Updated doc files with IF / FDD features

doc/RUNMODEM.md

@@ -132,6 +132,42 @@ With the RF simulator (on the same machine):
 
 `sudo RFSIMULATOR=127.0.0.1 ./nr-uesoftmodem --do-ra --rfsim --parallel-config PARALLEL_SINGLE_THREAD`
 
+## IF setup with OAI
+
+The -C and -CO flags can be used together at UE side to set custom downlink and uplink FR1 intermediate frequencies for the IF equipment.
+
+In order to run this setup, the following flags are needed at the UE side:
+
+`-C` 
+
+`--CO`
+
+and the following parameters must be configured in the RUs section of the gNB configuration file:
+
+`if_freq`
+
+`if_offset`
+
+### Run OAI with custom DL/UL intermediate frequencies
+
+The following example uses DL frequency 2169.080 MHz and UL frequency offset -400 MHz, with a configuration file for band 66 at gNB side.
+
+From the `cmake_targets/ran_build/build` folder:
+
+gNB on machine 1:
+
+`sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-LTE-EPC/CONF/gnb.band66.tm1.106PRB.usrpx300.conf`
+
+UE on machine 2:
+
+`sudo ./nr-uesoftmodem -C 2169080000 --CO -400000000`
+
+
+
+
+
+
+
 
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