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Effect of Channel-Estimation Error on BER Performance in Cooperative Transmission
Seungyoup Han,Seongwoo Ahn,Eunsung Oh,Daesik Hong IEEE 2009 IEEE Transactions on Vehicular Technology VT Vol.58 No.4
<P>In this paper, a framework for evaluating the bit-error-rate (BER) performance of amplify-and-forward (AF) relay-assisted cooperative transmission is provided in the presence of imperfect channel estimation. First, the AF relaying is classified into two cases - a variable gain and a fixed gain. For each case, the closed-form average BER is derived by using the moment-generating function (MGF) of the effective output SNR, which quantifies the SNR penalty due to the noisy channel estimate. Moreover, the asymptotic BER bound is also provided at a high SNR regime for the insight of our approach. In particular, the effect of the feedforward delay on informing the source-relay channel estimate as to the destination is presented in the variable-gain relay. Numerical investigation shows that the analytic result makes an exact match with the simulation, and the comparative superiority between the fixed- and variable-gain relay is discussed.</P>
Optical anisotropy in single-walled carbon nanotubes.
Yoo, Seongwoo,Jung, Yongmin,Lee, Dong Soo,Han, Won-Taek,Oh, Kyunghwan,Murakami, Y,Edamura, T,Maruyama, Shigeo Optical Society of America 2005 Optics letters Vol.30 No.23
<P>Optical anistropy at optical communication wavelength was observed in films of vertically aligned single-walled carbon nanotubes (SWNTs). We report the control of both the polarization state and transmission of incoming light at 1550 nm by azimuthal and axial tilting of SWNT film about its aligned axis. The experiments reveal that the polarization state of light is susceptible to the azimuthal angle of the aligned direction of a SWNT having semiconductor characteristics and the intensity of the output beam after SWNT film shows cosine function dependence on the axial tilting angle.</P>