Spectrum sharing method to form bundle of white space in cognitive radio

Spectrum sharing by using cognitive radio technology has attracted attention as an effective solution to shortage of spectrum resource. In the spectrum sharing, unlicensed users (secondary users: SUs) exploit white space (WS) which is unused band by licensed users (primary users: PUs). In the related works, the channel assignment method maximizing the SU communication quality while protecting the PU is proposed when multiple SUs exist. In this method, the distance between SUs on the same channel is maximized in order to minimize the mutual interference among SUs. Therefore, it may cause the spatial fragmentation of spectrum resource and new SUs are difficult to share the same spectrum. In this paper, a novel channel assignment method based on perimeter to area ratio of WS is proposed. In the proposed method, WS is formed for easy entry of new SUs when the channels are assigned to SUs. The central control server with SU information is prepared and it assigns a channel to new SUs successively. Through computer simulations, we show that the number of SUs with an assigned channel increases by using the proposed method and new SUs can utilize WS effectively.