陳光禎臺灣大學：電信工程學研究所倪慶昇Ni, Ching-ShengChing-ShengNi2007-11-272018-07-052007-11-272018-07-052005http://ntur.lib.ntu.edu.tw//handle/246246/58700Inspired by the multiuser detection theory, we exploit the signal structure of the sub-carriers and develop multiuser detectors to suppress co-channel interference (CCI) of unknown statistics for orthogonal frequency division multiplexing (OFDM) systems by considering each sub-carrier as an individual user and CCI as other unknown users. The linear minimum mean square error multiuser detectors (LMMSE MUD) of sub-carriers are proposed, which require no a prior information of CCI by using adaptive implementations. With known received waveforms of all sub-carriers, the proposed multistage interference canceller (MIC) based on multistage MUD improves the LMMSE MUD by eliminating the residual interference from other sub-carriers in the soft estimate of the LMMSE MUD by making use of tentative decisions. With the information of fre-quency location of the partial-band CCI, the LMMSE MUD and the MIC are proposed in frequency domain to significantly reduce the complexity with similar performance according to the complexity analysis. When the tentative decisions are highly reliable, further improvements can be achieved by the enhanced multistage interference canceller (EMIC) which replaces the combining at the second stage of the MIC. With the our developed algorithm, the combining of the EMIC can be correctly generated from those of the LMMSE MUDs of interfered sub-carriers, which shows the EMIC can be realized without a prior information of CCI. In OFDM systems with mutually un-orthogonal sub-carriers, the complexity to generate the combining of the EMIC is huge even if the CCI is a very narrowband signal. To reduce the complexity of the EMIC, the generalized multistage interference canceller (GMIC), an intermediate mode of the MIC and the EMIC, is proposed whose combining only assumes couples of adjacent sub-carriers of the desire sub-carrier are precisely removed. Due to the high sensitivity of the EMIC to the incorrect tentative decisions, the GMIC even outperforms the EMIC in OFDM systems with mutually un-orthogonal sub-carriers. The GMIC along with the generalized parameter generation algorithm is proposed to jointly suppress CCI and ICI over time-varying channels.Abstract i Contents iii 1 Introduction 1 1.1 An Introduction to Orthogonal frequency division multiplexing (OFDM) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 The Importance of Co-Channel Interference Suppression for OFDM . . . 4 1.3 Interference Suppression in Spread-Spectrum Systems . . . . . . . . . . . 5 1.3.1 Predictive Techniques . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.2 Multiuser Detection (MUD) Techniques . . . . . . . . . . . . . . 7 1.3.3 Interference Suppression in OFDM Systems . . . . . . . . . . . . 8 1.4 Preview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 Co-Channel Interference Suppression based on Multiuser Detectors over Stationary Multipath Channels 10 2.1 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.1 Co-Channel Interference Suppression in DS-CDMA Systems . . . 11 2.2 Signal Model and Assumptions . . . . . . . . . . . . . . . . . . . . . . . 12 2.3 Co-Channel Interference Suppression based on the Linear Minimum Mean- Square Error (LMMSE) Multiuser Detector (MUD) . . . . . . . . . . . . 14 2.4 The Multistage Interference Canceller (MIC) . . . . . . . . . . . . . . . . 16 2.5 Adaptive Implementation of the LMMSE MUD and the MIC . . . . . . . 19 2.5.1 Data-Aided Recursive Least-Square RLS Adaptive Implementa- tion of the LMMSE MUD and the MIC . . . . . . . . . . . . . . . 20 2.5.2 Complexity Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.6 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.6.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.6.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3 Frequency-Domain Multiuser Detectors to Suppress Partial-Band Co- Channel Interference over Stationary Multipath Channels 30 3.1 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.2 Signal Model and Assumptions . . . . . . . . . . . . . . . . . . . . . . . 31 3.2.1 The Frequency-Domain LMMSE MUD . . . . . . . . . . . . . . . 33 3.2.2 The Frequency-Domain MIC . . . . . . . . . . . . . . . . . . . . . 35 3.3 Adaptive Implementation of the Frequency-Domain LMMSE MUD and the MIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.3.1 Data-Aided Recursive Least-Square Adaptive Implementation of the LMMSE MUD and the MIC . . . . . . . . . . . . . . . . . . . 37 3.4 Complexity Analysis of Time-Domain Suppression and Frequency-Domain Suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.4.1 Complexity Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.4.2 A Practical Example . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.5 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.5.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4 The Frequency-Domain Enhanced Multistage Interference Canceller to Suppress Partial-Band Co-Channel Interference over Stationary Mul- tipath Channels 45 4.1 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.2 Signal Model and Assumptions . . . . . . . . . . . . . . . . . . . . . . . 46 4.3 The Frequency-Domain Enhanced Multistage Interference Canceller (EMIC) 49 4.3.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.3.2 The Frequency-Domain EMIC . . . . . . . . . . . . . . . . . . . . 50 4.4 The Implementation of the Frequency-Domain EMIC . . . . . . . . . . . 51 4.4.1 The Parameter Generation Algorithm of the Frequency-Domain EMIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 4.4.2 The Generalized Parameter Generation Algorithm for the EMIC . 54 4.4.3 Complexity Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.5 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 4.5.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 4.5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 5 Frequency-Domain Joint Suppression of Partial-Band Co-Channel In- terference and Inter-Carrier Interference for Zero-Padding OFDM Sys- tems over Stationary Multipath Channels 63 5.1 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.2 Signal Model and Assumptions . . . . . . . . . . . . . . . . . . . . . . . 64 5.3 The Complexity of the Frequency-Domain Enhanced Multistage Interfer- ence Canceller (EMIC) for ZP-OFDM without OLA . . . . . . . . . . . . 68 5.4 The Frequency-Domain Generalized Multistage Interference Canceller (GMIC) for ZP-OFDM without OLA . . . . . . . . . . . . . . . . . . . . . . . . 69 5.5 Application 1: ZP-OFDM Operating at 2.4GHz ISM Band with GFSK Interferers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 5.5.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 5.5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 5.6 Application 2: Multi-Band (MB) OFDM for Ultra-Wide Band Communi- cations in the Presence of Uncoordinated Simultaneously Operating MB- OFDM Piconets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 5.6.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 5.6.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 6 Future Work 80 6.1 Frequency-Domain Joint Suppression of Partial-Band Co-Channel Inter- ference and Inter-Carrier Interference for OFDM Systems over Time- Varying Multipath Channels . . . . . . . . . . . . . . . . . . . . . . . . . 80 6.1.1 Signal Model and Assumptions . . . . . . . . . . . . . . . . . . . 80 6.1.2 The Frequency-Domain Generalized Multistage Interference Can- celler (GMIC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 6.1.3 The Implementation of GMIC in Time-Varying Channels . . . . . 84 6.2 Frequency-Domain Joint Suppression of Partial-Band Co-Channel Inter- ference and Inter-Carrier Interference for OFDMA Systems over Time- Varying Multipath Channels . . . . . . . . . . . . . . . . . . . . . . . . . 85 7 Conclusions 86 Bibliography 86en-US正交分頻多工系統共通道雜訊OFDMCo-Channel Interferencethesis