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    NOMA multi-numerology and guard reduction methods in OFDM systems for 5g networks
    (İstanbul Medipol Üniversitesi Fen Bilimleri Enstitüsü, 2018) Sabah, Ayman Tayseer Ali Abu; Arslan, Hüseyin
    Non-orthogonal multiple access (NOMA) is a promising technique which outperforms the traditional multiple access schemes in many aspects. It uses superposition coding (SC) to share the available resources among the users and adopts successive interference cancellation (SIC) for multiuser detection (MUD). Detection is performed in the power domain where fairness can be supported through appropriate power allocation. Since power domain NOMA utilizes SC at the transmitter and SIC at the receiver, users cannot achieve equal rates and experience higher interference. In this thesis, a novel NOMA scheme is proposed for multi-numerology (NR) orthogonal frequency division multiplexing (OFDM) system, i.e., different subcarrier spacings (SCSs). The scheme uses the nature of mixed NR systems to reduce the constraints associated with the MUD operation. This scheme not only enhances the fairness among the users but it improves the bit error rate performance as well. Although the proposed scheme is less spectrally efficient than conventional NOMA schemes, it is still more spectrally efficient than orthogonal multiple access schemes. As another contribution, we propose a novel frame structure for fifth generation (5G) networks. Such the structure aims to increase the capability of adopting the NR in 5G networks. In particular, a common cyclic prefix is appended to multiple OFDM symbols. Therefore, adopting large SCSs or short OFDM symbols becomes more flexible and applicable.