Wang Hui, Dong Jian, Tang Kun, Shi Heyuan
School of Computer Science and Engineering, Central South University, No. 932 Lushannan Road, Changsha 410083, China.
Guangdong Provincial Key Laboratory of Millimeter-Wave and Terahertz, School of Electronic and Information Engineering, South China University of Technology, No. 381 Wushan Road, Guangzhou 510640, China.
Entropy (Basel). 2021 Nov 5;23(11):1463. doi: 10.3390/e23111463.
Improving spectral efficiency under a certain energy limitation is an important design metric for future wireless communications as a response to the growing transmission demand of wireless devices. In order to improve spectral efficiency for communication systems without increasing energy consumption, this paper considers a non-orthogonal multiple access (NOMA)-based cognitive radio network, with the assistance of a wireless-powered relay station (RS), and then analyzes the system outage performance under amplified-and-forward (AF) and decoded-and-forward (DF) cooperative transmission modes. Specifically, the base station (BS) has the opportunity to cooperate by transmitting information through the RS, depending on whether the RS can harvest sufficient RF energy for cooperative transmission. That is to say, when the energy stored by the RS is sufficient for cooperative transmission, the RS will assist the BS to forward information; otherwise, the BS will send information through direct links, while the RS converts the radio frequency (RF) signals sent by the BS into energy for future transmission. Moreover, the transmission power required by the RS for cooperative transmission is usually relatively large, while the amount of harvested energy by the RS in a transmission slot is usually low, so it takes several consecutive time slots to accumulate enough transmission energy. To this end, we utilize a discrete-time Markov chain to describe the processes of charging and discharging of the RS. Subsequently, we derive the closed-form outage probabilities of both the primary and secondary systems for the considered system in AF and DF modes through mathematical analysis, and verify the accuracy of the analyses through Monte Carlo simulation. The simulation results show that the two proposed cooperative transmission schemes with AF and DF relaying techniques outperform both direct transmission and other similar schemes in both the primary and secondary system, while the DF scheme can provide better performance than the AF scheme within the range of setting values.
在一定能量限制下提高频谱效率是未来无线通信的一项重要设计指标，以应对无线设备不断增长的传输需求。为了在不增加能耗的情况下提高通信系统的频谱效率，本文考虑了一种基于非正交多址接入（NOMA）的认知无线电网络，借助无线供电中继站（RS），然后分析了放大转发（AF）和解码转发（DF）协作传输模式下的系统中断性能。具体而言，基站（BS）有机会通过RS传输信息进行协作，这取决于RS是否能够收集到足够的射频能量用于协作传输。也就是说，当RS存储的能量足以进行协作传输时，RS将协助BS转发信息；否则，BS将通过直接链路发送信息，而RS将BS发送的射频（RF）信号转换为能量以供未来传输。此外，RS进行协作传输所需的发射功率通常相对较大，而RS在一个传输时隙中收集的能量量通常较低，因此需要几个连续的时隙来积累足够的传输能量。为此，我们利用离散时间马尔可夫链来描述RS的充电和放电过程。随后，我们通过数学分析推导了所考虑系统在AF和DF模式下主系统和次系统的闭式中断概率，并通过蒙特卡罗模拟验证了分析的准确性。仿真结果表明，所提出的采用AF和DF中继技术的两种协作传输方案在主系统和次系统中均优于直接传输和其他类似方案，而在设定值范围内，DF方案比AF方案能提供更好的性能。
