| dc.description.abstract | The purpose of Cognitive Radio (CR) technology is to improve the spectrum utilization. Several literatures proposed different approaches, which include the spectrum sensing, detection of the appearance of primary user (PU), collision detection, the channel selection, etc., to improve CR performance. Among them, the effective channel selection is more important if there are many secondary users (SU) that contend limited spectrum holes. Furthermore, as the SU may have different channel condition in each channel and this issue shall also be carefully considered during channel selection for better transmission performance. Thus, the transmission rates of SUs will be greatly affected due to their channel condition, which may be caused by the environment distance, multipath, fading and so on. This thesis proposes a systematic method for channel selection by taking the channel condition into consideration.
In this thesis, the Fusion Center (FC) is equipped to collect information sensed by SUs. The proposed schemes assist SU to choose the appropriate channel by applying the collected information by FU. Both of the centralized and distributed channel selection strategies are proposed. The centralized channel selection strategy is further divided into two approaches: One is based on the maximization of individual transmission rate; and the other considers the maximization of system throughput. The distributed approach has three options for channel selection, including handoff scheme, pre-handoff scheme with the remaining time to the appearance of PU and pre-handoff scheme with the remaining time to clear the buffer before the appearance of PU. The experimental results show that the proposed methods present better performance when compare to that of the random selection scheme.
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