Arrival of the Future: Dual Frequency Satellite Receivers, Smartphones, and Property Rights

In 2017 we wrote a pair of blog posts highlighting the arrival of new satellite technologies that offered to make high-precision location data widely and cheaply accessible for the first time with affordable dual-frequency receivers. Compared to single-frequency devices, dual-frequency receivers are more accurate, better in urban environments, and more resistant to interference, making them a powerful tool for mapping as well as for safety-critical applications like autonomous vehicle navigation.

The increasing availability and affordability of these receivers has two major causes. The first is the increasing number of satellites broadcasting a new, open navigation signal called L5 (or E5, the equivalent for the EU’s Galileo constellation) which can be used alongside the L1 signal. It is supported by all of the major constellations, including GPS, Galileo, BeiDou, QZSS, and IRNSS. Although the individual satellite constellations broadcasting this new signal have not yet been completed, as of 2017 they collectively provide enough coverage to make the L5 signal useful. Only four visible satellites are technically required for a position fix, but eight is preferable for the best service, a level of coverage that has only just become a possibility for large parts of the earth. This has helped to create a ballooning market for accurate location services, most notably for transportation, but also virtual reality and wearable medical devices.

In a previous article we estimated that investment in dual-frequency GNSS receivers for these mass market applications would see prices fall to $50 within five years and that this hardware would eventually appear in smartphones once battery and antenna limitations were addressed. That prediction was in some ways a conservative one. In September 2017 the chip manufacturer Broadcom announced that it was releasing a dual-frequency GNSS chip for the smartphone market called the BCM47755. The cost and performance of that chip were unknown, but Broadcom’s announcement that it would appear in a smartphone from a major manufacturer in 2018 signaled that a massive leap in mobile location technology was on the horizon. But Broadcom did not disclose which manufacturer they were partnering with. In May 2018 the Xiaomi Mi-8 was announced as the first phone to incorporate Broadcom’s new chip.

Mi-8 Cost and Performance

The Mi-8 may have a dual-frequency GNSS chip, but location accuracy is dependent on many factors beyond the use of multiple frequencies, including the quality of the antenna and signal processing software. The company claims that the Mi-8 is capable of 30cm accuracy, which would be a drastic improvement from the 5m achievable with a standard single-frequency chip. In urban settings where more signal paths are obstructed by buildings and there are many reflective surfaces, the accuracy difference will be even more pronounced, as the L5/E5 signal is designed to make it easier to identify and discard reflected signals. Anyone who has ever called an Uber in the downtown area of a major city can appreciate the difference this would make. In addition to the 16x greater accuracy, Broadcom claims the new chip actually improves battery consumption, requiring 50% less power than the previous generation of single-frequency chips.

As for cost, the new chip makes no discernible contribution to the cost of the phone, which starts at a little over $400, well below the price of flagships from Apple and Samsung. In 2017 a Broadcom representative told GPS World that OEM manufacturers would probably pay the same amount for the BCM47755 that they did for the older L1-only chips.

Xiaomi has emphasized the advantages of the Mi-8’s dual-frequency receiver for in-car navigation, conducting a demonstration in which a car with blacked-out windows navigated a closed road course using only the phone GPS. It is very likely that the first major impact for the consumer will be the ability to support lane-level navigation.

The real-world performance of the Mi-8 is not yet known. Some users have found that the location accuracy is no better, or even worse than that achieved with single-frequency devices in their areas. This may be due to inadequate signal availability or to software issues. Daily usage and experimentation with different augmentation methods will reveal the true capabilities of the device. And while the the Mi-8 does not deliver centimeter-level accuracy like a professional survey receiver, access to raw signal data means that differential techniques like RTK can be developed for Android devices.

Ecosystem

While the first appearance of a dual-frequency chip in a smartphone is a major step forward, the development of a high-precision location data ecosystem also requires software and services. The open-source Android operating system now gives developers access to raw signal data (including pseudoranges, doppler, and carrier phase) from multiple satellite constellations. Organizations betting on expansion of location services are helping to promote their growth and development. In June 2017 the EU launched a GNSS Raw Measurements Task Force to “boost innovation around this new feature” and “share knowledge and expertise on Android raw measurements and its use, including its potential for high accuracy positioning techniques.”

Impact for Land Rights

The introduction of dual-frequency GNSS in mobile devices has enormous implications for land rights. As access to high-accuracy location data becomes ubiquitous, it will become a powerful tool for anchoring claims of occupancy and land usage.

For example the Interethnic Association for the Development of the Peruvian Rainforest (AIDESEP) has been using drone imagery to document the encroachment of palm oil, mining, and logging companies on indigenous lands. According to an article in Fast Company, AIDESEP had previously “equipped community leaders with smartphones that allowed them to take GPS-tagged photographs of changes and infractions,” but “found that the evidence they were presenting was always questioned or pushed back on. But with drones, community leaders can present continuous footage that starts at a known location, and tracks over the site of whatever violation they’re trying to document.” Dual-frequency GNSS data has higher integrity than single-frequency data, and combined with proof of location and image hashing could allow photographic or video evidence from a $400 smartphone to provide the same assurance as video from a $25,000 drone.

In Puerto Rico roughly half of all properties are informal. In the aftermath of Hurricane Maria, many residents of these informal communities were unable to access FEMA aid because they had no legal documentation of their ownership. This became such an obstacle to the relief efforts that FEMA began accepting affidavits as evidence of property ownership in lieu of titles.

As mobile accuracy converges towards legal surveying standards there will be greater opportunity for crowd-sourced surveying projects like USAID’s MAST to bypass the surveyor bottleneck we have described elsewhere. Crowdsourced data collection will not replace surveying for the time being, but it will be a powerful tool to document the property rights of vulnerable populations.

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