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Broadcom announced that it is sampling the first mass-market chip that can take advantage of a new breed of global navigation satellite signals and will give the next generation of smartphones 30-centimeter accuracy instead of today’s 5 meters. Even better, the chip works in a city’s concrete canyons, and it consumes half the power of today’s generation of chips. The chip, the BCM47755, has been included in the design of some smartphones slated for release in 2018, but Broadcom would not reveal which.
[...]
All GNSS satellites—even the oldest generation still in use—broadcast a message called the L1 signal, which includes the satellite’s location, the time, and an identifying signature pattern. A newer generation broadcasts a more complex signal called L5 at a different frequency in addition to the legacy L1 signal. [...] it is much less prone to distortions from multipath reflections than L1.
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The direct signal and any reflections arrive at slightly different times, and if they overlap, they add up to form a sort of signal blob. The receiver is looking for the peak of that blob to fix the time of arrival.
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However, L5 signals are so brief that the reflections are unlikely to overlap with the direct signal. The receiver chip can simply ignore any signal after the first one it receives, which is the direct path. The Broadcom chip also uses information in the phase of the carrier signal to further improve accuracy.

Though there are advanced systems that use L5 on the market now, these are generally for industrial purposes, such as oil and gas exploration. Broadcom’s BCM47755 is the first mass-market chip that uses both L1 and L5.

Why is this only happening now? “Up to now there haven’t been enough L5 satellites in orbit,” says Manuel del Castillo, associate director of GNSS product marketing at Broadcom. At this point, there are about 30 such satellites in orbit [...] Even in a city’s “narrow window of sky you can see six or seven, [...] So now is the right moment to launch.”

Broadcom had to get the improved accuracy to work within a smartphone’s limited power budget. Fundamentally, that came down to three things: moving to a more power-efficient 28-nanometer-chip manufacturing process, adopting a new radio architecture (which Broadcom would not disclose the details of), and designing a power-saving dual-core sensor hub. In total, they add up to a 50 percent power savings over Broadcom’s previous, less accurate chip.
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The BCM4775 is just the latest development in a global push for centimeter-level navigation accuracy. Bosch, Geo++, Mitsubishi Electric, and U-blox established a joint venture called Sapcorda Services in August, to provide centimeter-level accuracy. Sapcorda seems to depend on using ground stations to measure errors in GPS and Galileo satellite signals due to atmospheric distortions. Those measurements would then be sent to receivers in handsets and other systems to improve accuracy.

Japan’s US $1.9 billion Quasi-Zenith Satellite System (QZSS) also relies on error correction, [...] the system is to come online in 2018.
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https://spectrum.ieee.org/tech-talk/semiconductors/design/superaccurate-gps-chips-coming-to-smartphones-in-2018
https://spectrum.ieee.org/tech-talk/semiconductors/design/superaccurate-gps-chips-coming-to-smartphones-in-2018

Labels: Oleg Zabluda

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