Slide attack: creating an actual attack on the Simon Cipher
You should read David Wagner's original paper.  You can see all of his work here.

He authored the 'Slide Attack', 'Advanced Slide Attacks' and a few more related to the attack.

Wikipedia has a good introduction here

Feistel ciphers like Simon are very vulnerable to Slide Attacks and similar.  Removing the round constants from the key schedule will likley lead to an easy break in the cipher.  Partial attacks on the real cipher seem possible if multiple round keys can be forced to collide in a related key attack.