Build Your Own Private 5G Network: A Hands-On Guide with Open5GS and srsRAN

Breaking Through the Wi-Fi Wall

Picture a smart warehouse where fifty autonomous mobile robots (AMRs) navigate tight aisles around the clock. You might start with high-end Wi-Fi 6, but the limitations appear quickly.

As device density grows, latency often spikes from a smooth 20ms to a jittery 500ms. When a robot roams between access points, handoff delays exceeding 100ms can trigger emergency safety halts. To make matters worse, the 2.4GHz and 5GHz bands are usually saturated by nearby office networks and machinery interference.

This is where private cellular networks change the game. Modern enterprises need the deterministic performance of 5G but often recoil at the high cost of public subscriptions and the lack of data sovereignty. A private setup gives you total control over your spectrum and your data.

The Technical Gap: Why Wi-Fi Struggles

The frustration stems from how these technologies handle traffic. Wi-Fi relies on a “listen-before-talk” mechanism (CSMA/CA). In a crowded room, devices effectively shout over each other, leading to collisions and unpredictable wait times. 5G operates differently. It uses scheduled resource blocks, ensuring every device has a precise time and frequency slot. No collisions, no shouting.

Historically, building a private cell was out of reach for most engineers. Three major hurdles stood in the way:

• Prohibitive Costs: Legacy vendors like Nokia or Ericsson typically sell “black box” solutions that start at $20,000 and scale rapidly.
• Standard Complexity: The 3GPP specifications span tens of thousands of pages, making custom implementations a nightmare.
• Spectrum Access: Licensing radio frequencies used to require massive government bids, though new options like CBRS (in the US) have lowered this barrier.

Choosing Your 5G Software Stack

You don’t need to write a core network from scratch. Several open-source projects have done the heavy lifting. Here is how the landscape looks today:

1. OpenAirInterface (OAI): This is the heavyweight champion. It is extremely feature-complete but requires a steep learning curve and specific hardware timing.
2. Free5GC: This project is fantastic for academic research and learning the 5G Core (5GC) architecture, though it can be finicky when paired with different radio vendors.
3. Open5GS & srsRAN: This is the “sweet spot” for most developers. Open5GS is a lightweight, high-performance C-based core. srsRAN provides a modular gNodeB (the base station) that is remarkably easy to configure.

I’ve deployed this combination in multiple testbeds. It consistently delivers the best stability for those moving from a lab environment toward a functional prototype.

The Blueprint: Building a Virtual 5G Lab

We will use Open5GS for the Core Network and srsRAN_Project for the radio side. To keep costs at zero, we will use ZeroMQ (ZMQ). This simulates radio waves over your local network, allowing you to skip buying a $1,000 USRP SDR until you’re ready to go wireless.

1. Prepare the Environment

Start with a clean Ubuntu 22.04 LTS installation. You will need MongoDB to store subscriber data and a few basic networking tools.

sudo apt update
sudo apt install -y software-properties-common mongodb curl
sudo systemctl start mongodb
sudo systemctl enable mongodb

2. Deploy the Open5GS Core

The Open5GS team maintains a stable PPA. This makes the installation as simple as any other Linux package.

sudo add-apt-repository ppa:open5gs/latest
sudo apt update
sudo apt install open5gs

After installation, the core functions like the AMF (Access and Mobility Management) and UPF (User Plane Function) run as background services. Verify they are active using systemctl status open5gs-amfd.

3. Configure the Virtual Network Interface

Your 5G devices need a way to reach the outside world. We create a TUN interface to bridge the cellular traffic to your Linux networking stack.

sudo ip tuntap add name ogstun mode tun
sudo ip addr add 10.45.0.1/16 dev ogstun
sudo ip link set ogstun up

# Enable NAT so your devices can hit the internet
sudo sysctl -w net.ipv4.ip_forward=1
sudo iptables -t nat -A POSTROUTING -s 10.45.0.0/16 ! -o ogstun -j MASQUERADE

4. Provision a Subscriber

5G security is strict. A device cannot attach to your network unless its unique ID (IMSI) and encryption keys are pre-registered. Open5GS includes a web-based dashboard for this. Set it up with Node.js:

curl -fsSL https://deb.nodesource.com/setup_18.x | sudo -E bash -
sudo apt install -y nodejs
cd /usr/lib/node_modules/open5gs/webui
sudo npm install
sudo npm run start

Open http://localhost:3000 in your browser. Log in with admin/12345 and add a subscriber using these test values:

• IMSI: 901700000000001
• K: 465B5CE8B199B49FAA5F0A2EE238A6BC
• OPC: E8ED289DEBA952E4283B54E88E6183CA

5. Compile srsRAN (The gNodeB)

Next, we build the radio access network. Compiling from source ensures we have the ZeroMQ plugins enabled for our virtual simulation.

sudo apt install -y build-essential cmake libfftw3-dev libmbedtls-dev libboost-program-options-dev libconfig++-dev libsctp-dev libzmq3-dev

git clone https://github.com/srsran/srsRAN_Project.git
cd srsRAN_Project
mkdir build && cd build
cmake ../ -DENABLE_ZEROMQ=ON
make -j$(nproc)
sudo make install

6. Fire Up the Network

First, launch the gNodeB. This acts as your virtual cell tower. Ensure the configuration file points to 127.0.0.1 for the AMF connection.

sudo gnb -c configs/gnb_rf_zmq.conf

In a second terminal, launch the UE (User Equipment) simulator. This mimics a 5G smartphone connecting to your tower.

sudo srsue configs/ue_zmq.conf

7. Confirm the Data Path

Watch the gNodeB logs. You should see a “Registration Request” followed by a successful attach. On the UE side, a new interface called tun_srsue will appear. It should automatically grab an IP address like 10.45.0.2.

Verify the end-to-end connection by pinging the gateway through the 5G tunnel:

ping -I tun_srsue 10.45.0.1

From Simulation to Reality

The transition from a virtual lab to a physical broadcast is surprisingly simple. Once your ZMQ tests pass, you only need to swap the ZMQ configuration for UHD (USRP Hardware Driver) settings. By plugging in a USRP B210 or a LimeSDR, you can begin broadcasting a live 5G signal.

Always remember to use a Faraday cage or shielded cables when testing on licensed frequencies. This setup moves cellular tech out of the “telco-only” world and makes it a versatile addition to your software-defined networking toolkit. You now have the power to build low-latency, highly secure networks that Wi-Fi simply cannot match.