發(fā)布時間：2018-06-13 17:18

  本文選題：正交頻分復用 + 認知無線網(wǎng)��； 參考：《西安電子科技大學》2014年博士論文

【摘要】：隨著新的高速無線應用的不斷涌現(xiàn),現(xiàn)有無線業(yè)務的不斷發(fā)展,帶寬的需求量在迅速增加,頻譜資源匱乏問題日益嚴重,然而,美國聯(lián)邦通信委員會(FCC)實測數(shù)據(jù)表明,頻譜資源匱乏的真實原因來源于頻譜利用率低下。為了解決頻譜資源短缺,提高頻譜利用率,認知無線電技術應運而生。在認知無線網(wǎng)絡中,認知用戶在頻譜感知的基礎上,機會式地接入授權用戶的空閑頻帶進行通信,在避免對授權用戶產(chǎn)生有害干擾的同時,應用動態(tài)資源分配技術,大大提高了頻譜利用率。作為一種多載波調(diào)制技術,正交頻分復用(OFDM)因其頻譜利用率高、抗多徑能力強等特點而被廣泛應用于寬帶無線通信。OFDM靈活的頻譜成形技術使得它不需要連續(xù)的頻帶即可進行數(shù)據(jù)傳輸,有助于高效利用授權用戶的空閑頻譜,這種頻譜不連續(xù)的OFDM調(diào)制技術稱之為非連續(xù)OFDM(NC-OFDM),成為了認知無線網(wǎng)絡物理層技術的首選。然而,自OFDM被提出至今,其固有的峰均比高的問題仍未得到完美的解決,同時,在非認知OFDM系統(tǒng)中,考慮用戶公平性的資源分配算法的研究仍顯得不足。在頻譜資源匱乏的今天,認知OFDM無線網(wǎng)絡的提出,具有重要的意義,然而,要實現(xiàn)認知系統(tǒng)和授權系統(tǒng)的真正共存,必須有效控制認知OFDM系統(tǒng)對授權系統(tǒng)的帶外干擾,同時,要實現(xiàn)頻譜利用率的有效提高,必須研究行之有效的認知OFDM系統(tǒng)的動態(tài)資源分配算法。針對非認知OFDM系統(tǒng)及認知OFDM系統(tǒng)存在的問題,本文將從非認知OFDM系統(tǒng)的峰均比、認知OFDM系統(tǒng)的帶外抑制,以及非認知OFDM系統(tǒng)及認知OFDM系統(tǒng)的資源分配算法等幾方面進行研究,具體的研究工作和創(chuàng)新性成果如下:1.針對OFDM信號高峰均比(PAPR)問題,提出了一種基于門限的分段壓擴算法,以較小的誤比特率(BER)損失,獲得了有效的峰均比抑制。該算法根據(jù)OFDM信號幅度的統(tǒng)計分布,將OFDM信號分成了三類:小(幅度)信號、平均(幅度)信號和大(幅度)信號,通過選擇合適的門限,對大信號進行壓縮以減小峰值,同時放大小信號,起到提升平均功率的作用,從而達到峰均比的降低。在接收端,通過迭代檢測算法估計并消除壓擴噪聲,有效減小了分段壓擴造成的帶內(nèi)失真,減小了系統(tǒng)的BER性能損失。另外,NC-OFDM信號頻譜的不連續(xù)性使得其峰均比的統(tǒng)計特性有別于傳統(tǒng)OFDM信號,文中還研究了NC-OFDM信號峰均比的統(tǒng)計分布,為進一步研究NC-OFDM信號峰均比抑制算法提供了幫助。2.針對多用戶非認知OFDM系統(tǒng)下行鏈路的動態(tài)資源分配問題,提出了一種考慮用戶優(yōu)先級的自適應子載波分配算法。首先,以兩個用戶的子載波分配為例分析了用戶選擇子載波的先后順序?qū)ο到y(tǒng)容量的影響,在此基礎上,提出了一種新的沖突解決算法。在該算法中,每個用戶獨立地在所有子載波中搜尋最佳信道增益的子載波,當出現(xiàn)沖突,即多個用戶同時選擇一個子載波時,由“平均信道增益”的大小決定用戶選擇沖突子載波的優(yōu)先級。文中定義了兩種不同的優(yōu)先級準則,一種定義平均信道增益較高的用戶優(yōu)先級較高,另一種則定義平均信道增益較低的用戶優(yōu)先級較高,相應地,給出了兩種不同的沖突解決方案。仿真結果表明,由平均信道增益較低的用戶優(yōu)先選擇沖突子載波,系統(tǒng)容量可以近似達到理論上限值。3.針對OFDM信號諧波功率較大的問題,在認知OFDM無線網(wǎng)絡中,提出了一種基于星座擴展的帶外抑制(諧波抑制)算法。在傳統(tǒng)的星座擴展算法中,由于原始數(shù)據(jù)符號獨立地進行星座擴展,很難實現(xiàn)對相鄰擴展星座點的控制,一旦相鄰擴展星座點出現(xiàn)實部或者虛部符號相同的情況,將對諧波抑制非常不利。與傳統(tǒng)星座擴展算法不同的是,該算法的星座擴展基于符號對,而不是單個符號,在該算法中,首先將相鄰的原始數(shù)據(jù)符號兩兩組成一組,然后以組為單位來進行星座擴展,控制擴展星座點反相或者接近反相來實現(xiàn)帶外輻射的抑制。在接收端,充分利用了發(fā)射端的星座擴展表來糾正判決過程中可能出現(xiàn)的錯誤,減小了由于星座擴展帶來的BER性能損失,理論和仿真結果均證明了該算法的有效性。4.針對認知OFDM無線網(wǎng)絡的資源分配問題,首先,分析了認知用戶因帶外輻射和非理想的感知信息對授權用戶造成的干擾,并在資源分配算法的干擾約束中進行了綜合考慮;其次,考慮到授權用戶的信道占用在評價資源分配算法的重要地位,介紹了確定性和隨機性兩種授權用戶的信道占用模型,在此基礎上,對認知OFDM無線網(wǎng)絡的資源分配問題進行建模。在本文所研究的認知無線網(wǎng)絡中,認知用戶分別支持實時(RT)業(yè)務(延遲敏感業(yè)務),和非實時(NRT)業(yè)務(延遲容忍業(yè)務),相應的認知用戶分別為遲延敏感用戶(DS-CUs)和遲延容忍用戶(DT-CUs)。由于延遲容忍用戶關心吞吐量的大小,而延遲敏感用戶則更關心切換時延的大小,將所研究的認知無線網(wǎng)絡資源分配問題建模為一個雙層規(guī)劃問題,在該雙層規(guī)劃中,上層優(yōu)化目標是在滿足延遲敏感用戶最小速率需求的基礎上最小化其切換時延,下層優(yōu)化目標是延遲容忍用戶的吞吐量。由于雙層規(guī)劃問題求解的復雜度較高,我們將該最優(yōu)化問題分解為子信道分配和功率增強兩個問題的求解,仿真結果證明了該算法在所研究場景中的有效性。
[Abstract]:With the continuous emergence of new high-speed wireless applications and the continuous development of the existing wireless services, the demand for bandwidth is increasing rapidly, and the shortage of spectrum resources is becoming more and more serious. However, the actual data from the Federal Communications Commission (FCC) of the United States shows that the real source of the lack of spectrum resources is derived from the low utilization of spectrum. In the cognitive wireless network, cognitive users have access to the free frequency band of authorized users on the basis of spectrum sensing in cognitive wireless networks. In order to avoid harmful interference to authorized users, the cognitive users should use dynamic resource allocation technology to improve the spectrum utilization greatly. As a multi carrier modulation technology, orthogonal frequency division multiplexing (OFDM) is widely used in broadband wireless communication.OFDM flexible spectrum forming technology because of its high spectrum utilization and strong anti multipath ability. It makes it not need continuous frequency band to carry out data transmission, and is helpful to efficiently use the free spectrum of authorized users, this frequency The discontinuous OFDM modulation technology is called discontinuous OFDM (NC-OFDM), which has become the first choice in the physical layer technology of cognitive wireless network. However, since OFDM has been proposed, its inherent peak to average high problem has not been solved perfectly. At the same time, in the non cognitive OFDM system, the research of resource allocation algorithm considering the fairness of the user still appears. In the lack of spectrum resources today, it is of great significance to recognize the OFDM wireless network. However, in order to realize the real coexistence of the cognitive system and the authorization system, it is necessary to effectively control the external interference of the cognitive OFDM system to the authorization system. At the same time, to realize the effective enhancement of the frequency utilization rate of the spectrum, the effective cognitive OFD must be studied. The dynamic resource allocation algorithm of M system, in view of the problems of non cognitive OFDM system and cognitive OFDM system, this paper will study the peak to average ratio of non cognitive OFDM system, out of band suppression of cognitive OFDM system, and the resource allocation algorithm of non cognitive OFDM system and cognitive OFDM system, and the specific research work and innovation will be made. The results are as follows: 1. in view of the peak to average ratio (PAPR) problem of OFDM signal, a threshold based segmented compression expansion algorithm is proposed. The effective peak to mean ratio suppression is obtained with smaller bit error rate (BER) loss. The algorithm divides the OFDM signal into three categories: small (amplitude) signal, average (amplitude) signal and large (amplitude) (amplitude) signal based on the statistical distribution of the amplitude of OFDM signal. ) the signal, by selecting the appropriate threshold to compress the large signal to reduce the peak value, and at the same time, play the role of increasing the average power, and thus achieve the decrease of the peak to average ratio. At the receiving end, the iterative detection algorithm is used to estimate and eliminate the pressure expansion noise, effectively reducing the intra band distortion caused by subsection compression and reducing the BER of the system. In addition, the discontinuity of the NC-OFDM signal spectrum makes the statistical characteristics of the peak to average ratio different from the traditional OFDM signal. The statistical distribution of the peak to average ratio of the NC-OFDM signal is also studied in this paper, which provides the dynamic capital for the further study of the NC-OFDM signal peak mean ratio suppression algorithm for the multiuser and non cognitive OFDM system downlink. An adaptive subcarrier allocation algorithm considering user priority is proposed. First, the effect of the sequence of user selection subcarriers on the system capacity is analyzed with two users' subcarrier allocation. On this basis, a new conflict resolution algorithm is proposed. In this algorithm, each user is independently in the algorithm. All subcarriers search for the best channel gain subcarrier. When there is a conflict, when multiple users select a subcarrier at the same time, the size of the "average channel gain" determines the priority of the user's choice of the conflict subcarrier. Two different priority criteria are defined in this paper, and a user priority with higher average channel gain is defined. The higher, the other is the higher priority of the user with lower average channel gain. Accordingly, two different conflict solutions are given. The simulation results show that the user with lower average channel gain preferred the conflict subcarrier, the system capacity can approximate to the theory upper limit value.3. for the higher harmonic power of the OFDM signal. In the cognitive OFDM wireless network, an extra band suppression (harmonic suppression) algorithm based on the constellation extension is proposed. In the traditional constellation extension algorithm, it is difficult to control the adjacent extension constellations because of the independent constellation expansion of the original data symbols. Once the adjacent extension constellations appear in the real or imaginary parts of the constellation, the same sign is the same. Different from the traditional constellation extension algorithm, the constellation extension of the algorithm is based on the symbol pair rather than the single symbol. In this algorithm, the adjacent original data symbol 22 is first formed, then the group is used to expand the constellation, control the inverse of the extension constellation or close to the inverse. At the receiving end, we make full use of the constellation extension table of the transmitter to correct the possible errors in the decision process and reduce the BER performance loss due to the constellation extension. Both the theoretical and simulation results prove the effectiveness of the algorithm for the allocation of the resources of the cognitive OFDM wireless network, first of all,.4.. First, it analyzes the interference caused by the cognitive users to the authorized users because of the out of band radiation and the non ideal perceptual information, and takes the comprehensive consideration in the interference constraints of the resource allocation algorithm. Secondly, considering the important status of the authorized user's channel occupancy in the evaluation of resource allocation algorithms, two kinds of authorized users are introduced. On this basis, we model the resource allocation problem of cognitive OFDM wireless networks. In this cognitive wireless network, cognitive users support real-time (RT) services (delayed sensitive services), and non real-time (NRT) services (delayed tolerant services), and corresponding cognitive users are delayed sensitive users (DS-CUs), respectively. And delay tolerant users (DT-CUs). Because the delay tolerant users are concerned about the size of the throughput, the delay sensitive users are more concerned with the size of the handover delay. The study of the cognitive wireless network resource allocation problem is modeled as a double layer programming problem. In the two-layer programming, the upper level optimization goal is to satisfy the minimum speed of the delay sensitive user. On the basis of the rate requirement, the switching delay is minimized. The lower layer optimization target is the throughput of the delay tolerant user. Because of the high complexity of the two-layer programming problem, we decompose the optimization problem into two problems of subchannel allocation and power enhancement. The simulation results prove the effectiveness of the algorithm in the research scene.
【學位授予單位】：西安電子科技大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TN925

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