Pilot Design for OFDM Amplify-and-Forward with Chunk Reordering

Amplify-and-forward (AF) is a simple but effective relaying concept for multihop networks that combines transparency regarding modulation format and coding scheme with ease of implementation. Recently, we introduced an OFDM-AF schemes that achieves significant SNR gains by reordering groups of received subcarriers (chunks) at the relay station to optimally couple them into the 2n hop channel. This reordering process, however, destroys the correlation between chunks, so channel estimation techniques based on interpolation no longer work. To mitigate this problem, we propose to insert a new pilot grid at the relay station in addition to the existing pilot grid. At the mobile, channel estimation is performed in two steps, where the 2n and 1 hop channels are estimated separately. The proposed pilot and channel estimation scheme allows to fully exploit the gains through chunk reordering at the relay station with only a small increase in complexity.