Browsing by Subject "Nonlinear programming."

Now showing 1 - 6 of 6

Open Access
Adaptive digital predistortion for linearization of power amplifier
(2009) Şekerlisoy, Burak
In most communication systems, power amplifiers are used to obtain high output power. The nonlinear characteristics of the power amplifier leads to the distortion of the output signal. This distortion affects the efficiency of the power amplifier. The way to reduce this effect is to linearize the power amplifier near the saturation region where it is nonlinear. The widely used technique for the linearization of power amplifiers is predistortion. The proposed technique for predistortion uses a LUT(look-up-table), a complex multiplier, an address calculator, delay elements and an adaptation logic. A new adaptation logic to update the LUT coefficients, is used. The predistorter is simulated in Matlab software using a baseband model for the power amplifier. 16-QAM baseband modulation is used to simulate the predistorter. In order to see the performance of the proposed predistorter, hardware logic is implemented in FPGA and experimental setup with RF circuits and RF power amplifier is used. For different LUT sizes, the algorithm is tested and for the LUT size of 64, nearly 15 dB improvement in power spectrum is observed. The LUT size of 64 is observed to be the optimal LUT size in the experiments.
Open Access
Adaptive digital predistortion for power amplifier linearization
(2008) Aslan, Makbule Pehlivan
High power amplification of linear modulation schemes which exhibit fluctuating envelopes, invariably leads to the generation of distortion and intermodulation products. In order to avoid these effects, maintaining both power and spectral efficiency, it is necessary to use linearization techniques. By using linearization techniques, the amplifier can be operated near the saturation with good efficiency and linearity. The technique proposed here is predistortion based on a look-up table (LUT) method using input and output signal envelopes. The predistortion is implemented using a LUT and an address generation block that selects the appropriate coefficient from the LUT, given the magnitude of the input signal. The testing of the predistorter is done by using a baseband system model which consists of a 16-QAM modulator, an upsampler, a raised cosine filter, the predistorter and a baseband behavioural amplifier model. The performance of the predistorter with a new LUT update method is evaluated in terms of power efficiency and spectrum efficiency. MATLAB simulations show that to obtain up to 25-30 dB improvement in power spectrum is possible and sufficiently large LUT size is needed to reduce the background noise level. Furthermore, the performance of the predistorter in the case of an amplifier with memory is also investigated. The algorithms have been implemented on an FPGA chip. The performance of the system is as predicted in MATLAB simulations.
Open Access
Aggregate production planning: an application in Özkaşıkçı Flour Mill
(1996) Çağan, Alpas
Aggregate planning is medium-range capacity planning that typically covers a time horizon of anywhere from 3 months to 18 months. The goal of aggregate planning is to achieve a feasible production plan that will effectively utilize the organization’s resources to satisfy expected demand. In this study. Aggregate Production Planning is applied to 0zka?ik9i Flour Mill in order to maximize the total profit by using the optimal allocation of export and domestic sales to the plant capacity. A nonlinear programming (NP) model is developed and the proposed model is run on GAMS (General Algebraic Modeling System) software package. Alternative scenarios are applied to the model in order to find optimal allocation of export and domestic production and to maximize the total profit.
Open Access
Implementation of a continuation method for nonlinear complementarity problems via normal maps
(1997) Erkan, Ali
In this thesis, a continuation method for nonlinear complementarity problems via normal maps that is developed by Chen, Harker and Pinar [8] is implemented. This continuation method uses the smooth function to approximate the normal map reformulation of nonlinear complementarity problems. The algorithm is implemented and tested with two different plussmoothing functions namely interior point plus-smooth function and piecewise quadratic plus-smoothing function. These two functions are compared. Testing of the algorithm is made with several known problems.
Open Access
Power amplifier linearization by predistortion
(2006) Durukal, Mustafa
Power amplifiers are important elements in communication systems but they are inherently nonlinear. This nonlinearity shows itself in the form of amplitude and phase distortion. One way to get rid of this nonlinear behaviour is to apply backoff which means to operate the amplifier at an output power smaller than its saturated output power. As the backoff is increased, the amplifier will behave more linearly. But this will also reduce the efficiency of the amplifier, which is undesirable. This tradeoff between efficiency and linearity is solved by linearization techniques. By using linearization techniques, the amplifier can be operated near to saturation with good efficiency and linearity. This thesis focuses on polar polynomial predistortion and polar look-up table predistortion, which are popular linearization techniques. A polar polynomial predistorter and a polar look-up table predistorter are implemented and tested with simulations in software. The implementation and testing is done by using IT++ which is a C++ library of mathematical, signal processing, speech processing, and communications classes and functions. The testing of the predistorters is done by using a baseband system model which consists of a 16-QAM modulator, an upsampler, a raised cosine filter, the predistorter and a baseband behavioural amplifier model. The performance of the predistorters is evaluated in terms of adjacent channel power ratio, AM/AM & AM/PM responses and BER under AWGN. Simulation results show that the predistorters have good performance. In the simulations, the polar polynomial predistorter achieved 20 dB reduction and the polar look-up table predistorter achieved 25 dB reduction in adjacent channel power ratio. The effect of polynomial order and table size on the performance of the predistorters is investigated. Furthermore, the effect of lowpass filtering on the performance of the predistorters is also investigated by placing a lowpass filter after the predistorters in the system model. It is observed that as the ratio of the bandwidth of the lowpass filter to the bandwidth of the raised cosine filter decreases, the negative effect of the lowpass filter on the performance of the predistorters increases.
Open Access
Solution of feasibility problems via non-smooth optimization
(1990) Ouveysi, Iradj
In this study we present a penalty function approach for linear feasibility problems. Our attempt is to find an eiL· coive algorithm based on an exterior method. Any given feasibility (for a set of linear inequalities) problem, is first transformed into an unconstrained minimization of a penalty function, and then the problem is reduced to minimizing a convex, non-smooth, quadratic function. Due to non-differentiability of the penalty function, the gradient type methods can not be applied directly, so a modified nonlinear programming technique will be used in order to overcome the difficulties of the break points. In this research we present a new algorithm for minimizing this non-smooth penalty function. By dropping the nonnegativity constraints and using conjugate gradient method we compute a maximum set of conjugate directions and then we perform line searches on these directions in order to minimize our penalty function. Whenever the optimality criteria is not satisfied and the improvements in all directions are not enough, we calculate the new set of conjugate directions by conjugate Gram Schmit process, but one of the directions is the element of sub differential at the present point.