Pilot-data power allocation for OFDM systems with amplify and forward relays

A three node amplify and forward (AF) relay system over a frequency-selective channel employing OFDM modulation is considered and the pilot-data power allocation that maximizes a lower bound on system capacity is obtained. The source transmits pilot tones, which are multiplexed with data tones, so that the destination can estimate the overall equivalent channel and perform data detection. Assuming no channel state information (CSI) at the transmitter and as in a practical system, allowing for imperfect channel estimation, a closed-form solution for the pilot-data power allocation is obtained at high SNR regime. An expression for the pilot-data power allocation is obtained for low SNR regime which can be solved numerically for the general case of arbitrary power delay profiles. For the special case of uniform power delay profile of the equivalent channel, a closed form solution is provided. Simulations are used to verify the derived results and show performance comparisons of capacity bound and symbol error rate.