6 research outputs found
Opportunistiset skedulointialgoritmit mobiileissa langattomissa järjestelmissä
Tutkielmassa käsiteltiin opportunistista skedulointia mobiilissa langattomassa radioverkossa. Opportunistinen skedulointi pyrkii valitsemaan aina käyttäjän, jolla on parhaat tiedonsiirtokanavaolosuhteet kullakin valinnan hetkellä, jolloin saavutetaan parempi järjestelmän tiedonsiirtokapasiteetti verrattuna kiinteästi ennalta määriteltyyn skedulointijärjestykseen.
Opportunistisen skeduloinnin haasteita ovat käyttäjien välisen reiluuden saavuttaminen sekä käyttäjä- ja palvelukohtaisten laatuvaatimusten huomioiminen. Skedulointi voidaan tehdä keskitetysti ja hajautetusti. Hajautetuissa skeduloinnin algoritmeissa voidaan luontevasti hyödyntää peliteorian tarjoamia formaaleja malleja. Myös kognitiiviset radiot ja LTE:n pienten solujen järjestelmät voivat hyödyntää vaihtelevia radiokanavaolosuhteita käyttämällä opportunistista skedulointia ja hajauttamalla skeduloinnin päätöksentekoa peliteoreettisia malleja hyödyntäen.
Tutkielma sisältää kirjallisuuskatsauksen opportunistisesta skeduloinnista sekä kahden opportunistisen ja yhden ei-opportunistisen skedulointialgoritmin simulointitestit Matlab-ohjelmalla. Kirjallisuuskatsauksesta nähdään, että ilman opportunistista skedulointia ilmara-japinnan tiedonsiirtokapasiteetin hyödyntäminen jää huomattavan vajavaiseksi. Peliteorian soveltaminen tuo uusia mahdollisuuksia hajautettujen skedulointien ratkaisujen toteutuksille. Simulointitestit osoittivat kahden opportunistisen skedulointialgoritmin erot suorituskyvyssä ja reiluudessa sekä opportunistisen skeduloinnin paremman suorituskyvyn vaihtelevissa kanavaolosuhteissa verrattuna ei-opportunistiseen skedulointiin
Interference management and system optimisation for Femtocells technology in LTE and future 4G/5G networks
Femtocells are seen to be the future of Long Term Evaluation (LTE) networks to improve the performance of indoor, outdoor and cell edge User Equipments (UEs). These small cells work efficiently in areas that suffer from high penetration loss and path-loss to improve the coverage area. It is said that 30% of total served UEs in LTE networks are vehicular, which poses challenges in LTE networks due to their high mobility, high vehicular penetration loss (VPL), high path loss and high interference. Therefore, self-optimising and dynamic solutions are required to incorporate more intelligence into the current standard of LTE system. This makes the network more adaptive, able to handle peak data demands and cope with the increasing capacity for vehicular UEs.
This research has drawn a performance comparison between vehicular UEs who are served by Mobile-Femto, Fixed-Femto and eNB under different VPL scales that range between highs and lows e.g. 0dB, 25dB and 40dB. Deploying Mobile-Femto under high VPLs has improved the vehicular UE Ergodic capacity by 1% and 5% under 25dB and 40dB VPL respectively as compared to other eNB technologies. A noticeable improvement is also seen in signal strength, throughput and spectral efficiency.
Furthermore, this research discusses the co-channel interference between the eNB and the Mobile-Femto as both share the same resources and bandwidth. This has created an interference issue from the downlink signals of each other to their UEs. There were no previous solutions that worked efficiently in cases where UEs and base stations are mobile. Therefore, this research has adapted an efficient frequency reuse scheme that worked dynamically over distance and achieved improved results in the signal strength and throughput of Macro and Mobile-Femto UE as compared to previous interference management schemes e.g. Fractional Frequency Reuse factor1 (NoFFR-3) and Fractional Frequency Reuse factor3 (FFR-3).
Also, the achieved results show that implementing the proposed handover scheme together with the Mobile-Femto deployment has reduced the dropped calls probability by 7% and the blocked calls probability by 14% compared to the direct transmission from the eNB. Furthermore, the outage signal probabilities under different VPLs have been reduced by 1.8% and 2% when the VPLs are 25dB and 40dB respectively compared to other eNB technologies
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System optimisation and radio planning for future LTE-advanced
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThis work is related to wireless communication. In this Thesis three main issues are addressed for future cellular networks: power consumption, interference and mobility. These issues continue to be a burden on the system’s performance as long as technology keeps evolving. In the presented chapters, the focus was to introduce greater intelligence to the LTE system algorithms and bring to them a dynamic and self-organizing approach. The first approach concerns power consumption in wireless terminals. The currently applied solution to save energy is the DRX mechanism. It organizes the time when the terminal wakes up and starts receiving data, and when it goes into sleep mode in order to save its battery power. The current DRX is described as static or fixed which makes its parameters unsuitable for the nature of the bursty traffic. In this work an adaptive DRX mechanism is proposed and evaluated as the wireless terminal battery saving algorithm. The second approach is co-channel interference mitigation. To increase the system’s capacity and avoid spectrum scarcity, small cells such as Femtocells are deployed and operate on the same frequency bands as the Macrocell. Although these small nodes increase the system capacity, however, the challenges will be in the femtocells planning and management in addition to the interference issues. Here a dynamic interference cancellation approach is presented to enable the Femtocell to track the allocated resources to the Macro-users, and to avoid using them. The third approach concerns mobility management in heterogeneous networks. The wireless terminal may have different mobility levels during handover which increases the handover failures due to failure in handover commands and aging of the reported parameters. This issue is presented in detail with the aim to avoid performance degradation and improve the reporting mechanisms during fast mobility levels. For this regard the presented method proposes more cooperation between the serving cell and the end-user so that the large amount of overhead and measurement are reduced. Simulations with different configurations are conducted to present the results of the proposed models. Results show that the proposed models bring improvements to the LTE system. The enhanced self-organized architecture in the three presented approaches performs well in terms of power saving, dynamic spectrum utilization by Femtocells, and mitigation of sudden throughput degradation due to the serving cell’s downlink signal outage during mobility.Brunel University Londo