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Projecte llegit

Títol: Study of space condition effect and analyzing digital techniques for improving RF power amplifier's linearity and efficiency for small satellites

Estudiants que han llegit aquest projecte:

Director/a: GILABERT PINAL, PERE LLUÍS

Departament: TSC

Títol: Study of space condition effect and analyzing digital techniques for improving RF power amplifier's linearity and efficiency for small satellites

Data inici oferta: 26-03-2015     Data finalització oferta: 26-11-2015


Estudis d'assignació del projecte:
    Tipus: Individual
     
    Lloc de realització: EETAC
     
    Segon director/a (UPC): MONTORO LÓPEZ, GABRIEL
     
    Paraules clau:
    digital predistortion, power amplifier, small satellites, power efficiency
     
    Descripció del contingut i pla d'activitats:
    The design and implementation of miniaturized satellites is growing rapidly with passage of time due to its large number benefits and applications. However, on the other side, these benefits comes with a compromise on reduction of mass and power for every component used on-board.
    The transmitter segment of communication subsystem of a small satellite is of foremost importance in terms of high downlink capabilities and power consumption. The core objective of a communication subsystem is to achieve the maximum possible downlink data rate to earth station during a pass of few minutes. The higher data rates demands high power consumption and large mass which is the certain limitation in case of small satellite. The Radio Frequency Power Amplifiers are an important component of satellite transmitter in terms of power consumption. During attaining the maximum efficiency from power amplifier, its behavior tends to become non-linear which ultimately vitiates the signal to distortion ratio.
    Furthermore, the transmitter premeditated for the space applications is to be designed by considering a large number of constraints. Each component used, must be operational under the extreme space conditions and has the capability to persist the effects induced by outer space.
    Therefore, this Master Thesis is basically sectioned into two phases. The first phase of thesis will include the study and analysis of transmitter components with respect to space conditions. The certain properties for example radiation effect, size constraint and heat dissipation abilities of the transmitter components (especially RF Power Amplifier) or the effects on frequency/wavelength of signals such as Doppler Effect/ Doppler shift will be analyzed. With this analysis, the idea is to find out the best suitable transmitter components for the small satellites which can operate at minimum power with more efficiency and linearity eventually having higher data rates.
    The second phase of Thesis will be composed of designing the Digital pre-Distorter to compensate the non-linear behavior of power amplifier. Digital pre-distortion technique is the most suitable method to apply in a communication chain which has non-linear output because of its efficiency and ease of implementation. The algorithm for digital pre-distorter will be written in Matlab and results of linear behavior of power amplifier will be analyzed with the help of simulating the algorithm. Various methods for finding the digital pre-distorter parameters will be examined to achieve desired results.

    Methodology:
    Developing know-how of the theoretical aspects related to topic and instruments/components used during project.
    - Study and Analysis of space envoirment/conditions effects on the components involved and communication chain for small satellite.
    - Design the algorithm in Matlab for the digital pre-distorter.
    - Perform Matlab-based simulations for the transmitter.
    - Observation, analysis and comparison of results obtained.
     
    Overview (resum en anglès):
    Objective of modern small satellite communication is to provide the end users with higher data rate downlink capability, in addition to, reliability and system efficiency. A significant device, with respect to power consumption and influence on system linearity, use in the transmission chain of small satellites, is power amplifier. The power amplifier tends to add distortion and non-linearity in the transmitted signal, when operating close to saturation point. For avoiding the non-linearity addition by the PA, it should be operated in linear region which causes the degradation in power efficiency. Therefore, for having the maximum power efficiency and improving linearity, the predistortion should be performed before inputting the signal to power amplifier. For compensating non-linear distortion, linearization scheme based on digital predistortion is used, which requires a feedback path for adaptation and extraction of new coefficients for DPD. Hence for making the DPD adaptive, ADC is required to add in the system. As a consequence of performing digital predistortion, the spectral regrowth occurs which causes the increase in bandwidth up to five times of original signal. Due to this reason, digital to analog converter has to sample the signal at five times of nyquist frequency which increases the cost and power consumption of DAC.
    This master thesis presents the methodology implementation for compensating the non-linear distortion in PAs, applicable for small satellite communication, with a cooperative technique of digital and analog predistortion. This thesis provides with the solution for the increased sampling rate of signal at analog to digital converter with a use of combination of digital and analog predistortion. The predistortion (digital and analog) is design to focus on maximizing the linearity and minimizing the distortion and spectral regrowth. While the adaptive scheme of combined digital predistortion and analog predistortion (simulated) is designed, with an ideal low-pass filter between them, for implementation ease of the digital-to-analog converter and decrease in signal sampling rate.
    The results provided in the thesis have shown that same linearity and efficiency can be achieved at amplifier’s output by implementing the above mentioned solution with a benefit of reducing the signal sampling frequency at DAC. A comparative analysis of power amplifier behavior in various configuration is presented in the dissertation.

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