感知無線電網路之多系統偵測

因為具有偵測頻譜進而更有效率使用的能力，感知無線電被視為未來無線通訊發展中的重要技術。當進一步將感知無線電系統及現存無線系統整合成感知無線電網路時，我們可對整體的網路使用效率最佳化。在考慮多系統的感知無線電網路中，有兩個重要的部份︰系統/網路偵測與無線電資源偵測。系統/網路偵測讓感知無線電可以辨認出周圍正在運作的通訊系統，這是達成合作式傳輸路徑選擇的重要初始步驟。我們在本論文中提出了一個可普遍適用於雷萊衰退通道的多系統偵測演算法。其中，我們利用了基本頻率、能量頻譜密度與四階統計特性等方法來達到辨識多系統的目的。當系統的事前資訊為已知時，此演算法也可適用於超寬頻通訊中所需要的偵測與迴避(DAA)。另一方面，感知無線電網路會受隱藏終端問題之苦使得系統性能變差。在無線電資源偵測中，次要系統(Secondary System)需決定能使用多少可用頻譜資源，此與傳統感知無線電中的頻譜偵測目的相同。從載波檢測多路存取網路與合作通訊的概念作延伸，我們提出了積極性偵測與合作式自適應調變編碼兩個新觀念來改善隱藏終端問題。感知無線電會傳送虛擬載波並改變其能量來控制對主要系統(Primary System)的干擾，而主要系統合作地改變調變與編碼的參數來最佳使用系統資源。透過偵測主要系統的調變與編碼參數變化，次要系統能推算出能傳送的最大能量，進而大幅改善整體感知無線電網路的系統容量。

關鍵字

感知無線電網路；頻譜使用效率；網路使用效率；多系統偵測；頻譜偵測；隱藏終端問題；積極性偵測；合作式自適應調變編碼

並列摘要

Cognitive radios (CRs) with capability of spectrum sensing to fully utilize radio spectrum have been considered as a key technology toward future wireless communications. We can further leverage CRs to form cognitive radio networks (CRN) which optimizes the total network instead of spectrum efficiency in conventional cognitive radios. When we consider CRN, there are two critical parts to sense the multiple systems environment: system/network sensing and radio resource sensing. In system/network sensing, CRs should identify the potential primary and secondary systems for construction of time-varying CRN. This is an important initial step in CRN since the cooperative routing transmission is allowable in the heterogeneous systems. In this thesis, we propose a general sensing algorithm to identify active systems under a multiple-systems coexisting environment over Rayleigh fading channel. We exploit unique characteristics of systems consisting of fundamental frequency, power spectrum density and four-order cumulant to accomplish the multiple systems sensing. This algorithm can also be applied in Detect and Avoid (DAA) for UWB with a priori knowledge of system parameters. On the other hand, cognitive radio networks may severely suffer from hidden terminal problem like transmission sensing wireless networks to degrade the outage performance. The function to determine the available radio resource for secondary system operation is the radio resource sensing which is similar to the spectrum sensing in conventional cognitive radio and should cope with the hidden terminal problem meanwhile. Modifying the concept from carrier sense multiple access (CSMA) networks, along with the cooperative communications, we propose aggressive sensing and cooperative adaptive modulation coding (AMC) to significantly enhance system outage probability performance and system capacity. CRs will transmit a pseudo carrier under acceptable interference level to primary system (PS). Then PS may cooperatively adjust modulation and coding parameters (MCP) so that CRs can determine optimal utilization of system power (and thus possible rate) under acceptable interference to PS. Consequently, the outage performance of PS in time duration and outage probability, and utilization of radio resource for CRs can be greatly enhanced.

並列關鍵字

Cognitive radio networks ； Spectrum efficiency ； Network efficiency ； Multiple systems sensing ； Hidden terminal problem ； Aggressive sensing ； Cooperative adaptive modulation and coding

參考文獻

[1] NTIA, “U.S. frequency allocations,” [online] http://www.ntia.doc.gov/osmhome/allochrt.pdf

[4] J. Mitola III, G. Q. Maguire, “Cognitive Radio: Making Software Radios More Personal”, IEEE Personal Communications, pp.13-18, Aug. 1999.

[6] Haykin, S., "Cognitive radio: brain-empowered wireless communications," Selected Areas in Communications, IEEE Journal on , vol.23, no.2, pp. 201-220, Feb. 2005.

[7] Kwang-Cheng Chen, Ling-Hung Kung, David Shiung, Ramjee Prasad, Shihi Chen, “Self-Organizing Terminal Architecture for Cognitive Radio Networks,” Wireless Personal Multimedia Communications, 2007. The 10th International Symposium on, Dec. 2007.

[9] A. Sahai, N. Hoven, and R. Tandra, “Some fundamental limits on cognitive radio,” in Proc. of Allerton Conf., Monticello, Oct. 2004.

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感知無線電網路之多系統偵測

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