Time synchronization is a vital concern for any Cognitive Radio Network (CRN) to perform dynamic spectrum management. Each Cognitive Radio (CR) node has to be environment aware and self adaptive and must have the ability to switch between multiple modulation schemes and frequencies. Achieving same notion of time within these CR nodes is essential to fulfill the requirements for simultaneous quiet periods for spectrum sensing. Current application layer time synchronization protocols require multiple timestamp exchanges to estimate skew between the clocks of CRN nodes. The proposed symbol timing recovery method already estimates the skew of hardware clock at the physical layer and use it for skew correction of application layer clock of each node. The heart of application layer clock is the hardware clock and hence application layer clock skew will be same as of physical layer and can be corrected from symbol timing recovery process. So one timestamp is enough to synchronize two CRN nodes. This conserves the energy utilized by application layer protocol and makes a CRN energy efficient and can achieve time synchronization in short span.

中文翻译：

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认知无线电网络中的节能跨层时间同步

时间同步是任何认知无线电网络 (CRN) 执行动态频谱管理的重要问题。每个认知无线电 (CR) 节点都必须具有环境感知能力和自适应能力，并且必须能够在多种调制方案和频率之间进行切换。在这些 CR 节点内实现相同的时间概念对于满足频谱感知同时静默期的要求至关重要。当前的应用层时间同步协议需要多次时间戳交换来估计 CRN 节点时钟之间的偏差。所提出的符号时序恢复方法已经在物理层估计了硬件时钟的偏斜，并将其用于每个节点应用层时钟的偏斜校正。应用层时钟的核心是硬件时钟，因此应用层时钟偏移将与物理层相同，可以通过符号时序恢复过程进行纠正。所以一个时间戳足以同步两个 CRN 节点。这节省了应用层协议使用的能量，使 CRN 高效节能，可以在短跨度内实现时间同步。