Joint Spectrum Sensing and Medium Access Control

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Cognitive Radio (CR) is highlighted as a future technology for wireless communications, expected to solve spectrum scarcity problem by allowing secondary use of spectrum which is detected as idle. For this brand-new technology, we face features that are not considered in traditional design approach: the spectrum sensing (SS) and the opportunistic spectrum access (OSA). The SS is a feature to detect if a channel is idle or busy reliably, and the OSA is another feature for effective utilization of the bandwidth that may be dynamically changing depending on the activity of the Primary User (PU) who has primary right to access channels. In addition, because the effective utilization is based on reliable detection of the idle bandwidth, we also have to deal with joint effect between the SS and OSA. To design the CR with solving these design problems, we need a cohesive design approach which can capture the interaction between the SS and OSA. Moreover, we want to apply any specific option for the SS or the OSA to this comprehensive design approach, so that we can evaluate and design any option proposed.

Therefore, we set up a framework to design the CR by jointly optimizing the SS and the OSA. Also, by deriving parameters in the framework based on specific options of the SS and the OSA, we can design the CR. As a first step, we apply this framework to small ad hoc network. Assuming one-hop network, we apply the collaborative sensing as a specific scheme for the SS, which is a well-known sensing strategy to make a decision of the channel availability based on sensing results of multiple users. Moreover, we assume that one channel is assigned to each user and the bandwidth of connection is not changed during connection. With this assumption, we consider two OSA strategies to deal with sudden PU appearance: buffering and switching. If a PU appears on a channel that is being utilized for data transmission, a CR user may terminate connection (non buffering with non switching), buffer data until the PU disappears (buffering with non switching), switch to other channel that is detected idle (non buffering with switching), or switch to idle channel if possible and otherwise buffer data (buffering with switching).

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Selected publications