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I noticed that in the file of PLCP_Preamble_gen.m, the preamble of 802.11 was defined. The variable is preamble = [repmat(sts_t, 1, 10) lts_t(33:64) lts_t lts_t]. Obviously, The length of CP is 32 samples (half of a lts). However, in the wlan_phy_tx_init.m, the length of CP is defined like PHY_CONFIG_CP_LEN = 16, which is not the same of the length of CP in the previous variable preamble. Why?
In addition, if I change the definition of the preamble (I mean the sequence of the LTS or STS) in the PLCP_Preamble_gen.m and want to transmit frames by applying the changed preamble , should I regenerate a bit file in the xilinx XPS?
Last edited by linron (2016-Feb-01 10:06:21)
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The preamble waveform is defined in IEEE 802.11-2012 18.3.3. The long training symbol is defined as a 64-sample sequence repeated 2.5 times. This structure has the same duration as two 64-sample sequences repeated 1.25 times each (2 x 80 samples). However the 2.5 repetitions ensures both delay spread tolerance (32-sample guard interval filled with cyclic extension) and that any pair of samples separated by 64 will be identical. This structure is very useful for frequency offset estimation- you can compare the phases of two samples spaced by 64 that were identical at Tx to calculate CFO (phase per time = frequency).
In addition, if I change the definition of the preamble (I mean the sequence of the LTS or STS) in the PLCP_Preamble_gen.m and want to transmit frames by applying the changed preamble , should I regenerate a bit file in the xilinx XPS?
Yes- if you change any part of the Sysgen model, including the contents of the preamble ROM blocks, you must re-generate the pcore and re-build the XPS project.
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