Bruno Feuvrie

Multiplier-Free Divide, Square Root, and Log Algorithms [DSP Tips and Tricks]

Many signal processing algorithms require the computation of the ratio of two numbers, the square root of a number, or a logarithm. These operations are difficult when using fixed point hardware that lack dedicated multipliers, such as low-cost microcontrollers, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs). This article presents straightforward, multiplier free algorithms that implement both division and square roots, based on a technique known as dichotomous coordinate descent (DCD) (See [1] as a starting point, where several articles by the same authors are referenced.) We also make available a multiplier-free logarithm algorithm. All these algo rithms are based on iterative methods, which compute the successive ele ments of a sequence of approximate solutions, just like the Gauss-Seidel, Jacobi, and conjugate gradient methods [2]. We begin our discussion with a scheme for computing the ratio of two real numbers.

Digital predistortion for RF power amplifiers: State of the art and advanced approaches

Digital predistortion (DPD) is one of the most promising techniques for the linearization of power amplifiers. In this overview paper, some of the most important aspects related to this technique are briefly covered. State of the art on the DPD techniques, the associated signal processing algorithms and crest-factor reduction techniques is presented.

LUT/Parametric Digital Predistortion Approach for the Linearization of Power Amplifiers Characteristics

This paper deals with the linearization of power amplifier characteristics by digital predistortion technique. A new approach for the implementation of the memoryless digital predistorter (PD) is proposed. It consists on using a look-up-table with few entries corresponding to large step segmentation of the amplitude range of the baseband input signal. For every segment, a low order mapping polynomial function was used to approximate the inverse AM/AM and AM/PM characteristics of the PA. A fully automatic test bench is used with a power amplifier from the market to evaluate this approach.

Piecewise Complex Circular Approximation of the Inverse Characteristics of Power Amplifiers for Digital Predistortion Techniques

This paper deals with the linearization of power amplifier characteristics by digital predistortion technique. A new approach for the implementation of the memoryless digital predistorter (PD) is proposed. It consists on using a Look-Up-Table with few entries corresponding to large step segmentation of the amplitude range of the baseband input signal. A new modeling approach was also presented. For every segment, a complex circular model was used to approximate the inverse AM/AM and AM/PM characteristics of the PA. The performance of this new modeling approach is evaluated through computer simulations.

Distortion in RF power amplifiers and adaptive digital base-band predistortion

Future communications systems will have to integrate multiple radio technologies in order to support a large number of wireless standards (cellular technology, WMAN, WLAN and WPAN). The concept of Software-Defined Radio (SDR) in which a common hardware platform is used to cover any communication channel in a wide frequency spectrum with any modulation and bandwidth, supports this trend (Mitola, 1995; Haykin, 2005). In light of the functional flexibility and platform programmability requirements, one of the major challenges of SDR clearly resides in energy consumption. Besides the energy constraints, spectrum is becoming also a major resource bottleneck because of the steady increase in the number of wireless users and applications. The accelerated deployment of broadband personal communication and the continuously increasing demand for higher data rates will crow the limited and precious frequency spectrum.