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Hi, I have a question concerning the rtsctsMac.c file. Can you short explain me what you mean by full/base rate, what is the difference?
Thanks
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The OFDM physical layer models implement two modulation schemes per frame- one meant for headers (the base rate) and one for the payload (full rate). The base rate modulation choice must be known ahead of time by every node in the network, so that headers can be universally understood. The full rate modulation choice for a packet is specified by a field in the header, so it can change per-packet and per-destination. Every MAC implementation uses this PHY feature, not just RTS/CTS.
More details are available in the OFDM frame format docs.
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And could you please explain me what you mean with Modulation Mask, I can't find any info on the web.
Thanks a lot!
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The PHY selects which modulation scheme to use per subcarrier based on two values. The first is a per-subcarrier value stored in buffers (one for Tx, one for Rx). Each subcarrier for each antennas has a 4-bit modulation value stored the buffer. Another 4-bit value is stored in the packet header; this value is AND'd with each subcarrier's value from the buffer. The result (of the AND) determines how many bits should be loaded for the subcarrier ([0,1,2,4,6] bits -> [0, BPSK, QPSK, 16-QAM, 64-QAM]). We call the 4-bit value in the header the modulation mask.
By default, the reference design configures the PHY for SISO, loading data modulated as QPSK in 48 subcarriers. In the Tx/Rx modulation buffers, we load 0 for 12 subcarriers and 0xF for the 48 that carry data. This value is AND'd with the header modulation mask (0x2 for QPSK).
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