Smartphone SatNavs to get centimetre-perfect GNSS receivers in 2018

Broadcom is now sampling silicon it says will make smartphones' SatNav systems accurate to a centimeter in 2018.

The company announced the new "BCM47755" chipset at the ION GNSS+ conference in Portland, Oregon, and says it will deliver 30cm accuracy even in the concrete canyons of cities where today's GPS can struggle.

The company thinks that level of accuracy will let SatNav systems advise which lane you should drive in, making it a bit easier to prepare for a turn.

According to IEEE Spectrum, the company also claimed the chip is being designed into future smartphones, but wouldn't identify the vendors.

The BCM47755 achieves its extra accuracy by locking on to three satellites using the L1-band transmission (the GPS broadcast of satellite location, time, and signature).

Once locked on, the chip uses L1 and the L5-band signal on new satellites (centred on 1,176.45 MHz). As well as providing two frequencies for location calculation, the L5 signal carries longer codes, giving it greater location precision.

The IEEE Spectrum report notes that Broadcom decided it was time to launch the dual-band chip, because there are now 30 suitable satellites in orbit. In most locations, between six and seven satellites should be visible from a receiver.

The higher-frequency shorter-pulse* L5 signals also help around tall buildings, because they make it easier to deal with multiple signal reflections.

In such environments, the receiver needs to work only with the first signal received – if it used a later signal, it would calculate the wrong location. The problem at the lower-frequency longer-pulse L1 band is that multiple signals smear across each other.

In L5 transmissions, the signal peaks the chip is seeking are much shorter, so there's a much better chance the receiver will correctly identify the first signal it receives.

Weary smartphone owners who find themselves choosing between location services and battery life will be cheered by Broadcom's claim that the chip consumers 50 per cent less power than the company's previous generation GNSS receiver.

A dual-core ARM CM-C40 sensor hub also helps save power, Broadcom says. The company's release is here. ®

*Correction: The author misread GNSS specs. L1 is at a higher frequency than L5, but that was incorrect. L5 is at a lower centre frequency, but it transmits shorter pulses, and is thus easier to discriminate in a high-reflection environment.