Thinking of Building Your Own Cellular Module? Here’s What It Takes

IoT engineers are the specialist’s specialists. They know computer science, hardware design, and how to align a feature set with specific use cases. They understand microcontrollers, firmware, and networking. They know how to put these elements together to bring real value to users. But even with expertise like that on your side, you shouldn’t necessarily build every element of your IoT product from scratch. 

For example, take cellular modules—the chipsets and software that send and receive data on a cellular IoT device. With the rise of IoT-specific cellular technologies like Cat 1, NB-IoT, and LTE-M, connecting products via mobile networks has never been more popular. In fact, the cellular IoT market is expected to nearly double between 2022 and 2026, reaching an estimated global value of $61 billion by the latter year.

But cellular connectivity has a lot of variables, and the modules that create these IoT connections are complicated. With the right team, you certainly could build your own. The trouble is, you will rarely see a return on that investment unless you’re deploying on a massive scale, with millions of devices in the field. 

Besides, there are plenty of flexible, reliable cellular modules available. Some are designed for virtual plug-and-play simplicity, featuring embedded SIMs with pre-provisioned network access, power-management firmware, and even prepaid connectivity through mobile virtual network operators (MVNOs). If you’re adding IoT features to existing products—or selling to any but the largest markets—the smart business move is usually to partner with an IoT module provider, rather than trying to build your own. 

Why? In a word: Complexity. Here’s what it takes to build a cellular IoT module—and why sourcing modules and support services from a trusted partner is often the better choice. 

The 4 Elements of Cellular Module Design

Building a cellular module isn’t a single task; it’s an extensive design project, covering multiple components and fields of computer science, each of which requires its own in-depth expertise. Essentially, designing a cellular module requires intense work on all four of these elements: 

#1: Hardware Design

Let’s start with the physical parts of a cellular module: the modem, antenna(s), and microcontroller unit (MCU) that handle data traffic. No one but a modem manufacturer is likely to build a modem from scratch. That means you must source third-party modems that match the technical requirements of your use cases, including regional deployment, bandwidth needs, and appropriate power consumption.

You’ll need to choose an antenna (for single-antenna cellular technology like Cat 1 bis) or antennas (for dual-antenna applications). And you'll need an MCU that interfaces seamlessly with the modem, handling the processing that connects your device to the user application. At a time of global supply chain disruption, there is no guarantee all three of these technologies will be available or affordable.  

But choosing the right equipment is just the beginning: 

• To get your modem functional, you must work closely, over long hours, with the manufacturer’s field applications engineers. 
• To transmit data, you must integrate your antenna perfectly.
• And you will need to optimize the integration for various cellular bands and connectivity options. 

Even if you get your hardware optimized, there is another important step: Regulatory compliance. Your hardware must be certified by PTCRB to ensure interoperability on global networks. Also, depending on where you deploy your devices, you will also need certification from the U.S. Federal Communications Commission (FCC), the European Union (for the CE mark), and/or other regional authorities. These certifications are not cheap, and they take a lot of work to obtain. 

#2: Firmware Development

Even experienced firmware developers may have a lot to learn when working with a cellular module, a field full of deep specialty. To illustrate the complexity, here is an incomplete task list for firmware developers working on a custom IoT chip: 

• Picking an ecosystem for the firmware stack: (Zephyr, FreeRTOS, ThreadX, Linux, etc)
• Ensuring that the ecosystem fully supports your chosen modems and chipsets
• Writing a new modem driver, capable of wrapping AT commands for all the modem’s functions
• Debugging all AT commands within the driver
• Designing all over-the-air updates for the MCU
• Choosing encryption technologies for physical memory on the device (VPN, secure element, TLS, etc.)
• Deciding how to package messages to and from the device
• Choosing a structured format for data (Protocol Buffers, JSON, etc)

Once the firmware’s written, of course, you have to maintain it. When you build a custom cellular module, you are on your own for the full lifespan of your system. 

#3: Cloud Development

Firmware handles data processing on the device. For a true connection, you also need a cloud service that supports your unique use cases. That requires extensive cloud development, including, but not limited to, the following jobs: 

• Full-scale development of a device service, capable of installing and updating firmware remotely
• Defining cloud architecture, and choosing the ideal technology for all microservices
• Full integration of all devices into the cloud service (note that major cloud vendors only provide an endpoint and a certificate, and the rest is up to you)
• Creating smooth device onboarding processes
• Defining all potential failure states, and implementing fixes for graceful failure and recovery in each
• Temporary storage for data between transmissions

All of this cloud development can be an unwelcome distraction for developers who would rather focus on user applications and device features which are the parts of your solution customers actually experience firsthand.

#4: MVNO Carrier Integration

The final piece of a working cellular module isn’t something you control: It’s the partnership with an MVNO, the connectivity provider who handles your access to the network itself. Depending on which MVNO you choose, your device may be limited to a particular type of SIM (multi-SMSI, eSIM, iSIM, native SIM, etc). 

Once you get your SIM technology aligned with your MVNO’s system, you have more decisions to make. You will need a platform that allows you to activate and retire devices and manage data consumption along the way. You must integrate your cloud application with the connectivity platform. And you will need to project your system’s data usage; that’s essential for successful negotiation with the MVNO, which may charge based on data rates. 

Cellular Module Competition

At every stage of the module design process, you will face competition, and unless you’re a huge, established presence in the market, you won’t have access to economies of scale. That means you will pay more for SIMs and more for data than larger competitors. 

That is another business argument for working with an integrated module vendor, rather than building your own IoT chips. These vendors leverage economies of scale to bring down the price of connectivity. Even better, they save you the cost and difficulty of building your own cellular modules—and rest assured, this article only scratches the surface of that complexity.