- 學位論文
為動態頻譜存取中異質網路間之共存設計之頻譜分配
Spectrum allocation for coexistence among heterogeneous secondary networks in Dynamic Spectrum Access
摘要
動態頻譜存取 (DSA) 已經被廣泛認為是提升電視頻譜使用度的一種方式：次要裝置被允許暫時至無人使用之電視頻帶與其他次要裝置溝通。現今已有許多通訊協定被設計出來以動態的方式分享電視白頻譜 (TVWS) 。但因為不同協定之間無法直接進行溝通，而且不同協定間都有相等的頻譜存取權，因而會互相干擾。因此在動態頻譜存取中，異質網路間的共存問題是至關重要。 在工業科學及醫療 (ISM) 頻帶中，異質網路間的之共存問題已經被研究許久，如WiFi、Zigbee及藍芽各自都有分散式的共存機制。但是在動態頻譜存取之頻帶中，分散式的機制因次要使用者傳輸功率的巨大差異而導致小功率網路極度不公平的頻譜使用，因此並無法像工業科學及醫療頻帶中順利運作。此外，因為電視白頻譜以及無執照頻譜之功率限制，異質網路就算具備相同規格之通訊能力，依然無法使其正常雙向溝通。因此，為了避免造成小功率網路的不公平頻譜使用，集中式的共存機制應為解決動態頻譜存取共存之較好方法。現存集中式共存方法已經涉略到很多動態頻譜存取中之特性，包括次要網路所觀察之可用頻道可能不同，以及可用頻道會隨時間改變。然而，現存之機制皆無考慮到頻道切換造成的延遲。 頻道切換延遲是由PHY層切換時間和MAC層以上之整體網路頻道切換所需傳送時間所構成，這個延遲在大型的網路中會長達數秒鐘甚或更久，因此會對服務品質造成很大傷害。在這個計畫中，我們提出了一個在動態頻譜存取中的頻譜分配模型，並且設計一考慮了頻道轉換延遲時間之頻譜分配演算法。模擬的結果顯示，跟現存的解法做比較，所提出之演算法可增加6%到13%的通訊時間增益。
並列摘要
Dynamic spectrum access (DSA) is now widely considered as a solution to improve utilization of the television (TV) spectrum, where secondary devices may be temporarily allowed to access unused TV white space (TVWS). As a result, many secondary protocols have been designed to dynamically share the TVWS. Since these protocols are not compatible with each other, there will be interferences when all secondary protocols access the shared TVWS with equal priority. Therefore, the coexistence mechanism among heterogeneous networks needs to be resolved in DSA. The coexistence among heterogeneous networks in industrial, scientific and medical (ISM) bands has been addressed, where distributed solutions are used to facilitate the coexistence among WiFi, Bluetooth and Zigbee networks. However, the distributed solutions in DSA bands do not work as well as in ISM bands. One reason is that the huge difference in transmission power of heterogeneous networks in the TVWS leads to extremely unfair utilization of small-power networks. Such difference also makes the common radio solution infeasible because the communication between heterogeneous networks will be asymmetric. A centralized solution is preferred as a coexistence solution for DSA as unfair utilization for small-power secondary networks can be avoided. The existing centralized solutions had addressed some coexistence issues in DSA, including different channel availability perceived by secondary networks and varying spectrum availability. Nevertheless, none of them considers the channel switching delay. The switching delay is composed of the PHY switching time and the MAC-layer delay for disseminating switching messages within the entire network. The switching delay may be up to a few seconds when there are many devices in a (multi-hop) network. Such a long switching delay can be harmful to QoS and therefore cannot be ignored. In this project, we proposed a novel centralized spectrum allocation algorithm for DSA. Simulation results show that the proposed algorithm can achieve 6% to 13% gain of channel utilization comparing to the existing solutions.
參考文獻
延伸閱讀
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