The Pros and Cons of Using an Embedded vs. an External Cellular Modem

May 16, 2014
 
A cellular modem can be a great communication tool for your product. If you do a quick search on cellular modems and modules you’ll be amazed at the variety of options available. Apart from choosing a reliable supplier with a quality product, there are many variables to consider such as which cellular technology to use, which carrier network, and whether you should integrate the modem as part of your product or not. We are frequently asked about these considerations. For this post I will focus on the choice between an embedded and an external cellular modem.
   

Embedded Cellular Modems

   
Most suppliers refer to embedded cellular modems as “cellular modules”. These are typically surface mount parts that require various external components such as a power supply, level translation, and antenna connection. Cellular modules also typically do not offer an onboard application processor, and communicate with a host processor via AT commands. There are also “super modules” available that may also include power circuitry, onboard antenna connections, and an application processor. Cellular modules are much cheaper than external modems but they also require a much larger investment in development effort, hardware design, and certification costs. Sometimes the small size of a product excludes the possibility of using an external modem.
   
Let’s look at some of the cons of cellular modules in more detail. Firstly, there is the hardware design, which requires the skill of an RF engineer for laying out the antenna traces. Secondly, the hardware has to be certified for FCC, PTCRB, and carrier approval in North America. If the product will be deployed in other countries, more certifications may be necessary. Companies that produce cellular modules do their best to make the certification process as simple as possible for their customers by having their modules certified. Using a module that is certified makes the testing process easier, but since your hardware design includes the antenna, the final product has to be certified as well. Certain super modules that include all the antenna connections carry certifications that remain valid as long as your antenna meets certain specifications. Lastly, sourcing all the necessary components, manufacturing, and testing add complexity to your product.
   

External Cellular Modems

   
On the other hand, an external modem doesn’t require any of the abovementioned design effort. External modems that are in their own enclosure are usually certified as end-products so none of the certifications have to be done. Using an external modem also allows easy switching between different cellular technologies, as long as the interface to the modem remains the same. The disadvantages of the external modem are mainly a high price tag and a large physical size. Some external modems are designed to be powered from a wall outlet, which can be a problem when your product requires low power consumption.
   
Regardless of which option you choose to go with, any product will require software to manage the cellular connection. For cellular modules this software runs on a host processor, but in super modules or external modems it may be included in an onboard processor. In addition to setting up the data or voice connection, it also intercepts messages from the network and adjusts the behavior of the module to comply with the rules of the network. Companies such as Etherios and ClearConnex specialize in developing software for cellular modules and can be a great resource for companies with limited software expertise.
   
Below is a quick summary of the main pros and cons discussed:
   
ConsiderationEmbedded cellular modulesExternal cellular modems
 ProsConsProsCons
CostLow  High
Physical sizeSmall  Large
Hardware Design High design effort, RF expertise neededNo hardware design needed 
Certification FCC, PTCRB, CarrierNone needed 
Power consumptionLower  Higher
   
If you need assistance with your cellular design, call Symmetry Electronics at (310) 536-6190, or contact us online.


Written By: Cobus Heukelman

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