doc: Add instructions for 5G NR gNB frequency configuration

doc/README.md

@@ -54,6 +54,7 @@ There is some general information in the [OpenAirInterface Gitlab Wiki](https://
 - [How to run the physical simulators](./physical-simulators.md)
 - [How to setup OAI with Nvidia Aerial and Foxconn](./Aerial_FAPI_Split_Tutorial.md)
 - [How to do a handover](./handover-tutorial.md)
+- [How to setup gNB frequency](./gNB_frequency_setup.md)
 
 Legacy unmaintained files:
 - [`L2NFAPI_NOS1.md`](./L2NFAPI_NOS1.md), [`L2NFAPI_S1.md`](./L2NFAPI_S1.md):

doc/gNB_frequency_setup.md

+# 5G gNB Frequency Configuration
+
+Configuring the frequency settings for a 5G gNB involves specifying multiple parameters in the gNB configuration file. This guide outlines the necessary parameters and provides step-by-step instructions for configuration.
+
+[TOC]
+
+## Configuration parameters
+
+To configure the gNB with the required frequency and bandwidth, modify following parameters in the configuration file:
+
+### `gNBs` Section
+
+* `absoluteFrequencySSB`: ARFCN (frequency number) of the middle frequency of the SSB. This value must align with the NR frequency raster defined in TS 38.104, Section 5.4.3.1.
+  * Steps to compute this value are provided below.
+* `dl_absoluteFrequencyPointA`: ARFCN (frequency number) for Point A, lowest subcarrier of the reference resource block (Common RB 0).
+  * Steps to compute this value are provided below.
+* `dl_frequencyBand`: downlink NR frequency band number.
+* `dl_subcarrierSpacing`: downlink subcarrier spacing.
+  * *Allowed values:* `0` = 15 kHz, `1` = 30 kHz, `2` = 60 kHz, `3` = 120 kHz
+* `dl_carrierBandwidth`: number of PRBs for downlink.
+* `initialDLBWPlocationAndBandwidth`: resource indicator value (RIV) of the initial BWP.
+  * Steps to compute this value are provided below.
+* `initialDLBWPsubcarrierSpacing`: initial downlink BWP subcarrier spacing.
+  * *Allowed values:* `0` = 15 kHz, `1` = 30 kHz, `2` = 60 kHz, `3` = 120 kHz
+* `initialDLBWPcontrolResourceSetZero`: CORESET0 index (valid configurations, based on SCS and frequency bandwith, are given in TS 38.213, Table 13.1 to Table 13.14).
+* `ul_frequencyBand`: uplink NR frequency band number.
+* `ul_absoluteFrequencyPointA`: ARFCN (frequency number) for Point A, lowest subcarrier of the reference resource block (Common RB 0).
+  * **Set only for FDD configurations.**
+  * Frequency separation between DL and UL channels for a specific 5G NR band is defined in 38.101-1 5.4.4-1 for FR1 bands and in 38.101-5 5.4.4-1 for FR1 NTN bands. `ul_absoluteFrequencyPointA` is calculated by substracting the given frequency offset from the `dl_absoluteFrequencyPointA`.
+* `ul_carrierBandwidth`: number of PRBs for uplink.
+* `initialULBWPlocationAndBandwidth`: resource indicator value (RIV) of the initial BWP.
+  * Steps to compute this value are provided below.
+* `initialULBWPsubcarrierSpacing`: initial uplink BWP subcarrier spacing.
+  * *Allowed values:* `0` = 15 kHz, `1` = 30 kHz, `2` = 60 kHz, `3` = 120 kHz
+* `subcarrierSpacing`: general subcarrier spacing for both DL and UL.
+  * *Allowed values:* `0` = 15 kHz, `1` = 30 kHz, `2` = 60 kHz, `3` = 120 kHz
+
+### `RUs` Section
+
+* `bands`: NR frequency band number for RU(s).
+
+## Determining the ARFCN value for `absoluteFrequencySSB` and `dl_absoluteFrequencyPointA`
+
+Follow these steps to find the ARFCN values for `absoluteFrequencySSB`, `dl_absoluteFrequencyPointA`, `initialDLBWPlocationAndBandwidth`, and `initialULBWPlocationAndBandwidth`:
+1. Convert RU center frequency to ARFCN value
+    * Example tool: [5G NR ARFCN Calculator](https://5g-tools.com/5g-nr-arfcn-calculator/)
+    * Input the center frequency of the RU (in MHz) into the tool to calculate the ARFCN value.
+
+2. Enter parameters into the online tool for NR Point A computation
+    * Example tool: [NR Reference Point A Tool](https://www.sqimway.com/nr_refA.php)
+    * Enter the NR frequency band, ARFCN value for center frequency (use the value calculated in step 1), subcarrier spacing, CORESET0 index (`initialDLBWPcontrolResourceSetZero` in the gNB config file) and bandwidth into the tool.
+
+3. Obtain required values
+    * From the tool's output, use the following results for your configuration:
+      * Arfcn GSCN: This corresponds to `absoluteFrequencySSB` - value for `absoluteFrequencySSB` can be selected freely from the table, if `Coreset(0) check` is "ok".
+      * Point A Arfcnc: This corresponds to `dl_absoluteFrequencyPointA`.
+      * locationAndBandwidth full: Use this value for both `initialDLBWPlocationAndBandwidth` and `initialULBWPlocationAndBandwidth`.
+
+4. Set `dl_absoluteFrequencyPointA`, `absoluteFrequencySSB`, `initialDLBWPlocationAndBandwidth`, and `initialULBWPlocationAndBandwidth` in the gNB configuration file
+
+## Example calculation
+1. Convert RU center frequency to ARFCN value
+    * Center frequency = 3450 MHz
+    * Center frequency ARFCN = 630000
+
+2. Enter parameters into the online tool for NR Point A computation
+    * Open the [NR Reference Point A Tool](https://www.sqimway.com/nr_refA.php) and input the following values:
+      * Frequency band = n78
+      * NR Arfcn scan (center frequency) = 630000
+      * SCS = 30 kHz
+      * Bandwidth = 100 MHz
+      * Control ResourceSet Zero = 11
+
+3. Obtain required values
+    * The tool provides following output values:
+      * Arfcn GSCN (`absoluteFrequencySSB`) = 630048
+      * Point A Arfcnc (`dl_absoluteFrequencyPointA`) = 626724
+      * locationAndBandwidth full (`initialDLBWPlocationAndBandwidth`) = 1099
+      * locationAndBandwidth full (`initialULBWPlocationAndBandwidth`) = 1099
+