Imperfectly synchronized cooperative network using distributed space-frequency coding
Yimin Zhang, Genyuan Wang, Moeness G. Amin · 2006
In distributed multiple-input-multiple-output (MIMO) systems, imperfect synchronization causes a unique problem in a coded cooperative diversity system. In the presence of a fractional-symbol delay between the signals transmitted from different relay nodes, the channels become highly dispersive even at a flat-fading environment. Existing methods solve such problem based on time-domain approaches where adaptive equalization is required at the receivers for combining the information transmitted from distributed sources. In this paper, we propose the use of OFDM-based approaches using distributed space-frequency codes. The proposed schemes are insensitive to fractional- symbol delays and lead to higher data rate transmission and simplified implementation. In addition, the proposed schemes permit the use of relatively simple amplify-and- forward algorithm in multi-hop wireless networks without delay accumulations. The proposed methods remove the time delay in each relaying hop by reconstructing the prefix and, as such, improve the spectral efficiency, while keeping a simplified relaying structure.