BPSK and QPSK non‐linear satellite communication system performance in the presence of cochannel interference

Taking the uplink and downlink cochannel interference and noise into account, the analytical expressions are derived for determining the bit error probability in detecting a binary phase‐shift‐keying (BPSK) and a quaternary phase‐shift‐keying (QPSK) Gray coded signal, transmitted over a satellite system exhibiting amplitude modulation‐to‐amplitude modulation (AM/AM) conversion effects and amplitude modulation‐to‐phase modulation (AM/PM) conversion effects. On the basis on the derived theoretic formulae, using real‐life system parameters, numerical results are obtained and presented. We point out the explicit comparisons of satellite communication system performance obtained when a satellite transponder amplifier is modelled by a hard‐limiter and those obtained when both AM/AM and AM/PM non‐linearities of the satellite transponder amplifier are taken into consideration. Copyright © 2003 John Wiley & Sons, Ltd.     

A transmitter architecture for nonconstant envelope modulation

This paper presents a transmitter architecture which is less sensitive to power amplifier AM/AM and AM/PM conversions. Indeed, most radio communication standards employ nonconstant envelope modulation such as in the 802.11 series. Owing to power amplifiers' nonlinearities, distortions on the modulations degrade the overall transmitter performance. As a consequence, linearization methods, such as envelope elimination and restoration, have to be employed. The architecture relies on the transformation of a nonconstant envelope modulation to a constant or switched one. This signal coding enables the efficient amplification of the signal without undergoing power amplifier distortions. The envelope variation is restored by bandpass filtering just after the power amplifier.     

Power-amplifier characterization using a two-tone measurementtechnique

An accurate nonlinear model is necessary to optimize the tradeoff between efficiency and linearity in power amplifiers. Gain compression (AM/AM) and amplitude-phase (AM/PM) distortion are the two primary model inputs used to characterize the nonlinearity. The amplifier's AM/AM and AM/PM characteristics are typically measured statically using a vector network analyzer. Since the input is typically a modulated signal, it is desirable to characterize the amplifier dynamically. This paper describes and demonstrates a dynamic AM/AM and AM/PM measurement and modeling technique involving a spectrum analyzer and two-tone input signals. A complete analysis of the measurement technique is presented, along with the data processing needed for the identification of a new three-box model. The test configuration and procedure are presented with special precautions to minimize measurement error. Results for a solid-state amplifier are used to accurately predict intermodulation distortion, while those for a traveling-wave tube amplifier show good agreement with that obtained dynamically using a 16 quadrature-amplitude-modulation signal     

Effects of One Large Signal on Small Signals in a Memoryless Nonlinear Bandpass Amplifier

The theoretical relationships are presented for determining the output amplitude and phase of each small signal when commonly amplified with a large signal by a memoryless nonlinear amplifier. Both the amplitude and phase of each output small signal depend on the input amplitude of the large signal and on the AM/AM and AM/PM characteristics of the nonlinear amplifier. If the nonlinear amplifier is a hard limiter without AM/PM conversion, then the well-known result can also be derived from a general formula developed in this paper. A numerical example is given and confirmed by laboratory measurement.     

Effects of low noise amplifier non‐linearities on blind adaptive beamforming performance in CDMA wireless systems

We report a new approach to analyse the effects of low noise amplifier (LNA) non‐linear distortions in the code division multiple access (CDMA) wireless communication systems using spatio‐temporal analysis and Volterra series theory. For this purpose, the bit error rate (BER) performance of three blind algorithms is studied based on post correlated model of received signal, and a time‐varying multiple vector channel model which is an extended form of the Gaussian wide sense stationary uncorrelated scattering (GWSSUS) channel. By using the Volterra series theory, an analytical expression for amplitude modulation to phase modulation (AM–PM) conversion is determined as a phase statement of LNA compression. In this approach, by combining the analytical expression for AM–PM conversion and CDMA blind beamforming techniques, we evaluate the AM–PM distortion effects on BER performance of a CDMA system originated from multiple non‐linear LNA blocks. Simulation results show that conditions are found to minimize AM–PM conversion introduced by multiple non‐linear blocks in the system leading to low BER. Copyright © 2006 John Wiley & Sons, Ltd.     

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     

An efficient method for nonlinear distortion calculation of the AM and PM noise spectra of FMCW radar transmitters

The demand for autonomous cruise control and collision warning/avoidance systems has increased in recent years. Many systems based on frequency-modulated continuous-wave (FMCW) radar have emerged and are still in development. Due to the high complexity of such systems, the accurate evaluation of the noise spectra in the transmitter chain driven by complex modulated signals is today a severe drawback due to the limitation of simulation tools. In this paper, a method is proposed to compute easily with any commercially available nonlinear simulator, the amplitude and phase modulated signal distortion introduced by the nonlinearities of the transmitter on an FMCW signal. First, the amplitude modulation (AM) and phase modulation (PM) noise spectra of the driving FMCW signal is derived from the knowledge of the continuous wave (CW) AM and PM noise spectra of the voltage-controlled oscillator (VCO), and the modulating saw-tooth signal applied. Using the narrow band envelope concept and a first-order expansion of the nonlinear transfer function of the transmitter, the transfer of the AM and PM noise spectra of the driving FMCW signal through the nonlinear transmitter chain and the resulting output distortion are then computed. This novel approach allows to compute with reduced computation time and very good accuracy the AM/AM, AM/PM, PM/PM, and PM/AM conversion terms in any nonlinear system driven by CW or FMCW signals. This new method has been applied to the characterization of a whole car radar transmitter operating at 77 GHz driven by an FMCW signal issuing from a VCO. A successful comparison between measured and simulated PM-to-AM conversion coefficients of this transmitter is shown, validating the proposed method.     

Transmitter linearity considerations for digital TV broadcasting

An introduction is given to the principles of digital modulation as it is being applied to advanced television by comparison with the way in which chrominance information modulates the NTC color subcarrier. The concept of the unit circle in constellation diagrams is explained for both signal-to-noise ratio and signal-to-interference. Using constellation diagrams, the effects of AM/AM and AM/PM and their combined effects are shown in terms of reducing noise/interference margins. it is seen that the dynamic range of the ATV transmitter must be sufficient to handle the transient peak power which results from filtering to constrain the data to the 6-MHz channel. Out-of-channel spectral components are generated by intermodulation in the high-power amplifier, as are in-channel intermodulation components which are responsible for reducing the eye opening. This results in reduction in noise/interference margins. It is shown that nonlinear amplification of the transient peaks results in intermodulation products that may cause interference to a signal on adjacent channels and reduce expected coverage     

A Polar Modulator Using Self-Oscillating Amplifiers and an Injection-Locked Upconversion Mixer

A polar modulator for use with non-constant envelope signals is presented. Techniques for efficient behavior of both the amplitude (AM) and phase (PM) path are introduced. The amplitude modulation technique is based on asynchronous pulse-width modulation of a phase-modulated RF signal. The digital signal generated in this way is suited for amplification using a nonlinear, efficient type of PA, while preserving the AM modulation, since this information is present in the signal. The efficiency of the switching amplifier is less dependent of the output power, compared to class B operation. Using a self-oscillating, asynchronous type of pulse-width modulator, the spurs are concentrated in narrow bands well separated from the signal band. These switching spurs are filtered out by the filters already present in the transmitter. The feasibility of this RF-pulse-width-modulation is proven by measurements with amplitude modulated signals on a prototype in 0.18 mum CMOS. Unmodulated, the circuit is able to deliver a peak output power of 8.26 dBm with a drain efficiency of 35%. In the phase-modulation path of the polar modulator, injection locking of an oscillator is used as a single-stage high-gain amplifier. Avoiding multiple stages and related power loss improves the overall power efficiency.     

通信行波管转移特性测试方法

行波管一般作为微波放大器的末级,其性能好坏直接影响到通信整机系统的性能。在测试过程中,由于受到矢量网络分析仪的信号源输出功率和行波管增益限制,多采用固态放大器作为前级放大器推动行波管达到所需功率要求,因此不能直接精确得到行波管自身的特性。采用本测试方法可以去除固态放大器的影响,提高测试行波管的转移特性曲线的准确度。     

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。     

Ka波段高精度模拟预失真线性化器

模拟预失真技术是改善行波管放大器非线性失真的一种有效方法,但补偿精度较低的缺点是制约其进一步发展的关键因素。增益相位独立调节技术和补偿曲线形状调节技术是提升模拟预失真补偿精度的重要技术。提出了一种适用于Ka波段行波管放大器的高精度模拟预失真器,该预失真器采用双路矢量合成式结构,在29~31 GHz 范围内,通过调节二极管偏置电压可以同时实现补偿曲线形状调节和增益相位扩张量独立调节,有效提升了补偿精度。与行波管放大器的联合测试结果表明,在30 GHz 时,该预失真器可以将行波管放大器的增益压缩从5.3 dB 减小到1.2 dB,相位偏移从62°减小到6.5°。线性化后的行波管放大器的非线性失真明显降低,在输出功率回退5 dB 时,三阶互调系数提高了9.3 dB。     

AM-PM conversion introduced by weakly nonlinear circuits

This paper is related to a novel model for the AM–PM conversion characterization of systems. By means of nonlinear transfer function analysis, AM–PM conversion is obtained as a phase statement of compression and desensitization, thus immunity against electromagnetic interference of radio systems can be evaluated when the signal undergoes fading or when it is received with interfering oscillations. The model is used to obtain the AM–PM conversion introduced by a feedforward amplifier. The results show that the maximum compensation of third-order intermodulation does not necessary coincide with the minimum AM–PM conversion condition.     

Theoretical analysis and performance of OFDM signals in nonlinearAWGN channels

Orthogonal frequency-division multiplexing (OFDM) baseband signals may be modeled by complex Gaussian processes with Rayleigh envelope distribution and uniform phase distribution, if the number of carriers is sufficiently large. The output correlation function of instantaneous nonlinear amplifiers and the signal-to-distortion ratio can be derived and expressed in an easy way. As a consequence, the output spectrum and the bit-error rate (BER) performance of OFDM systems in nonlinear additive white Gaussian noise channels are predictable both for uncompensated amplitude modulation/amplitude modulation (AM/AM) and amplitude modulation/pulse modulation (AM/PM) distortions and for ideal predistortion. The aim of this work is to obtain the analytical expressions for the output correlation function of a nonlinear device and for the BER performance. The results in closed-form solutions are derived for AM/AM and AM/PM curves approximated by Bessel series expansion and for the ideal predistortion case     

100-GHz cooled amplifier residual PM and AM noise measurements, noise figure, and jitter calculations

We report the first definitive PM and AM noise measurements at 100 GHz of indium phosphide (InP) amplifiers operating at 5 K, 77 K, and room temperature. Amplifier gain ranged from +7 to +30 dB, depending on input RF power levels and operating bias current and gate voltages. The measurement system, calibration procedure, and amplifier configuration are described along with strategies for reducing the measurement system noise floor in order to accurately make these measurements. We compute amplifier noise figure with an ideal oscillator signal applied and, based on the PM noise measurements, obtain NF=0.8 dB, or a noise temperature of 59 K. Measurement uncertainty is estimated at /spl plusmn/0.3 dB. Results show that the use of the amplifier with an ideal 100-GHz reference oscillator would set a lower limit on rms clock jitter of 44.2 fs in a 20-ps sampling interval if the power into the amplifier were -31.6 dBm. For comparison, clock jitter is 16 fs with a commercial room-temperature amplifier operating in saturation with an input power of -6.4 dBm.     

Modulation-transfer noise effects among FM and digital signals in memoryless nonlinear devices

When two or more frequency-modulated and/or digital carriers of various sizes and modulation formats are transmitted through a common memoryless nonlinear device with AM/AM and AM/PM characteristics such as a traveling-wave tube amplifier, interactions among the carriers will occur. One of the impairments caused by these interactions results in modulation-transfer noise effects. In particular, in satellite communications, depending on the manner multicarrier transponders are used, the modulation-transfer impairment manifests itself under various forms and subjective interference effects. This tutorial-review paper presents an introduction to this type of impairment, methods of analysis and examples, and measurement results. General practical guidelines are suggested for controlling these effects.     

一种新型线性化器的研究

介绍了固态功率放大器的线性化技术,并提出了一种新型反向并联肖特基二极管预失真器结构。对预失真器原理与基本结构进行了分析,通过改变预失真器中二极管的外加偏置电压和电阻值来调节失真信号的幅度和相位,达到线性化的目的。同时,利用ADS软件对加预失真器的固态功率放大器进行电路优化仿真,根据电路优化参数,对线性化固态功率放大器进行研制。测试结果表明,固态功率放大器三阶交调改善了15.8 dB,五阶交调也改善了10 dB,线性化改善效果明显,突破了工程化应用的技术瓶颈。     

雷达发射机射频性能分析

现代雷达发射机多半采用O型管放大链来放大固定载频信号，射频信号通过放大链会产生频率域或时间域失真。频率域失真是由放大链本身的非线性所引起的，而时间域失真主要是由幅度调制和相位调制引起的。     

雷达发射机射频性能分析

现代雷达发射机多半采用O型管放大链来放大固定载频信号,射频信号通过放大链会产生频率域或时间域失真。频率域失真是由放大链本身的非线性所引起的,而时间域失真主要是由幅度调制和相位调制引起的。