Cognitive Radio Spectrum Sensing Technology

As radio resource is becoming increasingly scarce, Cognitive Radio (CR) arises as a hot research topic in wireless communications, because it is believed that CR is a potential solution for contradiction between spectrum allocation and usage. Spectrum sensing, one heart technique in CR, plays a vital part in CR realization.This dissertation first looks back on the emergence of CR and corresponding notions. Background materials on CR and corresponding spectrum sensing techniques are then summarized, based on which the focus of this thesis is established.Chapter 2 covers various categories of existing techniques on spectrum sensing in CR: From signal existence sensing to signal coverage sensing; from single node sensing to multiple nodes sensing. These are all described and analyzed in principle.After investigation into multiple nodes sensing techniques, a problem is found out: Different nodes are in different wireless envioronment, resulting in different credibility in their sensing, which are not considered in the previous algorithms. To solve this big problem, Chaper 3 proposes a new sensing sheme, utilizing multiple sensing nodes and taking theire sensing credibility into account, namely, distributed sensing scheme based on credibility. Chapter 3 elaborates this algorithm in detail, and simulations are undertaken, based on energy detection under AWGN, as mentioned in Chapter 2. These simulations verify that this proposed algorithm outperforms existing ones significantly.As the contradiction between spectrum allocation and usage is realized by more and more people, the application of CR techniques is attracting increasing attention. In Chapter 4, spectrum sensing applications in WRAN (IEEE 802.22) are introduced first, and then spectrum sensing in GSM band application is analyzed.Although proposals for WRAN are in fierce discussion, in spectrum sensing area, particularly for digital broadcasting signals, however, their main concentration is on ATSC signal detection, which is adopted by only 3 countries so far, while DVB-T signal is accepted by more countries, which shows greater potential in the future market. So DVB-T signal characteristics are first analyzed in Chapter 5, and then sensing techniques are investigated, based on 2 different scenarios: single antenna and multiple antennas. In this way, various sensing algorithms (including both single and multiple receiver scenarios) are proposed and analyzed. Plus, simulations are performed as well, which are shown to have very good performance. This contribution has been put forward to IEEE 802.22 Proposal.In a word, CR provides potential solution for radio resource scarcity, which will definitely influence our daily life. Spectrum sensing is a vital part for CR to become reality, so deep investigation into this area is presented in this dissertation: A distributed sensing scheme based on credibility and evidence theory is proposed, which overcomes the shortage of existing algorithms; DVB-T signal detection algorithms proposed in Chapter 5 are also suitable for any OFDM signals with Cyclic Prefix (CP) or pilot. As will be seen, these have great potential for application in the future.