Quadrature Channels Research Articles

A Novel Equalizer for 112 Gb/s CAP-Based Data Transmission Over 150 m MMF Links

In this paper a novel feedforward and decision feedback equalizer is proposed for the first time for use in short-reach high-speed communication links based on carrierless amplitude and phase (CAP) modulation. The proposed new equalizer mitigates crosstalk between the in-phase (I-) and quadrature (Q-) channels resulting from the non-linear phase response of the link enabling significant improvement in the link performance when operating at high data rates. The structure of this novel equalizer is introduced, its operation is described, and simulation and experimental studies on short-reach high-speed MMF links using 850 nm multimode VCSELs are presented. Data transmission tests are carried out over 150 m of OM4 MMF at 112 Gb/s using CAP modulation and the proposed CAP equalizer, and a bit-error-rate (BER) within the hard-decision forward error-correction (HD-FEC) threshold of 3.8 × 10−3 is achieved. The link is also tested when a conventional equalizer is used instead of the CAP equalizer and when adaptive discrete multitone (DMT) modulation is applied. The performance of the link is compared for these different transmission schemes and it is shown that the use of the novel equalizer and CAP modulation outperforms the other two schemes. The proposed equalizer can be implemented with low additional complexity, providing a potential cost-effective solution enabling >100 Gb/s single-lane data transmission in short-reach MMF-based links.

Coherent ePIC Receiver for 64 GBaud QPSK in 0.25 μm Photonic BiCMOS Technology

In this paper, we present a monolithically integrated coherent receiver with on-chip grating couplers, 90° hybrid, photodiodes and transimpedance amplifiers. A transimpedance gain of 7.7 kΩ was achieved by the amplifiers. An opto-electrical 3 dB bandwidth of 34 GHz for in-phase and quadrature channel was measured. A real-time data transmission of 64 GBd-QPSK (128 Gb/s) for a single polarization was performed.

ОЦІНКА ЕФЕКТИВНОСТІ ПОЛЯРИЗАЦІЙНОЇ СЕЛЕКЦІЇ ЦІЛІ НА ФОНІ ПАСИВНОЇ ПЕРЕШКОДИ ЗА ДОПОМОГОЮ ПРИСТРОЮ, ЯКИЙ ВРАХОВУЄ ПРОСТОРОВІ ЗМІНИ КУТА ФАРАДЕЄВСЬКОГО ОБЕРТАННЯ В ІОНІЗОВАНОМУ СЕРЕДОВИЩІ В ПЛОЩИНІ ПОЛЯРИЗАЦІЇ СИГНАЛУ

The paper analyzes the studies of incoherently scattered ionospheric radio signals of long duration. The depolarization of the incoherently scattered signal was experimentally of incoherently scattered detected, which is due to the spatial variation of the Faraday rotation angle in the ionosphere of the signal polarization plane. It is proposed to use this effect for polarization selection of simple geometric shapes against the background of interference reflections from inhomogeneities in the electron concentration of the ionized medium. Also, a device was developed that implements the proposed method of polarization target selection. The scheme of the proposed polarization selection device contains two circular polarization antennas of the opposite direction of rotation, two optimal filters, two quadrature channels of synchronous detectors, four multipliers, two adders, two narrowband filters and a functional converter. It is assumed that the transmitting antenna is linearly polarized. In order to determine the operability of the device under various conditions and to evaluate its efficiency, the signal-to-noise ratio at the output of the device is calculated in the case where the backscattering matrix of the target and the matrix of the interference element (for example, dipole, angle reflector, etc.) are not diagonal, m .e. when a cross-polarization component appears when the signal from the target or from the interference element is reflected.

A mode-matched force-rebalance control for a MEMS vibratory gyroscope

The force-to-rebalance (FTR) closed-loop control is widely used in MEMS vibratory gyroscopes. However, most of these applications may operate in split modes, as mode matching is usually conducted open loop. There is a lack of discussion explicitly addressing the significance of mode matching in the FTR operation mode. This paper investigates the influence of mode mistuning on the FTR closed-loop control of a MEMS Coriolis vibratory gyroscope (CVG), and proposes a novel tuning method using real time control forces to achieve a mode-matched FTR control. The analysis and design of the FTR is based on the time averaged equations of motion, where the sense mode vibration is decomposed into the quadrature and in-phase channels with cross coupling determined by the frequency mismatch between the drive and sense modes of vibration. The control design is treated as a 2 × 2 multivariable control problem using the individual channel design (ICD) framework. Independent control design for each of the two channels allows the bandwidth of the quadrature loop to be significantly less than the in-phase loop. The characteristics of mode mistuning can be extracted from the real time feedback forces. Using this information, the desirable mode-matched uncoupled FTR can be implemented. The FTR closed-loop control eliminates the influences of frequency mismatch on the zero rate output and linearity of the scale factor. It therefore relaxes the degree to which the modes need to be tuned. It is shown in this study that matching the modes in the FTR control scheme improves noise performance and measurement accuracy over the non-tuned case. Experimental results of real time FTR control and Allan deviation tests are provided to verify the analysis.

Frequency downconversion with independent multichannel phase shifting and zero-intermediate-frequency receiving based on optical frequency shift and polarization multiplexing.

Photonic microwave frequency downconversion with independent multichannel phase shifting and zero-intermediate-frequency (IF) receiving via an integrated polarization multiplexing dual-parallel Mach-Zehnder modulator (MZM) is proposed. Based on the ideas of optical frequency shift and polarization multiplexing, the radio frequency (RF) signal is frequency downconverted to multichannel IF signals with the phases independently and arbitrarily tuned by adjusting the polarization controllers or even frequency downconverted to baseband directly by choosing two quadrature channels. In the simulation, the gain of our proposed frequency downconversion system is higher than that of the conventional two cascaded MZMs' system, and the phase shift with the range of 360° can be obtained concurrently. Furthermore, 2.5Gbit/s RF vector signals centered at 10GHz with different modulation formats are successfully demodulated.

Digital Complex Delta–Sigma Modulators With Highly Configurable Notches for Multi-Standard Coexistence in Wireless Transmitters

This paper presents a complex delta–sigma modulator (CDSM) designed for integration in a digital transmitter chain targeting multi-standard coexistence with nearby receivers. The use of a DSM has the advantage of increased performance in terms of signal-to-noise-ratio in the band of interest. However, the resulting out-of-band noise becomes an issue for multi-standard coexistence, thus increasing the complexity of the subsequent filtering stage. This constraint could be relaxed in the DSM stage, by placing a complex zero near the frequency band, where a low noise level is needed. This is achieved by cross coupling the in-phase (I) and quadrature (Q) channels, thus obtaining a CDSM. A review of known design methods for CDSM revealed limitations regarding the poles/zeros optimization, and the configurability of the complex zeros placement. The proposed architecture introduces two additional cross couplings from the I and Q quantizers outputs in order to decorrelate the zeros placement and the poles optimization problem. Hence, the improved CDSM can be implemented using existing optimization tools, which reduces considerably the number of iterations and the computational effort. In addition, the resulting modulator can target different coexistence scenarios without the need of redesign, unlike other known methods. Simulation results show a noise level reduction of approximately 20–30-dB near specific frequency bands by the proposed CDSM scheme with respect to standard DSM. Finally, we show an efficient coarse/fine configurability mechanism, which is obtained when introducing additional delays in the cross-coupling paths.

A Detection Algorithm for the BOC Signal Based on Quadrature Channel Correlation

In order to solve the problem of detecting a BOC signal, which uses a long-period pseudo random sequence, an algorithm is presented based on quadrature channel correlation. The quadrature channel correlation method eliminates the autocorrelation component of the carrier wave, allowing for the extraction of the absolute autocorrelation peaks of the BOC sequence. If the same lag difference and height difference exist for the adjacent peaks, the BOC signal can be detected effectively using a statistical analysis of the multiple autocorrelation peaks. The simulation results show that the interference of the carrier wave component is eliminated and the autocorrelation peaks of the BOC sequence are obtained effectively without demodulation. The BOC signal can be detected effectively when the SNR is greater than −12 dB. The detection ability can be improved further by increasing the number of sampling points. The higher the ratio of the square wave subcarrier speed to the pseudo random sequence speed is, the greater the detection ability is with a lower SNR. The algorithm presented in this paper is superior to the algorithm based on the spectral correlation.

A novel transmitter IQ imbalance and phase noise suppression method utilizing pilots in PDM CO-OFDM system

In this paper, we develop a novel pilot structure to suppress transmitter in-phase and quadrature (Tx IQ) imbalance, phase noise and channel distortion for polarization division multiplexed (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. Compared with the conventional approach, our method not only significantly improves the system tolerance of IQ imbalance as well as phase noise, but also provides higher transmission speed. Numerical simulations of PDM CO-OFDM system is used to validate the theoretical analysis under the simulation conditions: the amplitude mismatch 3 dB, the phase mismatch 15°, the transmission bit rate 100 Gb/s and 560 km standard signal-mode fiber transmission. Moreover, the proposed method is 63% less complex than the compared method.

Simultaneously frequency down-conversion, independent multichannel phase shifting and zero-IF receiving using a phase modulator in a sagnac loop and balanced detection

Photonic microwave frequency down-conversion with independent multichannel phase shifting and zero-intermediate frequency (IF) receiving is proposed and demonstrated by simulation. By combined use of a phase modulator (PM) in a sagnac loop and an optical bandpass filter (OBPF), orthogonal polarized carrier suppression single sideband (CS-SSB) signals are obtained. By adjusting the polarization controllers (PCs) to introduce the phase difference in the optical domain and using balanced detection to eliminate the direct current components, the phase of the generated IF signal can be arbitrarily tuned. Besides, the radio frequency (RF) vector signal can be also frequency down-converted to baseband directly by choosing two quadrature channels. In the simulation, high gain and continuously tunable phase shifts over the 360 degree range are verified. Furthermore, 2.5 Gbit/s RF vector signals centered at 10 GHz with different modulation formats are successfully demodulated.

Quadrature Channel Modulation

In this letter, we propose the concept of quadrature channel modulation (QCM) by combining quadrature spatial modulation (QSM) and media-based modulation (MBM) transmission principles. The proposed QCM schemes exploit not only the in-phase and quadrature components of complex data symbols for antenna indexing but also channel states for the transmission of additional information bits through index modulation by employing a single radio frequency (RF) chain. It is shown via numerical studies that the proposed QCM schemes can outperform the existing emerging schemes such as QSM, plain MBM, and spatial modulation-based MBM, which also employ a single RF chain at their transmitters.

The Features of the Frequency-Modulation Method When Studying the Shapes of the Spectral Lines of Nonlinear Absorption

We briefly consider the method of the frequency (phase) modulation and signal detection at the second harmonic of the modulation frequency for recording and analyzing the spectral-line shapes. The precision sub-Doppler spectrometer in the millimeter- and submillimeter-wave ranges, which operated in the regime of nonlinear saturation of the spectral transitions in a standing wave (the Lamb-dip method), was used during the measurements. The influence of the saturation degree on the value and shape of the recorded frequency-modulated signals in the quadrature channels during the synchronous detection is demonstrated. Variation in the relationships among the signals determined by dispersion and absorption was observed. The necessity of allowance for the influence of the group-velocity dispersion and coherent effects on the shape of the recorded spectral lines is experimentally shown.

Low-Complexity Sliding Window Block Decoding Using Bit-Flipping for OVFDM Systems

Overlapped frequency division multiplexing (OVFDM) systems can obtain high spectral efficiency (SE), which is proportional to the constraint length. However, high decoding complexity imposes the main challenge on OVFDM systems. This paper proposes a low-complexity sliding window (SW) block decoding algorithm for OVFDM systems, where data symbols are estimated based on the reception of a SW instead of a date frame. Specifically, block code of each SW is decoded by bit-flipping algorithm where the bits to be flipped are selected according to the largest absolute value criterion. Using this criterion, the complexity to obtain the near optimal bit-flipping vector grows only linearly with the SW length. In addition, the study of the decoding algorithm is based on the design of OVFDM encoding structure, where symbols can occupy orthogonal in-phase and quadrature channels simultaneously to further improve SE by a factor of two. Simulation results show that OVFDM SW decoding with bit-flipping algorithm can be used when constraint length is relatively high (constraint length ≥ 20) because the complexity goes roughly linearly with the increase of constraint length.

Simultaneously photonic frequency downconversion, multichannel phase shifting, and IQ demodulation for wideband microwave signals.

A single photonic system that can simultaneously perform frequency downconversion, multichannel phase shifting, and in-phase (I) and quadrature (Q) demodulation for microwave signals is proposed and experimentally demonstrated. Using an integrated polarization-division multiplexing Mach-Zehnder modulator, radio frequency (RF) signals can be frequency downconverted to multichannel intermediate frequency (IF) signals and the phase of each IF signal can be independently and arbitrarily tuned. Using two quadrature channels, the RF signal can be IQ demodulated. In the experiment, high and flat conversion gains from 8 to 40 GHz and continuously tunable phase shifts over the 360-deg range are demonstrated. In addition, vector signals with various modulation formats at 40 GHz are frequency downconverted to baseband and the IQ data are successfully extracted.

Simultaneous measurement of magnetic and density fluctuations via cross-polarization scattering and Doppler backscattering on the DIII-D tokamak.

An upgraded cross-polarization scattering (CPS) system for the simultaneous measurement of internal magnetic fluctuations B̃ and density fluctuations ñ is presented. The system has eight radial quadrature channels acquired simultaneously with an eight-channel Doppler backscattering system (measures density fluctuations ñ and flows). 3-D ray tracing calculations based on the GENRAY ray tracing code are used to illustrate the scattering and geometric considerations involved in the CPS implementation on DIII-D. A unique quasi-optical design and IF electronics system allow direct comparison of B̃ and ñ during dynamic or transient plasma events (e.g., Edge Localized Modes or ELMs, L to H-mode transitions, etc.). The system design allows the interesting possibility of both magnetic-density (B̃-ñ) fluctuation and magnetic-temperature (B̃-T̃) fluctuation cross-phase measurements suitable for detailed tests of turbulence simulations.

Low Complexity Switched Soft Demapper for Rotated QAM Constellations

In the digital video broadcasting-second generation terrestrial standard, the constellation rotation and cyclic Q-delay techniques have been adopted to improve the bit error rate performance in fading channels. However, they would lead to a substantially increased demapping complexity at the receiver. In order to reduce the demapping complexity, we propose a switched soft demapper, where different demapping algorithms with different level of complexities can be selected according to the in-phase (I) and the quadrature (Q) channel fading conditions. A decision block is applied to determine the demapping algorithm. Three kinds of decision criteria are discussed and compared to verify that the decision criterion has an impact on the performance of the soft demapper. In addition, the algorithm that determines the threshold in the decision block is presented. For the rotated 64-QAM, the performance loss of the proposed demapping scheme is proved to be negligible if a suitable threshold is applied, while the demapping complexity is reduced by up to 77% in Rayleigh fading channel without erasures. For the rotated 256-QAM, the complexity is reduced by up to 95% in Rayleigh fading channel without erasures.

Generalized Transmitter Compensation of Frequency Dependent I/Q Imbalance

This paper considers the formulation of a digital pre-distorter to eliminate distortions that are generated by a frequency-dependent imbalance between the analog in-phase (I) and quadrature (Q) channels of a direct conversion transmitter. Estimation of the imbalance occurs in the frequency domain, while compensation occurs in the time domain. We demonstrate the efficacy of the approach by estimating and eliminating transmitter distortions whose digital-to-analog converters (DACs) and filters have differing impulse responses, as well as a phase and amplitude imbalance between the local oscillators (LOs). The estimator developed includes a separation of the linear and nonlinear transmitter response, facilitating the application of nonlinear pre-distortion without architectural restriction. Furthermore, the estimator not only compensates for I/Q imbalances, but fully characterizes the frequency response and identifies the source of the imbalance. An interesting outcome of the analysis is that it may not be possible with baseband processing to compensate for an imbalance that occurs after up-conversion but prior to I/Q summing.

A Differential Monolithically Integrated Inductive Linear Displacement Measurement Microsystem.

An inductive linear displacement measurement microsystem realized as a monolithic Application-Specific Integrated Circuit (ASIC) is presented. The system comprises integrated microtransformers as sensing elements, and analog front-end electronics for signal processing and demodulation, both jointly fabricated in a conventional commercially available four-metal 350-nm CMOS process. The key novelty of the presented system is its full integration, straightforward fabrication, and ease of application, requiring no external light or magnetic field source. Such systems therefore have the possibility of substituting certain conventional position encoder types. The microtransformers are excited by an AC signal in MHz range. The displacement information is modulated into the AC signal by a metal grating scale placed over the microsystem, employing a differential measurement principle. Homodyne mixing is used for the demodulation of the scale displacement information, returned by the ASIC as a DC signal in two quadrature channels allowing the determination of linear position of the target scale. The microsystem design, simulations, and characterization are presented. Various system operating conditions such as frequency, phase, target scale material and distance have been experimentally evaluated. The best results have been achieved at 4 MHz, demonstrating a linear resolution of 20 µm with steel and copper scale, having respective sensitivities of 0.71 V/mm and 0.99 V/mm.

Optimization and comparison of two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging.

In this study, two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging (MRI) were designed and compared. Two 1.5 T dual-tuned birdcages, a four-ring birdcage (FRB) and an alternating rungs birdcage (ARB), were built and then characterized by bench and MRI measurements. The relative uniformity (RU) and the efficiency of the coils were compared using (23)Na and (1)H B1 maps. In vivo images of a volunteer were acquired. Bench measurements showed matching and decoupling coefficients of the quadrature channels lower than -20 dB. The RUs and 180° pulse amplitudes of the FRB/ARB were determined as: (1)H RU =94.4/74.4%, (23)Na RU =95.2/93.6%, (1)H 180° pulse amplitude =69.2/75.4 V and (23)Na 180° pulse amplitude =45.1/45.9 V. The in vivo (23)Na images acquired with the FRB show a signal-to-noise ratio (SNR) of 6 to 14 in the cartilage. Due to its superior (1)H homogeneity and efficiency and its slightly better (23)Na homogeneity, the FRB is the overall preferred coil for the given requirements of this study. The achieved in vivo SNR is adequate for quantitative (23)Na and high resolution (1)H imaging.

Channel Imbalance Effects and Compensation for Doppler Radar Physiological Measurements

Effects of quadrature channel imbalance on Doppler radar physiological measurements, and new compensation methods, are investigated in this paper. Parametric simulations and experiments were performed to investigate the effects of amplitude imbalance, phase imbalance, and initial phase on Doppler radar obtained pattern, displacement, and rate estimation. It is demonstrated that channel imbalance can introduce significant displacement error, and that error is sensitive to initial phase. Furthermore, it is shown that in-phase and quadrature mismatch can introduce error in heart rate estimation. Two methods to achieve accurate displacement estimation were proposed and demonstrated. Using several initial angle measurement points within quarter wavelength, displacement estimation with errors less than 1% was achieved without any imbalance correction. Alternatively, by combining data points at varying initial angle locations, imbalance factors are estimated with high accuracy. This technique provides another viable method of imbalance compensation without the need for hardware modification, or a target moving with a large displacement.

Effect of Rician Factor in Satellite Communication Signal with MAP-MQAM Demodulation

This paper presents the effect of rician factors in satellite communications with Maximum A Posteriori (MAP) demodulation. Conventional QAM presently in use where the high capacity signaling scheme is required, is characterized with high errors due to the Doppler Effect and the nature of the channel as the order of modulation increases in rician fading channel. MAP detection scheme was used to reduce the error and maximize the probability of choosing correctly at the output of the QAM demodulator. MAP QAM was used as a signaling technique and obtained by taking the logarithm of Likelihood Ratio of observed binary data of an observation random variable at both the Inphase and Quadrature channels. System model was developed around MAP-QAM demodulator over rician factors of 5, 10, and 15 at 90 km/h. System model was simulated and evaluated using Bit Error Rate (BER) to determine the performances of the MAP-MQAM and conventional MQAM for comparison at modulation order „M‟ of 4 and 16. The results obtained showed that as the rician factor increases, the BER values decreased indicating better performance with both MAP-MQAM and QAM signaling scheme.