## 3 Novel Framework for Wideband Cooperative Spectrum Sensing
### Novel Wideband Cooperative Spectrum Sensing Framework  
In order to avoid interfering to PU, it necessitates an efficient and reliable detection method of PU. The scheme of CSS has been proposed to mitigate the impact of fading and shadowing. The secondary system consists of \(K\) SUs and one FC. Figure 4 illustrates the general TDMA-based CSS frame structure designed for a CR network with PSS, where each frame consists of a compressed sensing (CS) slot, a reporting slot and a data transmission slot, ignoring the time consumed by FC to process the collected data and to broadcast the final decision. Supposing the frame duration is \(T\), the sensing duration is \(\tau\) and the individual reporting duration is \(t_{r}\). Prior to data transmission, CSS is performed synchronously by SU at the beginning of the frame, then each SU reports local sensing results to FC in a single reporting time slot following sensing slot to avoid transmission conflict. Finally, the FC makes a global decision on the state of PU. Only when the absence of PU is detected can transmission slot be used. Otherwise, SU must vacate the frequency band immediately and perform spectrum sensing again. Cooperation among SU can greatly improve sensing performance, however, it also introduces additional overhead since the sensing results need to be reported to FC periodically. In the conventional frame structure, the SU can sense the PU before sensing results reporting and data transmission. A serious problem is that when the incumbent SU reports its local sensing results, other SU have no any manipulation until allocated reporting slot arrival. There is a waste of \(K(K-1)t_{r}\) reporting duration that does not make any contribution to the performance of spectrum sensing. Therefore, the general cooperative sensing frame structure is inefficient. In this section, we propose a high-efficiency  
Figure 4: General TDMA-based cooperative spectrum sensing framework. CSS framework with optimal scheduling strategy to improve the performance of cooperative sensing without introducing additional time overhead. The core idea of the novel framework is that when the incumbent SU is reporting the sensing results, its succeeding SU continue local compressed sensing until their turns to report, which aims at extending the sensing duration as long as possible by fully utilizing the reporting slot. Considering the effects of dynamic and time-varying spectrum environment on CSS performance, most recent works [14; 15; 16; 27; 29; 30; 31; 32] regard PU as either present or absent for the whole sensing frame length. This is a reasonable model when the PU has low traffic. Furthermore, in respect of high traffic, [PERSON] et al. [34] and [PERSON] et al. [40] analyzed the PU's random arrival or departure during the sensing period. Although [PERSON] et al. [34] considered the case that PU could become busy again during SU's transmission, the sensing period is assumed to be short as compared to the average busy and idle periods of PU from the aspect of traffic with stringent quality of service (QoS) requirements. For simplicity, [PERSON] et al. [40] considered a common case that the status of licensed user (LU) is not changing very frequent and ignores the asynchronous activities of LU and smart devices (SD). Additionally, the effects of the PU's random departure/arrival behaviors on spectrum sensing are minimal [41]. On this basis, it is assumed that the PU does not leave or arrive within \(N\) frames for CSS frame structure with individual frame length of 160 ms [35], where the value of \(N\) is determined by the application scenarios. Thus, our proposed novel CSS frame structure can be applied to the scenario where the PU does not leave or arrive within one frame, which is the precondition of the proposed solution. As depicted in Figure 5, the \(i\)-th SU reporting time can be utilized for its following SU sensing. In other words, for the \(i\)-th SU, the \((i-1)t_{r}\) calculated in reporting slot can be employed for local compressed sensing.