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| dc.contributor.author | Dessie, Fikir | |
| dc.date.accessioned | 2025-03-03T07:53:14Z | |
| dc.date.available | 2025-03-03T07:53:14Z | |
| dc.date.issued | 2024-10 | |
| dc.identifier.uri | http://ir.bdu.edu.et/handle/123456789/16519 | |
| dc.description.abstract | The growth of network devices and services has caused a substantial rise in global data tra c demand. Cellular networks face challenges in meeting high data demands of future wireless networks due to uneven data rates between cell centers and edges. Cell-free massive multiple-input multiple-output (CF mMIMO) has emerged as a promising solution to support rising data demands by leveraging distributed access points (APs) to cooperatively serve users across a coverage area. Inter-user interference (IUI) from unpredictable phase shifts and ine cient power allocation should be addressed to improve performance. In this thesis, we analyzed CF mMIMO systems using power-domain non-orthogonal multiple access (PD-NOMA) and successive interference cancellation (SIC) with phase shift-aware channel estimation. Phase of the line-of-site (LoS) components are modeled as a uniformly distributed random variables to take phase-shifts concerning user equipment (UE) mobility in the estimation process. Three estimation methods|phase-aware minimum mean square error (PA-MMSE), non-phase-aware minimum mean square error (NPA-MMSE), and least squares (LS)|are applied. The favorable phase range of the APs' LoS component is investigated. For NOMA, we employed an e cient power allocation method where UEs are sorted based on the e ective channel gain connected to each AP. Lastly, phase-synchronized AP cooperation is compared to unsynchronized to analyze the e ect on phase shifts. Downlink spectral e ciency (SE) and energy e ciency (EE) are analyzed through Monte Carlo simulations. The results demonstrate improvements in system performance, showcasing the potential of phase shift-aware channel estimation in CF mMIMO-NOMA systems. PA-MMSE estimator with NOMA improves the SE by 14.2% and 4.1% from PA-MMSE and NPA-MMSE NOMA, respectively, while EE improves by 44% and 11.1% respectively. The employed power allocation technique outperforms the conventional method by achieving a gain of over 25.2% in SE performance. Keywords: Cell-Free Massive MIMO, Non-Orthogonal Multiple Access, Phase Shifts, Power Allocation, Successive Interference Cancellation, Spectral Effciency. | en_US |
| dc.language.iso | en_US | en_US |
| dc.subject | Electrical and Computer Engineering | en_US |
| dc.title | NOMA-Based Cell-Free Massive MIMO Systems with Phase Shift Estimation | en_US |
| dc.type | Thesis | en_US |
