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Hi
I am a new user, i would like to know how to change the modulation and demodulation schemes. I know that the MAC implementations provide BPSK, QPSK, QAM and that can be selected but I want to change the way it demodulates QAM but can not find any demodulation function to make the necessary changes.
Thanks
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It's actually the PHY that implements the various modulation schemes. Our MIMO OFDM PHY supports BPSK, QPSK, 16-QAM and 64-QAM. The MAC selects one of these schemes for each outgoing packet when constructing the packet's header. The Rx PHY reads the header to configure the demodulator for an incoming packet's payload. The mod/demod are implemented in the FPGA as part of the overall PHY model; the source Sysgen model is in the repository.
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Thanks for the reply and the hints. i did look into the .mdl file and figured out that if I need to make some changes in the way I need to demodulate a 64 QAM then the changes are need in the hard decision block. But I am not able to understand the inputs to the block i.e the width of the bits and what they represent. Could you please elaborate teh exact changes and how I get around doing them?
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I don't quite understand what you're trying to change- the mapping of bits-to-symbols for 64-QAM? Or the detection algorithm (i.e. something more sophisticated than symbol-by-symbol hard-decision)? The mapping can be changed by updating the modulation values in the Tx init script. The bits-to-symbol mapping are just values stored in lookup tables, and the values are initialized by the m code script. If you're trying to change the detection algorithm itself, this is much more complicated. You'll need to implement the algorithm in the FPGA fabric, either using Sysgen or wrapping Verilog/VHDL in a black box.
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Thank for the previous reply. I think I got a little confused. My goal is to implement a multilevel modulation and demodulation scheme. I want to use the OFDM reference design as I could integrate the rest of the layers( network, application etc.) easily. Now I understand that on the modulation side it is easy to make the change as all I need to do is change the bits to symbol mapping in the file you have specified. It is a 64-QAM like constellation. Now when i demodulate it what I want is that I do a multilevel demodulation i.e. I want to change the demodulation steps to something like I take the fist two bits determine the quadrant, then depending on the first pair I get the next two bits and then the last two bits based on the second pair. Can now please give me some hints on where exactly are the changes to be made and how do I achieve this? If this is not possible ten my next attempt would be to use the Warplab in which I can characterize the physical layer but how do I integrate the effects of the other layers especially when I want a system behavior with retransmissions etc in Warplab?
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WARPLab is not well-suited to building full network stacks, since the latency from antenna to detected symbol is so long. WARPLab is good for exploring physical layer algorithms over real wireless channels, to identify which algorithms are worth implementing in the FPGA. Then, once the PHY is in the FPGA, you can implement higher network layers and run everything in real-time.
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