IoT engineers are experts by experts. They know computer science, hardware design, and how to combine feature sets with specific use cases. They understand microcontrollers, firmware, and networking. They know how to bring these elements together to bring real value to users. But even with such expertise, you don't have to build every element of your IoT product from scratch.

For example, take a cellular module, the chipset and software that sends and receives data on a cellular IoT device. With the rise of IoT-specific cellular technologies such as 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 and is expected to be worth $61 billion globally by the following year.

But cellular connections have many variables, and the building blocks to create these IoT connections are complex. With the right team, you can certainly build your own. The problem is, unless you deploy at scale, with millions of devices in the field, you rarely see a return on your investment.

In addition, a large number of flexible and reliable cellular modules are available. Some of these are designed to simplify virtual plug-and-play, featuring embedded SIM cards with preconfigured network access, power management firmware, and even prepaid connections through mobile virtual network operators (MVNOs). If you're adding IoT capabilities to an existing product or selling into any market other than the largest, it's often a smart business move to partner with an IoT module provider rather than try to build one yourself.

Why? In a word: complexity. Here are the steps required to build a cellular IoT module and why sourcing the module and support services from a trusted partner is often a better option.

Four Elements of Cellular Module Design

Building a cellular module was no simple task; it was a broad design project spanning multiple components and fields of computer science, each requiring its own in-depth expertise. Essentially, designing a cellular module requires a lot of work on the following four elements:

1. Hardware design

Let's start with the physical parts of the cellular module: the modem, antenna, and microcontroller unit (MCU) that handles the data traffic. Only a modem manufacturer could potentially build a modem from scratch. This means you must purchase a third-party modem that meets the technical requirements of your use case, including regional deployment, bandwidth requirements, and appropriate power consumption.

You need to choose antenna (for single antenna cellular technology like Cat 1 bis) or antenna (for dual antenna applications). You need an MCU that interfaces seamlessly with the modem and handles the processing of connecting the device to the user application. There is no guarantee that all three technologies will be available or affordable at a time when global supply chains are disrupted.

But choosing the right equipment is only the beginning:

• Working closely with the manufacturer's field applications engineers over an extended period of time is necessary to get the modem to work properly.
• To transmit data, you must perfectly integrate the antenna.
• You need to optimize the integration of various cellular bands and connectivity options.

Even after you've optimized your hardware, there's one more important step: regulatory compliance. Your hardware must be PTCRB certified to ensure interoperability on global networks. Additionally, depending on where you deploy your equipment, you will need to be certified by the US Federal Communications Commission (FCC), the European Union (CE Mark), and/or other regional authorities. These certifications are not cheap and require a lot of work to earn.

2. Firmware development

Even experienced firmware developers may have a lot to learn when working with cellular modules, and it's an area rife with deep expertise. To illustrate the complexity, here is a non-exhaustive list of tasks for a firmware developer working on a custom IoT chip:

• Select an ecosystem for the firmware stack: (Zephyr, FreeRTOS, ThreadX, Linux, etc.)
• Make sure your modem and chipset of choice is fully supported by the ecosystem
• Write a new modem driver capable of wrapping AT commands for all modem functions
• Debug all AT commands in the driver
• 24/7 updates for MCU designs
• Choose encryption technology for physical memory on the device (VPN, Secure Element, TLS, etc.)
• Deciding how to pack mail to and from the device
• Choose the structured format of the data (Protocol Buffers, JSON, etc.)

Of course, once the firmware is written, you have to maintain it. When you build a custom cellular module, you do it yourself for the life of the system.

3. Cloud development

The firmware handles data processing on the device. For true connectivity, you also need cloud services that support your unique use case. This requires extensive cloud development, including but not limited to the following efforts:

• Full development of device services with the ability to remotely install and update firmware
• Define the cloud architecture and choose the ideal technology for all microservices
• Fully integrate all devices into cloud services (note that major cloud providers only provide endpoints and certificates, the rest is up to you)
• Create a smooth device onboarding process
• Define all potential failure states and implement fixes for graceful failure and recovery in each failure state
• Temporary storage of data between transfers

All this cloud development can be an unwelcome distraction for developers, who would rather focus on user applications and device capabilities that are part of the solution that customers actually experience.

4. MVNO operator integration

The last part of the cellular module that works isn't in your control: it's the partnership with the MVNO, the connectivity provider that handles your access to the network itself. Depending on the MVNO you choose, your device may be limited to a specific type of SIM (multi-SMSI, eSIM, iSIM, native SIM, etc.).

Once your SIM card technology is aligned with the MVNO's system, you have more decisions to make. You'll need a platform that allows you to activate and deactivate devices, and manage data consumption along the way. You must integrate cloud applications with connectivity platforms. You need to predict your system's data usage; this is critical to successfully negotiating with the MVNO, who may charge based on the data rate.

Cellular Module Competition

At every stage of the module design process, you will face competition and unless you have a huge presence in the market, you will not be able to gain economies of scale. That means you'll pay more for SIM cards and data than the bigger competitors.

This is another business reason to partner with an integrated module supplier instead of building your own IoT chip. These providers take advantage of economies of scale to lower connection prices. Even better, they save you the cost and difficulty of building your own cellular modules, rest assured this article only scratches the surface of the complexities.