From 2832c5d37984fd5fbaeb62207c64ea01333f960e Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Tue, 17 Sep 2019 00:58:34 +0200
Subject: [PATCH] Fix estimation of CN0 for low values

---
 src/algorithms/tracking/libs/lock_detectors.cc | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/algorithms/tracking/libs/lock_detectors.cc b/src/algorithms/tracking/libs/lock_detectors.cc
index a56d73bc8..ccf74e502 100644
--- a/src/algorithms/tracking/libs/lock_detectors.cc
+++ b/src/algorithms/tracking/libs/lock_detectors.cc
@@ -122,12 +122,16 @@ float cn0_mm_estimator(const gr_complex* Prompt_buffer, int length, float coh_in
     m_2 /= n;
     m_4 /= n;
     aux = std::sqrt(2.0 * m_2 * m_2 - m_4);
-    SNR_aux = aux / (m_2 - aux);
-    SNR_dB_Hz = 10.0 * std::log10(SNR_aux) - 10.0 * std::log10(coh_integration_time_s);
-    if (std::isnan(SNR_dB_Hz))
+    if (std::isnan(aux))
         {
-            SNR_dB_Hz = Psig / (m_2 - Psig);
+            SNR_aux = Psig / (m_2 - Psig);
         }
+    else
+        {
+            SNR_aux = aux / (m_2 - aux);
+        }
+    SNR_dB_Hz = 10.0 * std::log10(SNR_aux) - 10.0 * std::log10(coh_integration_time_s);
+
     return SNR_dB_Hz;
 }