Circular components in center of pressure signals

Static posturography provides an objective assessment of postural control by characterizing the body sway during upright standing. The Center-of-Pressure (CoP) signal is recorded by a force platform and it is analyzed by means of many different models and techniques. Most of the parameters calculated according to these different approaches are affected by relevant intra- and inter-subject variability and/or do not have a clear physiological interpretation. Traditional approaches decompose the CoP signal into antero-posterior and medio-lateral time series, corresponding to ankle plantar/dorsiflexion and hip adduction/abduction, respectively. In this study we hypothesized that CoP signals show inherent rotational characteristics. To verify our hypothesis we applied the rotary spectra analysis to the 2-dimensional CoP signal to decompose it into clockwise and counter-clockwise rotational components. We demonstrated the presence of rotational components in the CoP signal of healthy subjects, providing a reference data set of the spectral characteristics of these component

EMULACIÓN EN FPGA DE TECNICA PARA CORRECCION DEL DESEQUILIBRIO I/Q APLICADO EN UN MODULADOR DIGITAL 256-QAM

ResumenEn este trabajo se presenta la metodología de diseño e implementación de un sistema para corrección del desequilibrio I/Q basado en una tarjeta DSP-FPGA. Este sistema utiliza series de Volterra para modelar el comportamiento no lineal del desequilibrio I/Q. El desempeño del sistema se demuestra utilizando una señal compleja 256-QAM con desequilibrio en fase y amplitud. El sistema desarrollado tiene como característica un bajo costo de implementación y alta flexibilidad del diseño, lo que permite modificaciones o expansiones futuras. Se utiliza la tarjeta de desarrollo Stratix III de Altera para implementación practica y verificación de los resultados experimentales del sistema propuesto. El sistema desarrollado es capaz de corregir el desequilibrio I/Q satisfactoriamente, tanto en fase como en amplitud. Este trabajo puede ser considerado como una alternativa de bajo costo para corregir el desequilibrio I/Q ya que no requiere de algoritmos complejos o equipo de medición adicional.Palabras Claves: 256-QAM, corrección, desequilibrio, FPGA, modulador.EMULATION IN FPGA OF TECHNIQUE FOR CORRECTION OF IMBALANCE I/Q APPLIED IN A DIGITAL MODULATOR 256-QAMAbstractIn this paper the design methodology for a I/Q imbalance correction system is presented based on a DSP-FPGA board. This system employs Volterra series to model the non-linear behavior of the I/Q imbalance. The system performance is verified using a 256-QAM complex signal with phase and amplitude imbalance. The implemented system has the advantage of having low implementation cost and a high design flexibility, which allows for future revisions or enhancement. The Stratix III FPGA board from Altera is employed for the practical implementation and result verification of the system. The developed system can compensate the I/Q imbalance, in amplitude and phase. This work can be considered as a low-cost alternative for I/Q imbalance correction given that it doesn’t require additional measurement equipment nor uses complex algorithms.Keywords: 256-QAM, correction, imbalance, FPGA, modulator

Complex-Valued Random Vectors and Channels: Entropy, Divergence, and Capacity

Recent research has demonstrated significant achievable performance gains by exploiting circularity/non-circularity or propeness/improperness of complex-valued signals. In this paper, we investigate the influence of these properties on important information theoretic quantities such as entropy, divergence, and capacity. We prove two maximum entropy theorems that strengthen previously known results. The proof of the former theorem is based on the so-called circular analog of a given complex-valued random vector. Its introduction is supported by a characterization theorem that employs a minimum Kullback-Leibler divergence criterion. In the proof of latter theorem, on the other hand, results about the second-order structure of complex-valued random vectors are exploited. Furthermore, we address the capacity of multiple-input multiple-output (MIMO) channels. Regardless of the specific distribution of the channel parameters (noise vector and channel matrix, if modeled as random), we show that the capacity-achieving input vector is circular for a broad range of MIMO channels (including coherent and noncoherent scenarios). Finally, we investigate the situation of an improper and Gaussian distributed noise vector. We compute both capacity and capacity-achieving input vector and show that improperness increases capacity, provided that the complementary covariance matrix is exploited. Otherwise, a capacity loss occurs, for which we derive an explicit expression.Comment: 33 pages, 1 figure, slightly modified version of first paper revision submitted to IEEE Trans. Inf. Theory on October 31, 201

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

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

Techniques for low-cost spectrum analysis on quadrature demodulation architectures

The Decimator, an SED Systems Ltd. product, is a PCI slot card that performs both time and frequency domain measurements of given input signals. It is essentially a more economical version of a bench spectrum analyzer or oscilloscope, with a PC interface. Several issues limit the speed and accuracy of the results of the Decimator, and the study of these issues is the focus of this thesis. These issues, including but not limited to, are as follows: 1) Imbalances between the received In-phase and Quadrature-phase channels; 2) The FFT and Windowing functions are performed by a microcontroller, but it is desired that they be migrated to an FPGA. While solutions to improve the first issue is being implemented and verified, the second issue is not one of simply reducing a source of error. The second issue requires a cost-benefit analysis on the migration of these signal processing algorithms from an ARM microcontroller to a Xilinx FPGA

Modeling and Digital Mitigation of Transmitter Imperfections in Radio Communication Systems

To satisfy the continuously growing demands for higher data rates, modern radio communication systems employ larger bandwidths and more complex waveforms. Furthermore, radio devices are expected to support a rich mixture of standards such as cellular networks, wireless local-area networks, wireless personal area networks, positioning and navigation systems, etc. In general, a "smart'' device should be flexible to support all these requirements while being portable, cheap, and energy efficient. These seemingly conflicting expectations impose stringent radio frequency (RF) design challenges which, in turn, call for their proper understanding as well as developing cost-effective solutions to address them. The direct-conversion transceiver architecture is an appealing analog front-end for flexible and multi-standard radio systems. However, it is sensitive to various circuit impairments, and modern communication systems based on multi-carrier waveforms such as Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) are particularly vulnerable to RF front-end non-idealities.This thesis addresses the modeling and digital mitigation of selected transmitter (TX) RF impairments in radio communication devices. The contributions can be divided into two areas. First, new modeling and digital mitigation techniques are proposed for two essential front-end impairments in direct-conversion architecture-based OFDM and OFDMA systems, namely inphase and quadrature phase (I/Q) imbalance and carrier frequency offset (CFO). Both joint and de-coupled estimation and compensation schemes for frequency-selective TX I/Q imbalance and channel distortions are proposed for OFDM systems, to be adopted on the receiver side. Then, in the context of uplink OFDMA and Single Carrier FDMA (SC-FDMA), which are the air interface technologies of the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and LTE-Advanced systems, joint estimation and equalization techniques of RF impairments and channel distortions are proposed. Here, the challenging multi-user uplink scenario with unequal received power levels is investigated where I/Q imbalance causes inter-user interference. A joint mirror subcarrier processing-based minimum mean-square error (MMSE) equalizer with an arbitrary number of receiver antennas is formulated to effectively handle the mirror sub-band users of different power levels. Furthermore, the joint channel and impairments filter responses are efficiently approximated with polynomial-based basis function models, and the parameters of basis functions are estimated with the reference signals conforming to the LTE uplink sub-frame structure. The resulting receiver concept adopting the proposed techniques enables improved link performance without modifying the design of RF transceivers.Second, digital baseband mitigation solutions are developed for the TX leakage signal-induced self-interference in frequency division duplex (FDD) transceivers. In FDD transceivers, a duplexer is used to connect the TX and receiver (RX) chains to a common antenna while also providing isolation to the receiver chain against the powerful transmit signal. In general, the continuous miniaturization of hardware and adoption of larger bandwidths through carrier aggregation type noncontiguous allocations complicates achieving sufficient TX-RX isolation. Here, two different effects of the transmitter leakage signal are investigated. The first is TX out-of-band (OOB) emissions and TX spurious emissions at own receiver band, due to the transmitter nonlinearity, and the second is nonlinearity of down-converter in the RX that generates second-order intermodulation distortion (IMD2) due to the TX in-band leakage signal. This work shows that the transmitter leakage signal-induced interference depends on an equivalent leakage channel that models the TX path non-idealities, duplexer filter responses, and the RX path non-idealities. The work proposes algorithms that operate in the digital baseband of the transceiver to estimate the TX-RX non-idealities and the duplexer filter responses, and subsequently regenerating and canceling the self-interference, thereby potentially relaxing the TX-RX isolation requirements as well as increasing the transceiver flexibility.Overall, this thesis provides useful signal models to understand the implications of different RF non-idealities and proposes compensation solutions to cope with certain RF impairments. This is complemented with extensive computer simulations and practical RF measurements to validate their application in real-world radio transceivers