4 ms·
It sounds like the data rate is incredibly low. That allows for a lot of signal margin. GPS receivers are sensitive to something like -165dBm. It's probably ha
by sgtnoodle 4y ago
It sounds like the data rate is incredibly low. That allows for a lot of signal margin. GPS receivers are sensitive to something like -165dBm.
It's probably harder for the satellite to hear from the phone. Especially at a lower frequency like 700Mhz, a phone's tiny antenna is going to be a rather inefficient transmitter. Maybe 5g technology helps by allowing the phone to do some rudimentary beam forming using multiple antennas?
- mwint 4y ago(How) Does beamforming work in a moving device?
- sgtnoodle 4y agoI'm not an expert, but I believe a receiving radio can make note of the relative phase of the incoming signal across all antennas, and then simply transmit its signal with the same phase offsets. This can happen incredibly quickly on the time scale of milliseconds, and so the typical device really isn't moving that quickly to matter. I believe modern wifi has periodic "sounding packets" specifically designed for devices to robustly measure that sort of information for beam forming and multiple spatial streams.
- rkangel 4y agoThis is all roughly right except that when you say "incredibly quickly on the time scale of milliseconds" it's often actually microseconds. This sort of work is done either in custom hardware or FPGAs - that's the only way you can precisely control the phase offset of signals (and measure it). They can respond very quickly.