Section 5 Concepts of 3GPP LTE
•The unity circle produced by the DM-RS may look random but is the result of phase modulating each successive subcarrier to create a constant amplitude zero auto-correlation (CAZAC) sequence
•There are 30 different sequences defined providing orthogonality between users
•The sequence follows a Zadoff-chu progression
where 
is the first prime number less than the required number of subcarriers, and m is the subcarrier number of the qthsequence
•For allocations less than 3 resource blocks (36 subcarriers) it is not possible to use a zadoff-chu sequence so the RS are modulated with a simpler computer-generated QPSK sequence of length 12 or 24
