Designing Your First Cellular-Enabled IoT Device

The first step on the path to deploying a cellular-enabled IoT device is to determine what capabilities are needed from the cellular solution.

In this article, we will focus on the usage of modular cellular devices as opposed to “chip-down” cellular designs. This is the typical path forward for most new IoT devices, as chip-down cellular development typically requires highly specialized RF expertise and equipment, longer timelines, and much higher design, testing and certification costs. Generally, chip-down cellular development for an IoT product won’t make financial sense unless and until the product sales volume reaches many hundreds of thousands of units annually.

In general, there are five key parameters that should be considered early on:

1. Bandwidth
   Bandwidth is the data rate that the technology can support, usually measured in kilobits per second (kbps) or megabits per second (Mbps).

2. Latency
   Latency is the time it takes for a data packet to travel between a device and the cellular network, or vice versa. It may not be symmetrical.

3. Power consumption
   Power consumption is the electrical energy that the technology consumes, usually measured during data transmission, data reception, idle/standby mode and sleep.

4. Size
   Size is the physical volume that the technology requires from within and around your device. Things like SIM cards, antennas and supporting power supplies must be considered in addition to the cellular module itself.

5. Cost
   Cost is the monetary amount that the technology requires for design and development, testing, certification, manufacturing, and ongoing maintenance.

These parameters will drive the technology selection and help screen suitable cellular modules for further consideration.

For example, a wireless hotspot device may require high bandwidth suitable for streaming video, and high-power consumption may not matter if the device is wall-powered. However, for a remote temperature monitoring device, low bandwidth but long battery life may be the key parameters instead.

The next step on the development path is to identify which markets (geographical regions) to design the product towards. Available cellular technologies vary around the world, and to deploy a “global” product usually requires a phased approach, where key countries or regions are selected for initial rollout and subsequent countries are added after.

Each country will have its own set of available technologies, testing and certification requirements, and costs for network usage. To roll out a product to a new country is a non-trivial task, so we at NeuronicWorks generally recommend doing so in one or two countries at a time.

For example, a product rollout could target Canada and the US simultaneously (since the cellular technologies are very similar), followed by the UK, followed by France and Germany, etc. The order in which countries are prioritized will likely depend on the market opportunity for your product in each country.

This approach allows issues to be identified, mitigated and/or resolved on a manageable basis. Lessons learned can be applied to future rollouts before customer or financial obligations are made.

In addition to identifying target markets, suitable cellular technologies need to be considered.

As of writing, the prevailing cellular technologies for new IoT device development are as in Figure 1:

Figure 1: Cellular Technologies for IoT Device Development

The four technologies above represent the most common choices for new cellular IoT deployments today. Older technologies like UMTS (3G) and GSM (2G) are still sometimes deployed, but should not be preferred, as they provide less performance and are being phased out worldwide.

In order to sell a cellular-enabled product, regulatory requirements for the country of sale must be met. Because these requirements vary widely from country to country, we will be focusing on Canada and the USA in this article.

In Canada and the USA, the regulatory bodies involved are as follows:

• Innovation, Science and Economic Development (ISED) in Canada
  • Formerly, Industry Canada (IC)
• The Federal Communications Commission (FCC) in the USA
• PTCRB
  • Formerly, PTCRB stood for PCS-1900 Type Certification Review Board, but now is just referred to by PTCRB
• Mobile Network Operators (MNOs)
  • Bell Mobility, Rogers Wireless, AT&T, T-Mobile, Verizon, Vodafone and Deutsche Telekom are some examples

For FCC and ISED compliance, the product must be tested for unintentional RF emissions. The primary purpose of this testing is to ensure that the product does not emit harmful radiation or interfere with other products. Think of a pacemaker being affected by a rogue wireless transmitter - this is exactly what the testing is designed to prevent.

As long as a pre-certified cellular module is used, the FCC and ISED testing will be mostly the same as for any other unintentional radiator product (i.e., a device that does not have any radio interfaces that transmit), but with some additional tests to ensure the modem is not transmitting out-of-band or causing other harmful interference.

If additional radio modules are integrated into the device (e.g., a Wi-Fi module) that will be active at the same time as the cellular module, coexistence testing may also need to be performed. The purpose of this testing is to ensure that the system behavior when both radios are active is still as expected, without significant mixing or interference occurring from the interaction between multiple radios.

For PTCRB and MNO compliance, the product must be tested for both its unintentional RF emissions and its transmit and receive performance (TRP and TIS). The selection and implementation of the cellular module, RF cabling and antenna(s) are of paramount importance to pass these tests. The primary purpose of this testing is to ensure that the device will not negatively impact the carrier network or other devices sharing the network, as well as ensure that the performance of the device will be adequate to not reflect negatively on the network (from a consumer perspective).

In order to streamline compliance and minimize testing costs, it is essential to select a pre-certified cellular module, i.e., a cellular module that already has a modular approval number from the FCC and ISED, and is already approved by both PTCRB and the carrier(s) you intend to use.

In order to use a cellular device, one or more carriers must be engaged to provide network service, including the over-the-air (OTA) wireless access (e.g. tower communications) and backhaul (e.g. data routing to/from application servers).

It is prudent to begin discussions with potential carrier partners early in the product development cycle, as each carrier tends to have their own requirements for devices on their network, billing and fee structures, data packages, coverage, etc. which must all be considered.

A good option to consider when deploying your first cellular-enabled product is to look at mobile virtual network operators (MVNOs). These are companies that don’t build and run their own towers and switching equipment, but rather lease it from other carriers and provide you service under their name. This might sound counterintuitive, but what it allows you to do is to deal with one company for service across multiple countries. The intricacies of negotiating contracts with several carriers are handled by the MVNO, and you instead deal with one company for billing, deployment, and management.

In part two, we will look at the process of designing-in the cellular solution of choice, building prototypes, in-lab and in-field testing, certification, product launch and ongoing maintenance.