改善頻譜偵測延遲之次級使用者頻譜分享系統實作

Implementation of a Spectrum Sharing System Resilient to Spectrum Sensing Delay

黃騰輝(Teng-Hui Huang)

指導教授 ： 王奕翔

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201704353

摘要

頻譜分享被視為是提昇頻譜使用效率的關鍵技術之一，其初始構想專注於頻譜主要使用者 (PU)及次要使用者間的分享，而近年的發展更實際的考慮次要使用者間的具不同頻譜優先接取權的情況。此架構下，頻譜次要使用者皆可以動態的接取主要使用者在時間上或空間上未使用的頻譜資源，惟一般分享頻譜權限之次要使用者 (G-SU)須避免對具較高分享頻譜優先接取權之次要使用者 (ProU)造成影響其效能之干擾。相關文獻指出，頻譜偵測是能夠讓G-SU避免對ProU造成干擾同時增進頻譜使用效率之關鍵技術。前人的研究提出許多對於實現次要使用者間的頻譜分享可能的挑戰並且提出了解決的方法。其中，對於頻譜偵測延遲的問題仍然存有許多挑戰並未被完全解決。
本論文專注於分享頻譜之次要使用者間的分享並探討偵測延遲對頻譜分享系統帶來的挑戰。本論文指出兩項偵測延遲對頻譜分享系統帶來之影響。其一，G-SU將無可避免的對ProU造成干擾。其二，G-SU將會因延遲而失去可接取分享頻譜的機會。在指出偵測延遲帶來的影響後,本論文進一步提出一基於干擾消除之傳輸機制並與傳統之基於避免干擾之傳輸機制比較有效吞吐量。本論文提出之方法相較於傳統作法的好處為，G-SU因干擾而重傳的封包可以同時用以消除對於ProU造成之干擾。

本論文完成了對於基於干擾消除之頻譜分享系統的設計及實作。此系統有兩項特色。首先，G-SU及ProU間不需要事先協調傳輸的內容，時間或頻寬以作到干擾消除。次之，本論文提出之干擾消除機制並非針對特定的ProU傳輸方式而設計因此適用於不同的無線傳輸技術標準。本論文將提出之系統開發於GNUradio針對無線通信系統開發之開源軟體及USRP軟體無線電收發機之上。並且讓實作之系統在該實驗平台上於實際無線通信通道運作。實驗結果顯示，在ProU的傳輸吞吐量維持在點對點通信時的百分之九十之限制下，對於SU的有效吞吐量，本論文提出之基於干擾消除的傳輸機制相較於傳統之作法有38\%的效能提昇。

關鍵字

頻譜分享 ； 軟體無線電實作 ； 干擾消除 ； 信號同步演算法 ； 頻譜感測延遲

並列摘要

Spectrum sharing is a promising technology to improve spectral efficiency. While the original idea of spectrum sharing focuses on sharing for primary (PU) and secondary users. The implementation of spectrum sharing system further consider access priorities among secondary userscite{FCC15}. Both high-priority secondary user (ProU) and general-authorized secondary user (G-SU) can dynamically access unused PU spectrum but G-SU has to avoid causing harmful interference to both PU and ProU. In order to protect ProU and fully utilize unused ProU spectrum, previous studiescite{SBsharing:4804658} suggested that spectrum sensing for SU is necessary. While the challenges of spectrum sharing among secondary user are addressed to some extend, the challenge from practical sensing delay is not fully addressed to the furtherest of our knowledge.
In this thesis, we focus on spectrum sharing among secondary user and take practical sensing delay into consideration and identify the impact of it to both ProU and G-SU. Due to sensing delay, G-SU will inevitably cause interference to ProU. Furthermore, SU will lose opportunities to utilize unused secondary spectrum. In contrast to conventional interference avoidance-based approaches. We propose interference cancellation-based G-SU system to address the sensing delay challenge. The idea is to utilize G-SU retransmissions due to collision to enable interference cancellation for ProU.

We design and implement an interference cancellation based G-SU system that requires no coordination of ProU and G-SU in advance transmission. Our system reuses conventional decoder of ProU and is a general technique that is independent of ProU's technology. Furthermore, we implement a 4-node software radio prototype with GNUradio software and Universal Software Radio Peripheral (USRP) hardware. From the over-the-air experiment results, we show that when ProU's throughput is at least 90\% of that in point-to-point scenario, proposed G-SU system achieves 38\% higher goodput than conventional avoidance-based approaches.

並列關鍵字

spectrum sharing ； software radio prototyping ； interference cancellation ； signal synchronization algorithms ； spectrum sensing delay

參考文獻

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