Amplify-Forward Relays with Superimposed Pilot Signals for Frequency-Selective Fading Channels

In this paper, a new amplify-and-forward (AF) relay systems using superimposed pilot signals is proposed for frequency selective fading channel environments. In the proposed scheme, the relay superimposes an additional pilot sequence on the received signal from the source, and forwards the combined signal to the destination. The superimposed pilot signal in this way enables the destination node to estimate the channel between the relay and destination (R-D), and this channel information is used to process the received signal at the destination optimally; the noise correlation due to the frequency selective fading in the R-D channel is whitened. The optimal power ratio of the superimposed pilot to the incoming signal at the relay is obtained via simulations, and it is shown under frequency selective channel environments that the proposed scheme yields better bit-error- rate (BER) performance than the conventional method where all relay power is allocated only to the incoming signal.