Super Wi-Fi 시스템에서 효율적인 TV white space channel 관리 방안 연구
Efficient channel management of TV white spaces in super Wi-Fi systems
TV white space Super Wi-Fi Cognitive radio;
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Spectrum scarcity is one of the significant obstacles in accommodating ever-increasing wireless services. TV white space which is unused portions of the TV spectrum, can be a good wireless resource candidate with considerably wider bandwidth and longer transmission range for future wireless communications. Opportunistic spectrum utilization of the cognitive radio (CR) has particularly found their effective applications for exploiting the advantages of TV white spaces in order to deal with the spectrum scarcity problem. The Federal Communications Commission (FCC) released the ruling to make TV white spaces available for unlicensed broadband wireless services such as Super Wi-Fi, imposing a requirement that Super Wi-Fi devices must not interfere with incumbent users (IUs) such as wireless microphones . The operation of Super Wi-Fi devices rely on the abilities of detecting available TV white space spectrum and manipulating the spectrum for consistent service provisioning while avoiding harmful interference to IUs. The IEEE 802.11af standard imposes that the Super Wi-Fi systems should vacate spectrum mandatorily in the unit of TV channel band (e.g., Advanced Television Systems Committee (ATSC) TV channel: 6 MHz) when active microphones appear. Vacating the spectrum band used for ongoing data services and rearranging other available spectrum to make up for the given-up spectrum band should cause serious deterioration in service quality. Furthermore it becomes much more serious with increased number of the Super Wi-Fi systems and IUs. This dissertation describes the channel management scheme to improve the frequency usage efficiency and the service continuity in Super Wi-Fi systems. It includes an efficient method of providing a control channel for the Super Wi-Fi system, based on the proposition that the TV white space spectrum band is divided into many smaller sub-channels. The bandwidth of the sub-channels is considered as a basic unit of spectrum manipulation, so that the bandwidths of the Super Wi-Fi systems and IUs are counted by the number of sub-channels. By doing so, the given-up spectrum due to active IUs is considered as a part of a TV channel spectrum, not a whole 6 MHz TV channel band, giving the chance to use the spectrum portion unaffected by IUs. Such unaffected sub-channels are used as a control channel for immediately sharing the channelization information between access point (AP) and the associated mobile stations (MSs), removing an extra control channel provision process. Such the immediate control channeling method improves service continuity of Super Wi-Fi. In addition, an elaborate manipulation of spectrum can increase the probability of finding new spectrum band faster to replace the given-up spectrum at a nearer TV white space spectrum, resulting into an efficient TV white space spectrum management. This dissertation describes the utilization method of the proposed scheme and analyzes the performance in the Super Wi-Fi systems from the aspects of the frequency usage efficiency and the service continuity.