TY - JOUR ID - 307 TI - Fractional Fourier Transform Based OFDMA for Doubly Dispersive Channels JO - Journal of Communication Engineering JA - JCE LA - en SN - 2322-4088 AU - Sabbaghian, M. AU - Mokhtari, Z. AD - University of Tehran Y1 - 2016 PY - 2016 VL - 2 IS - 3 SP - 192 EP - 207 KW - Doubly dispersive channels KW - Fractional Fourier transform KW - OFDMA DO - N2 - The performance of Orthogonal Frequency Division Multiple Access (OFDMA) system degrades significantly in doubly dispersive channels. This is due to the fact that exponential sub-carriers do not match the singular functions of this type of channels. To solve this problem, we develop a system whose sub-carriers are chirp functions. This is equivalent to exploiting Fractional Fourier Transform (FrFT) instead of Fourier Transform (FT) in the structure of the aforementioned transmission scheme. We name the new system FrFT-OFDMA. The optimal angle of fractional Fourier transform for each user depends on its channel parameters. Thus, the angles of transform for different users are not necessarily identical. This destroys the orthogonality of users and generates Multi-User Interference (MUI). By analyzing MUI, we introduce quasi-orthogonality conditions where interference is negligible despite different angles of transform. For non-orthogonal users, we propose a method to mitigate MUI. We present the efficiency of this method through comparative performance evaluation of the conventional system based on FT and the new system based on FrFT. We show that our proposed transmission scheme outperforms the traditional OFDMA system significantly in doubly dispersive channels and channels impaired by frequency offset. UR - https://jce.shahed.ac.ir/article_307.html L1 - https://jce.shahed.ac.ir/article_307_84bb9e73a4558021f002a29be1e94a4f.pdf ER -