本文選題：VLC + 有效容量理論��； 參考：《吉林大學》2017年碩士論文

【摘要】：隨著人們對無線帶寬需求的增長,可用的射頻頻譜資源正逐漸減少�？梢姽馔ㄐ�(VLC)具有超寬帶寬、人體無害、保密性強、頻譜自由等優(yōu)勢,它已成為下一代通信網絡中最重要的寬帶無線網絡之一。正交頻分復用(OFDM)調制技術實現數據的并行傳輸,具有數據傳輸速率高的特點,被廣泛應用于VLC系統中。在VLC-OFDM系統中,合理的資源分配策略能夠有效提高系統的性能。下一代無線網絡是萬物互聯的網絡,一個接入點(AP)管理著大量的終端,集中式的資源管理方案會增加AP點的計算負擔,降低系統的可靠性。隨著硬件技術的飛速發(fā)展,終端的計算能力不斷增強,在下一代無線網中,終端參與的分布式算法將比集中式算法的性能更優(yōu)。未來無線網絡呈強異構性,如何在有限的頻譜資源下同時保障不同類型業(yè)務的服務質量將成為一項具有挑戰(zhàn)性的問題。時延是最基本的通信服務質量(Qo S)指標,然而無線衰落信道具有隨機性和時變性,業(yè)務的確定性時延難以保障。有效容量理論從鏈路層角度考慮統計時延Qo S約束,它反映了統計時延Qo S保障下的網絡吞吐量性能,能在給定時延約束時保障業(yè)務的時延違反概率不超過指定值。有效容量理論為下一代無線通信系統的統計時延保障研究提供了理論基礎。本文基于有效容量理論研究統計時延Qo S保障下VLC-OFDM系統的分布式子載波分配策略。本文引入直射鏈路阻擋概率對VLC-OFDM系統的有效容量進行建模,將子載波分配問題建模為系統有效容量最大的整型優(yōu)化問題,接著引入終端帶寬分配因子(表示終端帶寬占總帶寬的比重)將整型優(yōu)化問題轉化為連續(xù)優(yōu)化問題。經數學證明,轉化后的連續(xù)優(yōu)化問題為凸優(yōu)化問題,我們基于凸優(yōu)化理論提出了終端與AP點協作工作的準分布式算法以求解最優(yōu)的帶寬分配因子分配策略。在算法的執(zhí)行過程中,AP與終端需要進行信息交互,過慢的算法收斂速度將會導致過多的帶寬在算法執(zhí)行過程中時被浪費掉,進而降低帶寬利用率,因此本文接著對提出的準分布式算法進行優(yōu)化,以加快其收斂速度。OFDM系統中的子載波數為離散量,然而求解上述連續(xù)優(yōu)化問題得到的子載波是連續(xù)量,因此需進一步將連續(xù)子載波離散化。一般的離散化方法有向上取整法和向下取整法。向下取整法會導致帶寬浪費,向上取整法會導致終端帶寬超出系統總帶寬。針對這些問題,本文研究最優(yōu)的子載波離散化策略。為兼顧子載波分配的公平性,本文引入效用函數定義系統整體有效容量,引入帶寬分配因子構建兼顧公平性的連續(xù)優(yōu)化問題,并采用上述提出的準分布式算法求解。在得到終端的帶寬分配因子后,本文引入終端離散化因子將子載波離散化問題建模為系統整體有效容量最大的0-1優(yōu)化問題,并通過遺傳算法求解出最優(yōu)的離散化策略。
[Abstract]:With the increasing demand for wireless bandwidth, the available radio frequency spectrum resources are decreasing. Visible-light communication (VLC) has become one of the most important broadband wireless networks in the next generation communication networks because of its advantages of ultra-wide bandwidth, harmless human body, strong confidentiality and free spectrum. Orthogonal Frequency Division Multiplexing (OFDM) modulation is widely used in VLC systems because of its high data transmission rate. In VLC-OFDM systems, reasonable resource allocation strategy can effectively improve the performance of the system. The next generation wireless network is an interconnected network. An access point (AP) manages a large number of terminals. A centralized resource management scheme will increase the computing burden of AP points and reduce the reliability of the system. With the rapid development of hardware technology, the computing power of the terminal is continuously enhanced. In the next generation wireless network, the distributed algorithm in which the terminal participates will be better than the centralized algorithm. In the future, wireless networks are highly heterogeneous. How to ensure the QoS of different types of services simultaneously under limited spectrum resources will become a challenging problem. Delay is the most basic quality of service (QoS) index. However, the wireless fading channel is stochastic and time-varying, so it is difficult to guarantee the deterministic delay of traffic. The effective capacity theory considers the statistical delay QoS constraint from the link layer point of view. It reflects the throughput performance of the network guaranteed by the statistical delay QoS, and can guarantee the delay violation probability of the traffic not exceeding the specified value when the delay constraint is given. The theory of effective capacity provides a theoretical basis for the research of statistical delay guarantee in next generation wireless communication systems. Based on the effective capacity theory, the distributed subcarrier allocation strategy for VLC-OFDM systems with statistical delay QoS is studied in this paper. In this paper, direct link blocking probability is introduced to model the effective capacity of VLC-OFDM system, and the subcarrier allocation problem is modeled as the integer optimization problem of the maximum effective capacity of the system. Then the terminal bandwidth allocation factor (representing the proportion of the terminal bandwidth to the total bandwidth) is introduced to transform the integer optimization problem into a continuous optimization problem. It is proved by mathematics that the transformed continuous optimization problem is convex optimization problem. Based on convex optimization theory, we propose a quasi-distributed algorithm based on convex optimization theory to solve the optimal bandwidth allocation factor allocation strategy. In the process of executing the algorithm, the AP and the terminal need to communicate with each other. The slow convergence speed of the algorithm will lead to the wasting of too much bandwidth during the execution of the algorithm, which will reduce the bandwidth utilization. Therefore, this paper then optimizes the proposed quasi-distributed algorithm to speed up its convergence. The number of subcarriers in OFDM system is discrete. However, the subcarriers obtained by solving the above continuous optimization problems are continuous. Therefore, continuous subcarriers need to be further discretized. General discretization methods include upward rounding and downward rounding. The downward rounding method will lead to waste of bandwidth, while the upward rounding method will cause the terminal bandwidth to exceed the total bandwidth of the system. To solve these problems, the optimal subcarrier discretization strategy is studied in this paper. In order to take into account the fairness of subcarrier allocation, the utility function is introduced to define the overall effective capacity of the system, and the bandwidth allocation factor is introduced to construct the continuous optimization problem of fairness. The proposed quasi-distributed algorithm is used to solve the problem. After the bandwidth allocation factor of the terminal is obtained, the terminal discretization factor is introduced to model the subcarrier discretization problem as the 0-1 optimization problem with the maximum effective capacity of the system as a whole, and the optimal discretization strategy is solved by genetic algorithm.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN929.1

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