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A Low rank LMMSE(Linear Minimum Mean information. So, an effort to develop an appropriate channel Square Error) channel estimation with variable rank is proposed estimation and compensation algorithm is necessary [6]. for MB-OFDM(Multi-Band OFDM) system in this paper. A In this paper, we propose a Low rank LMMSE channel comparison is performed with an LS(Least Square), LMMSE .a. ' channel estimation, respectively. In the real time system, it is estiman. PfMaE marisonamong LS eLMEan difficult to implement LMMSE channel estimation because of its Low rank LMMSE is made by simulation with the IEEE high complexity though which superior channel estimation 802.15.3a channel model [4]. From the simulation results, the performance. On the other hand by using the Low rank LMMSE proper ranks that reduce complexity without the reduction of algorithm with proper rank size, we can reduce the complexity of the MSE(Mean Square Error) performance are obtained in the LMMSE but without channel estimation performance each channel. The complexity efficiency is also analyzed. degradation. We have analyzed the system performance of LS, LMMSE and Low rank LMMSE with variety of the number of After presenting the MB-OFDM system model in Section II, rank under the IEEE 802.15.3a channel model. The performance we introduce the system and channel models in Section III. analysis provides an appropriate number of rank depending onThe channel estimations are treated in Section IV. Simulation the channel characteristics. Low rank LMMSE can be results are shown in Section V and a summary and concluding implemented in the real time with obtained number of rank parts appears in Section VI. without performance degradation, which is shown by our simulation results.

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We address low complexity frequency offset estimation scheme with low complexity for Multi Band OFDM (MB-OFDM) system. The proposed methods estimate the frequency offset without highly increased complexity, using the auto-correlation property of the channel state information (CSI). Additionally, in order to reduce the channel estimation complexity Low-rank LMMSE channel estimation is adopted with the optimal number of rank. By using those two schemes, we can estimate the frequency offset and CSI with reduced hardware burden. We simulated the proposed algorithms under the IEEE 802.15 TG3a UWB (Ultrawide Band) channel model. Index Terms -MB-OFDM, frequency offset, LMMSE.