In this dissertation, I will consider the application of distributed space-time block code (DSTBC) to frequency selective fading channels. In the first part of my thesis, I present a new design of DSTBC to achieve full rate transmission and channel decoupling property as in conventional space-time block code by using zero-padding (ZP). Several receiver techniques in frequency domain are studied for the signal detection of the proposed DSTBC. The extension from ZP to unique-word (UW) will be proposed in the second part. Exploiting the properties of the UW, I will present in the third part of my thesis a method of channel estimation for relay networks.