Error probability analysis for continuous phase modulation withViterbi detection on a Gaussian channel with multiple signalinterference

The effects are studied on the symbol error probability of the Viterbi detector for continuous phase modulations with constant amplitude, when the desired signal is received in multiple interfering signals and white Gaussian noise. The detection is assumed to be coherent and, furthermore, perfect timing in the detector is also assumed. An upper bound on the symbol error probability is derived for the Viterbi detector. The bound is based on the union bound technique, and it is shown to be tight for small error probability levels. It is found that the smoothed binary and all quaternary modulations sustain much larger interference power in adjacent channel interference than minimum-shift keying (MSK) does and, thus, the adjacent channels can be spaced closer in frequency for these modulations, In particular, the smoothed quaternary modulations seem to be significantly more efficient than MSK. In cochannel interference the difference in error performance between the schemes is relatively small     

Cross Cancellation TechniqueEmploying an Error Amplifier

In this letter, we propose a new distortion cancellation mechanism for a balanced power amplifier (PA) structure using the cross cancellation technique employing an error amplifier. The proposed cross cancellation balanced linear PA is implemented in the IMT-2000 ( 2.14GHz) band. With commercial PAs with a peak power of 240 W for base-station application, the proposed system shows 18.6 dB improvement at an average output power of 40 dBm for adjacent channel leakage ratio measurement with wideband code division multiple access 4FA signal. The efficiency of the proposed structure is about 2% higher than the conventional feedforward amplifier for modulated carrier.     

Modeling nonlinear distortion of ultra wideband signals at X-band

Nonlinear distortion in the adjacent channels of an X-band amplifier driven by an ultra-wideband digitally-modulated carrier is analyzed. Statistical properties of the input signal with a complex power series-based behavioral model of the amplifier are used to calculate the output power spectrum. Comparisons are made between measured and predicted adjacent channel power rejection for the X-band monolithic microwave integrated circuit.     

WCDMA系统中基于查找表的预失真技术的研究

在无线通信系统中,高功率放大器因其非线性,导致AM／PM效应使得微分相位、微分增益和互调失真变坏。高质量的通信系统设计应尽可能减小功率放大器的AM／PM效应。因此,针对宽带码分多址（WCDMA）功放非线性失真问题,采用一种基于查找表（LUT）的自适应预失真方法,改善功放的非线性失真。仿真表明．该方法能有效补偿放大器产生的AM—AM、AM-PM失真,并将功放的邻道功率泄漏比（ACPR）改善到30dB左右。     

Phase-correcting feedback system for class E power amplifier

A phase-correcting feedback system which reduces the AM-to-PM distortion of Class E power amplifiers for wireless communication is presented in this paper. It comprises a novel limiting amplifier, a phase detector, and a phase shifter all operating at 835 MHz. The phase-correcting feedback together with a Class E power amplifier were fabricated in a 0.8-μm GaAs MESFET process. The limiting amplifier has a phase error less than 2.5°. The phase detector and phase shifter have a sensitivity of 10 mV/degree and 80°/V, respectively. The Class E power amplifier delivers 26.5 dBm to the load with a power added efficiency of 67%. The phase correcting feedback system reduces the 30° phase distortion of the Class E amplifier down to 4°, and its total power dissipation is 21.5 mW     

Phase error free LINC modulator

A new technique for linear amplification with nonlinear components (LINC) is described. LINC implementation is thought to be very difficult because of its sensitivity to phase error caused by the difference in electrical length between two power amplifier branches. The allowable limit of phase error for achieving the 60 dB suppression of the adjacent channel interference (ACI) power is estimated for roll-off bandlimited offset QPSK (OQPSK). Then, a compensating method for this phase error is presented. By using the proposed method, sufficient out-of-band spectrum suppression for mobile radio application is obtained. An output power of 7.5 W and a power efficiency of 21% are experimentally confirmed.<>     

EVM simulation and analysis in digital transmitter

The error vector magnitude (EVM) is extensively applied as a metric for digital transmitter signal quality compliance in modern communication systems. This article is focused on the effects of local oscillator (LO) phase noise and nonlinear distortion of power amplifier on EVM. This article contributes to below aspects. First, the relationships between EVM and two effects, LO phase noise and nonlinear distortion of power amplifier, are derived and expressed. Second, to simplify the expression, the third-order intermodulation distortion (IMD3) is used to calculate the EVM. Then, an expression for the EVM is derived based on the digital transmitter model that considers local oscillator phase noise and nonlinear distortion of power amplifier. Finally, the math formula of bit error rate (BER) versus EVM is given which can be easier and more useful to predict BER, according to analysis of the relationship between EVM and signal to noise rate (SNR), inspired by the works of Rishad, Md. Shahriar and AHM, 2006. Simulations are carried out to display the performance of EVM based on these relationships.     

An analytic approach for CDMA output of feedforward power amplifier

In this paper, a novel method is introduced to predict the Code-Division Multiple-Access (CDMA) output spectrum of an RF power amplifier linearized with feedforward technique based on transfer function. In this method, an RF power amplifier is modeled mathematically by nonlinear complex envelope transfer function based on AM-AM and AM-PM distortion diagrams. Using this model, analytic expressions of CDMA output spectrum of power amplifier is calculated. Having mathematical model of RF power amplifier leads to derive analytic expressions for InterModulation (IM) products in feedforward amplifier. Based on these expressions, IM products are related to nonlinear complex envelope transfer function of feedforward amplifier. Then, CDMA output spectrum of feedforward linearization technique is predicted. The loops imbalances in feedforward technique are considered in analysis. Finally, the results of derived expressions in MATLAB software are compared with ADS simulations results and good agreements were achieved. Employing this method gives insight for feedforward analysis and loops imbalances effects in feedforward amplifier for CDMA applications.     

基于压缩量化的非正弦时域正交调制信号预失真方法

针对基于椭圆球面波函数的非正弦时域正交调制信号峰均功率比较高,因而受功率放大器非线性失真影响较大的问题,该文设计了一种基于波形训练的非迭代查询表预失真结构。由于所选量化方法直接决定了查询表预失真器的精度,通过分析调制信号的幅值分布特性,提出一种综合考虑功率放大器特性及信号幅值分布特性的压缩量化方法。对采用所提预失真方法前后信号的带内带外失真特性进行了仿真,并与采用幅度均匀量化方式的性能进行了比较。结果表明,该文方法有效改善了非正弦时域正交调制信号功率谱及系统误码率特性,减小了功率放大器给信号带来的非线性失真。     

Novel Digital Compensation Approaches for Envelope Tracking Amplifiers

This paper considers the compensation of the envelope tracking (ET) amplifier. In particular, we propose a new predistortion architecture for the ET amplifier. In addition, we develop new algorithms for time misalignment compensation between the input signals of the ET amplifier and compare the methods to a previously presented method. Our results indicate that using the proposed architecture with optimal predistorter, we achieve over 40 dB better adjacent channel power than using a previously presented architecture. In addition, the time misalignment compensation methods give very accurate timing estimates. The time misalignment compensation with the predistortion reduces spectral regrowth due to the nonlinear ET amplifier and improves the power efficiency of the ET amplifier.     

Amplifier linearization using simultaneous harmonic and basebandinjection

A novel linearization scheme utilizing injection of distortion signal at the input of amplifier is described. Harmonic and baseband signal generated by predistortion circuits is fed to the input of the main amplifier and by controlling the power level of the harmonic and baseband signal properly, mixing products can be made to cancel out with the FET inherent distortion signals. Unlike many other techniques, no precise phase adjustment is required for the RF signal path. For verification, the two-tone performance of a constructed linearized amplifier is measured and a reduction of the third-order IMD power level of about 27 dB is observed     

A Low Distortion and Low Dissipation Power Amplifier with Gate Bias Control Circuit for Digital/Analog Dual-Mode Cellular Phones

A power amplifier operating at 3.3 V. has been developed for CDMA/AMPS dual-mode cellular phones. It consists of linear GaAs power MESFET's, a new gate bias control circuit, and an output matching circuit which prevents the drain terminal of the second MESFET from generating the harmonics. The relationship between the intermodulation distortion and the spectral regrowth of the power amplifier has been investigated with gate bias by using the two-tone test method and the adjacent channel leakage power ratio (ACPR) method of CDMA signals. The dissipation power of the power amplifier with a gate bias control circuit is minimized to below 1000 mW in the range of the low power levels while satisfying the ACPR of less than ?26 dBc for CDMA mode. The ACPR of the power amplifier is measured to be ?33 dBc at a high output power of 26 dBm.     

A high sensitivity and wide dynamic range zero-IF RF receiver for cognitive radio application

This paper presents an RF receiver of zero-Intermediate Frequency (IF) architecture for Cognitive Radio (CR) communication systems. Zero-IF architecture reduce the image reject filter and IF filter, so it is excellent in low cost, compact volume, and low power dissipation. The receiver employs three digital attenuator and a high gain, high linearity low noise amplifier to achieve wide dynamic range of 70 dB and high receiving sensitivity of −81 dBm. A fully balanced I/Q demodulator and a differential Local Oscillator (LO) chips are used to minimize the negative effects caused by second-order distortion and LO leakage. In order to select an 8 MHz-channel from 14 continuous ones located in UHF band (694–806 MHz) accurately, approach of channel selectivity circuits is proposed. The RF receiver has been designed, fabricated, and test. The measured result shows that the noise figure is 3.4 dB, and the error vector magnitude is 7.5% when the input power is −81 dBm.     

微波功率放大器非线性特性分析

为判断微波功率放大器非线性失真的主要影响因素,首先,在传统幂级数模型的基础上对功率放大器的非线性幅度失真和相位失真进行拟合,基于包络分析法给出了功率放大器非线性失真与幅度和相位失真间的解析关系;其次,对幅度失真和相位失真引起的非线性失真进行了分析,给出了两者之间的等效失真关系式,据此可对任意给定的功率放大器进行分析,以确定非线性失真的主要影响因素,并用于指导模拟预失真线性化器的设计与调试;最后,通过对一Ka频段行波管放大器的非线性测试及模拟预失真线性化,验证了所提出的功率放大器非线性分析的正确性及幅相等效失真关系式的有效性。     

On the bit error rate of lightwave systems with optical amplifiers

The problem of evaluating the performances of communication systems with optical amplifiers and a wideband optical filter is addressed. Exact probability of error expressions for optical signals in presence of amplifier spontaneous noise and photodetector shot noise are given and compared with those predicted by Gaussian approximations for amplitude shift keying (ASK), frequency shift keying (FSK), or differential phase shift keying (DPSK) modulations, both for ideal photodetectors and for the case where shot noise is significant     

Minimizing Spectral Leakage of Nonideal LINC Transmitters by Analysis of Component Impairments

LInear amplification with Nonlinear Components (LINC) is a distortion-free transmitter architecture under ideal conditions. However, in a realistic transmitter, imbalances such as dc offset, differential gain, and differential phase shift present in the quadrature modulators result in generation of out-of-band spectral components, even assuming that both amplifiers have identical characteristics. The level of distortion not only increases with the magnitude of the imbalances but also depends, to a large extent, on their relative phase arguments. The contribution of this paper is to provide a simplified characterization of the spectral leakage in the LINC transmitter in terms of quadrature modulator imbalances, with identical or mismatched amplifiers. This characterization allows identification of the transmitter with minimum spectral leakage under the constraint that the quadrature modulators perform equally well when used individually, i.e., in a transmitter composed of just the quadrature modulator followed by an amplifier. With reasonably small imbalances in the quadrature modulators and realistic amplifier mismatch, the spectral leakage at the output of a LINC transmitter driven by typical modulation schemes can be reduced by up to 10 dB, simply by a wise pairing of modulators     

An adaptive pre-distorter for the compensation of HPA nonlinearity

A high power amplifier (HPA) is used for the amplification of transmitting communication signals. However, it produces distortions by creating AM/AM and AM/PM modulations in the transmitting signal, Accordingly, this nonlinearity results in bandwidth expansion and nonlinear distortion in the in-band signal. This paper proposes an algorithm for the operation of a pre-distorter, which is composed of a look-up table (LUT), that can compensate for the distortion produced by an HPA. For the fast initialization of the LUT, an estimation algorithm is also proposed for the HPA characteristics. Furthermore, an adaptive algorithm based on the minimization of the mean square error is proposed to compensate for the time-varying property of an HPA. The performance of the proposed algorithm is analyzed by applying the algorithm to an 8-level vestigial sideband (VSB) modulation to be used in the ATSC terrestrial digital TV system     

Linearised mixer using frequency retranslation

A new linearisation technique using frequency retranslation for generating an error signal to predistort the input of a nonlinear mixer is presented. Results from a two-tone-test at 920 MHz yields a 25 dB reduction in the distortion products and also minimal adjacent channel interference was observed with a π/4 differential quadrature phase shift keying modulated carrier     

Distortion in polar modulated CMOS RF power amplifiers

Polar modulation of a switching RF amplifier is an excellent candidate to combine both linearity, efficiency and CMOS integration for RF power amplifiers used in mobile and wireless communication systems. In this paper, the different sources of distortion associated with polar modulation are discussed and verified by measurement results. A fully integrated linearized CMOS RF Power Amplifier for GSM–EDGE, realized in a 0.18 μm CMOS technology, is used as a benchmark to validate the presented theory. It is demonstrated how the combination of a differential delay between the amplitude signal and the phase signal, together with the AM–PM distortion of the Class E amplifier, generates an asymmetry in the output spectrum. The effect of low-pass filtering of the envelope signal is investigated and the degradation on the linearity with and without delay adjustment is given.     

An adaptive digital predistortion for compensating nonlinear distortions in RF power amplifier with memory effects

In this paper, an adaptive digital predistortion based on a memory polynomial model is proposed in order to linearize the power amplifier with memory effect. The coefficients of the power amplifier model have been extracted using a least square method and those of predistortion have been identified by applying an indirect learning structure. Finally, the performance of digital predistortion has been demonstrated using the simulation of the power amplifier and the digital predistortion excited by a modulated 16 QAM signal in Matlab software. According to the simulation results, the criterion of adjacent channel power ratio (ACPR) declined by around 15 dB and the input/output power spectrum density of the power amplifier has quite similar curves. The linearized power amplifier output spectrum demonstrates the superiority of the proposed predistorter in eliminating the spectral regrowth which is caused by the memory effect in comparison to the other linearization methods.