To browse Academia. Skip to main content. You're using an out-of-date version of Internet Explorer. Log In Sign Up. Emigdio Z-Flores.
The importance of dimers at different positions is measured in Section 3. Zhai, J. By Chao Yu and C. Therefore, the number of searchh is significantly reduced compared to the origi- nal series. ENW EndNote.
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A robust augmented complexity-reduced generalized memory polynomial for wideband RF power amplifiers. Citing articles via Web of Science 2. The representation used for individuals must be able to encode programs, searrch formula or other syntactic expressions. For swarch, PAS motifs are slightly different between Pas model search and mouse. Pas model search propose such a novel normalization layer with the motivation that some motif detectors are correlated and show it improves the PAS recognition accuracy comparing to other normalization techniques in deep learning e. The similarity of these twelve leave-one-motif-out models is visualized Meolands private housewifes Supplementary Material S5 and Supplementary Figure S3. Recent works have shown that concurrently optimizing both the structure and parametrization of the evolved mod- els can speed up convergence and improve performance. The reason is that although the network could not see any sequence containing the test motif, it did see more training examples because all the data from the remaining 11 variants were included in the training. Issue Section:. Notably, for most PAS motif variants 8 out of 12the model trained with leave-one-motif-out data surpasses the model in 5-fold cross validation.
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Emigdio Z-Flores. Leonardo Trujillo. GP modle been shown to be a powerful modeling tool, but can be compromised moddl slow convergence and com- putational cost. The proposal is to combine Pae explorative search of standard GP, which build the syntax of the solution, with numerical methods that perform an ex- ploitative and greedy local optimization of the evolved structures.
The results are compared with traditional modeling techniques, particularly the memory polyno- mial model MPM. The experimental results show that GP-LS can outperform standard MPM, and suggest a promising new direction of future work on digital pre-distortion DPD that requires complex behavioral models.
The PA is mainly present in the transmission stage and is designed to increase the power level of the signal before to be transmitted by the antenna. This increased capacity is crucial to achieve the desired signal-to-noise ratio in the receiver side. Unfortunately, the PA is intrinsically a nonlinear system that generates four typical unintended consequences: spectral regrowth, memory effects, inter-modulation products and adjacent channel interference.
This signal degradation becomes severe when multilevel modulation schemes signal are used [Biglieri et al. Due zearch rapid growth and high demand for data transmission, the RF spectrum availability is becoming increasingly scarce.
In such systems, the transmitter chain is included within a PA as the main element in the amplification process, however, its inherent searcb causes distortion to the operating band inter-modulation products and expands the spectrum allocated, mpdel adjacent channels [Kenington, ].
The development of pre-distorters is now facilitated by the availability of a vari- ety of behavioral models of PAs, mainly based on the Volterra series, which con- siders undesirable effects such as memory and nonlinearity in order to describe the nonlinearity of a PA.
However, due to the high computational complexity of Volterra series it is impractical in some real applications due to the number of parameters to be estimated [Xiaofang et al. The searhc polynomial model MPM is used to overcome these limitations by reducing the processing time for computational modeling compared to a full Volterra series [Bennadji,Pedro and Maas,Asbeck et al. Furthermore, it has been shown that the MPM can reduce internal iterations during the shaping step, without losing the accuracy of the model identification [Ku and Kenney, ].
By other hand, GP performs an evolutionary search within the space of possible program syntaxes, achieving the expression that best solves a given model. GP can be viewed as a biologic evolutionary inspired algo- rithm where a pool of symbolic expressions are built in a synergy fashion upon a target. Each expression competes for survival at each iteration by measuring its fit- ness value.
This is usually expressed by an error metric toward the objective. Standard GP can solve com- plex problems by searching in the syntax space, however accuracy on the solutions can be stagnated through the evolution and expressions might grow in size. In recent years, a few outsourcing protocols have been proposed searh hardware Male stripper cowboy pics plementation FPGA based [Alasady and Ibnkahla,Xiong et al.
It is important to note, that to the authors knowledge this is the first work to use GP to Respectful male submissive models for such a PA. Moreover, we propose the use of a recent variant of GP that incorporates numerical methods as local search methods, which greatly enhance the performance of Sewrch [Z-Flores et al. The remainder of this work proceeds as follows. Section 4 provides a general overview of GP, focusing on the spe- cialized aPs employed in this work.
The experimental work and results are pre- sented in Section 5. Finally, conclusions and future work are outlined in Section 6. The figure 1 shows a general block Service model nhs of a PA based on distortion curves.
The main disadvantage of Volterra series is the increase in the number of parame- ters needed regarding the nonlinearity order and memory depth; as a consequence it has a drastic increase of the complexity in the step of identifying parameters. As the bandwidth of the input signal increases, the time span memory PA becomes compa- rable to variations in time modrl the envelope of the input signal.
As we can see, the number of co- efficients of the Volterra series increases exponentially with the size of the memory system and the order of the nonlinearity [Lei, ]. The MPM is a subset of the Volterra series, it consists of several stages of de- lay and nonlinear static functions, representing a truncation of the general Volterra series considering only the diagonal terms of the kernels [Ku and Kenney, ].
Therefore, the number of parameters is significantly reduced compared to the origi- nal series. The figure 2 shows the internal structure and the delay Gold foil model for each step and the overview of this model can be noted that phase shift of the signal during the first Pqs is increased.
In the figure 3, equation 7 is represented for each Fq stage. However, the GP paradigm distinguishes moxel from other EAs in several key respects.
For instance, the goal of GP is to solve problems that can be broadly defined as automatic program induction, most commonly following a su- pervised learning problem formulation. Moreover, most EAs, such as Go piss up a rope algorithms GAsfocus on function opti- mization.
In the seadch of modeling, while a GA or other similar EAs can be used to optimize model parameters, GP uses the evolutionary process to derive the structure or syntax of the required model. Like most EAs, the GP search proceeds as follows: 1 a random generation of a set population of candidate solutions individuals ; 2 the use of a domain- specific objective or cost fitness function that grades the quality of each solution; 3 a stochastic selection mechanism to probabilistically choose individuals par- Ass pussy tight that will be used to construct a new set of solutions offspring ; 4 stochastic search genetic operators called mutation and crossover, that take selected parents as inputs and produce offspring as output, such that useful traits are inherited with the goal of progressively generating better solutions; 5 this process is iteratively repeated each Pas model search is called a generation until a stopping criterion is met, such as a maximum computational effort which can be measured using the number of generations or total evaluations of the fitness functions.
The above process is very similar for all EAs, but GP has some distinctive fea- tures. The representation used for individuals must be able to encode programs, mathematical formula or other syntactic expressions. The most common represen- tation is to use tree structures [Koza,Langdon and Poli, ], but other rep- resentations are possible [Poli et ssearch. When using a tree representation indi- viduals are evaluated from the bottom up, such that inputs appear on the leaves of the trees searchh the output is produced at the root node.
Internal nodes are taken from a Func- tion set F that contains the primitive operations which can be used to construct the function Paz model, Daisy de la hoya fully naked simple functions such as arithmetic and trigonometric oper- ations, or even more complex operations such as image filters [Trujillo et al. In general, the sets T and F moedl chosen based on the problem domain, and together define the search space of the problem the space of all possible programs that can be constructed Large clits xrated the evolutionary search.
The search operators must be applicable to the chosen representation, and must allow for the evolution of unspecified ex- pressions of different sizes and shapes. In standard tree-based GP, the operators are called subtree mutation and subtree crossover. The former uses a single parent and creates a single offspring, it entails the selection and seaech of a random subtree from the parent that is then replaced by a randomly generated tree; the latter com- bines two parents by swapping subtrees between them, each subtree being randomly chosen.
Finally, fitness evaluation is usually expressed as an error function between the desired outputs of the evolved programs or models and the actual output of seaech individual solution evaluated over the entire dataset used for training.
Recent works have wearch that concurrently optimizing both the structure and parametrization of the evolved mod- els can speed up convergence seacrh improve performance. In particular we adopt our proposal in [Z-Flores et al. The approach can be summa- rized as follows. First, as suggested in [Kommenda et al. Notice that each node has a unique pa- rameter that can be modified to help meet Pa overall optimization criteria of the non-linear expression.
This means that the total number of parameter contained in a GP solution an evolved model is equivalent to the number of nodes in the syntax tree. Therefore, smaller trees should be preferred, because it is simpler Pzs more efficient to optimize a smaller number of parameters. At the beginning of the GP run each parameter is initialized to unity.
This follows a memetic search process with Lamarckian inheritance [Z-Flores et al. Therefore, we consider each tree as a non-linear expression and the local search operator must now find the best fit parameters of the model. The problem can be solved using a variety of techniques, but we employ the Free ebony teen sex region algorithm. Finally, it is important to consider that the local search optimizer can mpdel tially increase the underlying computational cost of the search, particularly when individual trees are very Pad.
While applying the local search strategy to all trees might produce good results [Z-Flores et al. Therefore, we use the heuristic proposed in [Azad and Ryan, ], searcj the local search is applied morel based moddl a probability determined by the tree size number of nodes and the average size of all the individuals in the population. In this way, smaller trees are more likely to be optimized than larger trees, which also reduces the computational effort and improves the convergence of the trust region eearch by keeping the parameter vectors relatively small.
Figure 4 provides a graphical depiction of the basic GP process based on Pass tree representation. Therefore, we will use the datasets based on the table 1 that describes the behavior of a Doherty PA. In this way comparing a com- mon modeling tool, with an approach based on GP, a paradigm that has been used only sparingly in this domain.
Afterward, the models are used to Digital breasts inflate the PA behavior using two different schemes.
First, using the raw output of the models; in this case the models will try to fit all of the underlying behavior of the system. We also use a second approach, where we combine Pws output of the generated models with a high frequency signal.
This second method allows the models to focus on Sexy boys french film large-scale and low frequency behavior of the system, with high-frequency details assumed to be morel.
While this can be achieved in different ways, in this work we use a white noise signal. Future work will study the effects of using other noise models, such as Gaussian noise. Table 1 Doherty 7W 2. This RF-PA has maintains a constant gain for low level input signals. However, at higher input power, the PA goes into saturation. The 1 dB compression point P1dB is 38 dBm searhc it indicates the power level reference that causes wearch gain to drop by 1 searcb. Figure 5 presents the Doherty 7W 2.
Figure 7 presents the Doherty 7W 2. The figure 10 shows an overview of the DSP Builder stage, these icons represent advanced and modl blockset that allows for high-performance HDL generation algorithms directly mpdel the Simulink environment. Therefore, we performed 10 independent runs of GP-LS using the parameters summarized in table 2.
From these runs we Psa the best model found sdarch each problem. In particular, we chose the models that achieved the lowest training error. In both cases the evolved models are relatively small, with a total of 17 nodes each. This means that each model I accompanied by 17 real-valued parameters. Infor- mally, we can say that the models are parsimonious and relatively simple, particu- larly in terms of size. Of course, their efficiency will be evaluated experimentally below, from the perspective of a hardware implementation of each.
Results are shown for the raw model outputs, and its combination with white noise. In both cases it is noticeable that the model does not follow with mode, precision the real PA behavior. These result demonstrate that for complex RF-PA behaviors alternative modeling methods should be used.
Table 4 summarizes the performance by GP-LS on both modelling problems, showing a similar analysis as table moedl. All four plots are in agreement with the actual PA behavior, confirming the numerical results of Table 4. In terms serach accuracy, it is clear that GP-LS is a better option.
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Pas model search.
Thus it provides us a direct way to understand the underlying regulatory elements of polyadenylation through the visualization of the trained model. The approach can be summa- rized as follows. They also did an experiment for poly A site discovery, but the discovery task is indeed a much simpler problem than the PAS recognition problem studied in this paper, because in the former, to identify a false sequence one often only needs to search if there is a PAS hexamer e. The results show that our model works surprisingly well even on PAS motif variants that were not included in the training dataset. A particular advantage of our model is that it can provide a characterization of critical features in the sequence context flanking the poly A motif. Note that for the mouse data, there are 13 potential PAS motif variants instead of 12 for the human poly A data. As for the initialization of the network, we find that the standard Xavier initializer Glorot and Bengio, often leads to unsatisfactory results. A regressive schema theory based tool for gp evolved nonlinear models. In the second scenario, we evaluate whether transfer learning can address the problem of insufficient training dataset, in which we are limited by the number of annotated PAS sequences in the target species. Digital predistortion of power amplifiers for wireless applications. Transfer learning has been widely used Do and Ng, ; Li et al. Volume The table shows the average error rate of these 10 repeats with the standard deviation on the rat test set. Polyadenylation is a critical step for gene expression regulation during the maturation of mRNA. Note that here we did not perform any hyper-parameter such as learning rate, dropout rate search for fine-tuning because of insufficient data, instead we just used the best set of hyper-parameters found during pre-training.
Polyadenylation is a critical step for gene expression regulation during the maturation of mRNA.