Many people have GPS navigation a lot to blame. There is no cheating, standard maximum accuracy at 8 meters is insufficient even in car navigation. Therefore, the applications for the drivers must use some tricks. Soon, this problem will disappear, because the GPS modules will determine the position using two GPS signals: L2 and L5. The first one will be the Broadcom BCM47755.

This accuracy is determined for the ideal case when the user sees the so-called clear sky and receive a GPS signal from at least 4 satellites. Clear visibility means that there is no obstruction between the GPS receiver and the satellite. It also requires that no objects which could reflect a radio signal are nearby. So with this situation we are dealing only in the proverbial sincere field. Fortunately, the constellation of GPS satellites is dense, so our smartphones receive signals from up to 9 satellites.

With the L2 and L5 signals, the Broadcom BCM47755 will be able to determine the position with up to 30 centimetres accuracy.

GPS modules receiving only L2 signals have a problem with the exact positioning when the receiver is near high buildings. In this case, the phenomenon of multipath propagation (i.e. multiple reflections of radio signal from buildings and other obstacles) causes that GPS signal propagation time can not be uniquely determined. Of course, this translates into an increase in inaccuracy of the position. On the other hand, the L5 signal is transmitted by satellites at frequencies reserved worldwide for navigation needs. In addition, it is modulated with 10 Mbps code rate. Conversely, the L2 signal is modulated by ten times slower code, which is less “clear” after the receiver receives it from a few reflections.

Broadcom L2 L5

However, not all GPS satellites broadcast an L5 signal. This is why the Broadcom BCM47755 uses both signal types. First, the approximate location is determined by the L2 signals, while the L5 signal is used to increase the precision of the receiver’s distance from a particular satellite. Currently, about 30 GPS satellites on the orbit support L5 signal. This is enough for two-way GPS modules to be mass-produced and benefit from increased accuracy.

Source: IEEE Spectrum