5G ve ötesi kablosuz iletişim ağları için OFDM tabanlı özgün dalga formu tasarımı

Orthogonal frequency division multiplexing (OFDM) with index modulation (OFDMIM) appears as a promising multi-carrier waveform candidate for 5G and beyond wireless networks due to its attractive advantages such as superior error performance, operational flexibility, and ease of implementation. OFDM-IM itself may not be a proper choice for 5G services such as enhanced mobile broadband (eMBB) and ultra-reliable and low-latency communications (URLLC) since achieving high data rates is challenging because of its null subcarriers and also its error performance is not at a sufficient level for mission critical applications. However, the flexible structure of OFDM-IM has a great potential and more sophisticated OFDM-IM-based waveforms can be designed to meet the requirements of future eMBB and URLLC applications. For eMBB, one solution to enhance the spectral efficiency of OFDM-IM is the employment of multiple distinguishable constellations (modes) by also exploiting its null subcarriers for data transmission. Furthermore, an OFDM-IM block with a sparse structure can be utilized to generate a suitable waveform for URLLC applications. In this thesis, application-based novel waveforms are designed by enjoying the appealing features of OFDM-IM. In Chapter 1, a novel IM technique called super-mode OFDM-IM (SuM-OFDM-IM) is proposed, where mode activation patterns (MAPs) and subcarrier activation patterns (SAPs) are jointly selected and conventional data symbols are repetition coded over multiple subcarriers to achieve a diversity gain. For the proposed scheme, a low-complexity detector is designed, theoretical analyses are performed and a bit error rate (BER) upper bound is derived. The performance of the proposed system is also investigated through real-time experiments using a software-de fined radio (SDR) based prototype. It is shown that SuM-OFDM-IM exhibits promising results in terms of spectral efficiency and error performance; thus, appears as a potential candidate for 5G and beyond communication systems. In Chapter 2, OFDM with power distribution index modulation (OFDM-PIM) is proposed where a unique power distribution technique is applied to index modulated subcarriers. Furthermore, OFDM with in-phase/quadrature PIM (OFDM-I/Q-PIM), which independently performs the same power distribution process on the real and imaginary parts of the data symbols, is proposed. Average bit error probabilities (ABEP) of OFDM-PIM and OFDM-I/Q-PIM are obtained and the superiority of the proposed schemes over reference schemes is demonstrated via extensive computer simulations. Finally, in Chapter 3, a low-complexity encoding/decoding algorithm is proposed for the sparse vector coding (SVC) scheme, which allows the use of all possible activation patterns (APs) without the need for a look-up table. Computer simulation results reveal that the proposed low-complexity algorithm provides not only a superior BER performance but also improved spectral efficiency compared to the ordinary SVC approach.