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Hi,
I plan to add modulation and coding scheme in warplab in order to analyze the system's BER performance. I met two problems here:
(1) Using standard M-QAM modulation scheme, after power-normalization of the constellation, it is possible that some modulated signals are not within the range of [-1,1] (both real and image part). Do I have to constrain the signals within this range?
(2) Given a fixed length of 0-1 bit stream, after it is modulated (Bitstream[] is translated into Symbolstream[]), can I directly download this symbol sequence into the board, using the function warplab_writeSMWO(udp_node1, RADIO1_TXDATA, Symbolstream) ? How can I indicate the information of sampling frequency when downloading samples into the board? Or 40MHz is the default frequency in warp board?
Many thanks!
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1) The I/Q values you provide for a Tx node must be in the range of [-1,1). You can normalize various constellations however you like, subject to this constraint.
2) The hardware sampling rate is fixed at 40MHz. You can achieve arbitrary over-the-air bandwidth by interpolating your sample stream by whatever rate you want. For example, if you want 10MHz of over-the-air bandwidth, you would interpolate your sample stream by 4 before writing it to the WARPLab Tx buffers.
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Your answer is very helpful!
For the second question, what you meant is to insert some invalid samples between the elements in the stream vector Symbolstream[], is my understanding right? should I use 0 as the invalid samples?
many thanks!
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Every sample sent to the board via WARPLab will be driven into the DAC at 40MHz. If you want an over-the-air bandwidth lower than 40MHz, you need to do the appropriate signal processing in MATLAB (i.e. interpolation) before sending the samples to the WARP node.
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