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认知无线电指的是通信系统不是工作在一个固定的频段中,而是能自动搜寻一个合适的频段并在该频段上进行通信的体系结构。本文将从基本原理的角度探讨认知无线电系统为避免干扰其工作频段上可能存在的授权用户而要满足的基本要求。首先指出,为了能达到实际应用,认知无线电系统必须能够检测到无法解码的信号。接着说明如何权衡非授权用户的权限、可用空间和主营接收机干扰保护之间的关系。我们证明了在通常情况下,从一个已知零均值星座中检测微弱未知信号的最佳检测器是能量检测器(辐射计)。但是我们发现,已知的导频信号可以起到很大的帮助。因为仅仅在中等噪声不确定性的影响下,辐射计就会失去作用,因此我们又进一步强调对导频信号的需要。最后我们指出了包含不确定性噪声的量化分析,在低于一定的信噪比阈值时,任何检测器都绝对不可能检测到信号。
Cognitive radio refers to the fact that the communication system is not operating in a fixed frequency band but an architecture that automatically searches for an appropriate frequency band and communicates over that frequency band. This article examines the basic requirements of cognitive radio systems that must be met in order to avoid interfering with authorized users who may be present in their working frequency bands from a fundamental perspective. First of all, pointed out that, in order to achieve practical application, cognitive radio system must be able to detect the signal can not be decoded. Then explain how to balance the rights of unauthorized users, free space and the main receiver interference protection. We show that under normal conditions, the best detector for detecting weak unknown signals from a known zero-mean constellation is the energy detector (radiometer). However, we have found that the known pilot signals can be of great help. Because the radiometer is only detrimental to the effects of medium noise uncertainty, we further emphasize the need for pilot signals. Finally, we point out the quantitative analysis of uncertainty noise, and it is absolutely impossible for any detector to detect the signal below a certain signal-to-noise threshold.