Equalization and Co-channel Interference Suppression without Spatial Diversity

In a dense urban frequency reuse cellular environment, co-channel interference (CCI) is unavoidable due to channel reuse in neighboring cells. CCI cancellation/suppression is challenging in the downlink, because usually only one receive antenna is available at the subscriber (limited by the size and power consumption) such that the combining techniques can't be applied. Furthermore, CCI has seriously impairment when its power is comparable with the desired signal. The aim of this thesis is to design a receiver with multiuser techniques in the presence of co-channel interference and intersymbol interference (ISI). Two receiver detection schemes: sequence estimation and symbol-by-symbol detection, are considered. For sequence estimation, a linear filter using the interference whitening concept of [20] is used in front of maximum-likelihood sequence estimation equalizer. This front-end linear filter will suppress CCI. For symbol-by-symbol detection, the minimum mean-square error (MMSE) criterion is used for receiver design.Contents Acknowledgements i Abstract ii Contents iii List of Figures vi 1 Introduction 1 1.1 Introduction and Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Co-channel Interference and Multipath-induced Intersymbol Interfer- ence 3 2.1 Mulitpath-induced Intersymbol Interference . . . . . . . . . . . . . . . . 3 2.1.1 Characteristics of Multipath Propagation . . . . . . . . . . . . . . 4 2.1.2 Fading E®ects Due to Multipath Time Delay Spread . . . . . . . 7 2.1.2.1 Flat fading channels . . . . . . . . . . . . . . . . . . . . 7 2.1.2.2 Frequency selective fading channels . . . . . . . . . . . . 7 2.1.3 Fading E®ects Due to Doppler Spread . . . . . . . . . . . . . . . 8 2.1.3.1 Slow fading channels . . . . . . . . . . . . . . . . . . . . 8 2.1.3.2 Fast fading channels . . . . . . . . . . . . . . . . . . . . 8 2.1.4 Modeling Multipath Fading Channels . . . . . . . . . . . . . . . . 8 2.1.4.1 The channel response as an FIR ‾lter . . . . . . . . . . . 9 2.2 Co-channel Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3 Problem Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3 Survey of Interference Suppression Techniques in the Downlink with Single Antenna 13 4 Equalization 15 4.1 Matched Filter Bound (MBF) . . . . . . . . . . . . . . . . . . . . . . . . 15 4.2 Linear equalizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.2.1 Minimum Mean-Square Error (MMSE) Equalizer . . . . . . . . . 17 4.2.2 Result of MMSE-LE in the presence of CCI . . . . . . . . . . . . 20 4.3 Nonlinear equalizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 4.3.1 Minimum Mean-Square Error Decision-Feedback Equalizer (MMSE- DFE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 4.3.2 Result of MMSE-DFE in the presence of CCI . . . . . . . . . . . 27 4.3.3 Maximum-Likelihood Sequence Estimation (MLSE) Equalizer . . 28 5 Equalization with Co-Channel Interference Suppression 32 5.1 Symbol-by-symbol detection . . . . . . . . . . . . . . . . . . . . . . . . . 32 5.1.1 MMSE-LE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 5.1.1.1 MMSE-LE . . . . . . . . . . . . . . . . . . . . . . . . . 32 5.1.1.2 MMSE-LE FIR case . . . . . . . . . . . . . . . . . . . . 34 5.1.2 MMSE-DFE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.1.2.1 MMSE-DFE . . . . . . . . . . . . . . . . . . . . . . . . 36 5.1.2.2 MMSE-DFE FIR case . . . . . . . . . . . . . . . . . . . 40 5.2 Sequence Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 5.2.1 MLSE with Interference Whitening and Pre‾ltering . . . . . . . . 43 5.2.2 Computing Interference-Whitening ‾lter with Linear Prediction ‾lter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 5.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 5.3.1 Result of SINR for MMSE-LE and MMSE-DFE . . . . . . . . . . 47 5.3.2 Result of MLSE with CCI Suppression . . . . . . . . . . . . . . . 49 6 Conclusions and Future Works 53 6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 6.2 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Bibliography 5