【正文】 will be made. In contrast, the system model which has two thresholds of our interest is shown (b). Where ― Decision 0H ‖ and ―Decision 1H ‖ represent the absence and the presence of licensed user, respectively.“ No decision‖ means that the observation is not reliable enough and the i th cognitive user will send nothing to the mon receiver. But when all the secondary users don’t send their local decisions, only the cognitive user with the highest reputation is selected to sense spectrum based on conventional energy detection method, and send its local decision to the mon receiver. Reputation is obtained based on the accuracy of cognitive user’s sensing results. The reputation value is set to zero at the beginning. Whenever its local spectrum sensing report is consistent with the final sensing decision, its reputation is incremented by one。本文提出了認(rèn)知無線電環(huán)境下一種基于信任度的雙門限協(xié)同頻譜感知算法。 表 1 仿真參數(shù)設(shè)置 參數(shù) 數(shù)值 認(rèn)知用戶數(shù)目 10?N 平均信噪比 db10_ ?? 時間帶寬積 5?m 授權(quán)用戶占用信道概率 ?op 授權(quán)用戶不占用信道概率 ?p 圖 3 給出了在 ?? 的情況下算法的檢測性能。 則： KiK pTP )](1[}{ 21 ??? ???? ， KNiKN PTP ?? ??? )]([}{ 21` ???。 當(dāng) ??? 時，本地能量檢測器做出本地判 決 1?D ，表示授權(quán)用戶在工作，否則判決 D 為 0。當(dāng)所有的用戶都不可靠時，選取信任度最高的認(rèn)知用戶發(fā)射感知報告進(jìn)行判決。能量檢測算法因為應(yīng)用簡單且無需知道任何授權(quán)用戶信 號的先驗知識成為研究熱點。當(dāng)所有的用戶都不可靠時，選取信任度最高的認(rèn)知用戶發(fā)送本地感知結(jié)果進(jìn)行判決。然而根據(jù)現(xiàn)有的固定分配頻譜資源策略，絕大多數(shù)頻譜資源得不到有效利用。由于實際信道中的多徑和陰影效應(yīng)，單個認(rèn)知用戶頻譜感知的性能并不樂觀，針對這個問題 D. Cabric等人提出了協(xié)同頻譜感知算法 [5][6]。認(rèn)知無線網(wǎng)絡(luò)基站負(fù)責(zé)管理和聯(lián)系 N個認(rèn)知用戶，在收到認(rèn)知用戶的檢測報告后做出最終判決 。并發(fā)送感知報告給認(rèn)知無線電網(wǎng)絡(luò)基站。 檢測性能分析 設(shè) )(?F 和 )(?G 別 表示 ? 在假設(shè) 0H 和 1H 下的概率分布，則根據(jù)文獻(xiàn) [10]可知 : ? ????? ? ???? 0 0 )( )2/,(1)|()( mmdHFF (10) 黃石理工學(xué)院 畢業(yè)設(shè)計（論文）外文文獻(xiàn)翻譯 ?? ? ??? 0 1 )|()( dHfG =????????????????????????????????? ???????????? ?? ???????? 202__2)1(2201_22)1(2!11211 mnmnmneene ?????? ???? (11) 顯然 )()( 210 ?? FF ??? ， )()( 121 ?? GG ??? 。 黃石理工學(xué)院 畢業(yè)設(shè)計（論文）外文文獻(xiàn)翻譯 圖 3檢測性能示意圖 圖 4 描述了 在不同 0? 的條件下，基于信任度的雙門限協(xié)同頻譜感知算法對網(wǎng)絡(luò)開銷的影響。本文對該算法進(jìn)行了性能分析并通過仿真表明，本文方法比較常規(guī) 能量檢測算法， 在 減小網(wǎng)絡(luò)開銷的同時提高了檢測性能。00 }|{}|{}|{}|{ （ 6） D=0 D=1 (a) (b) 0 0? ? D=0 D=1 ND 0 1? 2? ?黃石理工學(xué)院 畢業(yè)設(shè)計（論文）外文文獻(xiàn)翻譯 For simplicity, we define: )|( 02110 HP ??? ???? ， )|( 02110 HP ??? ???? （ 7） Let navgK denote the normalized average number of sensing bits, then, we obtain navgK as follows： 11001 ????? PPK a v g （ 8） From (8), It can be seen that, the normalized average number of sensing bits navgK is always smaller than 1. the munication traffic of our method is are deduced as opposed to the conventional energy detection method. III. THE PERFORMANCE ANALYSIS OF SPECTRUM SENSING In this section, the spectrum sensing performance of the proposed method will be analyzed. Assume the control channel between the unlicensed users and the mon receiver is perfect, the local decisions are reported without any error. Let )(?F and )(?G denote the cumulative distribution function (CDF) of the local test statistic ? under the hypothesis 0H and 1H , respectively. Then, we have [10]: ??????? ????0 0 )()2/,(1)|()( mmdHFF (9) ?? ? ??? 0 1 )|()( dHfG (10) Obviously, )()( 210 ?? FF ??? ， )()( 121 ?? GG ??? . If no any local decision is reported to the mon receiver, ., K=0 , we call that fail sensing. For this case, the mon receiver will request the user which has the highest reputation to send its local decision based on conventional energy detection method. Let 0? and 1? denote the probability of fail sensing under hypothesis 0H and 1H , respectively. Here we have: NNFFHKP 01200 ))()((}|0{ ??????? ??? (11) NNGGHKP 11211 ))()((}|0{ ??????? ??? (12) Apparently, N00 ??? and N11 ??? .In our scheme, the false alarm probability fQ ,the detection probability dQ ,and the missing probability mQ : 黃石理工學(xué)院 畢業(yè)設(shè)計（論文）外文文獻(xiàn)翻譯 )1)(1(}1,|1{}|1{}|0,1{0000AfPKHuPHKPHKuPQ??????????? (13) mQ = dQHKuP ???? 1}|0,0{ 1 (14) )1)(1(}1,|1{}|1{}|0,1{1111?PaKHuPHKPHKuPQ d?????????? (15) For simplicity, we assume the channel between the unlicensed users and the base station are ideal, the local decision will be r