In this paper, we consider a two-way cognitive radio network where an energy-constrained secondary transmitter (ST) first performs energy accumulation and then assists bidirectional communication for a pair of primary users (PUs) based on the principle of two-way relaying (TWR) strategy. To be specific, the ST can harvest energy from the received radio frequency (RF) signals broadcasting by both the primary users. After the residual energy at the ST is sufficient for data transmission, the ST will forward PUs’ signals by using decode-and-forward (DF) manner. In return, the ST is allowed to access the primary spectrum for its own data transmission. Moreover, according to whether the ST can correctly decode PUs’ signals or not, the ST will opportunistically switch between the silent mode and data transmission mode. A discrete Markov chain is used to simulate the charging and discharging processes of the ST’s battery. Based on this, closed-form expressions of outage probabilities for both the primary and secondary systems are derived. In addition, the optimal sub-slot switching coefficient and power allocation coefficient are determined by maximizing the spectrum efficiency of the secondary system while the spectrum efficiency of the primary system exceeding a given threshold. Numerical results not only validate the accuracy of the analytical results but also show that the proposed spectrum sharing protocol can provide a better performance in terms of energy efficiency over other similar TWR schemes.

在本文中，我们考虑一个双向认知无线电网络，其中能量受限的辅助发射机（ST）首先执行能量积累，然后根据双向中继的原理协助一对主要用户（PU）进行双向通信（TWR）策略。具体而言，ST可以从两个主要用户广播的接收到的射频（RF）信号中获取能量。在ST处的剩余能量足以用于数据传输之后，ST将通过使用解码转发（DF）方式来转发PU的信号。作为回报，ST被允许访问主要频谱以用于其自身的数据传输。此外，根据ST是否可以正确解码PU的信号，ST将在静默模式和数据传输模式之间机会切换。离散马尔可夫链用于模拟ST电池的充电和放电过程。基于此，导出了主系统和次系统的停机概率的封闭式表达式。另外，当主系统的频谱效率超过给定阈值时，通过最大化次系统的频谱效率来确定最佳子时隙切换系数和功率分配系数。数值结果不仅验证了分析结果的准确性，而且还表明，与其他类似的TWR方案相比，所提出的频谱共享协议在能效方面可以提供更好的性能。导出了主系统和次系统的停机概率的封闭式表达式。另外，当主系统的频谱效率超过给定阈值时，通过最大化次系统的频谱效率来确定最佳子时隙切换系数和功率分配系数。数值结果不仅验证了分析结果的准确性，而且还表明，与其他类似的TWR方案相比，所提出的频谱共享协议在能效方面可以提供更好的性能。导出了主系统和次系统的停机概率的封闭式表达式。另外，当主系统的频谱效率超过给定阈值时，通过最大化次系统的频谱效率来确定最佳子时隙切换系数和功率分配系数。数值结果不仅验证了分析结果的准确性，而且还表明，与其他类似的TWR方案相比，所提出的频谱共享协议在能效方面可以提供更好的性能。