kopia lustrzana https://github.com/proto17/dji_droneid
57 wiersze
1.8 KiB
Matlab
57 wiersze
1.8 KiB
Matlab
% Generates a scrambler sequence for an arbitrary number of bits given an initial state value
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%
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% The initial value should always be the 31 bit sequence 0x12345678 *bit reversed*
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%
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% @param num_bits Number of bits to generate
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% @param x2_init Initial value of the second LFSR. Must be a row vector and only contain 0/1 values
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% @return bits Row vector of `num_bits` 1/0 values
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function [bits] = generate_scrambler_seq(num_bits, x2_init)
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assert(isrow(x2_init), "X2 initial value must be a row vector");
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assert(length(x2_init) == 31, "The X2 initial value must be 31 bits");
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must_be_member(x2_init, [0, 1]);
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% https://www.sharetechnote.com/html/Handbook_LTE_PseudoRandomSequence.html
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% https://edadocs.software.keysight.com/pages/viewpage.action?pageId=6076479
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% Initial condition of the polynomia x1(). This is fixed value as described in 36.211 7.2
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x1_init = [1 0 0 0 0 0 0 0 0 0 ...
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0 0 0 0 0 0 0 0 0 0 ...
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0 0 0 0 0 0 0 0 0 0 ...
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0];
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% Mpn is the length of the final sequence c()
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Mpn = num_bits;
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% Nc as defined in 36.211 7.2
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Nc = 1600;
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% Create a vector(array) for x1() and x2() all initialized with 0
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x1 = zeros(1,Nc + Mpn + 31);
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x2 = zeros(1,Nc + Mpn + 31);
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% Create a vector(array) for c() all initialized with 0
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c = zeros(1,Mpn);
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% Initialize x1() and x2()
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x1(1:31) = x1_init;
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x2(1:31) = x2_init;
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% generate the m-sequence : x1()
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for n = 1 : (Mpn+Nc)
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x1(n+31) = mod(x1(n+3) + x1(n), 2);
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end
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% generate the m-sequence : x2()
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for n = 1 : (Mpn+Nc)
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x2(n+31) = mod(x2(n+3) + x2(n+2) + x2(n+1) + x2(n),2);
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end
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% generate the resulting sequence (Gold Sequence) : c()
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for n = 1 : Mpn
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c(n)= mod(x1(n+Nc) + x2(n+Nc),2);
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end
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bits = c;
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end
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