Building a 4G LTE Network with VoLTE Support

Establishing a private cellular network often begins with providing mobile internet access. In a previous project, the focus was on launching a basic 4G LTE infrastructure. While that setup successfully delivered data connectivity, it lacked the ability to handle traditional cellular communications like voice and text. This limitation is common in early-stage private networks because data transmission relies on different protocols than voice calls. The current project marks a significant upgrade, moving from a simple internet hotspot to a comprehensive communication system.

The primary goal is to fill this gap. By integrating voice and SMS capabilities, the network becomes a true replacement for commercial cellular services. The guide emphasizes that achieving this requires a deeper understanding of the Evolved Packet Core (EPC) and specific voice handling technologies. The transition involves configuring the network to support IMS (IP Multimedia Subsystem), which is essential for delivering voice services over an IP-based network like LTE.

To build this advanced network, specific hardware and software components are required. The guide relies on Software Defined Radio (SDR) to act as the radio access network (RAN). SDR allows standard computers to process radio signals, effectively turning hardware into a flexible base station. This technology is crucial for creating the air interface that connects user devices to the core network. It provides the versatility needed to implement the specific LTE protocols required for voice and data.

On the software side, the guide utilizes Open5GS. This is an open-source implementation of the 5G and LTE core network. Open5GS manages the essential functions of the cellular network, including:

• Authentication and registration of devices
• Assigning IP addresses (via DHCP)
• Routing data traffic to the internet
• Connecting to the IMS for voice calls

By combining SDR hardware with the Open5GS software stack, users can create a complete, self-contained cellular environment that mimics commercial carrier networks on a smaller scale.

A central focus of the article is explaining how voice calls actually work in LTE networks. Unlike older 2G or 3G networks that used dedicated circuits for voice, LTE is an all-IP network designed primarily for data. To make voice calls, carriers use VoLTE technology. This process encapsulates voice data into IP packets, similar to how web browsing works, and transmits them over the LTE data connection. This method allows for higher quality voice calls and the ability to use data and voice simultaneously (if supported by the device).

The guide breaks down the steps required to enable this functionality in a private setup. It involves configuring the core network to route voice traffic to an IMS (IP Multimedia Subsystem) server. The IMS handles the signaling and session management for VoLTE calls. Without this specific configuration, the network can transport data, but it cannot initiate or receive voice calls. The article provides the necessary insights to bridge this technical gap, ensuring the network supports the full range of mobile communication features.

The guide serves as a practical manual for deploying these advanced features. It moves beyond theory to provide actionable steps for users to follow. The process involves setting up the Open5GS core, connecting the SDR hardware, and configuring the necessary network parameters to support VoLTE and SMS. The article suggests that while the technical complexity is higher than a standard Wi-Fi setup, the result is a robust and private cellular network.

By following the instructions, users can expect to replicate a fully functional mobile network environment. This includes the ability to connect smartphones, send text messages, and make voice calls without relying on a commercial carrier's infrastructure. The guide concludes that filling the "omission" of the previous data-only network results in a complete solution for enthusiasts and professionals looking to explore cellular technology.