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Self-organized radio resource management in OFDM based cellular systems
Citation Link: https://doi.org/10.15480/882.985
Other Titles
Selbstorganisierende Ressourcenvergabe in OFDM-basierten zellularen Systemen
Publikationstyp
Doctoral Thesis
Date Issued
2010
Sprache
English
Author(s)
Advisor
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2010-09-28
Institut
TORE-DOI
Future mobile communication systems require higher data rates and more flexibility. The OFDM transmission technique, as a special form of multi-carrier transmission, achieves high efficiency by subdividing the bandwidth into narrow and orthogonal subcarriers with specific spectra. The consequent long symbol duration also facilitates a simple receiver structure in a multi-path propagation environment. Moreover, each subcarrier can use independently individual transmission parameters. In this thesis, a scheme for a self-organized radio resource management (SO-RRM) is proposed for an OFDM based cellular system.
All base stations in a cellular network operate on the same central carrier frequency, but with different radio resources. A resource can be defined as a timeslot, a subcarrier, or any frequency-time block. All resources are accessible at any cell in the cellular network. Neither central controllers nor direct communication between base stations is needed. Each base station allocates radio resources and selects transmission parameters independently in accordance with the requirement and the measured real-time network condition. The powers of signal and interference are measured at both base stations and mobile terminals. To have an interference free measurement of the signal power, a dedicated signal measurement timeslot is designed in the uplink. A resource quality function is defined to predict the transmission result in a time variant channel, applying both adaptive modulation and coding, and link adaptation. Those resources with highest possible data rates are allocated. In this way, an adaptive and up-to-date resource reuse can be realized.
To reduce the amount of dropped connections due to unpredictable new interference after allocation, a security margin is introduced, which reserves a priori a space for new interference. A suitable margin brings a 13% capacity increase. More efficiently, a reallocation procedure can be triggered when service degradation is observed for certain duration. This method can even bring about two times more capacity.
The SO-RRM shows its high flexibility in a cellular network with a non-uniform or fast changing user distribution. Hotspot cells can claim more resources, while the cells with few users use only few resources. Furthermore, the multi-user diversity enables adaptive resource rearrangement in the downlink. Resources used inside a cell are exchanged based on instantaneous channel conditions. Three different algorithms are compared. They can bring a higher spectral efficiency of up to 80%.
All base stations in a cellular network operate on the same central carrier frequency, but with different radio resources. A resource can be defined as a timeslot, a subcarrier, or any frequency-time block. All resources are accessible at any cell in the cellular network. Neither central controllers nor direct communication between base stations is needed. Each base station allocates radio resources and selects transmission parameters independently in accordance with the requirement and the measured real-time network condition. The powers of signal and interference are measured at both base stations and mobile terminals. To have an interference free measurement of the signal power, a dedicated signal measurement timeslot is designed in the uplink. A resource quality function is defined to predict the transmission result in a time variant channel, applying both adaptive modulation and coding, and link adaptation. Those resources with highest possible data rates are allocated. In this way, an adaptive and up-to-date resource reuse can be realized.
To reduce the amount of dropped connections due to unpredictable new interference after allocation, a security margin is introduced, which reserves a priori a space for new interference. A suitable margin brings a 13% capacity increase. More efficiently, a reallocation procedure can be triggered when service degradation is observed for certain duration. This method can even bring about two times more capacity.
The SO-RRM shows its high flexibility in a cellular network with a non-uniform or fast changing user distribution. Hotspot cells can claim more resources, while the cells with few users use only few resources. Furthermore, the multi-user diversity enables adaptive resource rearrangement in the downlink. Resources used inside a cell are exchanged based on instantaneous channel conditions. Three different algorithms are compared. They can bring a higher spectral efficiency of up to 80%.
Subjects
zellulares Netz
Funkübertragung
cellular network
radio communication
DDC Class
620: Ingenieurwissenschaften
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