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https://olympias.lib.uoi.gr/jspui/handle/123456789/40510Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.author | Mouziouras, Nikolaos | en |
| dc.contributor.author | Μουζιούρας, Νικόλαος | el |
| dc.date.accessioned | 2026-10-19T07:39:29Z | - |
| dc.date.available | 2026-10-19T07:39:29Z | - |
| dc.identifier.uri | https://olympias.lib.uoi.gr/jspui/handle/123456789/40510 | - |
| dc.rights | Default License | - |
| dc.subject | Multiple-Input Multiple-Output (MIMO) | en |
| dc.subject | Non-ideal wireless propagation | |
| dc.subject | Imperfect channel state information | |
| dc.subject | Communication reliability | |
| dc.subject | Energy efficiency | |
| dc.subject | Adaptive MIMO | |
| dc.subject | Cooperative MIMO | |
| dc.subject | Reliability-aware optimization | |
| dc.title | Characterization and Optimization of MIMO Systems for Wireless Communications | en |
| dc.type | doctoralThesis | - |
| heal.type | doctoralThesis | el |
| heal.type.en | Doctoral thesis | en |
| heal.type.el | Διδακτορική διατριβή | el |
| heal.dateAvailable | 2026-10-19T07:40:30Z | - |
| heal.language | en | el |
| heal.access | free | el |
| heal.recordProvider | Πανεπιστήμιο Ιωαννίνων. Σχολή Πληροφορικής και Τηλεπικοινωνιών | el |
| heal.publicationDate | 2026-10-14 | - |
| heal.abstract | Modern wireless communication systems are evolving toward increasingly heterogeneous, dynamic and resource-constrained operating environments, driven by the requirements of beyond-5G and 6G networks, massive machine-type communications, ultra-reliable services and energy-constrained Internet of Things (IoT) applications. Within this context, Multiple-Input Multiple-Output (MIMO) technology has become a fundamental component of modern wireless communications due to its ability to improve reliability, spectral efficiency, coverage and network capacity. However, much of the existing understanding of MIMO system behavior and optimization relies on idealized assumptions that only partially represent non-ideal wireless operating conditions. In non-ideal environments, MIMO performance is jointly influenced by propagation characteristics, imperfect channel state information (CSI), reliability requirements, implementation constraints and energy limitations. The interaction of these factors can substantially alter system behavior and limit the applicability of conclusions derived under simplified assumptions. This dissertation addresses these limitations through a systematic investigation of MIMO communication systems under non-ideal propagation conditions and imperfect CSI, progressing from system characterization to reliability–energy analysis, adaptive transmission and cooperative communication. The first part of the dissertation investigates MIMO behavior under standardized 3GPP propagation models. The analysis examines the effects of propagation asymmetries, antenna geometry, polarization characteristics, user distribution, mobility and network load on key communication metrics. The results demonstrate that MIMO performance under non-ideal propagation conditions is governed by the combined interaction of spatial dimensionality, temporal channel dynamics, propagation heterogeneity and network load. Conditions that enhance channel symmetry and spatial diversity generally improve performance, whereas mobility, propagation asymmetry and unfavorable user distributions can lead to significant degradation. Building upon this characterization, the dissertation investigates the interaction between communication reliability and energy efficiency. By accounting for retransmissions, hardware-related energy consumption and signal-processing overhead, the analysis demonstrates that increasing the diversity order does not necessarily provide the most energy-efficient solution, since the energy-preferred MIMO configuration depends on propagation conditions, communication reliability and implementation costs. The investigation is further extended to energy-constrained IoT and LPWAN systems, including LoRa-based networks. Under these constrained operating conditions, spatial diversity improves link robustness, while imperfect CSI shifts the reliability transition toward more favorable SNR conditions and reduces the effective reliability advantage of higher-diversity configurations. These effects directly influence retransmission behavior and the energy required for successful packet delivery. The knowledge obtained from these analyses is subsequently exploited to develop an adaptive MIMO diversity-selection framework that dynamically selects the most energy-efficient feasible transmission configuration according to the prevailing operating conditions. The resulting adaptive policy exhibits structured operating regions characterized by progressive diversity activation as propagation conditions, CSI uncertainty and hardware overhead vary. Transition analysis further shows that adaptive evolution occurs predominantly between neighboring diversity configurations, while larger transitions arise selectively near feasibility boundaries. These results demonstrate that adaptive diversity selection can provide reliable and energy-efficient MIMO operation while maintaining structured and continuity-preserving behavior across the considered operating space. Finally, the dissertation extends the adaptive optimization perspective to cooperative relay-assisted MIMO systems operating under imperfect CSI. The analysis demonstrates that cooperative transmission is not universally beneficial and identifies a harmful cooperation region in which relay-assisted transmission becomes less reliable than direct MIMO communication. This behavior results from the combined effects of residual CSI-induced interference and relay decoding error propagation and becomes more pronounced as channel estimation accuracy deteriorates. To mitigate this effect, a reliability-aware relay activation mechanism is investigated, in which relay participation is controlled according to the estimated quality of the source–relay channel. The resulting adaptive strategy suppresses unreliable relay participation, reduces the harmful cooperation region and preserves the benefits of cooperative diversity when relay conditions are sufficiently reliable. Collectively, the investigations establish a unified perspective on the characterization and optimization of MIMO communication systems under non-ideal operating conditions. The results demonstrate that effective MIMO operation cannot be described by a universally optimal transmission strategy, since the preferred operating configuration depends on propagation conditions, CSI quality, reliability requirements and implementation constraints. By linking system characterization under non-ideal conditions with reliability–energy analysis, adaptive diversity selection and reliability-aware cooperative operation, this dissertation contributes to the understanding and design of robust and energy-efficient MIMO communication systems for next-generation wireless networks. | en |
| heal.advisorName | Angelis, Constantinos | en |
| heal.committeeMemberName | Tsormpatzoglou, Andreas | en |
| heal.committeeMemberName | Οικονόμου, Κωνσταντίνος | el |
| heal.committeeMemberName | Βαρτζιώτης, Φώτιος | el |
| heal.committeeMemberName | Γιαννακέας, Νικόλαος | el |
| heal.committeeMemberName | Δουμένης, Γρηγόριος | el |
| heal.committeeMemberName | Τσουμάνης, Γεώργιος | el |
| heal.academicPublisher | Πανεπιστήμιο Ιωαννίνων. Σχολή Πληροφορικής και Τηλεπικοινωνιών. Τμήμα Πληροφορικής και Τηλεπικοινωνιών | el |
| heal.academicPublisherID | uoi | el |
| heal.numberOfPages | 268 | el |
| heal.fullTextAvailability | true | - |
| Appears in Collections: | Διδακτορικές Διατριβές - ΤΠΤ | |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| Characterization_and_Optimization_of_MIMO_Systems.pdf | 32.29 MB | Adobe PDF | View/Open |
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