Apparatus and method of dynamically adapting the LUT spacing for linearizing a power amplifier

A method of dynamically adapting a look up table (LUT) spacing for linearizing a power amplifier (PA), in order to produce an amplified output signal in response to a predistorted input derived from an input modulated signal vm, said method comprising the steps of:

• dividing a whole unsaturated PA input amplitude range into N bins, each predistorted by an entry of a size-N LUT, N being a positive integer;
• indexing said size-N LUT by an input amplitude rm to implement an unconditionally non-uniform LUT spacing;
• and
• online adapting said LUT spacing, said adapted LUT spacing balancing inter-modulation distortion (IMD) power at a PA output corresponding to each bin so that total IMD power at said PA output is minimized;
• wherein said online adapting said LUT spacing is based on a histogram-based predistortion method derived from processing histograms of a plurality of input modulated signals using an iterative procedure including the steps of:
• initializing bin boundaries of said LUT and an iteration index k, and assigning a midpoint of each said bin;
• estimating a long-term histogram for said plurality of input modulated signals;
• updating N bin widths {di}, for i from 1 to N;
• waiting until all entry values in said LUT have been renewed;
• and
• checking if a difference of said LUT spacing between a current iteration and a previous iteration is convergent.

A method of dynamically adapting a look up table (LUT) spacing for linearizing a power amplifier (PA), in order to produce an amplified output signal in response to a predistorted input derived from an input modulated signal vm, said method comprising the steps of:

• indexing said LUT containing a plurality of entries by an input amplitude;
• and
• dynamically adapting said LUT spacing, and generating said adapted LUT spacing for which total inter-modulation distortion (IMD) power at said PA output is minimized;
• wherein said LUT divides a whole unsaturated PA input amplitude range into a plurality of bins, each predistorted by an entry of said LUT, and said total IMD power associated with each LUT entry is expressed in terms of variables other than backoff of said input modulated signal, PA characteristics and probability density function (PDF) of said input modulated signal, and said spacing adaptor adapts said LUT spacing based on a histogram-based predistortion method derived from processing histograms of a plurality of input modulated signals;
• wherein said dynamically adapting said LUT spacing is achieved through an iterative procedure including the steps of:
• initializing bin boundaries of said LUT and an iteration index k, and assigning a midpoint of each said bin;
• estimating a long-term histogram for said plurality of input modulated signals;
• updating a bin width to each said bin;
• waiting until all entry values in said LUT have been renewed;
• and
• checking convergence for said updated bin width to each said bin.