多網多節點感知無線電之同步可適性跳頻演算法設計與軟體無線電平台驗證

Algorithm Design and Software Radio Implementation of Slotted Adaptive Frequency Hopping Scheme for Cognitive Radio with Multi-node and Multi-net

李昕翰(Shin-Han Li)

指導教授 ： 黃正光

元智大學/電機通訊學院/通訊工程學系/碩士(2012年)

https://doi.org/10.6838/YZU.2012.00251

摘要

感知無線電(Cognitive Radio, CR)為一覆蓋於有照主要用戶(Primary User, PU)網路之上的次級用戶(Secondary User, SU)網路。為了能靈活地避開對主要網路的干擾，感知無線電必備之兩大能力為頻譜感測(Spectrum Sensing, SS)及動態頻譜接進(Dynamic Spectrum Access)，而後者之主要技術即為本論文所提之「適應性跳頻」(Adaptive Frequency Hopping, AFH)。本論文將探討在感知無線電多網路以及多節點兩種情況下的可適性跳頻演算法設計，並透過一基於電腦Matlab程式之硬體實現平台(Instruments-in-Matlab Software Defined Radio, IM-SDR)實驗平台進行驗證。
本論文首先將探討如何避開主要使用者(PU)之干擾，由於主要使用者相對於CR頻譜變化較慢，故吾人將設計一快速有效的集中式(Centralized)法則，用於每一CR cell的基地台，使其能整合各裝置之頻譜感測訊息狀況，以建立即持續更新本cell之動態頻道干擾狀態表，並盡可能迅速迴避主要使用者。此外吾人將研究現有的跳頻序列設計方法，利用平方質數碼(Quadratic Prime Code, QPC)產生本論文所需要之多節點跳頻序列。其次，吾人考慮除了主要使用者共存之外，尚有其它鄰近之感知無線電網路亦共存的情況，此時，原本避免靜態頻率干擾(Frequency-Static Interference, FSI)之可適性跳頻演算法則有所不足，必須設計能同時避免靜態頻率干擾及動態頻率干擾(Frequency-Dynamic Interference , FDI)之增強型可適性跳頻機制，故吾人將利用Adaptive Frequency Rolling (AFR)方式達到以上各種需求，接著，吾人將整合前述法則之優點並設計一稱為時槽同步可適性跳頻輪動(SAFHR)演算法，此法則除了能夠迴避兩個主要碰撞干擾之外，亦能透過雙層之平方質數碼事先分配節點達到充分利用頻譜、增加頻譜使用效益的功用。接續，吾人將利用電腦模擬，在有各種靜態以及動態頻率干擾之狀況下，探討以上各種跳頻演算法則之干擾、碰撞迴避能力，以研究其性能。
為了能夠更精確、更貼近實際狀況來測試上述法則，吾人著手建置一多功能 IM-SDR (Instruments-in-Matlab Software Defined Radio)硬體驗證平臺，此平台以MATLAB程式為核心，植入吾人撰寫之可適性跳頻演算法則並進行量測及驗証，此一IM-SDR平台具有一個獨立的感知基地台(Cognitive Radio-Base Station, CR BS)及雙CR網路，各含有2個收發節點，其中CR BS可以發送一個準確的外部同步脈衝訊號以觸發平台上各儀器之同步傳輸封包、跳頻、迴避PU干擾機制，也可以透過進行感知無線電之頻譜感測的動作，並將感測結果一併發送給各個儀器，而各個儀器之間的動作也幾乎都由電腦透過Matlab儀控，最後，在此IM-SDR平台上量測及驗證本論文設計之多網多節點CR可適性跳頻演算法則。

關鍵字

可適性跳頻 ； 平方質數碼 ； 可適性頻率輪動 ； 感知無線電 ； 軟體無線電平台

並列摘要

Cognitive radio (CR) is a secondary-user (SU) network overlaid on the primary-user (PU) network. To effectively avoid the interference to primary users, CR users are required to have two major capabilities: (1) spectrum sensing (SS), and (2) dynamic spectrum access (DSS). In this thesis, we focus on the adaptive frequency hopping (AFH) technology for enabling the DSS capability. As is well known in military communications applications, the frequency hopping technology can achieve multiple advantages, such as combating various types of jamming, against channel fading, faciltating multiple access, and low interception probability, etc. In the study of CR network, the AFH research is also closely linked to the above considerations, especially, the anti-jamming issue. Therefore, this thesis attempts to investigate the AFH algorithm design and verification in the context of CR network, and to conduct real-world CR experiments on an instruments-in-Matlab SDR platform.
we will first study the problem of avoiding the interference to PU. The major task is to design a fast and centralized AFH algorithm for running on the base station of each CR cell. The scheme can integrate the feedback spectrum sensing information as well as the PER status from all the CR users, in order to build and maintain a most up-to-date dynamic interference state table of all frequency channels. In such a way, the PU interference can be avoided quickly. Besides, we will also use Quadratic Prime Code (QPC) method to generate FH sequence. Then, besides the PU, we will extend the AFH problem to consider other co-existing CR nets. In such a case, the original anti-FSI AFH scheme is not sufficient to deal with the frequency dynamic interference (FDI) from other cells. Thus, we attempt to design an enhanced AFH scheme to avoid the FSI and FDI simultaneously. Here, we will exploit the adaptive frequency rolling (AFR) method to meet the above requirement. Then, we integrate the methods just discussed before to design a improved AFH, this scheme could not only avoid the two main frequency interference, but can also fully use all the frequency spectrum, and increasing the spectrum efficiency. Finally, we will use computer simulation to examine and analyze the interference/collision avoidance capability of the aforementioned methods, under various FSI and FDI situations.

Next, we build up an instruments-in-Matlab SDR platform to verify the feasibility of the developed AFH algorithms.To be able to more accurate and closer to the actual situation, this IM-SDR platform have an independent CR-BS(Cognitive Radio-Base Station) and two CR nets when each net contains two CR nodes for transmitting and receiving a sequence of packets. A synchronization channel is used to trigger all the instruments in the IM-SDR platform to transmit packets, frequency hopping, and avoid the frequency interference by using the broadcast synchronization signal. Besides, spectrum sensing is also done, and the results are sent to each CR nodes. In that way, all the SAFHR processing can be implemented on the IM-SDR platform for testing and verification through Matlab. Finally, we will test and verify the SAFHR algorithm with IM-SDR.

並列關鍵字

IM-SDR ； adaptive frequency hopping ； Quadratic Prime Code ； adaptive frequency rolling ； cognitive radio

參考文獻

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