When selecting wireless modems, there’s a checklist of features to consider. We’ve presented those here.
The growth rate of machine-to-machine (M2M) connections now far exceeds new connections between people, and soon there will be many more machines than people connecting over cellular networks, as shown in the GSM Association forecast in Figure 1. These machines include security systems, meters, robots, vending stations, asset trackers, and emergency call systems. The variety is growing by the day, as are the silent conversations between millions of machines exchanging data 24 hours a day, 7 days a week, with no human intervention.
At the same time, it’s becoming cheaper and easier to connect to the Internet and even mass produced computing devices are able to gather and process ever-larger volumes of data. The one potential bottleneck to greater M2M connectivity, the fact that all 4 billion+ IP version 4 (IPv4) addresses are already allocated, has been removed with the introduction of IP version 6 (IPv6). This supports 2128 addresses, more than enough for every grain of sand on Earth to have its own address. It’s perhaps no surprise then that LTE, the fourth generation of mobile networks (4G), is designed to deliver services such as data, voice, and video over IPv6.
To join the M2M networking revolution, all that’s needed is to embed machines with small, economical (wireless) modems. Where location, speed, or navigation information needs to be established, the machines also need a GPS or GNSS (Global Navigation Satellite System) receiver. Both components, with an antenna, can fit easily in a device smaller than a mobile phone. GNSS is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. It includes GPS (U.S.), GLONASS (Russia), Galileo (Europe), BeiDou (China), and other regional systems.
When thinking about how to equip a machine with communications capability, start by thinking about the needs of the application. Factors such as product longevity, geographical network coverage, or future-proofing to take account of future wireless network upgrades, are all important considerations. Here are some of the product features to consider when selecting wireless modems.
Battery life is critical
The time between battery charging or replacement is critical to the success of some products. A container-mounted tracking device, for example, may be required to run for several days if it’s being shipped by air or road, and up to several weeks if shipped by sea. Battery life must be adequate to support these timescales.
Mobile phones are typically expected to run for two or three days on a charge. Hence, consumer expectations for the operating life of health and fitness devices will be similar. When comparing modem and GNSS receiver specifications in these applications, both the operating and standby current consumption are important, as well as the power-saving functions. The latter may include auto-wakeup features and intelligent power-saving modes, such as the ability to log data autonomously without waking the host processor. Ideally, components should only wake up when needed.
Mobility demands multi-standards compliance
Global mobility is increasing for people and goods, so it’s important to consider where a modem needs to function today and where it may be required to work in the future. GSM is supported by four main frequency bands worldwide, UMTS by six, and LTE over 30. An electricity meter is usually static whereas a resource management system may be required to work in all regions of the world and should include either a quad- or dual-band GSM modem (depending on the location), or six-band UMTS modem.
Certified modems accelerate product approvals
Any cellular network device, whether for GSM, UMTS, or LTE, needs regulatory, industry, and operator certification. It significantly simplifies and speeds up the certification process if the modem embedded in the device is certified.
What’s needed today may be different tomorrow
While GSM/GPRS networks are perfectly capable of handling the small volumes of data transmitted in remote metering applications, GSM bands are already being considered for re-allocation to 3G and 4G services. To save the expense of future-proofing, it’s a good idea to design with future technology standards in mind. Today, this means designing with UMTS/HSPA or LTE modems, or at least future-proofing hardware to simplify upgrades.
Nested design simplifies technology upgrading
Cellular M2M technologies are in continuous evolution and when designing a new device enabling cellular connectivity, it’s important to consider its upgradability to newer technologies to optimize the design cost. Here, there’s layout compatibility across the entire cellular modem range (GSM, UMTS, CDMA, and LTE). With this approach, as shown in Figure 2, one PCB layout can be used for all end-product variations, ensuring an easy migration between cellular technologies and module generations, also thanks to the AT command compatibility within the different modules.
Bandwidth requirements rarely decrease
The bandwidth demand of tracking applications only goes in one direction – up – so it’s important to consider the lifetime costs of connection. Choose a modem based on what it may need to do in three to five years, or at least choose one that makes upgrades easy.
Automotive special needs
In vehicle-mounted systems, temperature, humidity, and vibration can be extreme. AEC-Q100 qualified devices manufactured in ISO/TS 16949 certified sites will ensure reliable, long-life operation. Qualification tests for each component should conform to ISO16750, Road vehicles – Environmental conditions and testing for electrical and electronic equipment. This applies to vehicle-mounted and industrial devices that operate in demanding environments, such as ships or railcars.
Emergency call systems are growing in popularity
Increasingly, cars are fitted with systems that automatically report accidents or aid recovery after theft. The U.S., Europe, Russia, and Brazil have established initiatives to support such systems and that will increasingly be required by government mandate. For these applications (see the example in Figure 3), an “in-band modem” is often needed. It sends data over the modem voice channel in a similar way to a fax machine sending data over the telephone lines. It’s needed because operators prioritize voice over data in mobile networks. In the event of an accident, the voice channel becomes the crucial link for transmitting data to emergency services. Check that the proposed solution supports in-band modems on both 2G and 3G networks.
Assisted positioning in urban environments
In urban environments where satellite may be blocked by tall buildings, the drop-out of positional overview can be overcome by calling up a remote A-GPS server. This simple process downloads a few bytes of satellite orbital data from the Internet using a wireless modem. With this aiding data, visible satellites need only be visible for a few seconds to calculate a position, and not the full 30 seconds it takes to receive an entire 1,500-bit satellite frame.
Check that the GPS receiver vendor offers online assistance with guaranteed availability and that this covers the geographic regions of interest. Client software should support the service transparently and the positioning receiver and wireless modem should both have an interface to support the service. It’s also increasingly important that the service is available for both GPS and GLONASS.
Dead reckoning support to extrapolate positioning data from sensors
Satellite signals can be supplemented with dead reckoning support, which extrapolates location and speed based on data from vehicle sensors, as illustrated in Figure 4. This approach helps determine vehicle position in tunnels or other locations where satellite reception is temporarily unavailable. It’s useful in vehicle-based telematics, including insurance tracking systems, where it accurately records position, heading, and velocity.
Check that positioning receivers are automotive-grade, support dead reckoning, and can be plugged into the vehicle’s CAN bus to acquire the data. Also, ensue that they can interface directly with vehicle sensors such as gyros and odometers and that the vendor offers an evaluation environment to speed product development.
Indoor positioning is possible by combining satellite and cellular data
Where an approximate indoor position needs to be established, combining a satellite receiver with a wireless modem overcomes the problem of satellite signals being blocked by walls or other obstructions. This hybrid solution exploits the visibility of 2G or 3G cells because GSM or UMTS signals easily penetrate walls. Where the boundaries of visible mobile cells are known, an approximate position can be calculated from knowing where the cells overlap. This approach needs a wireless connection to an external service, similar to assisted positioning. Check that the positioning receiver and wireless modem supplier can offer such a solution, and that it’s proven and provides an online service. It’s also important to ensure that the system’s accuracy is adequate.
Positioning system compatibility
Until recently, GPS was the only system designers needed to consider. Now, there’s Russia’s GLONASS, Japan’s QZSS, China’s BeiDou, and Europe’s Galileo. Compatibility with GPS plus at least one other satellite system will be needed to increase system reliability and accuracy, and to fulfill regional government mandates for compatibility with their own systems. Parallel operation that uses two systems simultaneously may be part of the specification. An example is Russia’s new ERA-GLONASS vehicle emergency call system that requires GLONASS compatibility. Look for GPS/GNSS receivers that provide multi-GNSS support and provide parallel GPS/GLONASS or GPS/BeiDou reception.
These are just some of the considerations when adding wireless connectivity to M2M products. Remember that many new standards, both wireless and positioning, are in transition. It’s important to consider the product’s operation over its lifetime and which markets it will serve. Also, consider whether it’s important to include design support for next-generation performance and network coverage, or opt to design for easy upgradeability of products in the field.