증폭 후 전달 릴레이 시스템에서 I/Q 불균형을 고려한 검출 기법 = Detectors in Amplify-Forward Relay Systems under I/Q Imbalance

다국어 초록 (Multilingual Abstract)

This thesis investigates the impact of in-phase/quadrature-phase imbalance (IQI) on amplify-forward (AF) relay communication systems consisting of single-antenna source, relay, and destination nodes. In-phase/quadrature-phase (I/Q) signal processing is a fundamental analog bandpass technique widely used in receiver down-conversion. However, unavoidable hardware imperfections introduce amplitude and phase mismatches between the I and Q branches, resulting in IQI and consequent performance degradation.
Although prior studies on IQI have been conducted in relay channel environments, most existing works are restricted to simplified scenarios—either assuming the absence of a direct source–destination (sd) link or neglecting the IQI at the relay node even when the sd link is present. As a result, a comprehensive and systematic investigation of AF relay systems in which IQI is present at all nodes has not yet been reported. Furthermore, the majority of existing approaches focus on IQI compensation in the complex-valued domain. Such methods not only suffer from inherent performance limitations due to the representational constraints of complex-valued channel models, but also result in highly complicated signal expressions.
To address these limitations, this thesis systematically analyzes the impact of IQI in AF relay channels by considering various detection schemes in both the complex-valued and real-valued domains. First, signal detection techniques based on complex-domain channel models are introduced. Subsequently, an equivalent real-domain system representation is derived, and corresponding real-domain detection methods are developed.
In the complex domain, complex-domain minimum distance (CMD) detection and complex-domain zero-forcing (CZF) detection are formulated without explicitly accounting for noise statistics, due to the difficulty of accurately modeling the noise covariance matrix. In addition, a widely linear complex-domain zero-forcing (WLCZF) detector is applied by employing an augmented received signal vector that includes both the original signal and its conjugate. However, these complex-domain detection schemes exhibit limited performance since they fail to fully capture the statistical characteristics of the noise.
To overcome this drawback, the complex-domain system is transformed into an equivalent real-domain model. Based on this representation, an optimal maximum-likelihood (ML) detector and several low-complexity linear detectors are proposed. Although the ML detector achieves optimal performance, its computational complexity limits its practical applicability. Therefore, real-domain zero-forcing (ZF), best linear unbiased (BLU), and linear minimum mean square error (LMMSE) detectors are developed as practical alternatives. Among these, the BLU and LMMSE detectors achieve near-optimal ML performance with significantly reduced computational complexity.
Furthermore, pairwise error probabilities (PEPs) for the proposed detection schemes are derived, and union bounds on the average symbol error probabilities (SEPs) are obtained. These analytical results provide valuable theoretical insights into the performance of AF relay systems affected by IQI.
Both theoretical analysis and simulation results demonstrate that the proposed real-domain detection techniques achieve excellent error performance with reasonable computational complexity. In particular, the BLU and LMMSE detectors closely approach ML performance while remaining well suited for practical implementation in real-world AF relay systems impaired by IQI.

목차 (Table of Contents)

• 1 서론 1
• 2 복소수 도메인에서 AF-IQI 통신 시스템 5
• 2.1 점대점(P2P) 시스템에서 IQI 모델 5
• 2.2 AF 릴레이 채널 모델 8
• 2.3 복소수 도메인에서 AF-IQI 채널 모델 9
• 2.4 검출 기법 11
• 2.4.1 켤레 수신 신호를 활용하지 않는 검출 12
• 2.4.2 켤레 수신 신호를 활용하는 검출 13
• 3 실수 도메인에서 AF-IQI 통신 시스템 16
• 3.1 시스템 모델 16
• 3.2 검출 기법 18
• 3.2.1 최대 우도(ML) 검출 18
• 3.2.2 선형 검출 19
• 4 시스템 성능 분석 23
• 4.1 복소수 도메인 23
• 4.2 실수 도메인 27
• 4.3 계산 복잡도 32
• 5 모의실험 결과 34
• 6 결론 40
• 부록 1 41
• 부록 2 42
• 부록 3 44
• 참고문헌 48