LabVIEW
Questions about using the ASK demodulator in Modulation toolkit
Hello everybody,
Recently I am making an RFID reader with labview. The tag data is modulated with ASK scheme at symbol rate 80k, and consists of two parts: 496 bits user data and 16 bits frame marker. The user data is encoded to avoid being same with the frame marker, as shown in the following figure.
To acquire the tag signal, I set the sample rate to 800k, so there will be 20 samples per symbol. After receiving the signal containing the tag data, I demodulate and decode the signal with the ASK demodulator in the labview modulation toolkit. From the received waveform, I can image the corrected output bitstream, but by using the demodulator, I find that it does not output correct bitstream. My problem is why the demodulator does not output correct bitstream? Is there anything wrong in my configuration for the demodulator?
In debuging the problem, I found another problem. When the center frequency of the receiver has a deviation with the sender(e.g. the sender is set to 915M, and the receiver is set to 914.999999M), the demodulator output is totally wrong. It just output a lot of "1"s. But from the measurement output of the ASK demodulator, I can see a 1Hz frequency deviation. Why the measurement output is correct, but the demodulation output is wrong?
Then I set the sender's central frequency to 915M, but set the receiver's central frequency to 914.999965M. The output of the demodulator is totally wrong again, and it still outputs a lot of "1"s. This time the measurement output of the ASK demodulator shows that there is a 35Hz frequency deviation.
Can anybody please help me about the above problem? Why does the ASK demodulator not work correctly. And why when the measurement output is right but the output bitstream is incorrect?
To demostrate the problem, I write a application which reads the received waveform, demodulates the waveform and shows the demodulated signal.
Can anyone please help me to solve the problem?
Thanks in advance!
