Added function to create the ZC sequence for symbols 4 and 6

matlab/create_zc.m

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+% Creates a ZC sequence that is mapped onto an OFDM symbol and FFT'd
+%
+% The results of this function can be used to cross correlate for the specified OFDM
+% symbol (numbers 4 or 6).  There is no cyclic prefix added by this function!
+%
+% 601 samples are created by the ZC, but the middle sample is zeroed out.  This is done
+% so that the DC carrier of the FFT is not populated
+%
+% @param fft_size Size of the OFDM FFT window (must be power of 2)
+% @param symbol_index Which ZC sequence symbol should be created (must be 4 or 6)
+%
+function [samples] = create_zc(fft_size, symbol_index)
+    % Validate inputs
+    assert(symbol_index == 4 || symbol_index == 6, "Invalid symbol index (must be 4 or 6)");
+    assert(log2(fft_size) == round(log2(fft_size)), "Invalid FFT size.  Must be power of 2");
+
+    % Pick the correct root for the ZC sequence
+    if (symbol_index == 4)
+        zc = zadoffChuSeq(600, 601);
+    else
+        zc = zadoffChuSeq(147, 601);
+    end
+    
+    % Figure out how many guard carriers there should be (purposely ignoring DC here)
+    guard_carriers = fft_size - 600;
+
+    % The left side will end up with one more guard than the right
+    % This may not be correct as it's a guess and the other way around failed to correlate
+    % as well as this way.
+    left_guards = (guard_carriers / 2);
+    right_guards = (guard_carriers / 2) - 1;
+    
+    % Populate all of the FFT bins with the ZC sequence in the middle (including the DC carrier)
+    samples_freq = [zeros(left_guards, 1); zc; zeros(right_guards, 1)];
+
+    % Null out the DC carrier
+    samples_freq(fft_size/2) = 0;
+    
+    % Convert to time domain making sure to flip the spectrum left to right first
+    samples = ifft(fftshift(samples_freq));
+end