3 ms·
> In a city, the satellite’s signals reach the receiver both directly and by bouncing off of one or more buildings. The direct signal and any reflections arrive
by roberttod 9y ago
> In a city, the satellite’s signals reach the receiver both directly and by bouncing off of one or more buildings. 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.
> 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.
Can someone explain this? Surely the first signal received will always be the direct signal, how could you receive signals from reflections first?
- DiThi 9y agoAt no point it says it receives reflections first. It says that L1 signals are so long, direct and reflected signals are merged and received as a single signal.
- Brotkrumen 9y agoThe key word here is "overlapping". I think the "old" L1 signal was long enough for the direct signal to arrive first, then have the reflected signal arrive while the direct signal was still being received. This would create the "signal blob". So yes, the direct signal always arrives first, but gets messed up during receiving by the reflected signal. The L5 signal is so short, that the likelihood of reflections overlapping is reduced. Think: so short that the signal starts and finishes during the time it takes a radio wave to propagate 1 meter through air or so.
- jhayward 9y agoThe direct path signal is sometimes attenuated by obstructions so the multipath peak is strongest and captures the correlator for that sample.