補零收發機系統之最佳化設計及效能分析

The OFDM and DMT systems have been popular techniques adopted in many wired and wireless digital communications. With redundant insertion of cyclic prefix(CP), the impact of interblock interference(IBI) and intersymbol interference(ISI) will be eliminated at the receiving end. It is well-known that when the channel has spectral nulls, some of the subchannels suffer seriously from the noise amplification problem. Hence, we will focus on the alternative OFDM system with zero padding and SC-ZP(single carrier with zero padding) system. At first, the receiver design of ZP-OFDM and SC-ZP systems will be discussed. Three types of receivers for the ZP system will be studied : DFT-based zero-forcing receiver, pseudo-inverse receiver and MMSE receiver. The DFT-based zero-forcing receiver can be implemented by FFT and has low implementation cost. However, like the CP-OFDM system, the BER performance of the DFT-based zero-forcing for ZP-OFDM system suffers from the channel spectral nulls. The pseudo-inverse and MMSE receivers outperform the DFT-based zero-forcing but they have a relatively high implementation cost. Therefore we propose a receiver structure that combines the DFT-based zero-forcing and the pseudo-inverse(or MMSE) receiver. Implementa- tion cost of the proposed receiver is close to the DFT-based zero-forcing, however, the BER performance of the proposed receiver approximates pseudo-inverse and MMSE receivers. In addition, we also propose a structurally constrained DFT-based MMSE receiver for SC-ZP system. It also minimizes mean square error for SC-ZP system but has implementation complexity equal to the DFT-based zero-forcing for SC-ZP system. Simulation results show that the proposed structurally constrained MMSE receiver has a good performance. Recently the problem of optimal precoder and equalizer for transceiver systems was solved by Vaidyanathan. In the second part, we apply the optimal precoder and equalizer to OFDM system to further minimize mean square error(MSE). The optimal precoder and equalizer indeed improves the BER performance of OFDM system by doing power allocation. It is well-known that another strategy to improve the 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 that the optimal bit allocation results in the best BER performance. When there is bit allocation, there is no need to use any precoders because they actually degrade the performance. In the last part, we apply the optimal transceiver derived by Vaidyanathan for nondiagonal channel to CP and ZP systems. The optimal transceiver is designed for minimizing transmitted power and jointly optimizing precoder, equalizer and bit allocation. We found that BER performance of zero-padded system is better than cyclic prefixing system when both of them are designed as optimal transceiver structure. And the optimal transceiver for cyclic prefixing system is actually CP-OFDM system. Finally, some simulation results and comparisons of BER performance for our proposed receivers will be demonstrated.

並列關鍵字

zero-padding

參考文獻

[1] L. J. Cimini, "Analysis and simulation of a digital mobile channel using orthog-

onal frequency division multiple access," IEEE Transactions on Communications,

[2] J. A. C. Binhgam, "Multicarrier modulation for data transmission: an idea whose

[3] A. N. AAkansu, et al., "Orthogonal transmultiplexers in communication: a re-

April 1998.

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補零收發機系統之最佳化設計及效能分析

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