Abstract
In mobile cooperative orthogonal frequency division multiplexing (OFDM) systems with amplify-and-forward (AF) relays, in which the source and relay terminals are moving, Doppler frequency might become very large due to the formation of double-hop channels, possibly causing very large intercarrier interference (ICI). Therefore, ICI mitigation technique capable of reducing the impact of high Doppler frequency is required. This paper reports the study of ICI mitigation technique that uses frequency domain equalizer (FDE) with improvements in three aspects, namely, better channel estimation using cubic-spline approximation, use of selection combining to utilize cooperative diversity in order to suppress ICI, and simple error correcting code with double interleaving to suppress errors due to residual ICI. By using the proposed ICI mitigation technique, error rate performance of mobile cooperative OFDM systems can be improved significantly. Even at high Doppler frequencies, error floors due to residual ICI can be decreased by up to two decades.
Highlights
Orthogonal frequency division multiplexing (OFDM) using a number of mutually orthogonal carriers to transmit data simultaneously has been widely used for high-speed data transmission
Our paper proposes several techniques to improve the performance of intercarrier interference (ICI) mitigation technique with frequency domain equalizer (FDE), so that the technique can still work well on mobile cooperative OFDM system with moving AF relays, in which Doppler frequency tends to be high
Selection combining is selected because when the equalizer fails to reduce ICI in one OFDM symbol, most of the symbols will be in error and should be replaced with the correct ones from the other branch
Summary
Orthogonal frequency division multiplexing (OFDM) using a number of mutually orthogonal carriers to transmit data simultaneously has been widely used for high-speed data transmission. Our paper proposes several techniques to improve the performance of ICI mitigation technique with FDE, so that the technique can still work well on mobile cooperative OFDM system with moving AF relays, in which Doppler frequency tends to be high. Selection combining is selected because when the equalizer fails to reduce ICI in one OFDM symbol, most of the symbols will be in error and should be replaced with the correct ones from the other branch In this paper, this system is referred to as LI system because it still uses piece-wise approach to linear interpolation. The second system is obtained by replacing the piecewise linear approximation interpolation with cubic-spline interpolation (third-order polynomial) to anticipate a fast channel change due to high Doppler so that channel estimation error can be suppressed using interpolation.
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