馮世邁臺灣大學：電信工程學研究所鐘元暉Chung, Yuan-HwuiYuan-HwuiChung2007-11-272018-07-052007-11-272018-07-052004http://ntur.lib.ntu.edu.tw//handle/246246/58696The OFDM system is receiving growing attention as an important transceiver for wireless communications. It is well-known that OFDM systems su er from the problems of spectral nulls. In general, a power error correction code is needed for OFDM system to perform well in the presence of spectral nulls. Several other methods have been proposed to solve the spectral problem. The first method is apply an antipodal paraunitary(APU) matrix to OFDM system. By adding APU precoder, the noise power between all subchannels will be equalized. It was known that a MMSE receiver for APU precoded OFDM system has a much better performance than the OFDM system. The second solution is to use multiple antennas. The probability that all antennas experience a deep fading at the same frequency is very small. If multiple antennas are available at the receiver, one can apply maximum ratio combining(MRC) technique. Its disadvantage is that multiple receive antennas are needed. If multiple antennas are available at the transmitter, one can use space-time coding such as the Alamouti scheme. In the rst part of this thesis, we will apply linear precoder to MIMO-OFDM system. Both space-time coded and space-frequency coded OFDM systems will be studied. Both zero-forcing(ZF) and minimum mean square error(MMSE)receivers are derived, and we will compare their performances. Moreover, the ISI-e ect if exists can be mitigated by adding the precoder. In the second part of this thesis, we consider an SISO-OFDM system where an OFDM block symbol contains several smaller repetitive blocks of information bearing symbols. At the receiver, we will receive multiple copies of corrupted versions of the same symbols. Maximum ratio combining(MRC) technique is employed to combine these received samples to obtain a high SNR output. Such a system will be called MRC-OFDM system. We can also apply APU precoder to the MRC-OFDM system to further improve the performance. Experiments show that under the conditions of equal transmission power and equal transmission rate, MRC-OFDM system has a much better BER performance than OFDM system.1 Introduction 1 2 Introduction to OFDM System 7 2.1 Introduction to OFDM Systems . . . . . . . . 8 2.2 Noise Enhancement Problem of OFDM Systems . . . . 13 2.3 Precoded-OFDM Systems . . . . . . . . . . . . . 15 2.3.1 Properties of APU Precoded-OFDM Systems . . . . 15 2.3.2 The APU Matrix Generation and the Buttery Method 17 2.4 Conclusion . . . . . . . . . . 22 3 MIMO Channel Systems 23 3.1 MIMO Channels . . . . . . . . . 24 3.1.1 SISO Sampled Signal Model . . . . . . . . .24 3.1.2 MIMO Sampled Signal Model . . . . . . . . . 25 3.1.3 Classical i.i.d. Uncorrelated Channel and Spatially Fading CorrelatedChannel . . . . . . 28 3.2 Receive Antenna Diversity . . . . . . . .29 3.3 Transmit Antenna Diversity . . . . . . . .31 3.3.1 Channel Unknown to the Transmitter . . .31 3.3.2 Channel Known to the Transmitter . . . .33 3.4 Conclusion . . . . . . . . . . .35 4 MIMO Precoded-OFDM Systems 37 4.1 MIMO-OFDM Systems . . . . . . 38 4.1.1 Space-Time OFDM Systems . . . . . . 38 4.1.2 Space-Frequency OFDM Systems . . . . 43 4.2 MIMO Precoded-OFDM System . . . . . . .46 4.2.1 APU Precoded ST-OFDM System . . . . .46 4.2.2 APU Precoded SF-OFDM Systems . . . . 48 4.3 Noise Variance of APU Precoded MIMO OFDM System . 50 4.3.1 Noise Variance in APU Precoded ST-OFDM System . .50 4.3.2 Noise Variance in APU Precoded SF-OFDM System . .52 4.4 MMSE for APU Precoded MIMO-OFDM Systems . . . . . .52 4.4.1 APU Precoded ST-OFDM System . . . . . . .53 4.4.2 APU Precoded SF-OFDM System . . . . . . .55 4.5 Simulation and Performance Analysis . . . .56 4.5.1 Uncorrelated Rayleigh Fading Channel . . 57 4.5.2 Spatially Correlated Channel . . . . . . 66 5 Application of MRC Technique to OFDM Systems 71 5.1 MRC in OFDM System . . . . . . . . . . . . 72 5.2 MRC in APU Precoded-OFDM System . . . . . .74 5.2.1 Noise Variance . . . . . . . . . . . 75 5.2.2 MMSE Receiver for APU Precoded-OFDM Systems with MRC Technique . .76 5.3 Comparison of MRC-OFDM and Conventional OFDM . . 77 5.4 OFDM System with a Fractionally Sampled Receiver . .80 5.5 Simulation and Performance Analysis . . . . .89 5.5.1 Uncorrelated Rayleigh Fading Channel . . . .89 6 Conclusion 932440228 bytesapplication/pdfen-US多重天線正交頻率分割多路系統OFDMMRCMultiple antennaAlamoutithesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/58696/1/ntu-93-R91942067-1.pdf