The following is the generic guideline for selecting wireless modules for M2M projects.
Form Factor
The main criteria for form factor is the size.
PCIe Modules – This form factor is standards-based that are primary used in mobile computing devices such as laptops, netbooks etc. However the dimensions (50x31x5 mm) of PCIe Modules are typically too big for M2M applications.
LGA Modules – Land Grid Array (LGA) modules uses surface mount technology. LGA Modules are suitable for M2M applications where size is an important consideration. From a mechanical perspective, LGA modules are also better than PCIe or board-to-board modules. LGA Modules also have better heat dissipation capabilities. Since LGA modules are soldered on to the host devices, it is not easy to replace them when the devices are returned.
Board-to-Board Connector Modules – These are the most commonly used in M2M applciations. The important consideration here is the forward compatibility, ie being able to updrage the technology while maintaining the same footprint and interfaces. Board-to-Board connector modules are easy to replace, however the connector interface is not robust as LGA interface.
Technology
The technology choice is really between CDMA(10 – 15% market share) and GSM (80 -85% market share). The prevalence of GSM systems around the world implies that GSM-based modules are generally cheaper than CDMA modules. In U.S, Verizon Wireless and Sprint has CDMA network, so those 2 carriers are the main market for CDMA-based modules. GSM-based modules can be launched on a world-wide market, although there is a considertion for frequency bands within different regions.
From a technology perspective, there is also a considertion for 2G Vs 3G modules. 2G modules supports lower speeds and are cheaper, but 3G modules which supports higher speed generally are more expensive. On the CDMA world, 1xRTT is considered 2G while EVDO is 3G. On the GSM side, GPRS/EDGE are 2G while UMTS/HSDPA/HSPA+ are considered 3G. From a carrier perspective, 3G modules are preferable because they use the wireless spectrum efficiently. Many are carriers, especially in U.S, are not planning to certify new 2G devices any more. Given the lower costs, 2G modules are still widely used in many parts of the world.
Speed
The uplink and downlink speeds of the modules are importation considertion for the M2M application. The choice of the modules will depend on the bandwidth requirement of the application.
Below are the peak download and upload speeds of the modules. However the actual speeds are dependent on the network conditions. Generally the actual speeds are 40%-60% of the peak speeds.
Download Speed Upload Speed
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GPRS Modules 86.5 Kbps 85.6 Kbps
1xRTT Modules 153 Kbps 153 Kbps
EDGE Modules 236.8 Kbps 236.8 Kbps
UMTS Modules 384 Kbps 384 Kbps
EVDO Modules 3.1 Mbps 1.8 Mbps
HSDPA 3.6 Modules 3.6 Mbps 384 Kbps
HSDPA 7.1 Modules 7.2 Mbps 5.76 Mbps
HSDPA 14.4 Modules 14.4 Mbps 5.76 Mbps
HSPA+ 21 Modules 21 Mbps 5.76 Mbps
DC-HSPA+ 42 Modules 42 Mbps 5.76 Mbps
LTE Modules 100 Mbps 50 Mbps
Features
All modules provides celluar connectivity at different speeds (see above). These are some of the features that are generally available on the modules.
- UART – This is primary host interface on most the modules are provides serial communication interface for data and module control.
- USB – Modules that supports high bandwidth will provide USB interface because UART speed may not be sufficient.
- Voice – Modules may support analog and/or digital voice support for applications that needs audio interface. Voice support will be a added cost.
- GPS – For location-based services applications, GPS support is available in many of the modules. Typically GPS support will cost extra though in many advanced chipsets, GPS feature is becoming standard.
- Frequency Bands – Carriers operate in specific frequency bands, so modules supports multiple configuraitons targetting spefic regions and/or carriers. Certian modules will support all bands therby enabling a global rollout.
- Extended temperature.- For applicaitons that operate in harsh environmental conditions, modules that support extended temperature may be a requirement.
Software
Software is the key component of any M2M implementation. AT commands provides all the required basic interfaces for modem control. AT commands are defined as a part of 3GPP specification, so they are required to supported by all modem vendors. AT commands provides interfaces to get device/manufacturer information, send/receive voice calls, make data calls, get network information, configure device settings, send/receive SMS etc. Apart from the standard AT commands , modules vendors generally provide support for extended AT commands for features such as HTTP, FTP, Email etc.
Apart from standard AT commands , many module vendors also provides proprietary software interfaces to the modules. These interfaces generally are programmer-friendly and provided enhanced capabilities. Adopting proprietary interface from module manufacturer will make it difficult to switch in the future. Standards based AT commands implementation will be modem-agnostic and provided flexibility to switch the module vendor in the future.
Cost
Cost of the module is most important selection criteria. From a technology perspective, the cost of the modules is in the below order,
GPRS Modules < EDGE Modules < 1xRTT Modules < UMTS Modules < HSDPA 3.6 Modules < EVDO Modules < HSDPA 7.1 Modules < HSDPA 14.4 Modules HSPA+ 21 Modules < DC-HSPA+ 42 Modules < LTE Modules
The cost of module can vary among the module vendors and in general it is dependent on the support that comes with it. The application developer needs to truly asses their capabilities in integrating a wireless module in to thier device.
Support
Wireless module integration is by no means a simple task. It requires diverse skill set in baseband, RF, software, carrier and regulatory certification processes. Support from module vendors is key for application developers even if they have in-house capabilities.
Certification
Devices needs to get type approval and in some cases carrier approval before they can operate on cellular networks. In the GSM world, PTCRB approval in U.S and GCF approval in Europe are required to launch commercial devices. PTCRB and GCF organizations are setup by the network operators to approve devices that operate on cellular standards (3GPP). Third-party test houses typically manage this process by testing the devices and submitting the results to teh approval bodies. In addition the device should also get governmental approvals such as FCC (U.S), CE (Europe), Anatel (Brazil) etc.Apart from the above approvals, in some cases the carriers also have their own device approval process.
Modules are required to go through all the above approvals as well. In most cases, devices can leverage the approvals of the module and are only required to do a subset of the testing. So it is important to select a module that has all the required certifications in order to be launched on a carrier network. Most carriers publish a list of approved modules on their network, so it is a good idea to start with that list. Here is list for some the carriers – AT&T approved modules, Verizon approved modules, Sprint approved modules and Vodafone approved modules.
Module Manufacturers
Below is the list of top module manufacturers who offer a broad portfolio of wireless modules,