在感知性網路中以部分探測馬可夫決策過程為基礎的頻帶換手機制

Abstract

近年的研究說明了靜態的頻帶分配是造成頻帶使用缺少效率的主因，為了增進頻帶使用率，可動態偵測且使用認證頻帶的感知無線電(CR)因應而生。 如何提供有效率的頻帶換手在CR 中是個很重要的議題。現存的頻帶換手方法假定感知無線電的使用者(CR user)可以正確的偵測每一個頻帶以便找到適合的頻帶進行換手。然而，這個假設在實際的情況下是不實際的，因為CR 使用者偵測頻帶所花費的時間將會太高而影響主要使用者的品質。 在這篇論文中，藉由部分可知的環境下的Marcov 決策過程(POMDP)的幫助，可以透過探測部分的頻帶來估測整個網路環境 。此篇論文提出以POMDP 為基準的頻帶換手機制(POSH)，其目的為藉由部分的通道狀態來找出最適合進行 換手的頻帶。除此之外，為了適應多位使用者的環境，此篇論文本著將頻寬資源充分分配給各使用者的概念提出了一個以POMDP 為基準的多使用者的換手機制(M-POSH)。 藉由POMDP 為基準的頻帶換手機制所選出的頻帶，可達到在每次換手時CR 使用者所需等待的時間最短，數據結果顯示出此方法可有效率地讓CR 使用者在每次頻帶換手時達到最少的等待時間。

Recent studies have been conducted to indicate the ineffective usage of licensed bands due to the static spectrum allocation. In order to improve the spectrum utilization, the cognitive radio (CR) is therefore suggested to dynamically exploit the opportunistic primary frequency spectrums. How to provide efficient spectrum handoff has been considered a crucial issue in the CR networks. Existing spectrum handoff algorithms assume that all the channels within the network can be correctly sensed by the CR users in order to perform appropriate spectrum handoff process. However, this assumption is considered impracticable in realistic circumstances primarily due to the excessive time required for the CR user to sense the entire spectrum space. In this paper, the partially observable Markov decision process (POMDP) is exploited to estimate the network information by partially sensing the frequency spectrums. A POMDP-based spectrum handoff (POSH) scheme is proposed to determine the optimal target channel for spectrum handoff according to the partially observable channel state information. Moreover, a POMDP-based multi-user spectrum handoff (M-POSH) protocol is proposed to adapt the POMDP policy into multi-user CR network by distributing CR users to opportunistic frequency spectrums. By adopting the policies resulted from the POSH and M-POSH algorithms for target channel selection, minimal waiting time at each occurrence of spectrum handoff can be achieved. Numerical results illustrate that the proposed spectrum handoff protocols can effectively minimize the required waiting time for spectrum handoff in the CR networks.