Dynamic spectrum access in cognitive radios

随着无线通信及其应用的快速发展，未来无线网络对宽带多媒体业务的需求将不断增加，这将引发对频谱带宽的巨大需求。然而，大多数相关的无线电频谱都被分配给了大多数地区的各种许可应用，从而导致了潜在的频谱稀缺问题。另一方面，最近对频谱的实际测量表明，在任何给定的地点和任何给定的时间，许多许可的频谱都没有得到利用。因此，动态频谱接入最近成为一种很有前途的解决方案，通过在主(授权)用户暂时不使用频谱时，允许次级(未授权)用户借用频谱，从而缓解频谱稀缺问题。认知无线电作为动态频谱接入的关键使能，受到了人们的广泛关注，二次用户可以智能地适应不断变化的环境。对于次用户来说，较低的频谱接入优先级给他们的信道接入协议的设计和分析带来了很大的挑战，因为主用户应该尽可能不受影响。当支持具有不同服务质量(Qos)要求的多媒体业务时，情况变得更加复杂。

With the rapid growth of wireless communications and their applications, the demand for broadband multimedia services will keep increasing in future wireless networks, which will trigger a huge demand for spectral bandwidth. However, most of the related radio spectrum has been assigned to various licensed applications in most regions, thus leading to a potential spectrum scarcity problem. On the other hand, recent real measurements of the spectrum have indicated that at any given location and any given time, much of the licensed spectrum is not utilized. Therefore, dynamic spectrum access has recently emerged as a promising solution to alleviate the spectrum scarcity problem by letting secondary (unlicensed) users borrow the spectrum when the spectrum is temporarily not in use by the primary (licensed) users. As a key enabler for dynamic spectrum access, cognitive radios have received much attention, where secondary users can intelligently adapt to the changing environment. For secondary users, the lower priority to access the spectrum poses a big challenge to the design and analysis of their channel access protocols because primary users should not be affected whenever possible. The situation becomes more complicated when multimedia traffic with heterogeneous quality-of-service (QoS) requirements is supported.