Reception of GPS signals
A GPS receiver is composed of four sections: an antenna, RF/IF conversion, digital signal processor, and microprocessor. The received RF signal is first sent to a low noise amplifier which sets the noise figure of the receiver. The amplified signal is then sent to a down converter where it is mixed with signals from a low oscillator to form an IF(Intermediate Frequency). This process generates both upper and lower sidebands while preserving the PRN codes and signal Dopplers of the signal. The signal is then sent to an A/D converter. The digitized IF signals can now be processed by the digital receiver channel where data demodulation takes place. The signal is multiplied by an in-phase copy of the carrier and then sent through a low-pass filter to retrieve the data. Received signals are used in smart phones and GPS systems across the globe. When a GPS device retrieves a signal, after demodulation, it sends one back. This is because the signal has to refresh because the device or 'world' in this case, is potentially moving. Also, it is important to note that when the signal is sent back, the satellites are synonymously communicating back and fourth to each other to tell each other where the signal should be sent in regards to if the satellite can see the device or not. Since there are 24 satellites used in GPS, we can be sure to get an accurately demodulated signal because there is less chance for a weak signal in sending and receiving to determine location.