5G NR-밴드 무선 주파수 송수신기의 검증을 위한 모델링 방법

학위논문(석사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2021.8. 김재하.도래한 초연결시대에서는 스마트폰뿐만 아니라 다양한 사물 인터넷 디바이스들이 5세대 이동통신 시스템을 활용하면서, 늘어난 데이터량과 트래픽을 감당하기 위해 밀리미터파 대역의 사용이 필수적일 것이다. 시스템이 보다 대용량화 그리고 광대역화 됨에 따라, 통신 규약을 만족시키기 위해, 점차 거대한 디지털 캘리브레이션 및 신호처리 로직이, 무선 통신 전단부 칩에 함께 집적되고 있다. 따라서 멀티-도메인의 신호(아날로그/디지털/무선통신 신호)가 복잡하게 혼성된 무선통신 집적회로 칩을, 짧은 개발 기간 동안 충분히 검증하기엔 어려움이 따른다. 일반적으로 혼성 신호 시스템을 검증하기 위해서는, 하위 시스템을 모두 포함해서 시간 도메인의 시뮬레이션을 수행해야 하는데, 이를 위한 스파이스와 스파이스-하드웨어 기술 언어의 co-시뮬레이션은 지나치게 느리다는 한계가 있기 때문이다. 따라서, 멀티-도메인의 신호를 빠르고 정확하게 시뮬레이션 가능하게 하는 모델링 방법과, 다양한 시나리오의 검증 완성도를 향상시켜줄 있는 검증 기술이 모두 요구된다. 혼성 시스템을 검증하기 위해서는, 아날로그와 무선 통신 블록들을 시스템 베릴로그 상에서 구현된 함수적 모델로 대체하고, 디지털 블록들과 함께 하나의 디지털 플랫폼에서 시뮬레이션하는 것이 효과적이다. 실제 설계할 때, 문제가 되는 대부분의 에러들은, 연결 오류, 부호 오류, 신호 순서 오류, 혹은 잘못된 파워 도메인과의 연결과 같이 사소한 오류들이다. 이러한 오류를 찾기 위해, 오래 걸리는 트랜지스터-레벨의 시뮬레이션을 수행하기보다는, 아날로그 스파이스 모델들을 시스템 베릴로그 모델들로 대체하고, 보다 다양한 시나리오를 빠르게 검증하는 방법이 검증 완성도를 향상시키는데 적합하다. 그럼에도, 지나치게 단순한 선형 모델이나, 중요한 회로 특성이 빠진 모델로는 원하는 수준의 검증이 불가능할 수 있다. 예를 들어, 직접 변조 구조의 무선통신 송수신기에서 발생하는 비이상 효과, 저전력 동작을 하면서 발생하는 비선형 효과, 그리고 흔히 메모리 효과는 모델에 효과를 충분히 반영해 주어야만, 주파수 도메인에서의 검증, 성능 예측 등의 검증을 의미 있게 수행할 수 있다. 문제는 비선형 시스템은 훨씬 복잡한 식으로 표현되며, 시뮬레이션 시 연산량도 크게 늘어나기 때문에, 비선형 모델을 만들고 시뮬레이션 하기가 쉽지 않다는 것이다. 따라서 모델이 비이상성들을 충분히 반영하면서도 효과적인 검증을 가능하게 하는 모델링/시뮬레이션 방법 역시 요구된다. 본 학위 논문에서는, 무선통신 송수신기 집적회로 전체의 모사 모델을 제안한다. 모델은 누설 신호와 신호 간 불일치에 의한 비-이상적인 효과를 엑스모델의 알고리즘을 활용해 반영하였고, 비선형성과 메모리 효과를 볼테라-섭동법을 활용해 반영하였다. 제안하는 모델은 다양한 주파수 대역과 동작 모드를 검증하는데, 기존 등가 베이스밴드 모델보다 30~1800배 빠르게 시뮬레이션 할 수 있었고, 비이상 효과에 대해, 통신 성능들(심볼의 오류 벡터의 크기, 인접 채널의 파워 그리고 비트 에러)을 평가 가능했다. 나아가, 아날로그 검사기를 활용한 기능 검증법과 모델 파라미터 커버리지 분석법을 적용하여, 시스템-레벨 검증의 완성도를 향상시켰다. 무선통신 집적회로 모델에 다양한 디자인/파라미터 오류를 주입하고, 시뮬레이션 동안 검사기가 찾은 에러의 개수와 커버리지 결과를 실험적으로 보였다.In mobile RF transceiver systems, the large number of digital circuits employed to compensate or calibrate the non-idealities of the RF circuits call for models that can work within the digital verification platform, such as SystemVerilog. While baseband-equivalent real-number models (RNMs) are the current state-of-the-art for modeling RF transceivers in SystemVerilog, their simulation speeds and accuracy are not adequate predicting performance degradation. Since, its signals can only model the frequency components near the carrier frequency but not the DC offsets or high-order harmonic effects arising due to nonlinearities. Therefore, the growing impacts of nonlinearities call for nonlinear modeling of their key components to predict the overall system's performance. This dissertation presents the models for a multi-standard, direct-conversion RF transceiver for evaluating its system-level performance and verifying its digital controllers. Also, this work demonstrates the Volterra series model for the nonlinear analysis of a low-noise amplifier circuit in SystemVerilog, leveraging the functional expression and event-driven simulation capability of XMODEL. The simulation results indicate that the presented models, including the digital configuration/calibration logic for the 5G sub-6GHz-band and mmWave-band transceiver, can deliver 30–1800× higher speeds than the baseband-equivalent RNMs while estimating the quadrature amplitude modulation signal constellation and error vector magnitude in the presence of non-idealities such as nonlinearities, DC offsets, and I/Q imbalances. In addition, it implements functionality checkers and parameter coverage analysis to advance the completeness of system-level verification of the RF transceivers model.Chapter 1. Introduction 1 1.1 Design and Verification Flow . 1.2 5G NR Band RF Transceiver IC . 1.3 Baseband-Equivalent and Passband Modeling . 1.4 Thesis Organization . Chapter 2. Modeling and Simulation of RF Transceiver 11 2.1 Direct Conversion RF Transceiver . 2.2 Proposed Transceiver Models . 2.3 System and Simulation Performance . Chapter 3. Nonlinear RF System Modeling 28 3.1 Volterra / Perturbation Method . 3.2 Low Noise Amplifier Example . 3.3 Nonlinearity Analysis . Chapter 4. Coverage Analysis and Functional Verification 42 4.1 Model Parameter Coverage Analysis . 4.2 Self-Checking Testbench . Chapter 5. Conclusion 54 Appendix 55 A.1 Trigonometric Equation for Non-Ideal Effects . A.2 RNM Baseband Equivalent Modeling . A.3 Parameter Coverage Analysis . A.4 List of Models . Bibliography 63 Abstract in Korean 66석

Living and dealing with RF impairments in communication transceivers

This paper provides an overview of the sources and effects of the RF impairments limiting and rendering the performance of the future wireless communication transceivers costly as well as hindering their wide-spread use in commercial products. As transmission bandwidths and carrier frequencies increase effect of these impairments worsen. This paper studies and presents analytical evaluations of the performance degradation due to the RF impairments in terms of bit-error-rate and image rejection ratio. The paper also give highlights of the various aspects of the research carried out in mitigating the effects of these impairments primarily in the digital signal processing domain at the baseband as well as providing low-complexity hardware implementations of such algorithms incorporating a number of power and area saving techniques

I/Q imbalance mitigation for space-time block coded communication systems

Multiple-input multiple-output (MIMO) space-time block coded (STBC) wireless communication systems provide reliable data transmissions by exploiting the spatial diversity in fading channels. However, due to component imperfections, the in-phase/quadrature (I/Q) imbalance caused by the non-ideal matching between the relative amplitudes and phases of the I and Q branches always exists in the practical implementation of MIMO STBC communication systems. Such distortion results in a complex conjugate term of the intended signal in the time domain, hence a mirror-image term in the frequency domain, in the data structure. Consequently, I/Q imbalance increases the symbol error rate (SER) drastically in MIMO STBC or STBC MIMO orthogonal frequency division multiplexing (OFDM) communication systems, where both the signal and its complex conjugate are utilized for the information transmission, hence should be mitigated effectively. In this dissertation, the impact of I/Q imbalance in MIMO STBC systems over flat fading channels, the impact of I/Q imbalance in STBC MIMO-OFDM systems and in time- reversal STBC (TR-STBC) systems over frequency-selective fading channels are studied systematically. With regard to the MIMO STBC and the STBC MIMO-OFDM systems with I/Q imbalance, orthogonal space-time block codes (OSTBCs), quasi-orthogonal STBCs (QOSTBCs) and rotated QOSTBCs (RQOSTBCs) are studied, respectively. By exploiting the special structure of the received signal, low-complexity solutions are provided to mitigate the distortion induced by I/Q imbalance successfully. In addition, to mitigate I/Q imbalance while at the same time to exploit the multipath diversity for STBC OFDM systems over frequency-selective fading channels, a new encoding/decoing scheme for the grouped linear constellation precoded (GLCP) OFDM systems with I/Q imbalance is studied. In Chapter 1, the objectives of the research are elaborated. In Chapter 2, the various I/Q imbalance models are introduced, and the model used in this dissertation is established. In Chapter 3, the performance degradation caused by I/Q imbalance of the transceivers in MIMO STBC wireless communication systems over flat fading channels and the solutions are studied. A 2 Tx Alamouti system, a 4 Tx quasi-orthogonal STBC (QOSTBC) system, and a 4 Tx rotated QOSTBC (RQOSTBC) system with I/Q imbalance are studied in detail. By exploiting the special structure of the received signal, low-complexity solutions are proposed to mitigate I/Q imbalance successfully. Since STBCs are developed for frequency-flat fading channels, to achieve the spatial diversity in frequency-selective fading channels, MIMO-OFDM arrangements have been suggested, where STBCs are used across different antennas in conjunction with OFDM. In Chapter 4, the performance degradation caused by I/Q imbalance in STBC MIMO-OFDM wireless systems over frequency-selective fading channels and the solutions are studied. Similarly, a 2 Tx Alamouti system, a 4 Tx quasi-orthogonal STBC (QOSTBC) system, and a 4 Tx rotated QOSTBC (RQOSTBC) system with I/Q imbalance are studied in detail, and low-complexity solutions are proposed to mitigate the distortion effectively. However, OFDM systems suffer from the loss of the multipath diversity by converting frequency-selective fading channels into parallel frequency-flat fading subchannels. To exploit the multipath diversity and reduce the decoding complexity, GLCP OFDM systems with I/Q imbalance are studied. By judiciously assigning the mirror-subcarrier pair into one group, a new encoding/decoding scheme with a low-complexity is proposed to mitigate I/Q imbalance for GLCP OFDM systems in Chapter 5. Since OFDM communication systems have high peak-to-average power ratio (PAPR) problem and are sensitive to carrier frequency offset (CFO), to achieve both the spatial and multipath diversity, time-reversal STBC (TR-STBC) communication systems are introduced. In Chapter 6, the I/Q imbalance mitigating solutions in TR-STBC systems, both in the time domain and in the frequency domain, are studied

Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

A low-complexity self-calibrating adaptive quadrature receiver

In this paper digital part of a self-calibrating quadrature-receiver is described, containing a digital calibration-engine. The blind source-separation-based calibration-engine eliminates the RF-impairments in real-time hence improving the receiver's performance without the need for test/pilot tones, trimming or use of power-hungry discrete components. Furthermore, an efficient time-multiplexed calibration-engine architecture is proposed and implemented on an FPGA utilising a reduced-range multiplier structure. The use of reduced-range multipliers results in substantial reduction of area as well as power consumption without a compromise in performance when compared with an efficiently designed general purpose multiplier. The performance of the calibration-engine does not depend on the modulation format or the constellation size of the received signal; hence it can be easily integrated into the digital signal processing paths of any receiver