Lin Huifa, Shin Won-Yong
The Communications & Networking Laboratory, Dankook University, Yongin 448-701, Republic of Korea.
The Department of Computer Science and Engineering, Dankook University, Yongin 448-701, Republic of Korea.
PLoS One. 2017 Jan 11;12(1):e0169902. doi: 10.1371/journal.pone.0169902. eCollection 2017.
We study secondary random access in multi-input multi-output cognitive radio networks, where a slotted ALOHA-type protocol and successive interference cancellation are used. We first introduce three types of transmit beamforming performed by secondary users, where multiple antennas are used to suppress the interference at the primary base station and/or to increase the received signal power at the secondary base station. Then, we show a simple decentralized power allocation along with the equivalent single-antenna conversion. To exploit the multiuser diversity gain, an opportunistic transmission protocol is proposed, where the secondary users generating less interference are opportunistically selected, resulting in a further reduction of the interference temperature. The proposed methods are validated via computer simulations. Numerical results show that increasing the number of transmit antennas can greatly reduce the interference temperature, while increasing the number of receive antennas leads to a reduction of the total transmit power. Optimal parameter values of the opportunistic transmission protocol are examined according to three types of beamforming and different antenna configurations, in terms of maximizing the cognitive transmission capacity. All the beamforming, decentralized power allocation, and opportunistic transmission protocol are performed by the secondary users in a decentralized manner, thus resulting in an easy implementation in practice.
我们研究多输入多输出认知无线电网络中的二次随机接入，其中采用了时隙ALOHA类型协议和连续干扰消除技术。我们首先介绍了由次用户执行的三种发射波束成形类型，其中使用多个天线来抑制主基站处的干扰和/或增加次基站处的接收信号功率。然后，我们展示了一种简单的分布式功率分配以及等效单天线转换。为了利用多用户分集增益，提出了一种机会性传输协议，其中机会性地选择产生较少干扰的次用户，从而进一步降低干扰温度。通过计算机仿真对所提出的方法进行了验证。数值结果表明，增加发射天线的数量可以大大降低干扰温度，而增加接收天线的数量会导致总发射功率的降低。根据三种波束成形类型和不同的天线配置，从最大化认知传输容量的角度研究了机会性传输协议的最优参数值。所有的波束成形、分布式功率分配和机会性传输协议均由次用户以分布式方式执行，因此在实际中易于实现。
