Distributed Space-Frequency Coding for Cooperative Diversity Over Broadband Relay Channels With DF Relaying

Multipath fading is one of the main challenges in transmission over wireless broadband relay channels due to frequency selectivity, which may deteriorate the received signal. Exploiting the extra source of multipath diversity, aside from cooperative (user) diversity, is important when coping with these wireless channel limitations. In this correspondence, we propose a new distributed space-frequency code (SFC) for broadband fading relay channels that can exploit both the spatial and multipath diversities in a distributed fashion. An upper bound for pairwise error probability (PEP) is derived, and from this PEP bound, we show that the proposed code achieves a diversity of order NL, where N is the number of relay nodes, and L is the channel memory length. The decode-and-forward (DF) protocol and erroneous decoding at the relay nodes are considered. Moreover, it is shown that the proposed code structure achieves the maximum coding gain among the linearly coded systems over channels with uniform power delay profiles.