Redundancy by Design: How to Build Fault-Tolerant Connectivity for Cellular, GNSS, NTN, and More

For decades, the telecom gold standard was 99.999% uptime. That’s a very high bar to clear with any type of wireless technology, even private 4G/5G, simply because there are so many variables.

For example, dense foliage and tall buildings often attenuate or block cellular and GNSS signals. And that’s under normal conditions. Wildfires, floods, and solar storms have knocked out cell sites and GNSS satellites for hours, days, or longer. Organized crime and defense organizations are increasingly spoofing and jamming GNSS to facilitate everything from hijacking trucks to sabotaging aircraft. The list goes on and on and on.

Even if an application isn’t mission critical per se, it’s still important from a business perspective to anticipate and address those variables. Take the example of a medical device designed for use in patient homes. Cellular is ideal for uploading vital signs and other data because the device doesn’t depend on patients having Wi-Fi in their home. The big catch is that it’s impossible to predict which mobile operator will have coverage at each patient’s home. More about that in a moment.

The solution in all of these scenarios is to design devices with a strength-in-numbers architecture because redundancy creates resiliency. Antennas play a critical role in that design strategy, which highlights why it’s important to begin considering them on day one of the project rather than day 90. Read on to learn how device OEMs and systems integrators can design solutions that fail gracefully and recover quickly.

Multiple Cellular Networks

No mobile operator covers a geographic area exactly like its rivals do. Sometimes it’s because one has more sites in a certain part of town and thus fewer or no coverage holes there than other operators. Sometimes two operators can be co-located on the same tower but have markedly different coverage because they use different bands with different propagation characteristics.

Resiliency could be achieved by designing the device to automatically switch operators based on KPIs such as signal strength or when coverage suddenly disappears because a cell site went offline. Many modern cellular modules support dozens of bands, such as from 600 MHz to 3.7 GHz, and use an electronic SIM (eSIM), which can be provisioned for multiple mobile operators.

The key component is a wideband antenna that covers all of those bands and operators. An example is the Taoglas TGX.45.A, a cross-polarized omnidirectional dipole antenna that covers 400 MHz to 6 GHz. That’s every LTE band and every 5G allocation up to the mid-band spectrum range.

A wideband antenna also provides business resiliency. Application providers can be confident that their devices will always have connectivity because they will always be able to connect to the right mobile network. No Wi-Fi? No problem. (For a case study, see “Healthcare Specialist Leverages LTE and GNSS for Next-Gen Wound Therapy in Patient Homes.”)

Multiple Air Interfaces

Strength in numbers also can mean using multiple air interfaces. An example is an outdoor security camera system that uses the homeowner’s Wi-Fi network because it’s free but automatically switches to 4G/5G when the WLAN is unavailable. Maybe that’s because the WLAN doesn’t have a reliable signal in some camera locations. Maybe it’s because a burglar cut power to the house, knocking out the router. Whatever the reason, the cameras revert to cellular to keep feeding video to the cloud and on to the homeowner’s app or security service.

Another emerging option is pairing cellular with Non-Terrestrial Networks (NTNs), which use LEO, MEO, or GEO satellite constellations such as Amazon/Kuiper, OneWeb, Skylo, and SpaceX/Starlink. Satellite fallback isn’t new, but today’s NTNs dramatically lower the cost to the point that it’s viable for more applications than ever.

This combination is a particularly good fit for devices that will be installed in or travel through places where cellular coverage is weak or nonexistent. An example is a telematics solution that needs to maintain constant connectivity with a truckload or shipping container of high-value cargo. If there’s no cellular coverage on the remote highway or rural rail siding, the telematics device can use an NTN to send an alert that a door has been breached or that a geofence excursion has occurred.

Adding NTN support to a device doesn’t necessarily require an additional transceiver and another antenna. Many LEO and 5G bands are close enough that a single antenna can cover both. That’s why modules that support both cellular and satellite have a single RF connector for the antenna.

For more information about combining cellular and NTNs, see:

• Introduction to Non-Terrestrial Networks, a portal that includes real-world case studies, blog posts, and the portfolio of Taoglas NTN embedded and external antennas.
• “Cell towers/satellites: The future of long-range connectivity,” an on-demand webinar with experts from Taoglas, Nordic Semiconductor, and DigiKey.
• “Beyond the Horizon: Designing for Unbreakable Connectivity,” an on-demand webinar featuring Taoglas, Murata, and Skylo.

Multiple GNSS Constellations

All GNSS signals are relatively weak by the time they reach the Earth. They’re also increasingly subject to spoofing and jamming. Devices that have access to multiple GNSS constellations can overcome those challenges and ensure that their applications have consistent access to high-quality PNT data.

For example, if one constellation’s signals are weak or unavailable, the device can switch to another’s. If jamming and spoofing are a concern, the device can compare the PNT data from multiple constellations to see if they align.

A strength-in-numbers design philosophy also overcomes coverage limitations. For example,

GPS satellites rise only 45 degrees above the horizon. A device that uses only GPS loses visibility of its satellites at higher latitudes, undermining accuracy for PNT applications such as tracking arctic mining equipment. But if its module and antenna system also support GLONASS and/or Galileo, the device’s application can take advantage of constellations whose orbits provide better coverage in higher latitudes.

Supporting multiple constellations’ bands and frequencies doesn’t necessarily mean the antenna system will be physically large and challenging to integrate. For example, the Taoglas Patriot series is a roof-mount antenna designed for first responder agencies and other fleets. Measuring just 205 mm long by 180 mm wide, a single Patriot enclosure accommodates up to 18 antenna elements not only for dual-band GNSS (L1 and L1/L5) and a secondary GNSS (L1), but also:

• 4G and 5G cellular (600-6000 MHz)
• Wi-Fi (2.4, 5.8, and 7.1 GHz)
• SDARS (2.3 GHz)
• LMR/TETRA (380-400 MHz and 700-900 MHz)

For more GNSS insights and design tips, see:

• “GNSS vs. GPS: What’s the Difference?”
• “Where the Rubber Meets the Road: Top Tips for Designing a Transportation-Grade GNSS Solution”
• “Right on Time: Understanding GNSS Timing Fundamentals”
• “How to Navigate the L1, L2, L5, E5a, E5b, and G2 Alphabet Soup of GNSS Constellations and Signals”
• “How to Leverage the L-Band to Balance Accuracy and Affordability for GNSS Applications”

Get in touch for orders or any queries: sales@rfdesign.co.za / +27 21 555 8400

Courtesy of Taoglas