proportional to the number of antennas in massive multiple-input multipleoutput (MIMO) systems [1]. However, the consumed power of the massive MIMO systems should include not only transmit power but also the fundamental power for operating the circuit at the(More)
In this letter, we propose an orthogonal spacetime-frequency block code for orthogonal frequency division multiplexing (STFBC-OFDM) systems, newly designed to be robust against both timeand frequency-selective fading. The performance of the proposed system is analyzed in spatially uncorrelated time-varying multipath Rayleigh-fading channels. The analytic(More)
In this paper, we propose an adaptive transmission technique for MIMO-OFDM systems which selects one of spacetime block coded OFDM (STBC-OFDM) and space-frequency block coded OFDM (SFBC-OFDM). STBC-OFDM and SFBCOFDM undergo severe performance degradation in time-varying and frequency-selective channel, respectively. In the adaptive scheme, either STBC-OFDM(More)
The ZigBee network has been considered to monitor electricity usage of home appliances in the smart grid network. Zig-Bee, however, may suffer from a coexistence problem with wireless local area network (WLAN). In this paper, to resolve the coexistence problem between ZigBee network and WLAN, we propose a new protocol constructing a cognitive smart grid(More)
In this paper, we consider a cooperative jammer to improve secrecy of the wireless transmission in a cellular downlink network. The private message intended for a single user should be kept from the remainder of the users who are regarded as internal eavesdroppers. To improve the secrecy of the intended user, we propose an employment of a helper with(More)