Dissertation > Industrial Technology > Radio electronics, telecommunications technology > Wireless communications > Radio relay communications,microwave communications

Adaptive Resource Allocation Algorithm in OFDM Cognitive Radio System

Author XuShuang
Tutor ZhaoXiaoZuo
School Jilin University
Course Signal and Information Processing
Keywords resource allocation cognitive radio OFDM QoS
Type Master's thesis
Year 2012
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1. IntroductionIn modern society, with the rapid development of communication technology,people are increasingly demanding on wireless communications business. A largenumber of reports have pointed out that, global available spectrum resources areincreasingly scarce, and the spectrum utilization is also very imbalance. CognitiveRadio (CR), which is a more intelligent spectrum sharing technology, is capable ofsensing the wireless communication environment and real-time adaptively to changethe operating parameters of the system. It allows multi-dimensional spectrummultiplex in time, frequency and space in order to using idle spectrum effectively. It ispredicted one of the most popular wireless communication technologies in the future.While Orthogonal Frequency Division Multiplexing (OFDM) technology is a specialmulti-carrier modulation technique, with very high spectrum efficiency and stronganti-jamming capability. At the same time, the OFDM dynamic resource allocationcan adjust subcarrier and power allocation based on the instantaneous channel status,which further improve the spectrum utilization efficiency and system performance.This technology is the preferred choice for modern broadband communication. Infrequency selective wireless fading channel, the combination of cognitive radiotechnology and OFDM dynamic resource allocation technology can give play to theadvantages of them. Therefore, it has received more and more extensive attentionsand researches.Dynamic resource allocation in OFDM system mainly follow two basicguidelines: one is the margin adaptive (MA) optimization problem, which is tominimize total transmission power under the constraints of it error rate and the users’rate requirements; another is the rate adaptive (RA) optimization problem, which is tomaximize the total transmission rate under the constraints of bit error rate and totalpower requirements.For the current development trend in the wireless communication as well as theproblems of resource allocation algorithm, an adaptive resource allocation strategy inOFDM cognitive radio system is proposed based on the RA criteria. Under theconstraints of the total transmit power of the secondary users and the maximumtolerable interference power of the primary user, the algorithm completes thesubcarrier and power allocation, which optimizes system performance and satisfiesthe quality of service (QoS) requirements for the different users. 2. Improved adaptive resource allocation algorithm for OFDM cognitive radiosystemThis paper proposes an adaptive resource allocation algorithm in OFDMcognitive radio system. In order to reducing the computational complexity, thealgorithm considers subcarrier allocation and power allocation separately. In theprocess of subcarrier allocation, by adjusting the fairness threshold to determine thepriority of the subcarrier, subcarrier resources are fully utilized and achieve theenhancement of capacity; in the process of power allocation, by adjusting theinterference threshold to make the primary user tolerate more interference power, thesecondary users get more capacity and the algorithm guarantees the ratio requirementsamong the different users which meets the actual condition.3. Simulation results and performance analysisThe simulation results show that the adaptive resource allocation algorithmproposed in this paper realizes the tradeoff among the fairness threshold, theinterference threshold and the total capacity, which satisfies the quality of servicerequirements of the different users and optimizes system performance. This algorithmis an effective combination of cognitive radio and OFDM dynamic resource allocationtechnology, and it is an innovative application of traditional resource allocationalgorithm for OFDM cognitive radio system.

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