iqbal: Add reference to SDR# blog post

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/iqbal.c b/src/iqbal.c
index 0bb6a54..1d0ea75 100644
--- a/src/iqbal.c
+++ b/src/iqbal.c
@@ -207,6 +207,17 @@ osmo_iqbal_cxvec_estimate(const struct osmo_cxvec *sig,
 /* IQ balance optimization                                                  */
 /* ------------------------------------------------------------------------ */
 
+/*
+ * The actual algorithm used here is inspired by the IQ balancer of SDR#
+ * by Youssef Touil and described here :
+ *
+ * http://sdrsharp.com/index.php/automatic-iq-correction-algorithm
+ *
+ * The main differences are:
+ *  - Objective function uses complex correlation of left/right side of FFT
+ *  - Optimization based on steepest gradient with dynamic step size
+ */
+
 /*! \brief Default values for the optimization algorithm */
 const struct osmo_iqbal_opts osmo_iqbal_default_opts = {
 	.fft_size	= 1024,