The Hierarchical Agglomerative Clustering (HAC) algorithm is a clustering algorithm that constructs a hierarchy of clusters by iteratively merging smaller clusters into larger ones. The HAC algorithm can be implemented in NS-3 using the following steps:

The following code snippet shows an example of how to implement the HAC algorithm in NS-3:

#include "ns3/core.h" #include "ns3/network-module.h" #include "ns3/mobility-module.h" #include "ns3/point-to-point-module.h" #include "ns3/applications-module.h"

using namespace ns3;

NS_APPLICATION_NS (HacExample)

void HacExample (Ptr node) { // Create a list of nodes NodeContainer nodes; nodes.Create (10);

// Create a mobility model for each node MobilityHelper mobility; mobility.SetMobilityModel ("ns3::RandomWaypointModel"); mobility.Install (nodes);

// Create a PointToPointNetDevice for each pair of nodes PointToPointHelper p2p; p2p.SetChannel ("ns3::Channel"); p2p.SetDeviceModel ("ns3::SimpleNetDevice"); p2p.SetQueue ("ns3::DropTailQueue"); p2p.Install (nodes);

// Calculate the distance between each pair of nodes DistanceMatrix dm (nodes);

// Create a minimum spanning tree (MST) of the nodes MinimumSpanningTree mst (dm);

// Cut the MST into clusters Clustering clusterer (mst);

// Update the list of nodes so that each node now represents a cluster for (uint32_t i = 0; i < clusterer.GetNumClusters (); ++i) { NodeContainer cluster = clusterer.GetCluster (i); nodes.Create (cluster.GetNumNodes ()); }

// Repeat steps 2 to 5 until the desired number of clusters is reached for (uint32_t i = 0; i < clusterer.GetNumClusters (); ++i) { NodeContainer cluster = clusterer.GetCluster (i); mobility.Install (cluster); p2p.Install (cluster); }

// The resulting list of nodes represents the hierarchy of clusters constructed by the HAC algorithm }

NS_PROGRAM_NS (HacExample)

While NS-3 is a powerful network simulation tool, it does not have built-in support for RIS-specific channel modeling. Therefore, extend NS-3's capabilities by implementing the RIS channel model yourself.

Steps to consider when implementing the RIS channel model in NS-3:

1. Familiarize yourself with NS-3: If you are new to NS-3, it's recommended to go through the official NS-3 documentation, tutorials, and examples to understand the basics of how NS-3 works.

2. Define the RIS channel model: Study the research literature on BS-RIS-UE channel models to understand the key parameters and characteristics. Design a suitable channel model for RIS-based communication that captures the signal propagation and reflection behavior specific to RIS deployments.

3. Implement the RIS channel model in NS-3: Write custom C++ code within the NS-3 framework to implement the RIS channel model. This involves defining classes and methods to handle the RIS's interaction with the base station (BS) and user equipment (UE), as well as modeling the signal reflection, absorption, and propagation across the RIS.

4. Validate and verify the implementation: Test your implementation by simulating various scenarios and comparing the results with expected outcomes. Validate the accuracy and correctness of your RIS channel model by comparing against analytical models or simulation results from other platforms.

There are no specific code references available for simulating BS-RIS-UE channels in NS-3. However, you can refer to NS-3's documentation, examples, and existing channel models (e.g., for MIMO, fading, or path loss) to understand how to implement custom channel models within NS-3.