In this paper, we propose a multi-user aware frame structure for doubly dispersive channels in order to increase both spectral efficiency and frequency spread immunity of orthogonal frequency division multiple accessing (OFDMA) based systems. Unlike the conventional OFDMA based system where the fixed cyclic prefix duration and subcarrier spacing are utilized within the frame structure considering the worst case communication channel, in the proposed approach, multiple cyclic prefix durations and subcarrier spacings are employed. In order to build the proposed frame structure, the statistics of the mobility and the range of the users are mapped to inter-carrier-interference and maximum excess delay to obtain multiple subcarrier spacings and cyclic prefix durations. As a result, better frequency spread immunity and spectral efficiency are achieved by exploiting the doubly dispersive channel characteristics of the users.
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