Queuing Analysis of Opportunistic Access in Multichannel Cognitive Radios

由于电磁波的传播特性，10MHz到6GHz之间的频率最适合用于无线通信目的。随着无线通信需求的不断增长和各种无线技术的普及，传统的基于固定频谱分配的频谱管理方法由于大部分可用频谱已被分配，导致无线电频谱稀缺。另一方面，研究表明，大部分授权频谱很少使用，导致大量频谱的利用不足。因此，需要能够提供利用可用频谱的新方法的创新技术。基于认知无线电终端和无线组网技术的认知无线电网络（CRN）是解决当前授权频谱利用率低的一种有效方法。CR技术向未授权（也称为次要）用户提供以机会主义方式与授权（也称为主要）用户共享无线信道的能力。认知无线电网络通过异构无线网络结构和动态频谱接入技术为移动的用户提供高带宽，同时提高信道环境的连通性和自适应性。

Due to the propagation characteristics of electromagnetic waves, the frequencies between 10MHz and 6 GHz are the most suitable for wireless communications purposes. With the ever-increasing demand for wireless communications and the popularity of various wireless technologies, the traditional approach to spectrum management based on fixed spectrum allocation, has resulted in scarcity of radio spectrum, due to the fact that most of the available spectrum has been allocated. On the other hand, studies have shown that vast portions of the licensed spectra are rarely used, leading to underutilization of a significant amount of spectrum. As a result, innovative techniques that can offer new ways of exploiting the available spectrum are needed. Cognitive Radio Networks (CRNs), which are based on Cognitive Radio (CR) terminals and wireless networking technologies have been proposed as the solution to current low usage of licensed spectrum problem. CR technology provides unlicensed (also known as secondary) users the capability to share the wireless channel with licensed (also known as primary) users in an opportunistic manner. CR networks are envisioned to provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques, while improving connectivity and self-adaptability of channel environment.