In-phase Channels Research Articles

Simple analytical calculation and experimental demonstration of optical 90° hybrids based on tapered 2×4 and 2×2 multimode interference couplers

We report a simple analytical calculation method for evaluating relative phase relations of tapered 2×4 multimode interference (MMI) couplers in a novel optical 90° hybrid. By using the proposed calculation model, the tapered 2×4 MMI coupler can easily be optimized to achieve phase matching with a 2×2 MMI coupler in the novel optical 90° hybrid. It was theoretically clarified that for several kinds of tapered MMI shapes, the proposed calculation model provides accurate solutions as long as the contribution of mode interference is much greater than that of mode conversion in the tapered MMI region. Based on the calculation model, we fabricated the optical 90° hybrid consisting of the linearly tapered 2×4 MMI coupler and the 2×2 MMI coupler. The extinction ratios of the measured transmission spectra via a delayed interferometer were comparable for in-phase and quadrature channels. This indicates that the phase matching was achieved by the tapered 2×4 MMI coupler and verifies the validity of the proposed calculation model.

A powerful veto for gravitational wave searches using data from Virgo's first scientific run

The use of vetoes generated from auxiliary channels suppresses most of the high amplitude noise triggers that impair gravitational wave (GW) burst and binary inspiral searches. During Virgo's first scientific run (VSR1), many of the remaining loud burst and inspiral Virgo triggers were observed with nearly equal significance in both the in-phase (ACp) and quadrature (ACq) interferometer output channels, while we expect the ACq channel to be insensitive to a GW signal. We describe a veto based on the ratio of the amplitude of the ACp and ACq signals. From studying hardware signal injections, we demonstrate that the ratio of the amplitude of coincident ACp and ACq triggers can be safely used to define a veto; we show its efficiency for the burst and binary inspiral analyses of the VRS1 data.

변형된 힐버트 변환을 이용한 디지털 TV 방송 채널 및 데이터 분석 시스템

ATSC 방식의 디지털 TV 방송의 수신환경을 분석하기 위해 다양한 채널 환경 분석 시스템이 사용되고 있다. 그러나 기존 장비들은 상용 수신기보다 성능이 떨어져 다중 경로 간섭에 의한 수신기의 수신 불량 현상을 측정하고 분석하기에 어려움이 있다. 이러한 문제점을 해결하기 위해서 상용 DTV 수신 칩세트를 채널 환경 분석 시스템에 직접 이용하는 것을 고려할 수 있다. 일반적으로 상용 DTV 칩세트들은 심볼 주파수로 샘플링된 기저대역의 I (In-phase) 채널 데이터 및 동기 신호들을 제공하므로 측정된 I 채널 데이터를 이용하여 좀 더 정확한 신호 품질 및 채널 신호의 분석을 위해서는 효과적인 Q (Quadrature) 채널 데이터의 추출이 필요하다. 본 논문에서는 DTV 방송 수신환경을 보다 정확하고 효율적으로 분석하기 위하여 DTV 수신 신호 및 채널 분석시스템의 기술적인 요구 사항을 제시하고, 이러한 요구 사항을 만족하게하고 좀 더 정확한 채널환경 분석을 위해 측정된 기저대역의 I 채널 데이터로부터 힐버트(Hilbert) 변환과정을 개선한 Q 채널 데이터 추출 방법을 제안한다. 제안된 데이터 및 채널 분석 시스템은 컴퓨터 모의실험과 실험실 테스트 결과를 통해서 성능을 입증하였으며, 방송신호 측정차량에 장착하여 DTV 동일채널중계기(DOCR) 필드테스트에서 다중경로간섭 신호의 분석에 적용하였다. To analyze reception environments of ATSC Digital TV, CIR (Channel Impulse Response) analysis systems are widely applied. The receiving performances of conventional CIR analysis systems are not as good as those of commercial state-of-the-art receivers. There are difficulties in measuring and analyzing reception problems caused by multi-path interferences. To solve these problems, commercial DTV chip sets embedded CIR analysis system is proposed. Generally, commercial chip sets provide baseband (In-phase) channel data and field or segment sync data. For more precise analysis of measured I channel data, it is necessary to extract Q (quadrature) channel data components as well. This paper presents the technical requirements of CIR analysis system for DTV. In order to satisfy such requirements and measure more accurate magnitude and phase of CIR, a method to derive the quadrature data from the measured in-phase channel data is proposed. The proposed channel analysis system is implemented with a commercial DTV chip set and expedites the data analysis for use on DTV field test vehicles. Computer simulation and laboratory test results are provided to demonstrate the performance of the proposed channel analysis system.

Digital Augmentation of RF Component Performance in Software-Defined Radio

This paper presents two tools for feedforward correction in transmitter chains in software-defined radio. The methods presume that the radio configuration already has a gate array and a mixer juxtaposed with one another. Programming is added in the gate array to affect preconditioning of the signals presented to in-phase and quadrature channels of a hybrid mixer so as to correct and enhance the analog RF performance of the mixer. The first of the methods comprises a realization with off-the-shelf components of feedback of the RF output of the mixer. Spectrum analysis in the gate array allows separation and cancellation of the unwanted difference-frequency sideband in the mixer's output. The second tool is a feedforward correction of imperfect performance of a hybrid mixer. The correction parameters are determined through sideband reduction via the feedback scheme in the first method. It is shown that the correction scheme performs well even for very large deviations from the ideal in the mixer parameters. As a consequence, the scheme may be used to extend the operating band of the gate-array/mixer combination to extreme bandwidths-approaching 200%.

Analog CMOS Design for Optical Coherence Tomography Signal Detection and Processing

A CMOS circuit was designed and fabricated for optical coherence tomography (OCT) signal detection and processing. The circuit includes a photoreceiver, differential gain stage and lock-in amplifier based demodulator. The photoreceiver consists of a CMOS photodetector and low noise differential transimpedance amplifier which converts the optical interference signal into a voltage. The differential gain stage further amplifies the signal. The in-phase and quadrature channels of the lock-in amplifier each include an analog mixer and switched-capacitor low-pass filter with an external mixer reference signal. The interferogram envelope and phase can be extracted with this configuration, enabling Doppler OCT measurements. A sensitivity of -80 dB is achieved with faithful reproduction of the interferometric signal envelope. A sample image of finger tip is presented.

Analytical Evaluation of Analog Component Effects on AMC Performance in HSDPA System

We analytically evaluated the effects of the analog components on a high-speed downlink packet access (HSDPA) system standardized by 3GPP. We considered the phase noise of synthesizers, the imbalance of demodulators between in-phase and quadrature channels, and the filters. The components are represented by the appropriate equations. We applied adaptive modulation and coding methods for HSDPA systems and base station transmission of adequate data rate signals complying with quality estimated by mobile stations (MSs). The quality represents a data rate indicating that MSs can receive the signals. We estimated the quality using a conventional signal-to-interference measurement of the common pilot channel (CPICH) and found that the phase noise creates a mismatch relationship between the quality and the data rate, while the demodulator imbalance and filters create a suitable relationship. We confirmed this using analytic methods and computer simulation.

A 75-dB Image Rejection IF-Input Quadrature-Sampling SC<tex>$SigmaDelta$</tex>Modulator

Quadrature sampling of intermediate frequency (IF) signals is subject to the well-known problem of gain and phase mismatches between the in-phase (I) and quadrature (Q) channels. This paper presents an IF-input quadrature-sampling switched-capacitor (SC) /spl Sigma//spl Delta/ modulator that circumvents the I/Q mismatch problem by time-sharing between the I and Q channels the critical circuit components, namely, the sampling capacitor and the capacitor of the first-stage feedback digital-to-analog converter (DAC). In addition, a clocking scheme that is insensitive to I/Q phase imbalance is used. A third-order single-loop 1-bit low-pass modulator has been designed and fabricated in a 0.35-/spl mu/m CMOS process with an active area of 0.57mm/sup 2/. The experimental results show that the modulator achieves an image-rejection ratio (IRR) of greater than 75dB throughout a 200-kHz signal bandwidth.

5.7 GHz GaInP/GaAs HBT sub-harmonic Gilbert downconverter with octet-phase LO generator

A 5.7 GHz GaInP/GaAs heterojunction bipolar transistor (HBT) sub-harmonic Gilbert downconversion mixer with octet-phase LO generator is demonstrated. The conversion gain is 15 dB, IP1dB is −13 dBm, IIP3 is 0 dBm, and IIP2 is 24 dBm when the LO power equals 3 dBm. The measured IF quadrature output waveforms indicate that the phase difference between the in-phase and quadrature-phase output channels is only 1.3°.

1.6-b/s/Hz 160-Gb/s 230-km RZ-DQPSK polarization multiplex transmission with tunable dispersion compensation

A 160-Gb/s (4/spl times/40 Gb/s) return-to-zero differential quadrature phase-shift keying polarization-division multiplex transmission is demonstrated with Q>15.6 dB in one of eight 100-GHz-spaced wavelength-division-multiplex channels after 230 km of fiber. Residual chromatic dispersion (CD) is equalized by a thermally tunable CD compensator for the 192.5-THz channel. Polarizations, in-phase and quadrature data channels are demultiplexed using a LiNbO/sub 3/-based automatic polarization control and a 1-bit interferometer, respectively.

An I/Q Mismatch-Free Switched-Capacitor Complex Sigma–Delta Modulator

This paper presents a technique to suppress the mismatch between the in-phase (I) and quadrature-phase (Q) channels of a switched-capacitor complex sigma-delta modulator that is used for the analog-to-digital conversion of a real intermediate-frequency radio signal. The mismatch is suppressed through time sharing of the critical capacitors, i.e., the input sampling capacitor and the capacitor of the feedback digital-to-analog converter, between the I and Q channels. Circuit simulations verifying the proposed technique are presented.

A 400-mhz processor for the conversion of rectangular to polar coordinates in 0.25-μm cmos

This paper describes the architecture and IC implementation of a rectangular-to-polar coordinate converter for digital communication applications. The architecture core uses small lookup ROMs, fast multipliers, and a single angle-rotation stage. Area and latency are reduced in comparison with traditional methods. The processor, implemented in 0.25-/spl mu/m five-metal CMOS, has 14-b in-phase and quadrature channel inputs and 15-b magnitude and phase channel outputs. The phase and magnitude calculations have a maximum error of 0.00024 (0.0078% of /spl pi/) and 0.03 (1% of 2/spl radic/2), respectively. Computational latency is 19 cycles, and power dissipation is 470 mW at 2.5 V and 406 MHz (Mconversions/s).

Correcting Drift Errors in HEM Data

Much HEM survey data suffers from low (spatial) frequency along-line variability in amplitude caused by slow changes in the system geometry and electronic drift. Even though the system is periodically taken up to a sufficient altitude to re-zero the primary field correction, the errors are not totally removed. This paper describes a procedure to reduce the effect of these errors. Each flight line is corrected by subtracting a slowly varying function of time that has been chosen so that the between-line differences over the whole survey area are minimized. The parameters of the correction functions are estimated using weighted, damped least squares. The procedure produces a marked improvement in the quality of the images of low frequency, in-phase channels that have been corrupted by drift noise.

Estimation of frequency offset in QPSK demodulation

AbstractIf there is a frequency offset in the local oscillator circuit in QPSK demodulation, the BER is degraded. Previously, methods for estimating this frequency offset have been proposed. However, few techniques that have been studied can estimate this offset in an environment with a large frequency offset or noise. A digital adaptive IIR notch filter is effective for estimation of a large frequency offset in an environment with noise. However, the noise is colored in the receiver due to the IF band BPF inserted in order to suppress out‐of‐band noise. Therefore, the converged value has a bias error with respect to the target value. The method proposed in this paper is based on the fact that the phase of the digital IIR‐BPF is zero at the center frequency of the amplitude characteristic. This characteristic is used for control by applying a negative feedback to the digital IIR‐BPF coefficients. Then, no bias error is generated because the noise in the in‐phase channel and that of the quadrature channel in QPSK are uncorrelated. Further, the proposed method does not drift but maintains the present status due to the uncorrelated character described above, even in the case of channel disconnection such as shadowing. Therefore, this is a frequency offset estimation method suitable for mobile communications. As a result of evaluation of the proposed method in terms of the BER in a white Gaussian noise channel, it is confirmed that the proposed method provides a BER lower than that of the conventional digital adaptive IIR notch filter. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 86(9): 1–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.10089

Relative Phase Change During Quantum Operations

Quantum operations represented by completely positive maps encompass many physical processes and have been very powerful in describing quantum computation and information processing tasks. We introduce the notion of relative phase change for a quantum system undergoing a quantum operation. We find that the relative phase shift of a system not only depends on the initial state of the system, but also depends on the initial state of an ancilla with which it might have interacted in the past. The relative phase change during a sequence of quantum operations is shown to be non-additive in nature. This property can attribute a “memory” to a quantum channel. Also the notion of relative phase shift helps us to define what we call “in-phase quantum channels.” We will present the relative phase shifts for a qubit undergoing both a depolarizing channel and complete randomization, and discuss their implications. PACS: 03.65.Vf; 03.67.-a; 03.65.Yz

Adaptive calibration of I and Q mismatch in quadrature receiver

The mismatch of in-phase and quadrature channels in quadrature receiver affects and constrains radar detection performance in colierent radar. It is necessary to keep the in-phase and quadrature branches symmetrical. In this letter, an adaptive method to detect imbalance parameters is derived by means of evaluating channel errors from the received signal sequences. No matter how the bias degree of the gain and phase errors in I/Q channels are, the proposed adaptive scheme can obtain good calibration results. And the required calculations are only a few multiplications and additions. No need of a special test signal, the introduced method is simple to implement and easy to operate.

Time-scale analysis of quadrature Doppler ultrasound signals

Most Doppler ultrasound systems employ quadrature demodulation techniques at the detection stage. The information concerning flow direction, encoded in the phase relationship between in-phase and quadrature-phase channels, is not obvious at this stage. The complex fast Fourier transform can be used to obtain directional information in the frequency domain, as well as time–frequency analysis of Doppler signals. However, it has an inherent time–frequency resolution limitation. The wavelet transform allows the time–frequency resolution compromise to be optimised. Mapping directional information in the scale domain is also desirable. A method is described, based on the utilisation of complex wavelets and negative scales. It eliminates the intermediate processing stages for obtaining directional Doppler signals for time-scale analysis.

Directional wavelet transform in the context of complex quadrature Doppler signals

Most Doppler ultrasound systems employ quadrature demodulation techniques at the detection stage. The information concerning flow direction encoded in the phase relationship between in-phase and quadrature phase channels is not obvious at this stage. A method based on the utilization of complex wavelets and negative scales has been described. It eliminates the intermediate processing stages by mapping directional information in the scale domain.

Performance analysis of extended OQPSK carrier phase recovery algorithm in satellite channel

This paper proposes a new extended decision-directed decision-estimated phase recovery algorithm based on maximum likelihood parameter estimation for OQPSK (offset QPSK). In this scheme, compared to the conventional one, the data dependent noise of the phase recovery loop is reduced by inserting a filter with 2 taps to the in-phase and quadrature channel respectively before the phase detector. The proposed scheme is compared to the conventional QPSK scheme with respect to BER (bit error rate) and phase error for roll-off factors of the baseband filter, output backoffs of the nonlinear satellite channel and loop bandwidth.

Signal quality estimation algorithm

An improved signal quality estimation algorithm, applicable to CDMA-based mobile communication systems, is proposed. The algorithm estimates the Eb/N0 at the receiver end by operating on the despread symbols of the received in-phase (I) and quadrature (Q) channels. The improvement in performance is obtained by the addition of a smoothing filter to the existing algorithm. The performance of the algorithm is compared initially in a Gaussian channel and then in a time-varying channel that emulates fast fading.

An adaptive modulation scheme for simultaneous voice and data transmission over fading channels

We propose a new adaptive modulation technique for simultaneous voice and data transmission over fading channels and study its performance. The proposed scheme takes advantage of the time-varying nature of fading to dynamically allocate the transmitted power between the inphase (I) and quadrature (Q) channels. It uses fixed-rate binary phase shift keying (BPSK) modulation on the Q channel for voice, and variable-rate M-ary amplitude modulation (M-AM) on the I channel for data. For favorable channel conditions, most of the power is allocated to high rate data transmission on the I channel. The remaining power is used to support the variable-power voice transmission on the Q channel. As the channel degrades, the modulation gradually reduces its data throughput and reallocates most of its available power to ensure a continuous and satisfactory voice transmission. The scheme is intended to provide a high average spectral efficiency for data communications while meeting the stringent delay requirements imposed by voice. We present closed-form expressions as well as numerical and simulation results for the outage probability, average allocated power, achievable spectral efficiency, and average bit error rate (BER) for both voice and data transmission over Nakagami-m fading channels. We also discuss the features and advantages of the proposed scheme. For example, in Rayleigh fading with an average signal-to-noise ratio (SNR) of 20 dB, our scheme is able to transmit about 2 bits/s/Hz of data at an average BER of 10/sup -5/ while sending about 1 bit/s/Hz of voice at an average BER of 10/sup -2/.