Designing Cellular Technology into Embedded Systems

What Cellular Module Type Should I Choose for My Application?

The number one influencer affecting the cellular module choice is to define where the product is going to be sold. Secondly, being able to get a service carrier plan in the region(s) your product will be offered affects the module choice.

 North America Deployment
o In North America, CDMA and GSM cellular service are both offered, so CDMA and

GSM are the module choices.

 Global Deployment
o GSM is the global standard for the rest of the world. Therefore, if you are going to

deploy your product in regions outside North America, GSM will be the module choice

Here are some additional features one needs to consider when selecting a cellular modem:

 Power consumption
o If you are running on batteries a 2G modem will consume much less power than a

LTE solution as an example. High bandwidth applications typically require more power.

 Data upload/download speeds and latency
o Depending on your application the need

to stream high definition video will require a faster connection. One such example is a security camera application. Latency of the network is another factor in choosing your cellular technology. 

 Module Size
o The end product size may dictate your cellular module choice. Designing a product

that is the size of a watch for example will drive your decision to either a module or chip level design. Integrating cellular into a legacy system in the field where redesigning is not possible, but a serial port is available, will allow you to add cellular connectivity via a box modem

 Module Cost
o Module cost needs to be understood two ways. One, the price of the device and two,

what is the total cost associated with the design. As an example, a chip level cellular solution costs $6.00, where as a 3G module may cost $35.00. Price wise clearly the chip solution is the lowest, but if we factor in the $3.5M required to do a chip level design and seek to amortize the NRE across 100K units, the cost of the chip solution is $41, but the time to market is much longer and the design risk much higher.

 Module Form Factors
o Choosing a form factor in a cellular modem which allows for multiple technologies

such as CDMA and GSM is a great strategy to service multiple needs. The ability to populate a cellular modem at final assembly or sell as an aftermarket add-on allows for modularity of the system. One common form factor is the miniPCI-e footprint used by suppliers like Telit. In this form factor the OEM can choose 2G/3G/4G as well as bundle the modem with and without a Subscriber Identity Module (SIM) and Global Positioning System (GPS) offering.

 Cellular Data Plan
o Additionally one must understand the cost of the data plan associated with the

module choice as this affects the total cost of ownership of the product. The cellular modem is a onetime expense whereas the cost of the data plan perpetuates as long as the devices is connected to a network. In an embedded system 7-10 years is not uncommon.

Do I Need a Special Processor to Run a Cellular Modem?

The short answer to this question is no. Your application will determine whether or not you need an additional processor. Many of the cellular modem solutions are based on high performance processor architecture like ARM9, so the module has additional resources on board to handle simple applications without the need for an extra processor.

How do I Interface to the Cellular Module?

The two most common interfaces are a serial Universal Asynchronous Receiver Transceiver (UART) and Universal Serial Bus (USB). Please check the datasheet for the precise interface.

Cellular Data Plans

Like your personal cellular phone, every embedded cellular device requires a service carrier plan. One of the first questions the designer must address is, “Where in the world will the device or product be used?” The answer will drive the cellular modem choice and service carrier selection. If the deployment is the United States, then CDMA or GSM can be a solution, however once the need to operate elsewhere in the world is required, GSM becomes the predominant solution. 

Typically embedded devices require a data only plan, however in some instances voice is also a requirement. When researching for the right data plan for your needs the following information will be required to help build a plan for your needs:

•   Number of devices deployed

•   What countries will you require service in

•   Amount of data consumed per month – typically measure in kilobytes or megabytes

•   SMS text messaging required

•   Static IP Addressing

•   Custom Access Point Name (APN)

•   Pooled data plans

  Other costs associated with cellular connectivity are, but not limited to:

•   SIM Card purchase

•   SIM Activation

•   Electronic Serial Number (ESN) and (MEID) activation

•   Suspend fees associated with seasonal plan

•   Test SIMs for manufacturing and test

  To effectively “manage” your devices multiple MNO and MVNO management platforms or portal may be required. The management platform provides you a means in which to view and manage all of your devices deployed. It is important to note that, depending where in the world you have deployed your products, it may require multiple platforms to effectively manage all your devices along with each of their dedicated M2M device management platforms and SIM cards. The industry has recognized this as a short coming and new and innovative providers like Device Cloud Networks allow you to manage and diagnose all your devices via one platform.

  To address the shortcomings of today’s management platforms DCN’s Innovative platform offers:

•   Programmable “soft” SIM card either as a polycarbonate solution or embedded Universal Integrated Circuit Card (eUICC) offering

•   Cloud-based, high-volume, automated self-provisioning system for wireless connectivity;

•   Cloud-based platform for device and machine diagnostics, management, programming and remote control;

•   Local connectivity in a growing number of countries;

•   Multi-currency, multi-lingual billing engine;

•   All offered as one SKU.

  What is the Role of a MNO, MVNO and MVNE?

  There are two types of operators where cellular data services can be procured, Mobile Network Operators (MNO) and Mobile Virtual Network Operators (MVNO).

  A MNO is a provider of wireless communications services that owns or controls all the elements necessary to sell and deliver services to an end user. AT&T, Verizon, Sprint, and T Mobile are examples of MNOs in the United States. In addition to obtaining revenue by offering retail services under its own brand, an MNO may also sell access to network services at wholesale rates to MVNO's.

  A MVNO is a wireless communications services provider that does not own the radio spectrum or wireless network infrastructure. An MVNO may use its own customer service and billing support systems, marketing and sales personnel or it may employ the services of a Mobile Virtual Network Enabler (MVNE). 

A Mobile Virtual Network Enabler (MVNE) is an organization that provides business infrastructure solutions to MVNOs. Services include billing, administration, operations, base station subsystem support, operations support systems and provisioning for back-end network elements.

Why Choose a MVNO Over a MNO?

Typically a MNO seeks larger opportunities than a MVNO, and in many cases may not support a smaller embedded client. Secondly, MVNOs have formed relationships with many regional and global carriers. This is important because many of the issues related to roaming and global service have been solved by the MVNOs. Without their service you would need to develop carrier relationships yourself region-by-region, country by country. Typically a MVNO may have up to 200 or more different carrier relationships.

Rates will generally be more favorable with a MNO, but if you require lots of support and are a smaller OEM, you may experience delays in support.

2G Sunset Issue

In August of 2012, AT&T Inc. announced they will shut down their second-generation, or "2G," wireless network by the end of 2016. The shutdown will not occur all at once, rather it will disappear sporadically across the country and on January 1, 2017, the 2G wireless network will cease to exist. AT&T has stopped certifying new 2G GSM applications for deployment on its network. Customers can no longer develop any more new 2G GSM M2M products for use or sale in the United States. AT&T has also stopped provisioning new SIMs for existing, certified, 2G GSM devices and applications. This means customers cannot deploy any more 2G GSM devices into their existing M2M applications installed base using AT&T’s network.

The GSM sunset is a major issue for the US M2M industry because such large numbers of GSM/GPRS devices have been deployed. To maintain service on the installed connections an estimated 10 to 12 million 2G GSM devices must be replaced or tended to by 2017. So what are some of the options for OEMs with deployed products?

•   Change service to another 2G GSM carrier using the same 2G GSM device

•   Replace the 2G GSM device with a 3G HSPA device

•   Replace the 2G GSM device with a 2G CDMA device

•   Replace the 2G GSM device with a 4G LTE device

  A point worth mentioning, the 2g sunset this issue is only a North America issue. Europe which has most of their M2M devices on 2G networks is continuing to operate their 2G networks.

  What is a SIM Card?

  Another difference between GSM and CDMA enabled devices are SIM cards. GSM uses SIM cards, whereas CDMA typically does not. However, to keep things a bit confusing LTE deployments both GSM and CDMA use SIM cards. SIM cards act as an onboard memory device providing subscriber identity, rate plan data, and other user data such as all of your contact and calendar information. CDMA stores the user’s data including the phone book and scheduler information, on the operator’s database. 

There are four basic SIM Card choices:  Consumer white label SIM card

o Used primarily in consumer products and smart phones.

 Enhanced ruggedized plastic SIM card
o Designed to operate in harsh industrial environments and excessive vibration.

Typically designed with harder polycarbonate plastic to withstand greater temperature and be less susceptible to warpage and other mechanical fluctuations. Typical size is 15mm x 25mm

 3FF SIM
o Third Form Factor (3FF) of the SIM standard and holds the same amount of data as

a Mini SIM. 3FF SIMs were developed by the European Telecommunications Standards Institute to fit into devices too small for a regular Mini SIM. A 3FF SIM card measures 12 mm x 15 mm. Available ruggedized for use in telematics type applications.

 eUICC
o The embedded Universal Integrated Circuit Card (eUICC) replaces the removable

SIM with an integrated circuit chip soldered to the circuit board of an embedded device. Such a technology evolution will trigger changes in the whole mobile communication ecosystem, as the customer relationship management may shift from the mobile network operator to the OEM vendor. 

When selecting which solution is right for your application you need to consider several tradeoffs as shown in the table above. However, as the industry evolves the need to update the service OTA globally on an embedded device is now a reality. Key to this revolution is a new SIM card form-factor set to launch in 2014 the eUICC. This SIM is designed to be embedded in machines permanently, and can be provisioned OTA after the machine is delivered anywhere in the world

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