Context Navigation

signal

v77	v78
115	115	However, we don't know the phase of the sine wave. Another way to think about this is we don't know when to start receiving the signal. AND, even though the machine might tell us that the carrier is 1 GHz, there's no way it can send EXACTLY 1 GHz and might actually be something like 999.9 MHz. If we don't account for these, we get an IQ plot that looks like below. This signal is BPSK so we expect IQ to be across the real axis, though that's clearly not what we received.
116	116
117		[[Image(Screen Shot 2024-08-06 at 5.44.33 PM.png, 400px)]]
	117	[[Image(Screen Shot 2024-08-06 at 5.44.33 PM.png, 300px)]]
118	118
119	119	The solution to this is to add something known as a barker code to the beginning of our signal. This is a special code that is "random," but both receiver and transmitter know what it is. So, at the transmitter, we compare the barker code to every timestamp in the signal and see which timestamps match the closest. We then know that the barker code occurred at those locations. Knowing one barker code can tell us where the signal starts. Knowing two can tell us the frequency offset based on the time difference between the two.