Update PEM documentation with PemEnabled flag

src/lte/doc/source/lte-phy-error-model-design.rst

@@ -55,6 +55,13 @@ Simulator Design
 
 The model implemented uses the curves for the LSM of the recently LTE PHY Error Model released in the ns3 community by the Signet Group [PaduaPEM]_ and the new ones generated for different CB sizes. The ``LteSpectrumPhy`` class is in charge of evaluating the TB BLER thanks to the methods provided by the ``LteMiErrorModel`` class, which is in charge of evaluating the TB BLER according to the vector of the perceived SINR per RB, the MCS and the size in order to proper model the segmentation of the TB in CBs. In order to obtain the vector of the perceived SINR two instances of ``LtePemSinrChunkProcessor`` (child of ``LteSinrChunkProcessor`` dedicated to evaluate the SINR for obtaining physical error performance) have been attached to UE downlink and eNB uplink ``LteSpectrumPhy`` modules for evaluating the error model distribution respectively of PDSCH (UE side) and ULSCH (eNB side).
 
+The model can be disabled for working with a zero-losses channel by setting the ``PemEnabled`` attribute of the ``LteSpectrumPhy`` class (by default is active). This can be done according to the standard ns3 attribute system procedure, that is::
+
+  Config::SetDefault ("ns3::LteSpectrumPhy::PemEnabled", BooleanValue (false));
+
+
+
+
 
 Test Environment
 ----------------