A transform-and-forward scheme for relay networks

We present a new means of implementing distributed space-time block codes (STBC) for wireless amplify-and-forward (AF) relay networks. In the proposed method, each source antenna transmits one column of an STBC matrix derived from a generalized complex orthogonal design (GCOD). Such designs were originally intended for single hop environments. At each relay antenna, a precoding matrix and a fixed gain amplification factor are applied before the resulting signal is forwarded to the next set of nodes. The precoding operation at the relays rearranges the elements of the received vector in such a way that the equivalent STBC code observed at the destination is quasi-orthogonal. The characteristics and one structure for the precoding matrices are proposed. Initially, a dual hop system is considered for convenience. We then demonstrate how the scheme can be readily extended to multihop networks. We refer to this type of relay system as the transform-and-forward scheme. Simulation results demonstrate the performance of the technique over an existing approach.