GPS signal in the air

　　When creating GPS waveform, its unique and increasingly common way is to directly extract it from the air. In this test, we use a vector signal analyzer (such as NI PXI 5661) to record signals, and then use a vector signal generator (such as NI PXIe-5672) to generate recorded signals. As the actual signal impairments can also be captured when recording GPS signals, the operation of the receiver in the deployment environment can be further understood when playing signals.

　　The GPS signal in the air can be captured only through a very direct way. In the RF recording system, we use the appropriate antenna and amplifier together with the PXI vector signal analyzer and hard disk to capture up to several hours of continuous data. For example, a group of 2 TB RAID disk arrays can record GPS waveforms for up to 25 hours. Since this technical document will not discuss the special technology of streaming, if relevant sample program code is required

　　Different types of wireless communication signals require different bandwidth, central frequency, and gain. In terms of GPS signal, the basic system requirement is to record 2.046 MHz RF bandwidth at a central frequency of 1.57542 GHz. Based on this bandwidth requirement, at least 2.5 MS/s (1.25 x 2 MHz) sampling rate must be achieved. Note: The 1.25 multiplier here is based on the Roll off filter of the PXI-5661 digital down converter (DDC) in the Decimation phase.

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