A Leakage Minimization Approach to Zero-Tail OFDM with Orthonormal Spreading in a Multiple Access Channel with Uncorrelated Scatterings

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A Leakage Minimization Approach to Zero-Tail OFDM with Orthonormal Spreading in a Multiple Access Channel with Uncorrelated Scatterings

Bourgeois, Thomas / Hashimoto, Noriyuki / Suegara, Yasuhiro

Motivated by the benefits of replacing the guard interval between OFDM symbols by a built-in low power tail, Zero-Tail DFT-Spread OFDM (ZT-DFT-S) modulation has been recently presented in the literature. Although ZT-DFT-S is a simple and elegant answer to the problem of multi-path propagation without guard interval, it still derives from an heuristic approach with no guarantee of optimality. In this paper, we relax the constraint of DFT-spreading of ZT-DFT-S and consider instead the spreading block as a variable to be optimized with respect to a specific performance metric. Considering a multiple access scenario, we treat the performance optimization as a leakage energy minimization problem with an orthonormality constraint on the spreading block. Under the commonly used assumption of uncorrelated scatterings, a closed form for the objective function is obtained. It is showed that knowledge of the power delay profile is sufficient to obtain an optimal solution with low complexity. Link level performance evaluation confirms the advantage of the proposed approach over conventional ZT-DFT-S in various conditions and its robustness to limited transmitter-side channel information.