Optimal Design and Performance Analysis of Zero-Padded Transceiver Systems
Date Issued
2008
Date
2008
Author(s)
Wang, Jen-Hsing
Abstract
The OFDM and DMT systems have been popular techniques adopted in manyired and wireless digital communications. With redundant insertion of cyclic prefix(CP), the impact of interblock interference(IBI) and intersymbol interference(ISI)ill be eliminated at the receiving end. It is well-known that when the channel haspectral nulls, some of the subchannels suffer seriously from the noise amplificationroblem. Hence, we will focus on the alternative OFDM system with zero paddingnd SC-ZP(single carrier with zero padding) system.t first, the receiver design of ZP-OFDM and SC-ZP systems will be discussed.hree types of receivers for the ZP system will be studied : DFT-based zero-forcingeceiver, pseudo-inverse receiver and MMSE receiver. The DFT-based zero-forcingeceiver can be implemented by FFT and has low implementation cost. However,ike the CP-OFDM system, the BER performance of the DFT-based zero-forcing forP-OFDM system suffers from the channel spectral nulls. The pseudo-inverse andMSE receivers outperform the DFT-based zero-forcing but they have a relativelyigh implementation cost. Therefore we propose a receiver structure that combineshe DFT-based zero-forcing and the pseudo-inverse(or MMSE) receiver. Implementa-ion cost of the proposed receiver is close to the DFT-based zero-forcing, however, theER performance of the proposed receiver approximates pseudo-inverse and MMSEeceivers. In addition, we also propose a structurally constrained DFT-based MMSEeceiver for SC-ZP system. It also minimizes mean square error for SC-ZP systemut has implementation complexity equal to the DFT-based zero-forcing for SC-ZPystem. Simulation results show that the proposed structurally constrained MMSEeceiver has a good performance.ecently the problem of optimal precoder and equalizer for transceiver systemsas solved by Vaidyanathan. In the second part, we apply the optimal precodernd equalizer to OFDM system to further minimize mean square error(MSE). Theptimal precoder and equalizer indeed improves the BER performance of OFDMystem by doing power allocation. It is well-known that another strategy to improvehe performance is bit allocation. We will apply the optimal bit allocation for OFDM system to minimize transmitted power at the speci?c BER. It will be shown thathe optimal bit allocation results in the best BER performance. When there is bitllocation, there is no need to use any precoders because they actually degrade theerformance.n the last part, we apply the optimal transceiver derived by Vaidyanathan for nondiagonal channel to CP and ZP systems. The optimal transceiver is designedor minimizing transmitted power and jointly optimizing precoder, equalizer and bitllocation. We found that BER performance of zero-padded system is better thanyclic prefixing system when both of them are designed as optimal transceiver structure. And the optimal transceiver for cyclic prefixing system is actually CP-OFDMystem. Finally, some simulation results and comparisons of BER performance forur proposed receivers will be demonstrated.
Subjects
zero-padding
Type
thesis
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