Direct RF modulation on semiconductor lasers of wavelength 1310 nm has been widely applied to amplitude modulation vestigial side-band(AM-VSB)lightwave cable television (CATV) systems. The channel capacity is limited mainly by the nonlinear distortion of laser diode, which induces system performance degradation of composite second order (CSO) and composite triple beats (CTB). Though the linearity of laser diode has been improved during the fabrication process, carrier to noise ratio (CNR), CSO, and CTB were still degraded by increasing either RF output power level or the channel loading. Thus, some linearization techniques were proposed to extend the channel capacity. The predistortion approach is the simplest and the lowest cost one among the techniques. This paper describes a distortion compensation method with an electrical ¡§branch¡¨ circuit configuration, which is designed to reduce the nonlinear distortion induced by the laser diode. In this architecture, we utilize the method of impedance non-matching and the reflection of signals. According to the experiment results, we have found that before predistortion compensation, CNR / CSO / CTB are 51.6 dB / 62 dBc / 70 dBc, respectively. After compensation, CNR / CSO / CTB are 51.5 dB / 70 dBc / 71 dBc, respectively. Comparing with and without the distortion compensation, we found that CSO has an improvement with 8 dB, which reveals that the predistorion circuit improves the linearity of laser obviously. This study may give a guideline of predistortion technique and help to design optical transmitter.

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / The CNES (French Space Agency) has studied memoryless predistortion techniques for power amplifier nonlinearity of satellite payload telemetry. These techniques are applied to high order modulations taken from the DVB-S2 standard and the associated CCSDS blue book. An easy-to-implement calibration method was also developed. The predistortion was implemented at two times the symbol rate after Square Root Raised Cosine shaping on a breadboard model of a 16APSK modulator associated to a Solid State Power Amplifier. It allows to reduce the amplifier back-off and thus to increase the power added efficiency for an equivalent signal quality.

Radio frequency power amplifiers (PAs) are the most challenging part of the design of radio systems since they dictate the overall system's performance in terms of power efficiency and distortion generation. The performance is further challenged by modern modulation schemes which are characterized by highly varying signal envelopes. In order to meet the spectrum mask requirements, PAs are usually operated at high power back-off to ensure linearity, at the cost of efficiency. To tackle this issue, many efficiency enhancement techniques have been presented in the literature. In fact, these techniques do increase the PA power efficiency at back-off, however, efficiency enhancement techniques do not ensure the linearity of the PA. Furthermore, these techniques may lead to additional distortion. On the other hand, several linearization techniques have been developed to mitigate the PA nonlinearity problem and allow the PA to operate at less back-off. Digital Pre-Distortion (DPD) technique is gaining more attention, as compared to other linearization techniques, thanks to its simple concept and advancements in digital signal processors (DSP) and signal converters. DPD technique consists of introducing a nonlinear function before the PA so that the overall cascaded system behaves linearly. It was clear from the literature that this technique showed good performance. Yet, it has primarily been validated using commercial test equipment, which has good capabilities, and far from the real world environment in which this technique would be implemented. Indeed, DPDs would need to be implemented in signal processors characterised by limited resources and computational accuracy. This thesis presents an implementation of several DPD models, namely look-up table (LUT), memoryless polynomial and memory polynomial (MP), on a field programmable gate array (FPGA). A novel model reformulation made this implementation possible in fixed-point arithmetic. Measurements were collected to validate the DPD models' implementation and an improvement of the signal quality was recorded in terms of error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR). As many wireless access technologies must continue to coexist, multi-standard radio systems are required to reduce the cost while maintaining the interoperability. This thesis presents a development platform for multimode radio which comprises mixed-signal modules. The platform provides the capacity for hardware and software development. In fact, the FPGA under investigation allowed for the implementation of a baseband transceiver and DPD schemes. In addition, a software tool was developed as a dashboard to control and monitor the system. The radio system in the platform was optimized through the equalization of the feedback receiver frequency response performed through a simultaneous measurement of the amplitude ripple of the transmitter and receiver. Furthermore, a phase-coherent frequency synthesizer was designed to bring more flexibility by allowing the transmitter's carrier frequency to be different from the receiver's frequency.

This thesis aims to use a hybrid quadrature polar modulator (HQPM) for enhancing average efficiency of 3G mobile transmitter with power control. The HQPM consists of a quadrature modulator instead of a phase modulator in the polar modulator for processing the RF modulated carrier and a Class-S modulator for processing the envelope signal. In addition, the instantaneous magnitude of the quadrature modulated signal is propotional to the instantaneous envelope magnitude. As a result, the output feed-through and gain-compression phenomenon in the polar modulator can be improved. The digital baseband processor realized by FPGA can generate CDMA2000 1x baseband signal with excellent modulation accuracy. For enhancing the average transmit efficiency, the output PA is realized as Class-E design. But the Vdd/AM and Vdd/PM nonlinear effects of the Class-E PA distort the output signal. To solve this problem, a digital predistorter is presented to compensate the nonlinear distortions. The proposed HQPM-based transmitter can simultaneously achieve high efficiency and high linearity over a wide modulated output power range.

This dissertation presents a hybrid quadrature polar modulator (HQPM) to drive the power amplifier (PA) highly efficiently in a wireless RF transmitter with good potential for multi-mode operation. For enhancing the efficiency, a Class-E PA is used in the transmitter. The HQPM consists of a quadrature modulator for processing the RF modulated carrier and a Class-S modulator for processing the supply-voltage signal. The quadrature modulator and the Class-S modulator deliver the output signals with envelope variation before being inserted into the RF-input terminal and the supply-voltage terminal of Class-E PA, respectively, causing the double envelope modulation to distort the modulated RF signal at the PA output. Therefore, a digital predistorter is proposed to be embedded in the HQPM for compensation. The use of such predistorted HQPM techniques can help reducing the average DC and RF input powers and the output feed-through levels so as to enhance power added efficiency and adjacent channel power rejection quite remarkably.

For millimeter wave applications, MMIC is the best contemporary technology. Considering the requirements of the commercial and military applications on amplitude and phase linearity, it is necessary to reduce the nonlinearity of the amplifiers. There are several linearization techniques that are used to reduce the nonlinearity effects. In the context of the thesis, a special analog predistortion technique that is called &ldquo / self cancellation scheme&rdquo / is used to linearize a 35GHz MMIC amplifier. The amplifier to be linearized is used in the design of the predistorter, that is why it is called self cancellation. This thesis contain the design of the amplifier, lumped element power divider and combiner circuits, and the complete analog predistortion linearizer. Layouts of linearizer system and its components are prepared and layout effects are taken into account.

The purpose of this thesis is to linearize a power amplifier using digital predistortion. A power amplifier is a nonlinear system, meaning that when fed with a pure input signal the output will be distorted. The idea behind digital predistortion is to distort the signal before feeding it to the power amplifier. The combined distortions from the predistorter and the power amplifier will then ideally cancel each other. In this thesis, two different approaches are investigated and implemented on an FPGA. The first approach uses a nonlinear model that tries to cancel out the nonlinearities of the power amplifier. The second approach is model-free and instead makes use of a look-up table that maps the input to a distorted output. Both approaches are made adaptive so that the parameters are continuously updated using adaptive algorithms. First the two approaches are simulated and tested thoroughly with different parameters and with a power amplifier model extracted from the real amplifier. The results are shown satisfactory in the simulations, giving good linearization for both the model and the model-free technique. The two techniques are then implemented on an FPGA and tested on the power amplifier. Even though the results are not as well as in the simulations, the system gets more linear for both the approaches. The results vary widely due to different circumstances such as input frequency and power. Typically, the distortions can be attenuated with around 10 dB. When comparing the two techniques with each other, the model-free method shows slightly better results.

Digital predistortion is a signal processing technique used to remove undesired distortions caused by nonlinear system effects. This method is predominately used to linearize power amplifiers in communication systems in order to achieve efficient transmitter circuits. However, the technique can readily be applied to cancel undesired nonlinear behavior in other types of systems. This thesis investigates the effectiveness of digital predistortion in the context of a wideband arbitrary waveform generator. A theoretical foundation discussing nonlinear system models, predistortion architectures and system identification methods is complemented with a simulation study and followed by verification on a real system. The best predistorter is able to fully suppress the undesired distortions for any fixed two-tone sinusoidal signal. Furthermore, the results indicate the existence of a wideband predistorter which yield acceptable suppression over a frequency range of several hundred MHz. / Digital predistorsion är en signalbehandlingsteknik som används för att undertrycka oönskade distorsioner orsakade av icke-linjära effekter i elektriska system. Denna metod används i huvudsak för att linjärisera effektförstärkare i kommunikationssystem för att erhålla effektiva sändarkedjor men tekniken kan utan större problem även tillämpas på andra typer av icke-linjära system. Denna uppsats undersöker i vilken utsräckning digital predistorsion kan användas för att undertrycka oönskade signaldistorsioner i en bredbandig signalgenerator. Uppsatsen presenterar en bakgrund som utgår ifrån teorin om icke-linjära systemmodeller, arkiteturer för predistorsion och systemidentifieringsmetoder. En kvantitativ studie i en simuleringsmiljö åtföjs av en utvärdering på ett verkligt system. Det bästa predistorsionssystemet åstadkommer en fullständig linjärisering i testfallet med en fix tvåtonssignal. Resultaten indikerar även att det existerar ett system som linjäriserar signaler i ett frekvensområde som uppgår till hundratals MHz.

Yes / This paper presents an improved mathematical model for calculation of distortion vectors of two aligned surface meshes. The model shows better accuracy when benchmarked to an existing model with exceptional mathematical conditions, such as sharp corners and small radii. The model was implemented into a developed distortion compensation digital tool and applied to an industrial component. The component was made of Inconel 718 and produced by laser powder bed fusion 3D printing technology. The digital tool was utilised to compensate the original design geometry by pre-distortion of its original geometry using the developed mathematical model. The distortion of an industrial component was reduced from approximately ±400 µm to ±100 µm for a challenging thin structure subjected to buckling during the build process.

The fusion of voice and data applications, along with the demand for high data-rate applications such as video-on-demand, is making radio frequency (RF) spectrum an increasingly expensive commodity for current and future communications. Although bandwidth-efficient digital modulation alleviates part of the problem by requiring a minimal use of spectral resources, they put an extra design burden on RF engineers. RF transmitters and power amplifiers account for more than half the total maintenance cost of a base-station, while occupying nearly the same portion of space. Therefore, power amplifiers become a bottleneck for digital systems in terms of space and power consumption. However, power-efficient use of the amplifiers, although desirable, is extremely detrimental to end-to-end performance due to the very high peak-to-average power ratios of modulations that are used today. In order to reduce distortion while maintaining high power conversion efficiency in a power amplifier, linearization schemes are needed. In addition, significant frequency-dependent Memory Effects result in high power amplifiers operating on wideband signals. Therefore, these effects need to be considered during any attempt to minimize amplifier distortion. In this thesis, we present two schemes to cancel nonlinear distortion of a power amplifier, along with its memory effects and results for one of the schemes. The results highlight the fact that in the presence of significant memory effects, cancellation of these effects is necessary to achieve reasonable improvement in performance through linearization. We focus on predistortive schemes due to their digital- friendly structure and simple implementation. The operating environment consists of a multi-carrier W-CDMA signal. All of the studies are performed using numerical simulation on MATLAB and Agilent's Advanced Design System (ADS). / Master of Science