Digital Quadrature Modulation Research Articles

Intelligent Interactive English Teaching System for Engineering Education

In order to improve the effect of English teaching, this paper combines with the intelligent algorithm to construct an intelligent interactive English teaching system for engineering education. In the process of interactive data processing, this paper specifies the time that a single pulse needs to be maintained and controls a counter to maintain a certain number of FPGA clocks. Moreover, data processing is completed in the digital domain, the modulation method is digital quadrature amplitude modulation, data transmission is generally in the form of a real signal, and the modulated IQ signal is converted back to a real signal. After constructing an intelligent interactive English teaching system for engineering education, this paper verifies that the intelligent interactive English teaching system for engineering education has certain effects through simulation teaching combined with the expert evaluation method.

Broadband injection-locked homodyne receiver for digital coherent transmission using a low Q Fabry-Perot LD.

We describe the broadband injection-locking performance of a Fabry-Perot laser diode (FP-LD) for digital coherent transmission. The dynamic locking bandwidth of the FP-LD was as wide as 28.8 GHz, which makes it possible to achieve precise carrier-phase synchronization with extremely low phase noise over a wide frequency range. By applying the FP-LD as an LO in an injection-locked homodyne receiver for digital coherent quadrature amplitude modulation (QAM) transmission, we demonstrate, for the first time, the precise demodulation of 3, 10 and 20 Gbaud 256 QAM signals even when using a widely and randomly phase-modulated transmitter laser. This is attributed to the excellent wideband dynamic injection-locking characteristics of the FP-LD.

Digital quadrature amplitude modulation with optimized non-rectangular constellations for 100 Gb/s transmission by a directly-modulated laser.

We study the performance of novel quadrature amplitude modulation (QAM) constellations for 100 Gb/s transmission by a directly-modulated laser. Due to the strong nonlinearity of a directly-modulated laser, rectangular constellations suffer a large penalty from their regular spacing between symbols. We present a method for synthesizing irregular constellations which position symbols more efficiently. We will demonstrate the improved performance of these novel constellations over the conventional rectangular constellation as well as the superior performance achievable with digital QAM compared to optimally bit-loaded discrete-multitone modulation.

A Pan-Function Model for the Utilization of Bandwidth Improvement and PAPR Reduction

Aiming at the digital quadrature modulation system, a mathematical Pan-function model of the optimized baseband symbol signals with a symbol length of4Twas established in accordance with the minimum out-band energy radiation criterion. The intersymbol interference (ISI), symbol-correlated characteristics, and attenuation factor were introduced to establish the mathematical Pan-function model. The Pan-function was added to the constraints of boundary conditions, energy of a single baseband symbol signal, and constant-envelope conditions. Baseband symbol signals with the optimum efficient spectrum were obtained by introducing Fourier series and minimizing the Pan-function. The characteristics of the spectrum and peak-to-average power ratio (PAPR) of the obtained signals were analyzed and compared with the minimum shift keying (MSK) and quadrature phase-shift keying (QPSK) signals. The obtained signals have the characteristics of a higher spectral roll-off rate, less out-band radiation, and quasi-constant envelope. We simulated the performance of the obtained signals, and the simulation results demonstrate that the method is feasible.

Frequency Offset Estimation for Optical Coherent M-QAM Detection Using Chirp z-Transform

The chirp z-Transform (CZT) is introduced to replace the traditional gradient descent (GD) in frequency offset estimation for digital coherent quadrature amplitude modulation reception. Different from GD, CZT is not sensitive to the changes of the parameters and is free of uncertain latency that GD suffers. The implementation of frequency offset estimator based on CZT is presented and numeric simulations demonstrate that CZT can reach the same accuracy as GD. The computation complexity of CZT is analyzed and is roughly equivalent to GD with three iterations.

All Digital-Quadrature-Modulator Based Wideband Wireless Transmitters

A novel architecture for a fully digital wideband wireless transmitter is presented. The proposed structure replaces high-dynamic-range analog circuits with high-speed digital circuits and offers a simple and flexible architecture, which requires less area, consumes less power, and delivers higher performance compared to those of the conventional modulators used for wideband systems. The design is based on a standard 65-nm CMOS process and is suitable for integration with a digital signal processor, memory, and logic implemented in such a process. The presented transmitter is based on a novel digital quadrature modulator (DQM), which achieves digital modulation in a Cartesian coordinate system. The novel architecture employs a single converter, referred to as the differential-like digital-to-RF converter (DDRC), as it is based on fully digitally combining the quadrature baseband signals. A DDRC, which is the heart of a DQM, combines functionalities of a mixer, a digital-to-analog converter, and an RF filter into a single circuit. The total area for the digital blocks is 0.04 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with a power consumption of roughly 5 mW. It is shown that the proposed transmitter meets the spectral mask, defined in the targeted IEEE 802.16e (WiMAX) standard, with a margin of 20 dB and achieves an error-vector-magnitude (EVM) performance of -36 dB with a margin of 6 dB.

Digital Modulator with Bandpass Delta-Sigma Modulator

A digital quadrature modulator with a bandpass ??-modulator is presented that interpolates orthogonal input carriers by 16 and performs a digital quadrature modulation at carrier frequencies fs/4, ?fs/4 (fs is the sampling frequency). After quadrature modulation, the signal is converted into an analogue IF signal using a bandpass ?? modulator and a 1-bit D/A converter. The die area of the chip is 5.2 mm2 (0.13 ?m CMOS technology). The total power consumption is 139 mW at 1.5 V with a clock frequency of 700 MHz (D/A converter full-scale output current 11.5 mA).

Performance Analysis of Blind Adaptive Phase Offset Correction Based on Dispersion Minimization

This paper presents an analysis of the performance and behavior of a blind adaptive carrier phase offset recovery scheme based on dispersion minimization (DM). The algorithm, called the DM-derotator, is a kind of simple equalizer that attempts to correct the carrier phase offset by minimizing the dispersion of the projection of the real part of the (complex) data signal. The recent application of this algorithm to digital broadcasting signals motivates our analysis. This paper classifies the stationary points of the DM-derotator for a variety of source signals including digital vestigial side band (VSB) and quadrature amplitude modulation (QAM) and discusses initialization strategies. The analysis is extended to a variety of situations including i) its behavior in the presence of intersymbol interference, ii) its behavior when there is statistical dependence between the in-phase and quadrature components, and iii) its tracking ability.

A digital quadrature modulator with on-chip d/a converter

The first analog IF mixer stage of a transmitter can be replaced with this digital quadrature modulator. The modulator interpolates orthogonal input carriers by 16 and performs digital quadrature modulation at carrier frequencies f/sub s//4, -f/sub s//4,f/sub s//2 (f/sub s/ is the sampling frequency). A 12-b digital-to-analog (D/A) converter is integrated with the digital quadrature modulator. A segmented current source architecture is combined with a proper switching technique to reduce spurious components and to enhance dynamic performance. The digital quadrature modulator is designed to fulfill the spectral, phase, and EVM specifications of GSM, EDGE, and WCDMA base stations. The die area of the chip is 27.09 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0.35-μm CMOS technology) and the total power consumption is 1.02 W with 2.8 V at 500-MHz output sampling rate (0.78-W digital modulator, 0.24-W D/A converter).

A 1.5-V CMOS all-N-logic true-single-phase bootstrapped dynamic-logic circuit suitable for low supply voltage and high-speed pipelined system operation

This paper presents a 1.5-V CMOS true-single-phase (TSP) bootstrapped dynamic-logic (BDL) circuit using all-N-logic and bootstrapped circuit techniques for high-speed operation at a low supply voltage. As confirmed by the experimental results from the test chip implemented using a 0.8-/spl mu/m CMOS technology, the speed performance of this CMOS all-N-logic TSP BDL circuit with four serial inputs is 75% faster at a supply voltage of 1.5 V, as compared to the conventional TSP dynamic-logic circuit. Using an all-N-logic TSP BDL circuit, the maximum operating frequency of an implemented digital quadrature modulator is 482 MHz at 5 V, and 68 MHz at 1.5 V, which is 27% faster compared to the circuit without using the BDL circuit.

A CMOS quadrature modulator for wireless communication IC

This brief presents a CMOS digital quadrature modulator, which is based on a CMOS digital modulator and a five-level digital-to-analog converter, for wireless communication IC. In the digital modulator, a circular shift register is used to produce a continuous sinusoidal wave with different phases. With this technique, the quadrature modulator has advantages in low power consumption, small area, and expansion capability.

A comparison of fully digital quadrature modulation for modem systems

AbstractThis paper presents and evaluates the results obtained by computer simulations of different current modulation techniques by the use of DSP‐based systems and computer simulations. The modulation‐demodulation methods evaluated herein are QPSK, OQPSK, MSK, λ/4‐QPSK and Q2PSK. The constant envelope property and the relatively high power efficiency of the above‐mentioned modulation techniques makes them very suitable for digital satellite and mobile radio communications. Digital algorithms for data‐decision, carrier phase offset and timing delay estimation for each of the modems are given. Maximum likelihood carrier phase recovery performances for the different quadrature phase modulations are compared and evaluated. Results in terms of BER performances and statistical properties of the synchronization procedures are shown for the AWGN channels. Computational loads of the different modem systems evaluated are also given.