QPSK coding

• hello i m working on implementing a QPSK coded system with hamming(7,4) without using actual coding function, but the G and H matrix i choose doesnt give me G*H'=0, the proff said the matrix are ok, u need to change the mod of the matrix, i dont get it, can anyone explain me this mod thing,,

    the G matrix i choose is 

     [1 0 0 0 1 1 0
      0 1 0 0 0 1 1
      0 0 1 0 1 1 1
      0 0 0 1 1 0 1]

    and the H matrix is 

     [1 0 1 1 1 0 0
      1 1 1 0 0 1 0
      0 1 1 1 0 0 1]

please anyone help me that where i m wrong

Answer 1

[Walter Roberson]

Please refer to http://www.mathworks.com/matlabcentral/answers/16990-galois-field-to-find-the-inverse-of-a-binary-matrix which will not give you the direct answer but should give you the background in to changing the "mod".