Custom tablets and other handheld devices, whether used for consumer, military, commercial, or medical purposes, frequently include GPS (Global Positioning System) to assist in determining current location and time. Specifically, GPS refers to the US owned and Air Force operated network of 24+ middle-earth orbit satellites. This global system has reliably been supplying location and clock synchronization services to both the military and civilian sectors since it became fully operational in 1995; however, it is not the only satellite system in use for freely providing location services.

What you say? Isn’t the venerable GPS system the only satellite-based game in town?

Well, that used to be the case, but this is no longer true.

The other global satellite navigation systems in current use, or in various stages of development, are:

• Galileo: a global system developed by the European Union (EU) and other partner countries and began operation in 2016, with the expectation of full deployment by 2020
• GLONASS: Russia’s global navigation system, which is currently fully operational worldwide.
• Beidou: People’s Republic of China’s regional system, but planned for global operation by 2020

There are additionally some regional systems, where geolocation operates within and in near proximity to these regions:

• IRNSS: a regional navigation system developed by the Indian Space Research Organization
• QZSS: a regional navigation system in development that is currently operational within Japan.

Generically, each satellite-based geolocation and time system is referred to as a Global Navigation Satellite System (GNSS). This term is typically used to encompass multiple systems without distinguishing a particular constellation. The country (or countries) backing each GNSS constellation are pushing to have their system adopted not only in-country, but worldwide. Russia is pushing for adoption of support for GLONASS through tariffs applied to non-GLONASS-based devices. All Chinese phone makers and most commercial Chinese vehicles are mandated to support Beidou. The EU promotes Galileo through incentives and emphasizing that their system is managed by civilians and is not intended for dual military use.

Many global component-level companies such as Qualcomm, Broadcom, u-blox, and STM make GNSS-enabled chips sets. These GNSS chipsets, and modules based on these chipsets, incorporate one or more of the GNSS systems. The larger global smartphone and tablet developers such as Samsung, Apple, HTC and others support multiple GNSS constellations, in some cases all of them. This is great for the typical user, who in most cases does not care where the source of their location information originates, as long as they can transparently receive signals meeting their required precision. However, developers of custom medical devices, military tablets, custom handheld devices, and most Linux single board computers must consciously make the choice of what GNSS system(s) to use. In the US, most devices are typically designed around a single GNSS constellation – specifically GPS. However, there are some key differences in the various GNSS systems, so developers and users need to be savvy on the application domain and be prepared to take advantage of the best solutions – which in many cases means supporting more than a single constellation.

One of the issues to consider is that these are very expensive systems to develop and maintain and that the controlling government or coalition that operates each system is the final authority on how it is used. For example, during the 1990s, the US Department of Defense degraded the GPS quality for the civilian sector in a program called “Selective Availability,” which in effect made commercial location less precise than military location capabilities. The GLONASS and Beidou systems have similar features. This degradation was discontinued in 2000 and since then both the military and civilian sectors worldwide have had full access to precision-location information from the GPS constellation of satellites. The US-government can still selectively degrade or deny non-military access to the system, while still maintaining precision through special receivers known as SAASM (Selective Availability Anti-Spoofing Module) devices – but the point is that most users will have no access or control in this contingency.

Despite this potential for the US government to deny service at any time, the use of GPS has exploded worldwide since 2000. Smartphones, tablets, and other portable electronic devices in North America routinely use GPS for real time location services. GPS has continued to improve in its capabilities since its introduction. In 2000, high-quality Federal Aviation Administration (FAA) grade GPS receivers had horizontal accuracies of 5m, which improved to 3m by early 2015 – and in late 2018, by using the newer L5 band, location precision offers unaugmented accuracies of ~30cm. Additional precision and capabilities will be available as the full contingent of satellites, as a part of GPS Block III, are fully deployed.

As wonderful as the GPS system is – and will be – it still suffers from some limitations. For starters, although the US system is global – and legislated by our government to stay in continuous operation – the US government could at any time elect to deny or degrade access. Further, although the system is typically robust, depending on the satellite orbital paths, the time-of-day, and the surroundings, it is possible to lose the relatively weak signal – especially in cities with tall buildings or in covered or sheltered areas. The GPS system has limited coverage in the high latitudes (in both the northern and southern hemispheres) and many specialty applications (such as high-speed and high-altitude devices) are denied access. Although the US system was first, and will likely continue to be one of the best navigation systems worldwide, it is important to consider the several other competing or augmentative systems.

From a design standpoint, the appropriate chips sets, antennas, and software must be selected to operate with the selected GNSS system(s) – but with the current availability of multi-constellation components, this is not a difficult task, although it is one that must be decided on in the custom design. As 2020 approaches and additional GNSS options become available, custom embedded products can be designed to take advantage of this infrastructure. Most portable device applications do not require the use of one GNSS system over another, but can support multiple constellations with minimal changes to the design electronics and offer improved overall performance.

SECO USA designs rugged tablets and handheld devices for the military, medical and industrial markets. Our commercial off-the-shelf (COTS) single board computer (SBC) and tablet products are designed internally from the ground-up, including circuitry, Android or Linux operating systems, and packaging. SECO USA’s Modified-COTS design services leverage these verified COTS design to incorporate customer-specific requirements and features, which includes expanded geographic use or specific GNSS configuration. Contact SECO USA for an evaluation of your custom tablet or handheld device requirements, and let our expert team of embedded design engineers help you consider trade-offs for your application.