In this paper, we propose a spectrum sharing protocol for cognitive radio networks with an energy-constraint primary transmitter (PT), which performs energy harvesting from the received radio frequency (RF) signals broadcasting by two secondary users (SUs). After the amount of harvested energy at the PT is sufficient for data transmission, a SU will cooperatively forward PT's signal using amplify-and-forward (AF) scheme along with transmitting its own signal to increase the spectrum efficiency of the system. To be specific, the data transmission block can be divided into two phases. During the first phase, the PT will optimally select a relay from nodes S1 and S2 in order to further improve the overall throughput, then the PT transmits primary signal to the selected SU and primary receiver (PR), respectively, while the non-selected SU transmits signal to secondary receiver (SR). In the second phase, the selected SU transmits signals of both the primary and secondary systems simultaneously. A discrete Markov chain is used to simulate the charging and discharging processes of the PT's battery. In order to avoid mutual interference between the primary and secondary systems, a fraction of spectrum is used to transmit primary data and the residual spectrum is served for data transmission of the secondary system. An appropriate bandpass filter (BF) is deployed at the receive front-end of each receiver to extract the desired signals from assigned bandwidth. Based on this, the exact expressions of the outage probabilities for both the primary and secondary systems are derived. Moreover, the optimal bandwidth allocation coefficient is determined by utilizing convex optimization to maximize the achievable rate of the secondary system while guaranteeing the achievable rate of the secondary system in information transmission mode. Numerical results show that the proposed spectrum sharing protocol outperforms to other scheme and non-cooperative scenario in terms of average spectrum efficiency.

在本文中，我们提出了一种具有能量约束主发射机（PT）的认知无线电网络的频谱共享协议，该协议从两个次要用户（SU）广播的接收射频（RF）信号中进行能量收集。在PT处收集到的能量足以用于数据传输之后，SU将使用放大转发（AF）方案协同传输PT的信号，同时传输自己的信号以提高系统的频谱效率。具体而言，数据传输块可以分为两个阶段。在第一阶段，PT将从节点S1和S2中最佳选择一个中继，以进一步提高整体吞吐量，然后PT分别将主信号发送到所选的SU和主接收器（PR），未选择的SU将信号发送到辅助接收器（SR）。在第二阶段，所选择的SU同时发送一次系统和二次系统的信号。离散马尔可夫链用于模拟PT电池的充电和放电过程。为了避免初级和次级系统之间的相互干扰，频谱的一部分用于传输初级数据，而剩余频谱用于次级系统的数据传输。在每个接收器的接收前端部署一个适当的带通滤波器（BF），以从分配的带宽中提取所需的信号。基于此，导出了主系统和次系统的停机概率的精确表达式。而且，最优带宽分配系数是通过利用凸优化来最大化二次系统的可实现速率，同时保证信息传输模式下二次系统的可实现速率来确定的。数值结果表明，提出的频谱共享协议在平均频谱效率方面优于其他方案和非合作方案。