From 9f1f0def3b3de6901aa8aa1abaca21bf67f5671e Mon Sep 17 00:00:00 2001 From: bemasher Date: Wed, 17 Aug 2016 23:18:15 -0600 Subject: [PATCH] Remove reference to alpha-max beta-min magnitude calculation. --- docs/signal.md | 13 +------------ 1 file changed, 1 insertion(+), 12 deletions(-) diff --git a/docs/signal.md b/docs/signal.md index 73d589b51..55f6fec20 100644 --- a/docs/signal.md +++ b/docs/signal.md @@ -25,18 +25,7 @@ The signal is made up of interleaved in-phase and quadrature samples, 8-bits per $$\vert z\vert = \sqrt{\Re(z)^2 + \Im(z)^2}$$ -To meet performance requirements the magnitude computation has two implementations. The first uses a pre-computed lookup table which maps all possible 8-bit values to their floating-point squares. Calculating the magnitude using the lookup table then only involves two lookups, one addition and one square-root. - -The second implementation is an approximation known as Alpha-Max plus Beta-Min whose efficiency comes from eliminating the square root operation: - -
-$$ - \begin{aligned} - &\alpha = \frac{2\cos\frac{\pi}{8}}{1+cos\frac{\pi}{8}} \qquad \beta = \frac{2\sin\frac{\pi}{8}}{1+cos\frac{\pi}{8}} \\ \\ - \vert z\vert \approx \,&\alpha\cdot\max(\Re(z),\Im(z)) + \beta\cdot\min(\Re(z),\Im(z)) - \end{aligned} -$$ -
+To meet performance requirements the magnitude computation is done using a pre-computed lookup table which maps all possible 8-bit values to their floating-point squares. Calculating the magnitude using the lookup table then only involves two lookups, one addition and one square-root. ## Filtering ***