Add README for the nr-cu-nrppa tester

doc/README.md

@@ -121,8 +121,9 @@ The other SDRs (AW2S, LimeSDR, ...) have no READMEs.
 ## Testing
 
 - [UnitTests.md](./UnitTests.md) explains the unit testing setup
-- Component tests are under `tests/`. Currently, there is a simple CU-UP
-  tester, see the corresponding [README.md](../tests/nr-cuup/README.md).
+- Component tests are under `tests/`. Currently, the following component tests are supported
+  - A simple CU-UP tester, see the corresponding [README.md](../tests/nr-cuup/README.md).
+  - A CU-NRPPA tester, see the corresponding [README.md](../tests/nr-cu-nrppa/README.md).
 - [TESTBenches.md](./TESTBenches.md) lists the CI setup and links to pipelines
 - The CI setup uses a [custom framework](../ci-scripts/README.md) to run
   end-to-end tests.

tests/nr-cu-nrppa/README.md

+This is a simple standalone tester for NRPPA and NGAP positioning messages. It connects to the AMF to perform NGAP and NRPPA encoding/decoding and validates the exchange of positioning data.
+
+[[_TOC_]]
+
+# Overview
+From a schematic point of view, the tester and Core Network interaction looks like this:
+```
+        +-------+                 +-------+
+        |  LMF  |<--- HTTP POST---| User  |
+        +-------+                 +-------+
+            |
+            | Nlmf
+            |
+        +-------+
+        |  AMF  |
+        +-------+
+            |
+ NGAP/NRPPA |
+            |
+        +-------+
+        |tester | (nr-cu-nrppa-test)
+        +-------+
+```
+The tester is designed to validate the integration of NRPPA and NGAP messages required for 5G positioning (*3GPP 38.413 V16.0.0* and *3GPP 38.455 V16.7.1*). It acts as a simulated RAN node (like a CU) connecting to the 5G Core Network's AMF.
+
+The following messages are integrated and tested:
+* **NGAP:** Uplink/Downlink UE Associated NRPPA Transport, Uplink/Downlink Non-UE Associated NRPPA Transport.
+* **NRPPA:** TRP Information Request/Response, Positioning Information Request/Response, Positioning Activation Request/Response, Measurement Request/Response.
+
+A test scenario is fixed to these steps:
+1. The 5G Core Network, specifically including the Location Management Function (LMF), is deployed via Docker.
+2. The tester connects to the AMF and establishes the NGAP connection.
+3. The user initiates a positioning procedure via a API call to the LMF.
+4. The AMF and the tester exchange the required NGAP and NRPPA messages to determine location.
+
+# Usage
+To run this test, you need to set up the Core Network and build the tester.
+
+**1. Core Network Deployment**
+
+Pull the required Docker images for the OAI 5G Core:
+
+    docker pull oaisoftwarealliance/ims:latest
+    docker pull oaisoftwarealliance/oai-amf:develop
+    docker pull oaisoftwarealliance/oai-nrf:develop
+    docker pull oaisoftwarealliance/oai-smf:develop
+    docker pull oaisoftwarealliance/oai-udr:develop
+    docker pull oaisoftwarealliance/oai-upf:develop
+    docker pull oaisoftwarealliance/oai-udm:develop
+    docker pull oaisoftwarealliance/oai-ausf:develop
+    docker pull oaisoftwarealliance/oai-lmf:develop
+
+Deploy the network using the positioning compose file:
+
+    cd doc/tutorial_resources/oai-cn5g
+    docker compose -f docker-compose-positioning.yaml up -d
+
+*(To undeploy later, run `docker compose -f docker-compose-positioning.yaml down -t 0`)*
+
+**2. Building the Tester**
+
+You can build the NRPPA tester like so:
+
+    cd ~/openairinterface5g
+    mkdir build && cd build && cmake .. -GNinja && ninja nr-cu-nrppa-test
+
+**3. Running the Tester**
+
+Start the tester with the dedicated configuration file:
+
+    LD_LIBRARY_PATH=. ./tests/nr-cu-nrppa/nr-cu-nrppa-test -O ../tests/nr-cu-nrppa/nr-nrppa-test.conf
+
+**4. Initiating the Procedure**
+
+Trigger the location determination by sending an HTTP POST request to the LMF:
+
+    cd ~/openairinterface5g/doc/tutorial_resources/positioning/
+    curl --http2-prior-knowledge -H "Content-Type: application/json" -d "@InputData.json" -X POST http://192.168.70.141:8080/nlmf-loc/v1/determine-location
+
+# Limitations
+- The tester is a standalone validation tool (`nr-cu-nrppa-test`) and does not represent a fully integrated, end-to-end gNB positioning setup.